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'Battery Isolators (Totally Unrelated to PIC)'
1997\02\05@185456 by Brian Boles

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    Does anyone know what is in a battery isolator, the devices that let
    one alternator charge 2 batteries on seperate circuits in a truck or
    boat.  Is it low forward drop diodes or some kind of relay???

    I would go for a newsgroup but our IS dept. won't set us up for that.

    Rgds, Brian.                    spam_OUTbbolesTakeThisOuTspammicrochip.com

1997\02\05@194133 by bigb

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Brian Boles wrote:
>
>      Does anyone know what is in a battery isolator, the devices that let
>      one alternator charge 2 batteries on seperate circuits in a truck or
>      boat.  Is it low forward drop diodes or some kind of relay???
>
>      I would go for a newsgroup but our IS dept. won't set us up for that.
>
>      Rgds, Brian.                    .....bbolesKILLspamspam@spam@microchip.com
The only ones i've seen contain 2 low forward drop diodes.
Brian Hurst

1997\02\05@195346 by Tony Matthews

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Brian Boles wrote:
>
>      Does anyone know what is in a battery isolator, the devices that let
>      one alternator charge 2 batteries on seperate circuits in a truck or
>      boat.  Is it low forward drop diodes or some kind of relay???
>
>      I would go for a newsgroup but our IS dept. won't set us up for that.
>
>      Rgds, Brian.                    bbolesspamKILLspammicrochip.com
Two diodes is my experience in the maritime buis. Tony m.

1997\02\05@230517 by Bob Blick

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At 04:47 PM 2/5/97 -0700, you wrote:
>     Does anyone know what is in a battery isolator, the devices that let
>     one alternator charge 2 batteries on seperate circuits in a truck or
>     boat.  Is it low forward drop diodes or some kind of relay???

The diodes are not low drop. The voltage regulator monitors the actual
battery voltage and the alternator just produces a little more voltage. The
secondary battery is not directly regulated, just regulated because of its
similar connection.

-Bob

1997\02\06@090213 by William Sadler

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On  5 Feb 97 at 16:47, Brian Boles wrote:

>     Does anyone know what is in a battery isolator, the devices that let
>     one alternator charge 2 batteries on seperate circuits in a truck or
>     boat.  Is it low forward drop diodes or some kind of relay???
>
>     I would go for a newsgroup but our IS dept. won't set us up for that.
>
>     Rgds, Brian.                    .....bbolesKILLspamspam.....microchip.com
>

In the UK for a second battery in a towed caravan a relay is usually
used. The relay is switched on when the ignition of the vehicle is
switched on, (ie. when the engine is running).

William Sadler

1997\02\06@105520 by Martin McCormick

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       I privately wrote Bryan, but one of the replies to the group makes
me a bit curious.  I told Bryan that one would need a voltage regulator
for each path since the batteries might be in different states of discharge.
If one battery sulphated or was, for some reason, discharged more than the
other, the one that was most charged would get an overcharge while the
deader battery was trying to catch up.  Is this possible or am I just mistaken?
The battery with the highest voltage will totally carry the system since the
diodes won't let current flow any other direction.

Martin McCormick

1997\02\06@112229 by Bradley, Larry

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Except that in a lot of standard marine alternators, the voltage
regulator is built into the alternator directly, and only can monitor
the alternator output voltage, not the battery voltage.

West Marine sells a device (which would be easy to build) that is a
relay that parallels the two batteries when the voltage is "high",
indicating that the alternator is charging the batteries. When the
voltage drops to a level that suggests discharge, the relay opens and
the two batteries are disconnected form one another.

Larry

{Quote hidden}

1997\02\06@182736 by William Chops Westfield

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   I privately wrote Bryan, but one of the replies to the group makes me a
   bit curious.  I told Bryan that one would need a voltage regulator for
   each path since the batteries might be in different states of discharge.

Lead acid batteries, unlike NiCd's/etc, are usually charged from a
constant-volatge supply (ie same voltage regardless of charge state.)

BillW

1997\02\06@201600 by Bob Blick

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At 11:21 AM 2/6/97 -0500, you wrote:
>Except that in a lot of standard marine alternators, the voltage
>regulator is built into the alternator directly, and only can monitor
>the alternator output voltage, not the battery voltage.
>

Yes and no. The regulator is built into many alternators, but that does not
mean it can't monitor the battery voltage.

I don't want to contradict you, but if you check with alternator
manufacturers, you will find that the alternator output wire is "never"
used for sensing the battery voltage. There is always another wire used to
sense the battery voltage, even if it does not appear that way, ie the
"idiot light" wire serves two purposes, both sensing(input) and
indicating(output)(Mercury Capri among others).

Alternators can be incorrectly connected, and monitor their output voltage
rather than the battery voltage, but no boat or automobile manufacturer
will do it that way. Mechanics and do-it-yourselfers, on the other hand,
will do whatever they want, whether it's right or not, and it might "work"
sort of.

Cheers, Bob

1997\02\06@215204 by Tony Matthews

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Bradley, Larry wrote:
{Quote hidden}

It's only .7 volt and I have used the two diode method to charge and
maintain starter motor battery /lighting electronics battery many times
in commercial enviroments.

1997\02\07@001539 by *optoeng

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Bob Blick wrote:
>
> At 11:21 AM 2/6/97 -0500, you wrote:
> >Except that in a lot of standard marine alternators, the voltage
> >regulator is built into the alternator directly, and only can monitor
> >the alternator output voltage, not the battery voltage.
> >
>
> Yes and no. The regulator is built into many alternators, but that does not
> mean it can't monitor the battery voltage.
>
> I don't want to contradict you, but if you check with alternator
> manufacturers, you will find that the alternator output wire is "never"
> used for sensing the battery voltage. There is always another wire used to
> sense the battery voltage, even if it does not appear that way, ie the
> "idiot light" wire serves two purposes, both sensing(input) and
> indicating(output)(Mercury Capri among others).


Never say 'never'.  There are definitely alternators that have only 2
external electrical connections.

>
> Alternators can be incorrectly connected, and monitor their output voltage
> rather than the battery voltage, but no boat or automobile manufacturer
> will do it that way. Mechanics and do-it-yourselfers, on the other hand,
> will do whatever they want, whether it's right or not, and it might "work"
> sort of.
>
> Cheers, Bob

--
NOTE: remove asterisks from email address to reply directly

Paul Mathews, consulting engineer
AEngineering Co.

email: @spam@optoengKILLspamspamwhidbey.com
non-contact sensing and optoelectronics specialists

1997\02\07@035433 by Bob Blick

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At 09:06 PM 2/6/97 -0800, you wrote:

>Never say 'never'.

I didn't. I intentionally said "never" :-)

Cheers, Bob

1997\02\07@150259 by peter

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Anyone interested in alternators read on
if not delete

Before I start I would like to say that I am talking
about the type of alternator found on most European cars
and I'm sure there are exceptions

The alternator is a three phase AC generator
the three windings are connected in delta( triangle )
The three corners each go to two diodes (one to earth called D-
the other to 12V called D+ )

Now we come to the first variation
some alternators have three more diodes
which are connected to each corner to give a second
+ V.  These diodes are small (5amps)
This second + V. source powers, via the regulator,
the field ( also called DF )
This source is also connected to the ignition + via a
charge warning light, this has a double function,
first it powers the field (lamp lit) when the engine first starts
and indicates that the alternator is not charging

Regulators are normaly combinded with the brushes
but some are external normaly connected to the alternator
via a three pin plug, similar to a headlight bulb,
marked D-, D+ and DF

Regulators normaly use two transistors a Zener diode
one small cap (22n) and a few resistors
and the output is set to 13.8V
though a few are made for 14 or 14.2

Anyone want a circuit for a car regulator
email me direct and I'll send it to you
--
Peter Cousens
email: KILLspampeterKILLspamspamcousens.her.forthnet.gr
snailmail: Peter Cousens, karteros, Heraklion, Crete, 75100, Greece,
phone: + 3081 380534,    +3081 324450   voice/fax

After Bill Gates announced to the world that he was Microsoft,
his wife was asked to comment. She said that as his wife, she
had been the first to notice this problem

1997\02\10@131527 by Bradley, Larry

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The regulator on the Motorola alternator on my boat (>25 years old)
appears to use pulse width modulation to control the field current ...
at least, that's what it looks like on a 'scope
Larry
{Quote hidden}

1997\02\10@164903 by peter

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Bradley, Larry wrote:
>
> The regulator on the Motorola alternator on my boat (>25 years old)
> appears to use pulse width modulation to control the field current ...
> at least, that's what it looks like on a 'scope
> Larry
> >----------
> >From:  Peter Cousens[SMTP:TakeThisOuTpeterEraseMEspamspam_OUTcousens.her.forthnet.gr]
> >Sent:  Saturday, February 08, 1997 12:56 AM
> >To:    RemoveMEPICLISTspamTakeThisOuTMITVMA.MIT.EDU
> >Subject:       Re: Battery Isolators (Totally Unrelated to PIC)
> >
> >(SNIP)
> >Regulators normaly use two transistors a Zener diode
> >one small cap (22n) and a few resistors
> >and the output is set to 13.8V
> >though a few are made for 14 or 14.2

Yes they do work in switchmode
thats what the 22n cap is for

--
Peter Cousens
email: peterEraseMEspam.....cousens.her.forthnet.gr
snailmail: Peter Cousens, karteros, Heraklion, Crete, 75100, Greece,
phone: + 3081 380534,    +3081 324450   voice/fax

After Bill Gates announced to the world that he was Microsoft,
his wife was asked to comment. She said that as his wife, she
had been the first to notice this problem

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