Searching \ for '[PIC] Possible problems using solar panel to power' in subject line. ()
Make payments with PayPal - it's fast, free and secure! Help us get a faster server
FAQ page: www.piclist.com/techref/power.htm?key=power
Search entire site for: 'Possible problems using solar panel to power'.

Exact match. Not showing close matches.
PICList Thread
'[PIC] Possible problems using solar panel to power'
2005\08\30@142241 by John Nall

picon face
While I have some confidence in my ability as a programmer, I have no
confidence at all in my knowledge of electronics (not that I don't give
it my best shot, though).  So would appreciate any comments on a little
scheme I am thinking about.  Without going into the messy details, it
will involve a PIC which will get no power except from a solar panel.  
The voltage from the panel will go to a voltage regulator (probably a
7805) to power the PIC.  The idea is that the PIC will start its work
when the sun comes up and raises the voltage from the panel high enough
to start things.  When the sun is going down, voltage from the panel
will continue to drop (and eventually cease altogether) and the PIC will
go off.  It is a non-critical application, and so long as I get 4 or 5
hours of operation on most days, that will be fine.

Now this seems too simple, so I figure I must be missing something.  
Does anyone see any possible problems that would make it a non-starter?  
(The project has to do with a trickle charger for my sailboat, which
normally has no access to shore power).

John

2005\08\30@145124 by Marcel Duchamp

picon face
One area of interest is the transition as the sun comes up/goes down.
If it does this in a way to make the supply voltage change very slowly
the pic may not get a good start.  Solutions might include using the
pics built in brown-out settings or perhaps a supervisory chip. I would
verify safe, good operation at startup especially to avoid having the
system hang and not produce any power all day.
Good luck!

John Nall wrote:
{Quote hidden}

2005\08\30@150151 by Jose Da Silva

flavicon
face
On August 30, 2005 11:22 am, John Nall wrote:
> Now this seems too simple, so I figure I must be missing something.
> Does anyone see any possible problems that would make it a
> non-starter? (The project has to do with a trickle charger for my
> sailboat, which normally has no access to shore power).

Some processors such as the older Z80 has/had trouble with a slow rising
voltage and so would not reset properly, therefore, use the watchdog
timer to your advantage by using few of them interspersed about as far
apart as possible (aim for about 2 Sec if you decide to use the
x256counter else use a smaller spacing if you use a smaller divide on
the watchdog counter, i.e. about 8msec if no counter used).
If your processor starts dropping-out due to lack of voltage, the long
distance between (your program) watchdog resets should help stop your
program from creating havoc on the hardware.

2005\08\30@151131 by John Nall

picon face
Marcel Duchamp wrote:

> > One area of interest is the transition as the sun comes up/goes
> down. If it does this in a way to make the supply voltage change very
> slowly the pic may not get a good start.

My experience with solar panels (while cruising) is that it does ramp up
very slowly, from zero volts to the max (which is about 16 volts).  It
also is not consistent when starting up, because a cloud moving over the
sun or the boat swinging on the mooring will change the voltage.  Once
the sun gets up good this is normally not a problem, but would be until
it gets up in the sky good.  And the same holds true of the sun going down.

John

2005\08\30@152226 by Jan-Erik Soderholm

face picon face
On August 30, 2005 11:22 am, John Nall wrote:

> Now this seems too simple, so I figure I must be missing something.
> Does anyone see any possible problems that would make it a
> non-starter? (The project has to do with a trickle charger for my
> sailboat, which normally has no access to shore power).

Is the trickle charger run from the same solarpanel ?
And does it charge a normal 12V led battery ?
If so, you must have like 14-15 volt from the panel, not ?
Then you will burn quite a lot of power in the 7805/78L05.

Maybe having a small switcher with a wide input voltage range
för better efficency ?

Jan-Erik.


2005\08\30@154505 by John Nall

picon face
Jan-Erik Soderholm wrote:

>> Is the trickle charger run from the same solarpanel ?
>And does it charge a normal 12V led battery ?
>If so, you must have like 14-15 volt from the panel, not
>
It actually is a bit more complex than that.  It does charge a normal
12V lead battery, yes.  The panel will supply about 3.2 amps in maximum
sunlight, and the output voltage from the panel in maximum sunlight is
about 16 volts.  But this goes through a "charge controller" which
ensures that the battery doesn't get overcharged.  I agree that at that
voltage the 7805 would release a lot of heat, and that might be a
problem (although I can mount it on a heatsink).   There will be a lot
of power wasted because normally the batteries will stay topped up
(unless the boat springs a leak and the bilge pump comes on). The entire
purpose of the pic is to make the charge controller smarter than it
presently is (this is the M+ charge controller which some of you may be
familiar with).

I'm making careful note of all these suggestions, so keep 'em coming.  
:-)  Haven't seen anything yet which says that it is completely a
non-starter.  Not yet.

John

2005\08\30@160107 by Jose Da Silva

flavicon
face
On August 30, 2005 12:22 pm, Jan-Erik Soderholm wrote:
> On August 30, 2005 11:22 am, John Nall wrote:
> > Now this seems too simple, so I figure I must be missing something.
> > Does anyone see any possible problems that would make it a
> > non-starter? (The project has to do with a trickle charger for my
> > sailboat, which normally has no access to shore power).
>
> Is the trickle charger run from the same solarpanel ?
> And does it charge a normal 12V led battery ?
> If so, you must have like 14-15 volt from the panel, not ?
> Then you will burn quite a lot of power in the 7805/78L05.
>
> Maybe having a small switcher with a wide input voltage range
> för better efficency ?

using 2 2N3904 type generic NPN transistors should do quite well compared to a 7805 and don't forget to add some sort of choke in front of this whole power supply assembly to keep switching noises out of your cpu power supply circuit.
For to transistors, add a 100k on the 12v to 1st transistor base, while a zener 6.1v on base to ground. Add a 100n ceramic cap in front of base to ground.
Both collectors go to 12v. 1st transistor emitter goes to base of 2nd transistor. 2nd transistor emitter is your 5v output. Put a cap on the 5v output before running it to your 5v circuit.

Lot simpler circuit than a switcher and doesn't produce "noise" on the radio or power lines.

2005\08\30@162509 by Thomas C. Sefranek

face picon face

-----Original Message-----
From: spam_OUTpiclist-bouncesTakeThisOuTspammit.edu [.....piclist-bouncesKILLspamspam@spam@mit.edu] On Behalf Of
Jose Da Silva
Sent: Tuesday, August 30, 2005 4:05 PM
To: Microcontroller discussion list - Public.
Subject: Re: [PIC] Possible problems using solar panel to power PIC

On August 30, 2005 12:22 pm, Jan-Erik Soderholm wrote:
{Quote hidden}

using 2 2N3904 type generic NPN transistors should do quite well compared to a 7805 and don't forget to add some sort of choke in front of this whole power supply assembly to keep switching noises out of your cpu power supply circuit.
For to transistors, add a 100k on the 12v to 1st transistor base, while a zener 6.1v on base to ground. Add a 100n ceramic cap in front of base to ground.
Both collectors go to 12v. 1st transistor emitter goes to base of 2nd transistor. 2nd transistor emitter is your 5v output. Put a cap on the 5v output before running it to your 5v circuit.

Lot simpler circuit than a switcher and doesn't produce "noise" on the radio or power lines.


Why do you believe this is comparable to a 7805?
It is still a linear (darlington) regulator, still has to dissipate the same
power, but now you have smaller transistors with no easy heat sinking
ablility.
And it is a lot of parts and it's regulation is poor compared to a 7805.
No temperature shutdown, no current protection, etc...


 *
 |  __O    Thomas C. Sefranek  tcsspamKILLspamcmcorp.com
 |_-\<,_   Amateur Radio Operator: WA1RHP
 (*)/ (*)  Bicycle mobile on 145.41MHz PL74.4
ARRL Instructor, Technical Specialist, VE Contact.
hamradio.cmcorp.com/inventory/Inventory.html
http://www.harvardrepeater.org

2005\08\30@173114 by olin piclist

face picon face
John Nall wrote:
> While I have some confidence in my ability as a programmer, I have no
> confidence at all in my knowledge of electronics (not that I don't
> give it my best shot, though).  So would appreciate any comments on a
> little scheme I am thinking about.  Without going into the messy
> details, it will involve a PIC which will get no power except from a
> solar panel. The voltage from the panel will go to a voltage
> regulator (probably a 7805) to power the PIC.  The idea is that the
> PIC will start its work when the sun comes up and raises the voltage
> from the panel high enough to start things.  When the sun is going
> down, voltage from the panel will continue to drop (and eventually
> cease altogether) and the PIC will go off.  It is a non-critical
> application, and so long as I get 4 or 5 hours of operation on most
> days, that will be fine.
>
> Now this seems too simple, so I figure I must be missing something.
> Does anyone see any possible problems that would make it a
> non-starter? (The project has to do with a trickle charger for my
> sailboat, which normally has no access to shore power).

The basic scheme for running the PIC sounds good enough, depending on what
the normal sunlight and maximum output voltages of the solar panel are.  If
it's normally well above 5V, then a 7805 might be OK.  It requires a lot of
headroom though and an LDO may be more appropriate.  Also make sure to
enable the brown out detection module in the PIC.


*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com

2005\08\30@174314 by olin piclist

face picon face
Jan-Erik Soderholm wrote:
> Is the trickle charger run from the same solarpanel ?
> And does it charge a normal 12V led battery ?

If the goal is to charge a standard lead-acid battery, then you could leave
the PIC permanently powered from the battery via a low quiescent current
LDO.  The PIC only needs to wake up every minute or so for a few uS to see
if there is enough panel voltage to bother running the power supply.

On the other hand, the panel current will be limited to some maximum amount.
If that's an acceptable long term charge current for the battery, then just
connect the panel to the battery with a diode.  No PIC or any smarts needed.


*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com

2005\08\30@174706 by olin piclist

face picon face
John Nall wrote:
> The entire purpose of the pic is to make the charge
> controller smarter than it presently is

Smarter in what way?  It sounds like the existing systems works.  What more
do you want it to do?


*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com

2005\08\30@181656 by Jose Da Silva

flavicon
face
On August 30, 2005 01:25 pm, Thomas C. Sefranek wrote:

> Why do you believe this is comparable to a 7805?

It's in reply to the switching power supply versus the 7805 solution.

> It is still a linear (darlington) regulator, still has to dissipate
> the same power, but now you have smaller transistors with no easy
> heat sinking ablility.

> And it is a lot of parts and it's regulation is poor compared to a
> 7805. No temperature shutdown, no current protection, etc...

Seeing "now" that the solar panel is providing a respectable amount of
power of 3.2amps, there is no need to go this way. The 7805 is just
fine but the switching power supply appears over-kill.
Based on the suggestion of using a switching power supply to increase
efficiency, this may be a slightly better compromise than the 7805 if
the power from the solar panel was miniscule, which it isn't.

Okay, now that you pointed-out the disadvantages, here are some
advantages:

Lower starting voltage than 7805. The 7805 has a 2v dropout.

Peak input voltage is 40Vdc on a 2N3904.

Less wasted power than 7805 but still sufficient for a PIC and the PIC
shouldn't be doing anything active until it is needed (basically
everything is in off-mode until charger is overcharging).
Your overhead would be (16v - 6.1v)/100k=0.1mA if you have nothing
hooked up on the 5v output, but the 7805 will use 5 to 8mA of current
while doing nothing (see quiescent current here).
http://www.fairchildsemi.com/ds/KA/KA7805.pdf

You still need to deal with noise on the inputs and outputs, so that
means you still should have a choke on the front, an input cap and an
output cap regardless of this circuit idea or a 7805. The choke isn't
to deal with voltage ripple from the solar panel, but to deal with
spark generated noises that you would get from an on board engine,
otherwise, voltage ripple isn't likely an issue here. you don't need
flat/perfect voltage regulation, so whether the voltage drifts 0.8mV
(for a 7805) or 20mV is not going to make much difference here.

The difference between the 7805 is you have 2 transistors, 1 resistor
and 1 zener, which is more complicated than a 1 7805 but simpler and
less noisy than a switching power supply. since it's a hobbyist
project, it may be more interesting to build than a plain 7805 type
circuit, but less complicated than building and testing a switching
power supply circuit.

In terms of heatsinking, what type of circuit are we talking about?
I'm guessing on the active side, a PIC for sure, maybe 1 or 2 NPN
transistors switching some hi-voltage relay. The relay(s) +ve should be
connected to the 12v and not the 5v supply and the PIC should control
the relay(s) using an NPN between ground/relay(s).
With no sleep modes, we are probably talking about 2mA if the PIC runs
continually, or let's more than double it and say maybe 5mA.

2mA * (16v - 5v) = 22mW
5mA * (16v - 5v) = 55mW

2N3904 at 60degrees celcius max dissipation=210mW

It's a sailboat, so you don't get that much engine vibration, so clamp
an alligator clip to the head of the transistor if you think it's not
enough heatsinking.    ;-)

2005\08\30@182246 by John Nall

picon face
Olin Lathrop wrote:

>>> Smarter in what way?  It sounds like the existing systems works.  What more
>>do you want it to do?
>>    
>>

Certainly a fair question.  As it is presently set up, the solar panel
(when active) either charges at full capacity or else it does not charge
at all.  This is because it is controlled by a hard-wired  "charge
controller" which monitors the battery voltage.   When the battery
voltage reaches 14.3 volts (that figure is adjusted by a pot on the
controller) then the current flow is shut off.  For this particular
small panel that is probably OK, because the maximum charge rate is 3.2
amps.  However, I have some 15 amp solar panels up under the house, and
once things get to working right then I would replace the small panel
with a large panel.  The recommended way of charging the battery is not
to do an all or nothing charge, but to taper off as the battery voltage
begins to rise.  So that is where the smarts would come in.  This is
nothing particularly new -- I have a Heart battery charger on the boat
which does exactly that.  But it requires shore power, and right now I
do not have shore power available.  The charge controller  that I have
would certainly work -- but with the 15 amp panel it would not be as
good for the battery bank as tapered charging.  I have $500 worth of
golf-cart batteries on the boat and would like them to last their
maximum life.  Not only for the money, but also because taking 8
golf-cart batteries out of a sailboat and replacing them is a heck of a
hard job.  :-)

John

2005\08\30@212447 by Tom Sefranek

face picon face
Jose Da Silva wrote:

>On August 30, 2005 01:25 pm, Thomas C. Sefranek wrote:
>  
>
>Seeing "now" that the solar panel is providing a respectable amount of
>power of 3.2amps, there is no need to go this way. The 7805 is just
>fine but the switching power supply appears over-kill.
>Based on the suggestion of using a switching power supply to increase
>efficiency, this may be a slightly better compromise than the 7805 if
>the power from the solar panel was miniscule, which it isn't.
>
>Okay, now that you pointed-out the disadvantages, here are some
>advantages:
>
>Lower starting voltage than 7805. The 7805 has a 2v dropout.
>
Not according to Motorola specs...

@200ma., 60c, I get 1.5 volts min. 7805
Well that's not fair, your circuit can't do 200 ma. @ 6.5 volts in.
.4 volts/100K* gain of 100 (darlington 3904s) @ 200 ma. = huh? .4 ma.
I'll grant  that you can get a bit more,...  (lower current , higher
gain.), no where even close to 200 ma.

So, say 30 ma. 25c, I get 1.5 volts min. 7808
.4 volts/100K* gain of 4,900 (darlington 3904s) @ 30ma. = huh? 19.6 ma.
I'll grant you that some 3904' s have more than 60 gain at  30 ma, but
not enought to make a difference.

>Peak input voltage is 40Vdc on a 2N3904.
>
With a 6 milliamp maximum load ability.

Look at the 7805's 35 volt "limit", 5 volts less,  at  60c it has a load
limit of 300 milliamps,
vs. 7 ma. for a 3904.

>Less wasted power than 7805 but still sufficient for a PIC and the PIC
>shouldn't be doing anything active until it is needed (basically
>everything is in off-mode until charger is overcharging).
>Your overhead would be (16v - 6.1v)/100k=0.1mA if you have nothing
>hooked up on the 5v output, but the 7805 will use 5 to 8mA of current
>while doing nothing (see quiescent current here).
>http://www.fairchildsemi.com/ds/KA/KA7805.pdf
>  
>
And source only 10 ma., one LED!
A 78L05 of the same package as a single 3904 has 3.5 ma burden, but it
can source 100 ma.

>You still need to deal with noise on the inputs and outputs, so that
>means you still should have a choke on the front, an input cap and an
>output cap regardless of this circuit idea or a 7805. The choke isn't
>to deal with voltage ripple from the solar panel, but to deal with
>spark generated noises that you would get from an on board engine,
>otherwise, voltage ripple isn't likely an issue here. you don't need
>flat/perfect voltage regulation, so whether the voltage drifts 0.8mV
>(for a 7805) or 20mV is not going to make much difference here.
>  
>
With a 7805 and it's 70 db of rejection, a choke is unnecessary,
provided the bypass capacitors
are correct.

The difference between the 7805 is you have 2 transistors, 1 resistor

{Quote hidden}

On a sailboat I'd opt for the best, reliable, least parts circuit.

--
 *
 |  __O    Thomas C. Sefranek   .....WA1RHPKILLspamspam.....ARRL.net
 |_-\<,_   Amateur Radio Operator: WA1RHP  
 (*)/ (*)  Bicycle mobile on 145.41, 448.625 MHz

hamradio.cmcorp.com/inventory/Inventory.html
http://www.harvardrepeater.org


2005\08\31@003828 by Herman Aalderink

picon face


>> Smarter in what way?  It sounds like the existing systems works.  
What more do you want it to do?

>  When the battery voltage reaches 14.3 volts (that figure is adjusted
> by a pot on the controller) then the current flow is shut off.  For
> this particular small panel that is probably OK, because the maximum
> charge rate is 3.2 amps.  However, I have some 15 amp solar panels up
> under the house, and once things get to working right then I would
> replace the small panel with a large panel.

First ..... you have gotten some excellent answers from the PIClist.

The charge-current tapers off (at least somewhat) because the
battery-voltage rises.
You can re-inforce that affect by putting a diode in line. Effectively
reducing the solar-panel-voltage.
This narrows the battery-panel voltage and the current is reduced
accordingly.

For easy understanding of this effect: If you put enough diodes in-line
so the (panel-)voltage is reduced to 14.3 volt, your system has become
automatic (with no need for a charge-controller).  It has become a
constant-voltage charger. 14.3 Volt in your case. (I use 14.0 Volt, the
batteries will pay back in terms of a longer life. Cars use 13.8V afaik.)

If you really want to put your own smarts in the system, this is a good
opportunity : throw out your present charge-controllers and use a PIC.
Full charge below 12.7V battery voltage (no diode or resistor),
tapered-off charge above 27V (add diode or resistor to get your desired
charge current. At least 1 diode).

> I have $500 worth of golf-cart batteries on the boat and would like
> them to last their maximum life.  Not only for the money, but also
> because taking 8 golf-cart batteries out of a sailboat and replacing
> them is a heck of a hard job.  :-)


Lead-acid batteries are quite hardy. The only way to damage them quickly
is by serious overcharging. Especially the sealed type is sensitive to
overcharging. First-hand experience (on small sealed batteries).
You get long life with careful charging. The weak point is the operator
..... so the system should be fully automatic and fail-safe.

Herman in PHL.


2005\08\31@092706 by alan smith

picon face
dumb question...but what exactly is the PIC going to be doing?  Seems to me, if you choose a nanowatt part, you could just run it right off the battery bank?

__________________________________________________
Do You Yahoo!?
Tired of spam?  Yahoo! Mail has the best spam protection around
http://mail.yahoo.com

2005\08\31@093613 by olin piclist

face picon face
alan smith wrote:
> dumb question...but what exactly is the PIC going to be doing?  Seems
> to me, if you choose a nanowatt part, you could just run it right off
> the battery bank?

As long as you use a low quiescent current regulator.

*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com

2005\08\31@094934 by John Nall

picon face
alan smith wrote:

>dumb question...but what exactly is the PIC going to be doing?  Seems to me, if you choose a nanowatt part, you could just run it right off the battery bank
>  
>
Of course it could run right off the battery bank!  And it may well be
that I will wind up doing that.  But I like to have the option of
powering it from the solar panel, and wondered about what problems might
arise if I did so.  From my viewpoint, doing it that way offers some
benefits, such as automatically turning the pic on in the morning and
automatically turning it off at night.  It also makes the wiring
easier.  So far as the first question, the pic will be used to implement
a multi-stage battery charging algorithm.  Keep in mind, now, that this
is a hobbyist project, and as such it does not have to necessarily be
economically "reasonable." :-)

John

2005\08\31@095654 by alan smith

picon face
yes....guess that was an assumption without even stating it.

Olin Lathrop <EraseMEolin_piclistspam_OUTspamTakeThisOuTembedinc.com> wrote:alan smith wrote:
> dumb question...but what exactly is the PIC going to be doing? Seems
> to me, if you choose a nanowatt part, you could just run it right off
> the battery bank?

As long as you use a low quiescent current regulator.

*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com

2005\08\31@101329 by alan smith

picon face
Micrel and probably others make a dual input LDO that can accept a voltage from two sources...ie...a AC charger or battery.  So maybe using one of these so you can run from either source.  I don't recall if one is dominant over the other, I havent used them just looked at the spec sheet once when I was looking for a LDO sourcing from two supplies.

John Nall <jwnallspamspam_OUTgmail.com> wrote:alan smith wrote:

>dumb question...but what exactly is the PIC going to be doing? Seems to me, if you choose a nanowatt part, you could just run it right off the battery bank
>
>
Of course it could run right off the battery bank! And it may well be
that I will wind up doing that. But I like to have the option of
powering it from the solar panel, and wondered about what problems might
arise if I did so. From my viewpoint, doing it that way offers some
benefits, such as automatically turning the pic on in the morning and
automatically turning it off at night. It also makes the wiring
easier. So far as the first question, the pic will be used to implement
a multi-stage battery charging algorithm. Keep in mind, now, that this
is a hobbyist project, and as such it does not have to necessarily be
economically "reasonable." :-)

John

2005\08\31@112154 by olin piclist

face picon face
John Nall wrote:
> From my viewpoint, doing it that way offers some
> benefits, such as automatically turning the pic on in the morning and
> automatically turning it off at night.

How is that a benefit when turning it off saves 10uA drain on a large lead
acid battery?  It takes over 11 years at 10uA to amount to 1 amp-hour.


*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com

2005\08\31@113811 by John Nall

picon face
Olin Lathrop wrote:

> > How is that a benefit when turning it off saves 10uA drain on a
> large lead
> acid battery?  It takes over 11 years at 10uA to amount to 1 amp-hour.

Hey, 11 years can pass like a flash!!  :-)  Seriously, it is more
ethestically pleasing to me that way.  I already said that this was a
hobbyist project and didn't have to make good sense.  Loosen up, Olin,
and smell the roses like us modern day hippies do.

John

2005\08\31@150618 by Jose Da Silva

flavicon
face
On August 31, 2005 08:37 am, John Nall wrote:
> Olin Lathrop wrote:
> > > How is that a benefit when turning it off saves 10uA drain on a
> >
> > large lead
> > acid battery?  It takes over 11 years at 10uA to amount to 1
> > amp-hour.
>
> Hey, 11 years can pass like a flash!!  :-)  Seriously, it is more
> ethestically pleasing to me that way.  I already said that this was a
> hobbyist project and didn't have to make good sense.  Loosen up,
> Olin, and smell the roses like us modern day hippies do.

A lead-acid disconnected from everything will drain on it's own due to
internal leakage, so 10uA or even 10mA is nothing to a golf-cart type
battery.  I don't think you'll get that 11 year span.  ;-)

Reading the suggestion of powering the circuit via the battery only...
has anyone thought about...
How do you turn on the charge circuit if the battery is dead?

Consider this a vote for, if you decide to power it via battery, to also
get alternate power via the solar panel.  ;-)

2005\08\31@150638 by Jose Da Silva

flavicon
face
On August 30, 2005 06:24 pm, Tom Sefranek wrote:
> Jose Da Silva wrote:
> >On August 30, 2005 01:25 pm, Thomas C. Sefranek wrote:
> >
> >Seeing "now" that the solar panel is providing a respectable amount
> > of power of 3.2amps, there is no need to go this way. The 7805 is
> > just fine but the switching power supply appears over-kill.
> >Based on the suggestion of using a switching power supply to
> > increase efficiency, this may be a slightly better compromise than
> > the 7805 if the power from the solar panel was miniscule, which it
> > isn't.
> >
> >Okay, now that you pointed-out the disadvantages, here are some
> >advantages:
> >
> >Lower starting voltage than 7805. The 7805 has a 2v dropout.
>
> Not according to Motorola specs...

If you are a hobbyist, it is understandable and forgivable, but that is
a very bad sentence if you are a designer.

As a designer, if you spec a 7805 part into a design, you "should" be
looking at average specs, and "should" if possible, be testing your
design with bottom of the barrel parts for worst-case scenarios if
possible so that if you send a design to get manufactured, they can use
anybody's 7805 whether that is Motorola, Philips, or anyone's
7805 ....etc. If you go designing with top-line, or near top-of-breed
parts, then from a manufacturing point of view, you just limited the
number of possible suppliers to Motorola or anyone that can match or
exceed your "Not according to Motorola specs..."

For myself, I did not actively search out bad specs, I simply just went
to http://www.google.com, typed in 7805 and picked the 1st *.pdf in the list.
I wasn't looking for any particular brand part, however, the phrase
"Not according to Motorola specs..." to me suggests actively searching
out "better" specs to fit your argument.
If you are a hobbyist, don't worry about all this fuss, but if you
design equipment for a living, that is plainly poor behaviour.

As a true living example:
One of the places I worked at, we had "a" designed board which was
supposed to use generic 74something digital parts.
Let's say it was a 7404 or something like that for argument's sake.
The engineer who designed the board used Motorola parts when designing
the board and didn't use more liberal tolerances.
In manufacturing, we were forced to use that same Motorola part.
The reason was not because it was popular or generic, but because it was
the best-of-breed for that particular 7404 part.

Okay, if you are a hobbyist, ignore the bonking on the head above.
.... now to continue on with the debate.  :-(   :-/    :-P

> @200ma., 60c, I get 1.5 volts min. 7805
> Well that's not fair, your circuit can't do 200 ma. @ 6.5 volts in.

I think you failed to see the point here.
Is it necessary to build a Cadillac if all you need is a VW bug?
Great if the 7805 does 200mA, but does the circuit need 200mA?

> .4 volts/100K* gain of 100 (darlington 3904s) @ 200 ma. = huh? .4 ma.
> I'll grant  that you can get a bit more,...  (lower current , higher
> gain.), no where even close to 200 ma.

I grabbed the 1st *.pdf and you want to quote "better" specs for a 7805.
On the other hand, where did this 100gain come from? that looks
particularly bad. Did you search-out the worse 2N3904 specs you could
find to compare to your Motorola specs, because you certainly cut no
slack here hehehe.
...yes, I notice the 0.4 in respect to the 6.5v too.

Isn't it closer to 1000?
Again, doing a http://www.google.com search for 2n3904, here's the 1st *.pdf I
found (I'm not trying to aim for best or worse here... just a number):
http://web.mit.edu/6.301/www/2N3904o.pdf
Don't see 200mA, but it is a logarithmic scale, it has hFE = 30 for
100mA, so I'm going to guess maybe hFE = 15 for 200mA
200mA / 15 = 13mA
hfe for 13mA is about 100, so 13mA / 100 = .13mA

...so to get .13mA to the 1st transistor, you need about .13mA x 100k +
6.1v = 20v minimum on power supply. Yes, 200mA is not realistic, but
gain of 100 appears in error as well since I guess about 1500 above.

Anyhow, I was talking about 2 to 5mA, not 200mA, so...
5mA / (probably about 80) = 63uA
63uA / (maybe about 20) = 3uA
3uA x 100k + 6.1v = 6.4v
I guess this suggested circuit can give 5mA @ 5v if the input voltage
goes between 6.5v and 16v.

I don't know why you would need 200mA.

> So, say 30 ma. 25c, I get 1.5 volts min. 7808
> .4 volts/100K* gain of 4,900 (darlington 3904s) @ 30ma. = huh? 19.6
> ma. I'll grant you that some 3904' s have more than 60 gain at  30
> ma, but not enought to make a difference.

110K gain seems more reasonable, but I suggested a 100k resistor for a
5v 5ma supply.
If you wish to challenge best-of-breed 7805@6.5v versus gain of 100
mentioned earlier, how about trying use your 2N3904 packaged 7805
example with a 3.5ma burden below.
So instead of a 100k resistor, that would suggest a 2.8k resistor if we
want to leak 3.5mA like the 2N3904package-type 7805 you suggested.
Does it now come out okay to reach 30mA? how about 100mA?
How about your 200mA example.... I'll leave it to you:
0.4v/2.8k .....
If you want to quote specs like gain of 100 above, it would be
reasonable to level the playing field by using the suggestion I made of
2v drop found earlier versus the one you found of 1.5v, so instead of
0.4 try again using 0.9v/2.8k....

;-)

> >Peak input voltage is 40Vdc on a 2N3904.
>
> With a 6 milliamp maximum load ability.

We should factor in heat too, but that's okay if all you need is 2mA.

> Look at the 7805's 35 volt "limit", 5 volts less,  at  60c it has a
> load limit of 300 milliamps,
> vs. 7 ma. for a 3904.

Great.
As long as you select a 7805 that is above 16v plus a bit extra voltage,
then you should be okay.
You aren't going to be getting 300mA without a heatsink.
What would you do with 300mA?

{Quote hidden}

Well, if you like LEDs, guess you could put one on the output side
between the NPN transistor collector and the -ve side of the relay
coil.... which I was suggesting to the 12v side. Let's call it your
"Relay ON LED".  ;-)
You could add another LED in series between the +12v to darlington
collector 5v supply. Let's call it your "Power ON LED".  ;-)
Then put a whole row of NPN transistors driven by PORT X which pull-down
LEDs sourced from the 12v rail via 1k resistors. I don't know what you
would want to do with all these LEDs, but you can use them.  ;-)
Say goodbye to the 10mA, hello lots of LEDs.

You know what... I was thinking relays would be the best way to go since
you get virtually zero voltage dropout on the contacts giving you best
voltage at the battery... but this is really something John Nall is
building, so perhaps he has other plans and other circuits in mind.
It is, as he suggested, a hobbyist thing, so the field is wide open.

> A 78L05 of the same package as a single 3904 has 3.5 ma burden, but
> it can source 100 ma.

100mA at 16v needs a heatsink.
Like I stated earlier, in comparison to a switching power supply, the
darlington is simpler to build than a switching power supply and saves
more power than the 7805, and at the suggestion of about 2 to 5 mA has
virtually no 3.5mA leak.

{Quote hidden}

The suggested circuit doesn't need a choke either, but this is a
sailboat and there are likely a couple of fluorescent lamps (that
have ballasts) and if there is an engine (that has an ignition coil),
and if you use power tools, a shaver or blender to mix some cocktails in
the bar (more motors and inductors), it really does not matter if a
7805 has 70db of rejection because semiconductors don't last very long
in the presence of inductive voltage spikes.

The choke is still recommended if you want your semiconductors to live a
long time versus getting pulverized to death by inductive loads spiking
on the main power lines.
The choke blocks the spikes, the capacitor behind the choke forms a
low-pass filter, and this keeps the voltage somewhat regulated behind
the choke towards your semiconductors.
Having said that, it may be a wise idea to put a choke between the solar
panel and the main power-line because the solar panel is a
semiconductor.

{Quote hidden}

Fine, but it's not your sailboat, or your project.
All we do is throw suggestions and leave it to John to collect the info
and decide.

I found it interesting that you put a lot of emphasis on trying to
persuade on using the 7805. That's okay, but I'll re-quote my last
response concerning the darlington pair.
Seeing "now" that the solar panel is providing a respectable amount of
power of 3.2amps, there is no need to go this way. The 7805 is just fine
but the switching power supply appears over-kill.

Furthermore, sailboats have radios, and linear power supplies will
probably be a better choice over switching power supplies if dealing
with noise on the radio. Seeing in another thread that we are talking
about golf-cart type batteries and not tiny little nicads or something
miniscule in power, there is little point in trying to aim for a
maximum burden of 0.1ma versus as you suggest 3.5mA for the 7805.
If you look at the big picture, 0.1ma or 3.5mA is nothing compared to
internal battery leakage losses when speaking of golf-cart batteries.

If you use the darlington suggestion as a matter of interest. Fine.
If you use the 7805 suggestion for simplicity. Fine.

Cheers!


'[PIC] Possible problems using solar panel to power'
2005\09\01@064948 by Tim ODriscoll
flavicon
face
On Tue, 2005-08-30 at 14:22 -0400, John Nall wrote:
> While I have some confidence in my ability as a programmer, I have no
> confidence at all in my knowledge of electronics (not that I don't give
> it my best shot, though).  So would appreciate any comments on a little
> scheme I am thinking about.  Without going into the messy details, it
> will involve a PIC which will get no power except from a solar panel.  
> The voltage from the panel will go to a voltage regulator (probably a
> 7805) to power the PIC.  The idea is that the PIC will start its work
> when the sun comes up and raises the voltage from the panel high enough
> to start things.  When the sun is going down, voltage from the panel
> will continue to drop (and eventually cease altogether) and the PIC will
> go off.  It is a non-critical application, and so long as I get 4 or 5
> hours of operation on most days, that will be fine

Once you've decided how to power the PIC, Microchip's app note AN626
might be useful for you. It explains a circuit to charge a 12v SLA,
stopping when the voltage reaches a predefined level and checking it
every second or so afterwards.

Plus, if you've got other electronics running off the battery while it's
charging, the voltage read on the battery terminals will drop a little.
I've read that you're supposed to leave it open-circuit for a minute
before doing any voltage readings with respect to recharging.

I've been thinking of something similar to you, but on a campervan
instead. I've not done it yet, but was intending to have two batteries
in parallel, but only allow one of them to be connected at a time so I
could get accurate open-circuit voltages on the other. And it would
double the overall capacity, of course. I was going to run my charging
circuit off the battery being charged.

Good luck with it,

Tim

2005\09\01@092631 by John Nall

picon face
Tim ODriscoll wrote:

>Once you've decided how to power the PIC, Microchip's app note AN626
>might be useful for you. It explains a circuit to charge a 12v SLA,
>stopping when the voltage reaches a predefined level and checking it
>every second or so afterwards.
>  
>

I always hate like the dickens to just blatantly display my ignorance,
but sometimes it just cannot be avoided.  :-(  How do I access AN626?  I
went to the Microchip web site and clicked on application notes, but
didn't see any way to specify one by that designation (AN626).  I
realize there is a way, but just can't seem to find it.

John

2005\09\01@100214 by Tim ODriscoll

flavicon
face
On Thu, 2005-09-01 at 09:26 -0400, John Nall wrote:
> I always hate like the dickens to just blatantly display my ignorance,
> but sometimes it just cannot be avoided.  :-(  How do I access AN626?  I
> went to the Microchip web site and clicked on application notes, but
> didn't see any way to specify one by that designation (AN626).  I
> realize there is a way, but just can't seem to find it.

Go to http://www.microchip.com, click in the search box at the top left, type
in 'an626', then press the [enter] key on your keyboard.

AN626 is the first match. It's written for the 'pic14c000', but it'll
work with other PICs as long as they've got the same features; PWM, CCP
and an a2d converter, I think.

Cheers,

Tim



2005\09\01@110201 by Gerhard Fiedler

picon face
Jose Da Silva wrote:

>>> How is that a benefit when turning it off saves 10uA drain on a large
>>> lead acid battery?  It takes over 11 years at 10uA to amount to 1
>>> amp-hour.
>>
>> Seriously, it is more ethestically pleasing to me that way.  
>
> Reading the suggestion of powering the circuit via the battery only...
> has anyone thought about... How do you turn on the charge circuit if the
> battery is dead?

Yes, I also think it makes more sense to power the charge controller from
the charging source rather than from the to be charged battery.

OTOH, if you want to double-source it, you could add a deep-discharge
warning to your PIC (in several levels maybe); this way it would not only
be a charge controller, but starting to become a battery management system.

Gerhard

More... (looser matching)
- Last day of these posts
- In 2005 , 2006 only
- Today
- New search...