Isolator

T

travism

New member
Jan 18, 2000
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Your instincts are right; you have a problem with your isolator. As the name
implies, all of the outputs should be isolated from each other.

It is nothing more than three large diodes with a suitable heat sink. The
normal failure mode for semiconductor devices, like diodes, is to short;
this is not unusual.

You might want to consider replacing the isolator with a combiner; they have
several advantages.

Best,

Travis in Lubbock, Texas....78 Palm Beach (am I still the newest
ex-wannabe?)

> Netters: Need input. While attending to my batteries I experienced the
> following what I detect may be a problem. The configuration is two
batterys
> up front and the gen set battery in the rear. I have a SurePower isolator
> with 1 pole in and three out. I also have a relay for connecting the two
> (truck and house) batterys together. As I moved my positive truck battery
> cable around ( with the truck battery out of the coach) I touched it to
the
> frame and saw a slight spark. The source is from the wire connected to one
of
> the three output poles on the isolator which comes from the rear gen set
> battery. This wire is obviously used to charge the gen set battery when
the
> alternator is running. But should one of the other 2 output poles be
> "energized " by this wire? The 3rd is not, but the one that runs to the
relay
> and to the truck positive cable is, thus giving feed back thus the spark.
> This does not seem right but don't know how to check an isolator. TIA Dean
> Hanson
 
>This does not seem right but don't know how to check an isolator. TIA Dean
>Hanson

Hi Dean,
One way assumes you have the isolator disconnected. If you have a
multimeter to allow resistance checks, use it to check for forward and
reverse resistance of each of the three diodes. Place the negative lead of
the meter on the common anode (the input pole) and the positive lead of the
meter on each of the cathodes (the output poles) in turn. The resistance
should be around 100 K ohms or better. Reversing the leads and repeating
the tests should yield a low resistance on each pole.

Without a meter, and the isolator installed and otherwise connected
normally, another way to test is to remove the 12v from the input pole,
place a small 12 volt bulb (a test light should work OK) from there to
ground and see it it lights. If it does, then one of the diodes in the
isolator is bad. Make sure there are no relay bypasses engaged for this test.

Regards,
Steve in N. Texas
 
> Travis: what are the advantages of a combiner? Dean

Mostly that there is essentially no loss in a combiner. A combiner is a
relay that ties the batteries together through contacts, together with the
associated controls to determine when to connect them.

A silicon diode, as in the isolator, has an inherent voltage drop of around
6 or 7 tenths of a volt; this voltage drop, multiplied by the charging
current flowing through the diode, equals a pretty fair amount of power that
is simply converted to heat...that's why the isolator has to have a large
heat sink. Since the combiner is copper contacts, there is practically no
loss in it. There are those who think them more reliable also, but that's
hard to say; a quality diode will generally last forever if it is not abused
and it has the advantage of no moving parts. A good case can be made for
each.

My GMC has an isolator and it is working well; I can't see any reason to
change it. If it were to fail I'd have to give some consideration to a
combiner. Most likely several of the guys that have tried both will jump in
with their experiences to help you decide.

Travis
 
> also read the links listed here
>
> http://www.california.com/~eagle/batt.htm
>
> gene

Wow; I keep forgetting how much is archived there! This kinda reminds me of
the old saw about the guys who had told each other the same jokes so many
times that they assigned them all numbers---then all one of them would have
to do is say "37" and the other would break out in laughter...there just
aren't many questions that you can come up with that haven't already been
hashed and re-hashed and then archived.

What a resource!

Best,

Travis
 
56

ha
ha
ah ha

yep just like that. When we find we have something wrong , then we can
change it right away,,,,, power of the net

gene

>> also read the links listed here
>>
>> http://www.california.com/~eagle/batt.htm
>>
>> gene
>
>
>Wow; I keep forgetting how much is archived there! This kinda reminds me of
>the old saw about the guys who had told each other the same jokes so many
>times that they assigned them all numbers---then all one of them would have
>to do is say "37" and the other would break out in laughter...there just
>aren't many questions that you can come up with that haven't already been
>hashed and re-hashed and then archived.
>
>What a resource!
>
>Best,
>
>Travis
>
>
Genef -- 77PB/ore/ca
GMC MOTORHOME INFORMATION
mr.erf
http://www.california.com/~eagle/
 
>In a message dated 07/08/2000 6:10:07 PM Central Daylight Time,

>
> > You might want to consider replacing the isolator with a combiner; they
> have
> > several advantages.
> >
>Travis
>
>I have some questions about isolators and combiners. I have seen all
>this stuff about not charging the batteries in parallel. Well, from where
>I sit that seems to be what a combiner does. Is an isolator any better
>at this task? I honestly dont know.

An isolator is simply a series of diodes configured so that they block
current from flowing form one battery to the other. At the same time, the
diode configuration permits current to flow from the alternator to BOTH
batteries.

Charging both batteries in parallel isn't the problem - discharging them in
parallel is the real culprit. IT's possible to configure battery banks so
that they can be paralleled to discharge but not recommended for extended
use. The problem with paralleling battery banks is that the batteries will
discharge each other unless they have exactly the same charge state. What
happens in the discharge scenario is that the bank with greater charge
tries to charge up the weaker bank, so it discharges itself until the two
banks appear to be equal. The bank that started out stronger actually
discharges itself to a lower state because of the way the battery chemistry
works. Now the batteries switch roles - the one that previously discharged
in order to charge the other now gets charged instead. Since there are
losses during the charging process (heat), the two banks see-saw back and
forth until they are both dead.

> I do know that my fancy 40 amp
>charger comes on at an over 20 amp charge when I first hook up shore
>power after being on the road all day. I have an isolator.

The biggest advantages to the combiner are lowered voltage drop as compared
to the isolator and the intelligence to parallel the battery banks when the
alternator voltage is high enough.

> While I was on my
>trip my Ragusa 3 battery front tray came in. Yeah I am all done working
>on my rig. I sure would like to hear some talk about charging 3 battery
>banks.

You have the TrueCharge 40. It has two separate charging outputs. Run one
to your new house batteries and the other to your existing house batteries.
Use a combiner to allow the engine battery to be charged when the
TrueCharge puts out enough voltage. OR, use two combiners to allow all
batteries to be charged whenever enough voltage is present.

There are other alternatives as well. It all depends on how you'll use your
coach.

Henry
 
Arch

If your charger will charge 3 isolated banks you can use a three battery
diode isolator for the alternator charging. This will let the alternator
charge all three banks. If your charger will only charge two banks, you
can put a combiner from either of the first two banks to the third bank,
and the combiner will maintain the charge from any of the chargers.

Rememeber diode isolators have a big heat sink for a reason, they use up
power during charging. They always fail shorted so they will connect the
banks togeather when they fail. They provide charging from only one source.

gene

>In a message dated 7/8/00 9:10:49 PM Mountain Daylight Time, Gcbr
>writes:
>
>> I sure would like to hear some talk about charging 3 battery
>> banks.
>
>Arch,
> I'd use a 3-Battery isolator. BTW, since our alternators are (supposed
to
>be) "battery-sense" type, they should automatically compensate for the
>voltage drop through the isolator. (ie: they have a separate wire running
to
>the battery to sense voltage. The regulator then adjusts output so that the
>battery receives proper charging voltage, regardless of voltage drop.
> This, of course, means that one should not install a so-called
>"one-terminal" alternator (AKA "machine sense") on a GMC.
>
> OBTW, WELCOME BACK! Sounds like you had a great trip.
>
>Rick Staples
>'75 Eleganza
>Louisville, CO
>
Genef -- 77PB/ore/ca
GMC MOTORHOME INFORMATION
mr.erf
http://www.california.com/~eagle/
 
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