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PICList Thread
'[EE]: Battery charger design'
2001\05\21@223045 by Bob Ammerman

picon face
part 1 2497 bytes content-type:text/plain; (decoded 7bit)

Attached is a schematic for part of a PIC-controlled charger for the NiMH
battery packs recently obtained by quite a few piclisters.

I am really a software guy at heart, so I'd appreciate some hardware guys
looking at this and telling me how stupid I really am, and to go back to my
code. :-)

This ciruit is based on two cascaded voltage controlled current sources.

The first current source is based on Q1. The voltage on the base of Q1
determines the voltage across Rscale, which in turn determines the emitter
current. The collector current is simply the emitter current minus the much
smaller base current.

The voltage on the base of Q1 is set relative to the unregulated positive
rail by the current flowing thru Rb. This current is in turn determined by
the second current source.

The second current source is built around Q2. The voltage on the base of Q2
determines the voltage across Re, which in turn determines the emitter
current. The collector current is simply the emitter current minus the much
smaller base current.

The voltage on the base of Q2 is determined by the 3 resistors Rup, Rdown
and Rpic.

This circuit takes advantage of the 3-state capability of the PIC pin. When
the PIC pin is floated, the base voltage is set by the voltage divider
created by Rup and Rdown. When the PIC pin is driven high, the upper half of
the divider now consists of the parallel combination of Rpic and Rup, thus
raising the voltage. When the PIC pin is driven low the transistor is forced
into cutoff thru the shottkey diode D1.

By the way, this particular scheme was chosen to allow the PIC to control
the high side current source, while keep the battery grounded allowing for
easy sensing of Vbat during charging.

Also attached is an EXCEL spreadsheet showing the derivation of component
values. I used this spreadsheet to see how sensitive the results were to
variations in component parameters/values.

I was thinking I would make Rdown and Rpic trimmers to set the two output
current values.

Does this circuit have a chance of working?

[[[

An aside: if I get this working I intend to release the source and schematic
of the
charger for free use by those on PICLIST.

The software will support the simultaneous but independent charging of at
least 3 or 4 of the packs. (ie: this hardware will be replicated N times for
each pack).

]]]

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)





part 2 10674 bytes content-type:application/pdf; (decode)

part 3 19493 bytes content-type:application/x-msexcel; (decode)

part 4 105 bytes
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2001\05\22@030141 by Vasile Surducan

flavicon
face
On 21 May 01, at 21:49, Bob Ammerman wrote:


> I am really a software guy at heart, so I'd appreciate some hardware guys
> looking at this and telling me how stupid I really am, and to go back to my
> code. :-)
>
  Bob, you can stay on hardware too, it seems ok to my eyes...


> By the way, this particular scheme was chosen to allow the PIC to control
> the high side current source, while keep the battery grounded allowing for
> easy sensing of Vbat during charging.

  However, I don't see the sensing battery circuit, if you don't need
this one, your schematic may be simplified, also the battery may
be measured even if it's floated ( no pin to ground ) using a simple
converter and an optocoupler.
  But light me please ! Why need this charger a microcontroller
inside ? [smile]
Vasile

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2001\05\22@054035 by Bob Ammerman

picon face
> On 21 May 01, at 21:49, Bob Ammerman wrote:
>
>
> > I am really a software guy at heart, so I'd appreciate some hardware
guys
> > looking at this and telling me how stupid I really am, and to go back to
my
> > code. :-)
> >
>    Bob, you can stay on hardware too, it seems ok to my eyes...
>
>
> > By the way, this particular scheme was chosen to allow the PIC to
control
> > the high side current source, while keep the battery grounded allowing
for
> > easy sensing of Vbat during charging.
>
>    However, I don't see the sensing battery circuit, if you don't need
> this one, your schematic may be simplified, also the battery may
> be measured even if it's floated ( no pin to ground ) using a simple
> converter and an optocoupler.
>    But light me please ! Why need this charger a microcontroller
> inside ? [smile]
> Vasile

Yes, I left the voltage sensing out of the schematic at this point to avoid
complicating the issue. For voltage sensing I intend to connect the Vbat+ of
several copies of this circuit to PIC analog inputs, both directly, for full
0-5V measurement, and if necessary for precision, thru an op-amp wired as a
gain-of-10 differential amplifier to allow me to expand the range near the
charging voltage peak.

The microcontroller is intended to control charging rate and timing using
peak voltage detection techniques (I am hoping to avoid the need for thermal
sensing).

I am undecided at this point about whether to add a controlled discharge
load, too.

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)

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2001\05\22@062913 by Roman Black

flavicon
face
Bob Ammerman wrote:


Hi Bob, looks pretty good. So the one PIC pin controls
3 states, OFF/low current/high current? Hope you don't mind
my criticisms.

1. it's open loop, with no current feedback the constant
current will vary somewhat with battery level and temp
changes. That's cool, i've been doing some open-loop CC
stuff for stepper driving lately and there are a few tricks.


> The first current source is based on Q1. The voltage on the base of Q1
> determines the voltage across Rscale, which in turn determines the emitter
> current. The collector current is simply the emitter current minus the much
> smaller base current.


Ok, rscale resistance can change up to 5% depending how
hot it gets. You can pay for an expensive resistor, or
simply calbrate it when hot, or use a huge (10w??)
resistor so that its temp doesn't rise much. Likewise
with Q1 and temp, so use a big transistor and heatsink
will help. Luckily this circuit only has 2 fixed currents,
so the "calibrate when hot" suggestion might be best.
So watch Vbe of Q1 and Vrsense.


> The voltage on the base of Q1 is set relative to the unregulated positive
> rail by the current flowing thru Rb. This current is in turn determined by
> the second current source.
>
> The second current source is built around Q2. The voltage on the base of Q2
> determines the voltage across Re, which in turn determines the emitter
> current. The collector current is simply the emitter current minus the much
> smaller base current.


This is similar to what I am doing with one open-loop
CC driver, you will find that you have two stages of
amlification here and heat errors will multiply.
Also, Q2 Vbe varies with current, it's not fixed
at 0.6v of course... :o)

My solution here is to make the voltage across Re
higher, say 2v or 3v. This reduces the error from
Q2 Vbe changing. Again not so critical with two fixed
currents but you may want to change it to PWM etc
later.:o)


> The voltage on the base of Q2 is determined by the 3 resistors Rup, Rdown
> and Rpic.
>
> This circuit takes advantage of the 3-state capability of the PIC pin. When
> the PIC pin is floated, the base voltage is set by the voltage divider
> created by Rup and Rdown. When the PIC pin is driven high, the upper half of
> the divider now consists of the parallel combination of Rpic and Rup, thus
> raising the voltage. When the PIC pin is driven low the transistor is forced
> into cutoff thru the shottkey diode D1.

Cool, will work well, you can use IN4148 as you
don't need schottky. Plenty of volts headroom for
turnoff.


> By the way, this particular scheme was chosen to allow the PIC to control
> the high side current source, while keep the battery grounded allowing for
> easy sensing of Vbat during charging.

Cool.

>
> Also attached is an EXCEL spreadsheet showing the derivation of component
> values. I used this spreadsheet to see how sensitive the results were to
> variations in component parameters/values.
>
> I was thinking I would make Rdown and Rpic trimmers to set the two output
> current values.

Absolutely, forget the calcs, changes in Vbe from
different current values and heat effects will make
them pretty worthless. Go with the 2 trimpots, rdown
to adjust the low current and then rpic for the high.
Do it when hot! If the device needs to turn on/off
(heat cycle) I suggest doing the stuff I mentioned
above, or at least keeping heat rise under 10'C
from off/max states.


> Does this circuit have a chance of working?

Absolutely, but could I also suggest a few safe
goodies;
* series power diode to battery (saves reverse!)
* load R across battery, important.
* capacitor across battery, (disconnect spikes)
* small cap across Rdown, (ramps current changes,
nice gentle feature)
* Rpic >2k (possible safety if transistor(s) fail)

Hope that helps. :o)
-Roman

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2001\05\22@064536 by Spehro Pefhany

picon face
At 09:49 PM 5/21/01 -0400, you wrote:
>
>The voltage on the base of Q1 is set relative to the unregulated positive
>rail by the current flowing thru Rb. This current is in turn determined by
>the second current source.

Bob, this is fine at 400mA, but at 40mA it become inordinately sensitive
to the exact Vbe of Q1, which has a tempco of -2mV/K (Q1 will get hot) and
is not all that well controlled. The signal is only 200mV with a 5-ohm
resistor.
You can get around this by making it a current mirror (add another PNP
transistor,
with a Re of (say) 100 ohms for a 20:1 ratio. You might want to put a
series resistor in there as well to limit the current.

>The second current source is built around Q2. The voltage on the base of Q2
>determines the voltage across Re, which in turn determines the emitter
>current. The collector current is simply the emitter current minus the much
>smaller base current.
>
>The voltage on the base of Q2 is determined by the 3 resistors Rup, Rdown
>and Rpic.

Similar problem at this side, because of the 10:1 change you want.
Simplest way is to use two port pins and two NPN transistors, one with
(say) 215 ohm emitter resistor and one with a 2.15K emitter resistor,
that would give you 40mA/400mA/440mA/0mA. No diode required.
So, my proposed circuit uses 4 transistors (only one of them a power
one), two port pins, and 4 or 5 resistors, and should be within 10% of the
design value with no adjustment, assuming the two PNP transistors are
thermally coupled. If you use op-amps, of course, you can easily get as
accurate as you want, but that's probably unnecessary.

Best regards,
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
Spehro Pefhany --"it's the network..."            "The Journey is the reward"
.....speffKILLspamspam@spam@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
Contributions invited->The AVR-gcc FAQ is at: http://www.bluecollarlinux.com
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=

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2001\05\22@064917 by Vasile Surducan

flavicon
face
On Tue, 22 May 2001, Bob Ammerman wrote:

> >    But light me please ! Why need this charger a microcontroller
> > inside ? [smile]
> > Vasile
>
   I've asked that, because I have an old Canon laptop with bubble jet
printer inside. Charging accumulator (Ni-Cd) under processor supervising
using peak techniques has fault when accumulators become oldest.
As a result I can't use the laptop only about 2 hours from battery without
using "on-board" printer.
An old accumulator will charge quickly to peak value without having enough
time to reach at nominal capacity even at small charging current.
If I charge accu's with small current a much longer time, the usage of my
laptop becomes twice longer ( with printer two, who eats a lot...)

> The microcontroller is intended to control charging rate and timing using
> peak voltage detection techniques (I am hoping to avoid the need for thermal
> sensing).
>
> I am undecided at this point about whether to add a controlled discharge
> load, too.
>
 This function is extremely important. If you check the peak voltage only
after you spend a small discharge time ( in charging procedure ! ) you'll
read the real ni-mh voltage and you'll be able to improve battery life.
Vasile

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2001\05\22@090442 by Bob Ammerman

picon face
> Bob Ammerman wrote:
>
>
> Hi Bob, looks pretty good. So the one PIC pin controls
> 3 states, OFF/low current/high current? Hope you don't mind
> my criticisms.

Not at all, that's why I asked.

> 1. it's open loop, with no current feedback the constant
> current will vary somewhat with battery level and temp
> changes. That's cool, i've been doing some open-loop CC
> stuff for stepper driving lately and there are a few tricks.

The loop will be kinda closed by voltage sensing of the battery. Exact
currents are not that important.

>
> > The first current source is based on Q1. The voltage on the base of Q1
> > determines the voltage across Rscale, which in turn determines the
emitter
> > current. The collector current is simply the emitter current minus the
much
{Quote hidden}

Yeah, I figured I'd use a pretty big resistor here: 400ma @ 2V = 800mw. A
five watter shouldn't get too hot. How does a heatsinked TIP30 sound?

> > The voltage on the base of Q1 is set relative to the unregulated
positive
> > rail by the current flowing thru Rb. This current is in turn determined
by
> > the second current source.
> >
> > The second current source is built around Q2. The voltage on the base of
Q2
> > determines the voltage across Re, which in turn determines the emitter
> > current. The collector current is simply the emitter current minus the
much
> > smaller base current.
>
>
> This is similar to what I am doing with one open-loop
> CC driver, you will find that you have two stages of
> amlification here and heat errors will multiply.
> Also, Q2 Vbe varies with current, it's not fixed
> at 0.6v of course... :o)

Of course.

> My solution here is to make the voltage across Re
> higher, say 2v or 3v. This reduces the error from
> Q2 Vbe changing. Again not so critical with two fixed
> currents but you may want to change it to PWM etc
> later.:o)

The problem with this is that my downside compliance gets rather high.

> > The voltage on the base of Q2 is determined by the 3 resistors Rup,
Rdown
> > and Rpic.
> >
> > This circuit takes advantage of the 3-state capability of the PIC pin.
When
> > the PIC pin is floated, the base voltage is set by the voltage divider
> > created by Rup and Rdown. When the PIC pin is driven high, the upper
half of
> > the divider now consists of the parallel combination of Rpic and Rup,
thus
> > raising the voltage. When the PIC pin is driven low the transistor is
forced
> > into cutoff thru the shottkey diode D1.

> Cool, will work well, you can use IN4148 as you
> don't need schottky. Plenty of volts headroom for
> turnoff.

Don't I have to bring Vb below Vbe to ensure turnoff?

> > By the way, this particular scheme was chosen to allow the PIC to
control
> > the high side current source, while keep the battery grounded allowing
for
> > easy sensing of Vbat during charging.
>
> Cool.

> >
> > Also attached is an EXCEL spreadsheet showing the derivation of
component
> > values. I used this spreadsheet to see how sensitive the results were to
> > variations in component parameters/values.
> >
> > I was thinking I would make Rdown and Rpic trimmers to set the two
output
{Quote hidden}

Thanks, Roman!

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)

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2001\05\22@090659 by Olin Lathrop

face picon face
> I am undecided at this point about whether to add a controlled discharge
> load, too.

I think it will be necessary.  I plan on having one per pack.  This can be
very simple.  Battery to ground thru resistor and NPN, which is switched
from PIC via base resistor.


********************************************************************
Olin Lathrop, embedded systems consultant in Littleton Massachusetts
(978) 742-9014, olinspamKILLspamembedinc.com, http://www.embedinc.com

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2001\05\22@090725 by Bob Ammerman

picon face
----- Original Message -----
From: "Spehro Pefhany" <.....speffKILLspamspam.....INTERLOG.COM>
To: <EraseMEPICLISTspam_OUTspamTakeThisOuTMITVMA.MIT.EDU>
Sent: Tuesday, May 22, 2001 6:46 AM
Subject: Re: [EE]: Battery charger design


> At 09:49 PM 5/21/01 -0400, you wrote:
> >
> >The voltage on the base of Q1 is set relative to the unregulated positive
> >rail by the current flowing thru Rb. This current is in turn determined
by
> >the second current source.
>
> Bob, this is fine at 400mA, but at 40mA it become inordinately sensitive
> to the exact Vbe of Q1, which has a tempco of -2mV/K (Q1 will get hot) and
> is not all that well controlled. The signal is only 200mV with a 5-ohm
> resistor.

It shouldn't get too hot at only 40ma. Also, I don't have to be too precise.

> You can get around this by making it a current mirror (add another PNP
> transistor,
> with a Re of (say) 100 ohms for a 20:1 ratio. You might want to put a
> series resistor in there as well to limit the current.

I guess I need a little help understanding what you mean here.

> >The second current source is built around Q2. The voltage on the base of
Q2
> >determines the voltage across Re, which in turn determines the emitter
> >current. The collector current is simply the emitter current minus the
much
{Quote hidden}

Can't afford the port pins.

> Best regards,
>
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
=
> Spehro Pefhany --"it's the network..."            "The Journey is the
reward"

Thanks Spehro

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)

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2001\05\22@091505 by Bob Ammerman

picon face
----- Original Message -----
From: "Vasile Surducan" <vasilespamspam_OUTL30.ITIM-CJ.RO>
To: <@spam@PICLISTKILLspamspamMITVMA.MIT.EDU>
Sent: Tuesday, May 22, 2001 5:45 AM
Subject: Re: [EE]: Battery charger design


{Quote hidden}

using
> > peak voltage detection techniques (I am hoping to avoid the need for
thermal
> > sensing).
> >
> > I am undecided at this point about whether to add a controlled discharge
> > load, too.

>   This function is extremely important. If you check the peak voltage only
> after you spend a small discharge time ( in charging procedure ! ) you'll
> read the real ni-mh voltage and you'll be able to improve battery life.
> Vasile

I am undecided about this because I have control over the ways the batteries
will be used. I can pretty much ensure that packs are pretty well discharged
before they get to the charger. I might add it to increase the general
usefullness of the circuit.

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)

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2001\05\22@091732 by Olin Lathrop

face picon face
> Attached is a schematic for part of a PIC-controlled charger for the NiMH
> battery packs recently obtained by quite a few piclisters.
>
> ...
>
> Does this circuit have a chance of working?

I think it will work as you described it.  I also plan on making a PIC
controlled charger for these packs, so I've had to think thru some of the
same issues you encountered.  I guess your schematic addresses the question
of how to make a current source controlled by a PIC.  Your current source
can be adjusted to produce 3 different currents from one output pin.  That's
a clever idea I hadn't thought of.  The only potential problem I see with
this design is that it is totally open loop, and therefore dependent on the
E-B voltage drops on the two transistors, which are in turn very dependent
on temperature.  The output current will be especially dependent on the E-B
drop accross Q2 at low currents.  However, I'm not sure this matters much.
It the battery voltage is monitored properly, it probably doesn't matter
whether the current is 80, 100, or 120 mA, for example.

I haven't had much spare time in the last week to think about the battery
charger, so all I've got to offer are a few ideas that I've considered.
These are only ideas that admittedly have not been thought thru.  In
arbitrary order:

1  -  Use software PWM, then low pass filter the outputs to drive the
current sources.  I say software PWM because even the fancy PICs have only
two hardware PWM outputs and I want to drive more packs than that from one
PIC.  Fortunately, the filtered current drive output signal requires a very
low bandwidth, so this is well within software capabilities to still get
good resolution on a whole bunch of pins simultaneously.

2  -  Use software to close the current source feedback loop.  Software is
cheaper than an op amp, and the bandwidths are certainly low enough.  Again,
this is only an idea.  It would require and extra A/D per pack, which is
probably a good reason not to do it.  Also, there will probably be an op amp
anyway to sense the current.  This could possibly double to close the
feedback loop without much extra hardware. B7dz  -  The PIC needs to be protected from a disconnected or open battery
pack.  With no load, the current sources will go to their maximum voltage.
The circuit has to make sure that this somehow doesn't exceed 5V by the time
it gets to the PIC.

4  -  The whole circuit must be protected from power going down with fully
charged packs connected.  This means, among other things, that the battery
voltage sense circuit has to deal with the battery voltage being up to 5V
above the power rail (since the power rail will be at 0V in this case).  It
would also be unacceptable to draw more than a few microamps from the
battery in this case.


********************************************************************
Olin Lathrop, embedded systems consultant in Littleton Massachusetts
(978) 742-9014, KILLspamolinKILLspamspamembedinc.com, http://www.embedinc.com

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2001\05\22@092153 by Bob Ammerman

picon face
>     I've asked that, because I have an old Canon laptop with bubble jet
> printer inside. Charging accumulator (Ni-Cd) under processor supervising
> using peak techniques has fault when accumulators become oldest.
> As a result I can't use the laptop only about 2 hours from battery without
> using "on-board" printer.
> An old accumulator will charge quickly to peak value without having enough
> time to reach at nominal capacity even at small charging current.
> If I charge accu's with small current a much longer time, the usage of my
> laptop becomes twice longer ( with printer two, who eats a lot...)

I am blessed in having plenty of batteries so I can just toss 'em if they
don't get a good charge on peak detect.

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)

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2001\05\22@092847 by Roman Black

flavicon
face
Bob Ammerman wrote:

> > 1. it's open loop, with no current feedback the constant

> The loop will be kinda closed by voltage sensing of the battery. Exact
> currents are not that important.

If exact currents are not important stick with the
two transistor design. Spehros current-mirror is
more accurate but maybe the complexity is not
justified.



> >
> > Ok, rscale resistance can change up to 5% depending how
> > hot it gets. You can pay for an expensive resistor, or
> > simply calbrate it when hot, or use a huge (10w??)
> > resistor so that its temp doesn't rise much.
>
> Yeah, I figured I'd use a pretty big resistor here: 400ma @ 2V = 800mw. A
> five watter shouldn't get too hot. How does a heatsinked TIP30 sound?

Hmm. A 5w resistor for 1w disspate is about the limit
I would use for a HOT resistor. Run a standard 5w resistor
at 1w and measure it, i've seen 30'C rise, which makes
it about hot coffee temp and the value will change at
least 2% with most cheap resistors.

I suggest maybe 1v @ 400mA, with the 5w resistor.
1v is plenty for a decent current sense.


>
> > My solution here is to make the voltage across Re
> > higher, say 2v or 3v. This reduces the error from
> > Q2 Vbe changing. Again not so critical with two fixed
> > currents but you may want to change it to PWM etc
> > later.:o)
>
> The problem with this is that my downside compliance gets rather high.

But you only need 10:1 difference between the 2 currents?
400mA CC = 2v Re + 0.6vbe =2.6v
40mA CC = 0.2v+ 0.6 = 0.8v
PIC pin will supply 3.5v ok, at 10mA. I don't see
a problem.

> > Cool, will work well, you can use IN4148 as you
> > don't need schottky. Plenty of volts headroom for
> > turnoff.
>
> Don't I have to bring Vb below Vbe to ensure turnoff?


Using the figures above, for the volts at the base
of Q2;
PIC pin high = 2.6v base = 400mA CC
PIC pin float = 0.8v base = 40mA CC
PIC pin low = <0.6v base = 0mA CC

Just forget the diode, with the PIC pin floating
the R ladder is holding Q2 almost off anyway, once
that PIC pin goes low (to about 0.14v) through the
Rpic resistor Q2 will definitely turn off. :o)

You could make this circuit very accurate, but if
all you really want is one PIC pin to give 400mA
or 40mA or off, and you can tolerate a few percent
current error, it will work great. Better to make
it simple I think than too perfect.

For efficiency I think you could drop Rsense to maybe
0.4v at 400mA, but I would still keep that series
diode to the battery...
-Roman

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2001\05\22@093657 by Bob Ammerman

picon face
----- Original Message -----
From: "Olin Lathrop" <RemoveMEolin_piclistTakeThisOuTspamEMBEDINC.COM>
To: <spamBeGonePICLISTspamBeGonespamMITVMA.MIT.EDU>
Sent: Tuesday, May 22, 2001 8:00 AM
Subject: Re: [EE]: Battery charger design


> > Attached is a schematic for part of a PIC-controlled charger for the
NiMH
> > battery packs recently obtained by quite a few piclisters.
> >
> > ...
> >
> > Does this circuit have a chance of working?
>
> I think it will work as you described it.  I also plan on making a PIC
> controlled charger for these packs, so I've had to think thru some of the
> same issues you encountered.  I guess your schematic addresses the
question
> of how to make a current source controlled by a PIC.  Your current source
> can be adjusted to produce 3 different currents from one output pin.
That's
> a clever idea I hadn't thought of.  The only potential problem I see with
> this design is that it is totally open loop, and therefore dependent on
the
> E-B voltage drops on the two transistors, which are in turn very dependent
> on temperature.  The output current will be especially dependent on the
E-B
> drop accross Q2 at low currents.  However, I'm not sure this matters much.
> It the battery voltage is monitored properly, it probably doesn't matter
> whether the current is 80, 100, or 120 mA, for example.

My thinking exactly.

> I haven't had much spare time in the last week to think about the battery
> charger, so all I've got to offer are a few ideas that I've considered.
> These are only ideas that admittedly have not been thought thru.  In
> arbitrary order:

> 1  -  Use software PWM, then low pass filter the outputs to drive the
> current sources.  I say software PWM because even the fancy PICs have only
> two hardware PWM outputs and I want to drive more packs than that from one
> PIC.  Fortunately, the filtered current drive output signal requires a
very
> low bandwidth, so this is well within software capabilities to still get
> good resolution on a whole bunch of pins simultaneously.

Yeah, I planned to do this in a primitive way to actually get 3 effective
currents: fast-charge rate (about 400ma == C) , top-off rate (about 40ma ==
C/10) and trickle rate (about 5ma == C/80 ??). The last would be by using a
1/8 duty cycle PWM at 40ma.

> 2  -  Use software to close the current source feedback loop.  Software is
> cheaper than an op amp, and the bandwidths are certainly low enough.
Again,
> this is only an idea.  It would require and extra A/D per pack, which is
> probably a good reason not to do it.  Also, there will probably be an op
amp
> anyway to sense the current.  This could possibly double to close the
> feedback loop without much extra hardware.

Yeah, one possibility I considered was a low-ohm low side sense resistor to
an op-amp to scale the current sense to 0-5V. VBat could then be computed as
the (VBat+ - Vsense) in software.

> 3  -  The PIC needs to be protected from a disconnected or open battery
> pack.  With no load, the current sources will go to their maximum voltage.
> The circuit has to make sure that this somehow doesn't exceed 5V by the
time
> it gets to the PIC.

Yep. Probably a typical resistor and clamping diode scheme.

> 4  -  The whole circuit must be protected from power going down with fully
> charged packs connected.  This means, among other things, that the battery
> voltage sense circuit has to deal with the battery voltage being up to 5V
> above the power rail (since the power rail will be at 0V in this case).
It
> would also be unacceptable to draw more than a few microamps from the
> battery in this case.

A diode in series with the pack?

>
> ********************************************************************
> Olin Lathrop, embedded systems consultant in Littleton Massachusetts
> (978) 742-9014, TakeThisOuTolinEraseMEspamspam_OUTembedinc.com, http://www.embedinc.com
>

Thanks Olin.

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)

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2001\05\22@094705 by Bob Ammerman

picon face
----- Original Message -----
From: "Roman Black" <RemoveMEfastvidspamTakeThisOuTEZY.NET.AU>
To: <PICLISTEraseMEspam.....MITVMA.MIT.EDU>
Sent: Tuesday, May 22, 2001 9:22 AM
Subject: Re: [EE]: Battery charger design


{Quote hidden}

Yeah, I don't think the complexity is needed. But I would like to know how
to build this 'current mirror'.

{Quote hidden}

How hot do they get at 5W then?

Ok, 10W then. I was kinda figuring on using an aluminum case and sinking the
PNPs to it. I could sink the resistors to it also or would the additional
rise on the PNPs make that a bad idea?

> I suggest maybe 1v @ 400mA, with the 5w resistor.
> 1v is plenty for a decent current sense.

Yeah but at 0.1 @ 40ma that isn't giving me much slop at all in the Vbe
number. (That's why I created the spreadsheet, so I could play with these
things easily).

{Quote hidden}

Yeah, that was dumb. I was thinking that I had to keep the collector of Q2
below Vbat, but that isn't true. Dumb!

{Quote hidden}

The diode is a very good idea, I think.

Thanks again, Roman.

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)

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2001\05\22@120158 by Spehro Pefhany

picon face
At 08:31 AM 5/22/01 -0400, you wrote:
>
>> Bob, this is fine at 400mA, but at 40mA it become inordinately sensitive
>> to the exact Vbe of Q1, which has a tempco of -2mV/K (Q1 will get hot) and
>> is not all that well controlled. The signal is only 200mV with a 5-ohm
>> resistor.
>
>It shouldn't get too hot at only 40ma. Also, I don't have to be too precise.

It could be more than 50% off.

>> You can get around this by making it a current mirror (add another PNP
>> transistor,
>> with a Re of (say) 100 ohms for a 20:1 ratio. You might want to put a
>> series resistor in there as well to limit the current.
>
>I guess I need a little help understanding what you mean here.

Sure: (PNP current mirror)

+10---x----------x
     |          |
     Ra         Rb
   E |        E |
      \|         \|
 PNP   |--x-------| PNP power
      /|  |      /|
      |   |     |
      x---x     |
      |         |
      |         |
     Iin       Iout

Iout ~= Iin * Ra/Rb ; thermally couple the two transistors

Say Ra = 100 Ohms, Rb = 5 Ohms 2W (0.8W max dissipation)

{Quote hidden}

Alright. I've had some sleep. ;-)
Same configuration as above schematic on the low side, but NPNs to 0V.
             +5
              |
             RC
              |
Port pin ------x----> to current mirror

Make the first emitter resistor 2.15K and the second 215 ohms.
(ratio 10:1)
We need 200uA through RC to complete this.. so Rc =  19.85K.


Now, port pin = low  for OFF
    port pin = high for 400mA (controlled by 215 ohm resistor)
    port pin = open for 40mA (controlled by Rc)

5 resistors and 4 transistors (1 power), no diode.

Best regards,
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
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EraseMEspeffspaminterlog.com             Info for manufacturers: http://www.trexon.com
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2001\05\22@120612 by Spehro Pefhany

picon face
At 09:12 AM 5/22/01 -0400, you wrote:


>Yeah, I don't think the complexity is needed. But I would like to know how
>to build this 'current mirror'.

See previous message, but the complexity is actually the same as the
original (9 parts in both cases).

Best regards,
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
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2001\05\22@121849 by Lawrence Lile

flavicon
face
part 1 1428 bytes content-type:text/plain; (decoded 7bit)

Bob,

I ran a sumulation of the charger circuit in Bspice.   Results are attached.
So far I was not modeling temperature effects, just wanted to model the
circuit to see if it regulated current OK with an unregulated power supply.

My assumptions were:  I want a 12V battery so my battery was modeleld as a
9.6V voltage source in series with a 3 ohm resistor, Voltage source was 15V
with 1Vp-p ripple.  Pass transistor was a 2n2955.  PIC diode was a  1n914,
pic is in high impedance state.

Of course you are looking to charge a 4.5 volt stack, so "Your mileage may
vary" Still I think the results will be similar.

Current into the battery varied from 151 milliamps to 192 milliamps, while
my supply ripple went from 16V to 14V.  This means the current varied by 27%
whereas the supply voltage varied by only 14%.  You can draw your own
conclusions as to whether this is a good enough current source.

Perhaps the PIC feedback loop will be really neccesary to get this thing
into line.

OK, now the flame wars and rock throwers start: "Why did you use such a
battery model?  Why did you use a 12V battery?  Why didn't you model
temperature effects?  Why did you treat your first wife so badly? Why didn't
you buy Microsoft stock in 1980 whan you had the money?" etc.etc.etc.   Let
us suffice to say this was a first stab at a model of Bob's noble effort.


-- Lawrence




part 2 4552 bytes content-type:application/octet-stream; (decode)

part 3 7432 bytes content-type:application/octet-stream; (decode)

part 4 154 bytes
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2001\05\22@123436 by Lawrence Lile

flavicon
face
Bob,

I re-ran the Bspice simulation with the following assumptions:

Power supply 5 volts with 0.7Vp-p ripple

Battery 4.5V  modeled as a 3V source with 3 ohm series resistance
Pic input in 3 different states - open, high and low


With the pic output open or low, the current in the battery was essentially
zero

With the PIC output at 5V, the current into the battery was
29.7mA  to 6mA
while the power supply ripple was 5.7 to 4.3V


I'm scratching my head about the constant current regulation right now.

Anybody else use Bspice?

-- Lawrence Lile

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2001\05\22@150644 by Olin Lathrop

face picon face
> Yeah, one possibility I considered was a low-ohm low side sense resistor
to
> an op-amp to scale the current sense to 0-5V. VBat could then be computed
as
> the (VBat+ - Vsense) in software.

With the same op amp and a few resistors you can make a diff amp and use a
high side current sense.  I'm considering doing this and also have the same
current sense resistor be big enough to automatically provide current
limiting at around 1C, dissipate most of the power at the higher currents,
and be the current control resistor for the current source.

> > 4  -  The whole circuit must be protected from power going down with
fully
> > charged packs connected.  This means, among other things, that the
battery
> > voltage sense circuit has to deal with the battery voltage being up to
5V
> > above the power rail (since the power rail will be at 0V in this case).
> It
> > would also be unacceptable to draw more than a few microamps from the
> > battery in this case.
>
> A diode in series with the pack?

I don't think it's that easy.  It's easy enough to keep the battery from
feeding current backwards thru the current source with a diode, or just
design the current source so that the output is the collector of a PNP.
It's not so easy to protect the voltage sense circuit.  I don't want a diode
in series because it will mess up the voltage measurements.  The PIC A/D
inputs don't like impedances above 10K ohms.  Even with at 10K resistor and
a 4.5V battery pack, that is still 450uA of drain on the battery and thru
the PIC protection diode.  One possibility is to use a FET switch on the low
side of the battery.  Another is to run the battery voltage thru 1M ohm to a
FET input opamp, which buffers it to the PIC.


********************************************************************
Olin Lathrop, embedded systems consultant in Littleton Massachusetts
(978) 742-9014, RemoveMEolinspam_OUTspamKILLspamembedinc.com, http://www.embedinc.com

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2001\05\22@162122 by Spehro Pefhany

picon face
At 12:03 PM 5/22/01 -0400, I wrote:
>Iout ~= Iin * Ra/Rb ; thermally couple the two transistors

This relationship is oversimplified for this problem, you'd have
to go to the diode equation to get an accurate enough value, I've
ignored a term based on log(Ia/Ib), something like 50mV or more,
which is significant in terms of the 200mV signal.

Anyway, I built this, and with some changes to the component values
to account for this factor it works fine.

Resistors 5 Ohms, 150 Ohms (PNP current mirror), 16K (Rc),
220 Ohms/2.2K (NPN current mirror)
I used a TIP32 and some K8050/8550 BJTs.

Vin = 0         Iout  < 1uA
Vin = open      Iout = 39.2mA
Vin = Vdd       Iout = 405 mA

Best regards,


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2001\05\22@170859 by Dwayne Reid

flavicon
face
At 12:59 PM 5/22/01 -0400, Olin Lathrop wrote:

> > A diode in series with the pack?
>
>I don't think it's that easy.  It's easy enough to keep the battery from
>feeding current backwards thru the current source with a diode, or just
>design the current source so that the output is the collector of a PNP.
>It's not so easy to protect the voltage sense circuit.  I don't want a diode
>in series because it will mess up the voltage measurements.  The PIC A/D
>inputs don't like impedances above 10K ohms.  Even with at 10K resistor and
>a 4.5V battery pack, that is still 450uA of drain on the battery and thru
>the PIC protection diode.  One possibility is to use a FET switch on the low
>side of the battery.  Another is to run the battery voltage thru 1M ohm to a
>FET input opamp, which buffers it to the PIC.

A solution that works for me is to use a large series resistor and have a
decent sized cap right at the PIC pin.  I maintain full 8 bit accuracy when
doing this on the 16C73B parts, using 220K and 1uF tantalum cap.  I haven't
tried it with larger values of resistor, nor have I tried it with the 10
bit a/d convertors on the F87x parts.  Not yet, that is.

dwayne



Dwayne Reid   <EraseMEdwaynerspamspamspamBeGoneplanet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
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Celebrating 17 years of Engineering Innovation (1984 - 2001)

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2001\05\22@180152 by Bob Ammerman

picon face
> At 12:59 PM 5/22/01 -0400, Olin Lathrop wrote:
>
> > > A diode in series with the pack?
> >
> >I don't think it's that easy.  It's easy enough to keep the battery from
> >feeding current backwards thru the current source with a diode, or just
> >design the current source so that the output is the collector of a PNP.
> >It's not so easy to protect the voltage sense circuit.  I don't want a
diode
> >in series because it will mess up the voltage measurements.  The PIC A/D
> >inputs don't like impedances above 10K ohms.  Even with at 10K resistor
and
> >a 4.5V battery pack, that is still 450uA of drain on the battery and thru
> >the PIC protection diode.  One possibility is to use a FET switch on the
low
> >side of the battery.  Another is to run the battery voltage thru 1M ohm
to a
> >FET input opamp, which buffers it to the PIC.
>
> A solution that works for me is to use a large series resistor and have a
> decent sized cap right at the PIC pin.  I maintain full 8 bit accuracy
when
> doing this on the 16C73B parts, using 220K and 1uF tantalum cap.  I
haven't
> tried it with larger values of resistor, nor have I tried it with the 10
> bit a/d convertors on the F87x parts.  Not yet, that is.
>
> dwayne

Yep, that should work just fine.

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)

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2001\05\22@203328 by Ian Hynes

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part 0 44 bytes
his is a multi-part message in MIME format.
part 1 1985 bytes content-type:text/plain; charset=us-ascii (decoded 7bit)

Bob,

Yeah, I think it _could_ work. You've always got a current drain thru
R5 and you have to tap into a 5V rail- the PIC's probably? Also you
need to watch the divider ratio cuz Re can easily push Vb1 over
VR4/R5. the thing could turn on or off when it shouldn't. why do you
need tri-sate control over the voltage level? The charger would be
either on or off. I'd maybe do something like :-

Bob's battery charger ... see attachment (~100 mA charging current.,
~1.8mA from the PIC pin)

I'm not sure about ni-hydrides - do they need a constant currnet
source like NiCads or constant voltage like lead acids?

Ian's cct : with PIC_LO, Q1 & Q2 are OFF, battery sees an o/c (or
anyway, a really high resistance. With PIC_HI, Q1 & Q2 are ON (SAT),
battery sees constant current source from the 10V rail. D1 protects Q1
against -ve excursions, R2 clamps Q1 to GND when PIC is tristate.
when PIC is low or tristate the only currents flowing are the various
leakages - Icbo, Ieco.
R3 limits I thru Q1 and Vr3 sets the voltage across R5 which
determines current thru the battery. You could leave the battery on
constant charge or pulse it, for some unknown reason. You might want
to think about reverse polarity protection too.

Ian

Bob Ammerman wrote:
{Quote hidden}


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part 3 154 bytes
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2001\05\23@040848 by Vasile Surducan

flavicon
face
On Tue, 22 May 2001, Bob Ammerman wrote:

I said:
> > An old accumulator will charge quickly to peak value without having enough
> > time to reach at nominal capacity even at small charging current.

You reply:
> I am blessed in having plenty of batteries so I can just toss 'em if they
> don't get a good charge on peak detect.
>

 I have no doubt you have batteries, but in the situation mentioned above
your charger will signalize ( probable with a flashing led ) that your
battery is charged and in reality you have a defective battery.
Once again, my test indicate that "peak detection" must be done or with
nominal load on the battery ( difficult ) either after a time in which
battery was connected to a fraction of the full load.

 I'm agree, there is no need for software loop in charging process, only
for small and accurate charging currents ( not applicable to ordinary
batteries ). Talking about -2.2 mV/C Vbe variations in these
consumer application have nonsense. For a 50 C temperature variations
a Vbe may change from 650mV to about 540mV. Negligible for a good design
in which transistor was correct dimensioned. So there is no need for
thermal compensated current mirrors.

 But thermal detection failure may be important if your charger will have
fast charge option. This one is usual the death of most batteries.
( I forgot, you have plenty... [grin])

Cheers,
Vasile

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2001\05\23@061908 by Roman Black

flavicon
face
Bob, don't let all the hardware talk put you off,
the two-transistor CC design you have is quite workable.
I have used very similar things for *important*
battery chargers and even stepper motor controllers.
Just calibrate it when hot so the two current
ranges are right, resign yourself to a few percent
current error (big deal) and it's done.

I don't see the point in building the "ultra-super
perfect" battery charger when most NiCds and NiMHs
are unreliable chemical time-bombs anyway. Many of
them are discharged when purchased, so they are
partially corroded and some life is gone already
anyway. We stock many types and order every other
type for our customers.
For the record, we trickle charge all ours at 10% C
current and always get many years from them. And a good
batery charger can be a simple as ONE resistor and
a regulated voltage, the resistor sets a safe trickle
current when charged, and limits the max current
when the battery is connected discharged. :o)
-Roman

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2001\05\23@072220 by Bob Ammerman

picon face
>   But thermal detection failure may be important if your charger will have
> fast charge option. This one is usual the death of most batteries.
> ( I forgot, you have plenty... [grin])
>
> Cheers,
> Vasile

Yeah, I have plenty, but death be detonation would _not_ be a good thing.

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)

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2001\05\23@154238 by Peter L. Peres

picon face
Use PWM (slow PWM) and forget the resistors (you need only one). You can
PWM discharge a battery fine (400mA with 10% duty cycle is 40mA) and it's
ok to have slow PWM (1/10 second even).

Peter

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2001\05\23@183827 by Olin Lathrop

face picon face
> Use PWM (slow PWM) and forget the resistors (you need only one). You can
> PWM discharge a battery fineter 0mA with 10% duty cycle is 40mA) and it's
> ok to have slow PWM (1/10 second even).

What about charging?  I've been looking but haven't found any definative
answer about how fast is fast enough (if at all) to charge a battery with
pulses.  For example, if a battery wants to be charged at 500mA, is it OK to
charge at 1A for 100mS, then 0 for 100mS?  I bet 1S - 1S is too long.  Does
it need 10mS - 10mS, 1mS - 1mS?  Is it EVER acceptable to run 1A charge
current thru the battery, no matter how short the individual pulses with the
average current being within spec?


********************************************************************
Olin Lathrop, embedded systems consultant in Littleton Massachusetts
(978) 742-9014, RemoveMEolinKILLspamspamembedinc.com, http://www.embedinc.com

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2001\05\23@184603 by Spehro Pefhany

picon face
At 06:21 PM 5/23/01 -0700, you wrote:
>> Use PWM (slow PWM) and forget the resistors (you need only one). You can
>> PWM discharge a battery fineter 0mA with 10% duty cycle is 40mA) and it's
>> ok to have slow PWM (1/10 second even).
>
>What about charging?  I've been looking but haven't found any definative
>answer about how fast is fast enough (if at all) to charge a battery with
>pulses.  For example, if a battery wants to be charged at 500mA, is it OK to
>charge at 1A for 100mS, then 0 for 100mS?  I bet 1S - 1S is too long.  Does
>it need 10mS - 10mS, 1mS - 1mS?  Is it EVER acceptable to run 1A charge
>current thru the battery, no matter how short the individual pulses with the
>average current being within spec?

I'd like to know the answer to this. Obviously the I^2*R heating will be
higher with pulsed current. At 50% duty cycle, you have average current of
0.5A, RMS current of 0.707 A.

Best regards,
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2001\05\23@225553 by Martin Wehner

flavicon
face
Hello Everyone-

during the last few days, there have been quite a few posts regarding the
design of battery chargers for the NiMH battery packs some of us received a
while ago.

To be honest, most of the posts went "over my head," as my experience has been
with software systems so far.

However, I am very eager to learn, and tried to design my own charger, based
on a 7805 voltage regulator.
The charger is not fully completed yet, as I simply did not have enough time
to program the PIC to turn the charging current on and off; I do not, however,
anticipate any problems doing so.

Any comments/thoughts/critique of my charging circuit would be greatly
appreciated.

You can find the humble beginnings of my current charger design on my web-site
at: http://www.cyclotomic.com/~martin/projects.html#NiMHCharger

Thank you for taking the time to read & review this!


       Martin



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Martin Wehner

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2001\05\24@051151 by Roman Black

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Martin Wehner wrote:
>
> Hello Everyone-
>
> during the last few days, there have been quite a few posts regarding the
> design of battery chargers for the NiMH battery packs some of us received a
> while ago.
> You can find the humble beginnings of my current charger design on my web-site
> at: http://www.cyclotomic.com/~martin/projects.html#NiMHCharger
>
> Thank you for taking the time to read & review this!


Looks pretty cool Martin! Maybe a couple of caps on
the 7805 will help keep it happy, and I would add
a load resistor so the 7805 still has a tiny load
(and doesn't go O/C) when the PIC disconnects the battery.
:o)
-Roman

PS. Nice web page, the Micromouse is cool. That is a
hard competition if you used the "pro" 16x16 maze.
Not an easy thing to build.

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2001\05\24@144843 by Peter L. Peres

picon face
> pulsed charge

In theory (the theory that I have read) the main effect is thermal. There
are also some nonlinear issues if you exceed the normal battery currents
grossly. 1/10 second is fast enough that even the smallest cells don't
have time to cool or heat significantly. I do not know what happens when
the cells are underdischarged and 1C current pulses are applied. NiCd
seems to like this anyway (it is one of the techniques used to 'revive'
dead cells as a last resort).

Remember that about half the 'fast' SLA chargers out there use pulsed
current (active thyristor rectifier on 16Vac transformer). NiCd is
supposed to be less sensitive to this than SLA. Ditto NimH.

Peter

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2001\05\24@180921 by goflo

flavicon
face
Lead-Acid pulse charging data:

http://www.ipenz.org.nz/Knowledge/Transactions/Transactions98/EMCh/1contents.htm

regards, Jack

Peter L. Peres wrote:
>
> > pulsed charge
>
> In theory ...

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2001\05\25@042710 by Peter L. Peres

picon face
Attn: John Gardner <KILLspamgoflospamBeGonespamPACBELL.NET> &others:

In my copy of Acrobat (3) on Unix all the pictures in the PDF document
appear as blank squares. Can anyone confirm this ?

The URL was:

http://www.ipenz.org.nz/Knowledge/Transactions/Transactions98/EMCh/1contents.htm

tia,

Peter

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2001\05\25@084946 by Bob Barr

picon face
Peter L. Peres" <@spam@plp@spam@spamspam_OUTACTCOM.CO.IL> wrote:
>
>Subject: Re: [EE]: Battery charger design
>Date: Fri, 25 May 2001 11:11:56 +0300
>
>Attn: John Gardner <spamBeGonegoflospamKILLspamPACBELL.NET> &others:
>
>In my copy of Acrobat (3) on Unix all the pictures in the PDF document
>appear as blank squares. Can anyone confirm this ?
>
>The URL was:
>
>http://www.ipenz.org.nz/Knowledge/Transactions/Transactions98/EMCh/1contents.htm
>
>tia,
>
>Peter
>

It's not much better under Acrobat Reader 5.0 version, some graphs are
there, most are blank.


_________________________________________________________________
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2001\05\25@102922 by goflo

flavicon
face
Mine too. The graphs describing battery behaviour in
the different charging regimes came up 5/5, though.
This weekend I'm going to cobble together a test rig,
have a go at reproducing their results.

regards, Jack

Peter L. Peres wrote:

> Attn: John Gardner <TakeThisOuTgoflo.....spamTakeThisOuTPACBELL.NET> &others:

> In my copy of Acrobat (3) on Unix all the pictures in the PDF document
> appear as blank squares. Can anyone confirm this ?

> The URL was:
http://www.ipenz.org.nz/Knowledge/Transactions/Transactions98/EMCh/1contents.htm

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2001\05\25@150058 by Martin Wehner

flavicon
face
Hello PICListers-

thank you so much for the input regarding my modest NiMH charger circuit!

Roman, I will make sure to add a few caps, as well as a load resistor. Great
idea!

Vasile, you are absolutely right: the circuit, as was posted on my web-site,
does not have enough head-room voltage-wise. I had plotted the graphs before
adding the diode and transistor to the circuit. Now that I have made those
additions, there isn't enough voltage to fully charge the batteries.
As soon as I finish making some adjustments, I will follow your advice, and
test it again with a higher supply voltage.

Thanks also for the comments regarding the micro-mouse. I will post more
pictures later on.
If you are involved in micro-mouse related activities do take a look at the
debugging tool I came up with; it proved to be incredibly helpful to me.

Thank you all & have a great holiday weekend!

       Martin



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web:    http://www.cyclotomic.com/~martin
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2001\05\26@051947 by Peter L. Peres

picon face
> This weekend I'm going to cobble together a test rig,
> have a go at reproducing their results.

Go easy on the current. Notice that they used 28A on a 28Ah battery (1C).
I'd suggest 0.5C for starters on a smaller battery and temperature
monitoring. In my experience charging with 1C directly does not cause
problems on the short term but the temperature must be kept under 40
degrees at any cost (sealed NiCd). The battery is normally full after 1.5
hours. I have not used pulsed charge for NiCd yet (only discharge). I have
used pulsed SLA chargers and they work as advertised.

Peter

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