Be careful with using combiners. They work OK when the two banks are of
equal size and equal charging needs, but if the house bank is large and
needs a long charge, while the gen set battery is small and is already
charged, the combiner will result in grossly overcharging the gen set
battery and boiling off its water.

Remember, the combiner is only looking to see if a charge voltage is present
on the main battery, and if so, it kicks in and parallels the second
battery. It does not sense the state of charge for the second battery, and
it will not keep the connection open if the charge is not needed.

The best solution I've seen on this thread so far was the advice to find out
why the gen set alternator was not charging the gen set battery and/or find
what was draining the battery. Fix the main problem and there is no need to
go to all sorts of fancy work-arounds.

Kevin
www.BoatMoves.com

Kevin makes a great point. I cooked my engine battery just that way. I
recently re-wired all the "up front" battery circuits. I got rid of the
combiner and all associated wiring. Today the charging system(s) are very
simple. Engine alternator and battery is now only for just the engine, bilge
pump, and engine helm console lights. The genny battery and alternator are
on there own, except for a dingy winch. The house batteries are only for the
house. They charge two ways. I added a 100 amp high output alternator with
three stage external regulator for charging underway, (much less genny run
time!) OR while on shore power or genny power, the inverter / charger takes
care of the charging of the house bank. The setup is much simpler and
straight forward. I purchased a three stage battery charger that will handle
three banks and was going to charge the genny batt and the engine bat with
it. Well it's mounted and the wires are run but I don't think I need it! We
are full time cruisers and even if we park the boat for a month, the engine
and genny batts never need a charge. Well..I spoze I'll hook the new charger
up to the engine battery just in case that bilge pump kills it. Oh yea...I
carry jumper cables just in case! Fix the Genny alternator.

Respectfully,

Ken

I am reading my messages from the bottom up, so perhaps someone else has
already made a comment similar to mine.

Sorry I disagree. As far as I know, the size of the batteries (banks) and
their charge levels at the beginning of the charge cycle are irrelevant.

Maybe there is more than one brand of combiner?

The one I know allows the charging source to charge the 'primary' battery
(bank) until it gets to about 13.3 volts, then puts the secondary battery
(bank) into parallel. The charging voltage only increases when both batteries
have reached an equal charge (voltage) level (13.3). If the secondary battery
was already fully charged it would slightly discharge as IT CHARGES THE
PRIMARY BATTERY. They then continue charging at exactly the same levels
(instantanious voltage level) until the charger decides it is time to stop.

To my mind, a combiner is an electronic set of jumper cables. If you had a
high charged battery and a low charged battery 'jumped' together, then allowed
you car engine to run, you would not 'overcharge' the high one. The low one
would be charged by the alternator and the high one. The high one would
discharge into the low one, in spite of the energy from the alternator. When
both batteries had an equal charge level (voltage) then BOTH would continue
charging at identical levels (voltages) until the alternator was shut down.

The combiner has no influence on the volyages reached, nor any potential
overcharging. That will only happen if the charger (alternator, genset, line
charger) is defective.

Arild .. if you haven't already jumped in ... please do so.

Seasons greetings
Peter

Peter

present

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secondary

CHARGES THE

It appears that some listees have swallowed the Kool Aid that some combiner
manufactures have put out. The 13.3 volts specified above would only be seen
during the bulk charge or float charge part of the three stage charger
cycle, not during the longer absorption phase which typically runs between
14.2 and 14.5 volts, and can last for many hours. Even my old 6 amp Sears
ferroresonant charger puts out 14.3 volts (yes, I measured it - I don't post
guesses on this topic), and I've watched that charger cook a fully charged
battery with its 14.3 VDC.

Please don't get me wrong - battery combiners are great devices and have
their use - in the proper circumstances. However, the situation that we are
dealing with in this tread is that of a small gen set battery being put in
parallel with a large house bank.

Some people believe the myth that the gen set battery cannot be overcharged
with a combiner. That is a fallacy that the combiner makers would like you
to believe, but is not supported by fact. When the three stage charger is
pumping out 14.4 volts in absorption mode, using a combiner to bring in the
gen set battery is electrically no different at all from having the gen set
battery all by itself with an old ferroresonant charger putting out a
constant 14.4 volts. Whether it is getting it from the combiner terminals or
from a separate charger, 14.4 volts is 14.4 volts - and a long or continued
exposure to that can overcharge a fully charged battery. As Ken Williams
posted on Monday, that is exactly what happened to him when the use of a
combiner resulted in his engine start battery being cooked.

One combiner manufacturer's web site I reviewed provides their flavor of
Kool Aid with lots of mumbo jumbo about plate size and Ohms Law, but ignores
that simple fact that if you keep an elevated charger voltage across the
terminals of a fully charged battery, you are overcharging the battery! I
believe the battery manufacturers and my own measurements on this, not the
combiner manufacturer's sales claims.

Remember, all the combiner does is to jumper the two batteries together,
just as the 1-2-Both switch does in the Both position (or a set of jumper
cables would do). When combined, the gen set battery is going to see the
terminal voltage presented by the charger - and that is around 14.2 to 14.4
volts in absorption mode depending on temperature (you do have a temperature
probe from your battery to charger don't you?).

For the hours that the house bank takes to come to full charge, that same
1.4 volts will be overcharging the already full gen set battery. Not, it
cannot discharge into the house bank as some other have posted. That blarney
would require the charger voltage to be almost a full volt lower, but since
it is really over 14 volts, the gen set battery will be accepting current
instead of contributing it as claimed.

If you really want to know what your batteries are doing, one of the best
additions you can make for your boat is a smart battery monitor such as the
Xantrex Link monitors. These monitors allow you to see the voltages and
resulting currents going both in and out of the batteries. You can watch the
charger go through its three stages, and see how the three different voltage
levels result in different current flow.

A good explanation of the three stage charging process can be found at
www.xantrex.com/web/id/1802/docserve.asp

Exide batteries addresses the issue of overcharging batteries at
www.exide.com/faq/faq_marine.html#overcharge  On that page, straight from
the horse's mouth you can see what the manufacturer says about overcharging

• and the battery doesn't care whether the charge current is being routed
  via a combiner, and 1-2-Both switch or a dedicated charger!

Kevin
www.BoatMoves.com

in answer to a post by Kevin ;

I think it is unfortunate that you might be biasing certain boat owners on
this forum against the use of a combiner. For anyone who spends time away from
the dock, and/or has a smaller house bank than might be wished and/or who has
a generator and/or who has a large windlass, a combiner is a gift from
heaven!

Batteries charge by current, not by voltage. As the current into the battery
'fills them up' and raises their voltage, their ability to accept additional
current decreases. As in .. a depleted battery will accept a higher current
from a charging source than a 'full' battery

You state,> For the hours that the house bank takes to come to full charge,
that same

I don't accept that.
Because of the combiner, the gen set battery is in parallel with the house
bank. If it were a 50ah battery and were put in parallel with a 450ah house
bank, it would be 10% of the total circuit. It would only accept 10% of the
(miniscule) current the charging source was able to provide. It will be no
more, no less 'overcharged' at the end of the charging process than the house
bank.

More importantly!

You make several references to 'Kool Aid'  Are you in any way connected to
this product?
How about Minute Maid?
Tang?
Are you implying that Kool Aid is better than these products?
Worse?
Is Kool Aid a complimentary or purgerative description?
Have you ever ingested Kool Aid?
Alone or with others?
Did you swallow?

Like you, when I don't understand the technical description of a product, I
call it names.
I really like 'mumbo_jumbo'  I was using the term 'gobbledygook'. But I
realize that 'gobbledygook' is politically incorrect, and may bring back
certain negative memories to people of our generation. On the other hand
'gobbledy_person_who_lived_in_the_Northern_province_of_a_certain_part_of_Indo
-china' is much too long to write. So I'll use mumbo_jumbo from now on.

OK .. I'll trust the word of the battery manufactures rather than the word of
the combiner manufacturers. The battery manufacturers wouldn't want to deceive
me, would they? If they did, I could ruin my battery and I'd have to buy
another one. They wouldn't want that, would they?

I think we have gotten into the 'Nit' picking stage of the discussion. I
suggest that the prime killer of batteries is heavy discharge. Next is poor
control of the charging source. Next comes neglect, next comes age. The
advantages of using an automatic combiner far, far, far outweighs its
potential disadvantages.

And as long as none of the batteries are defective, mixing small and large,
old and new is a non-issue.

Peter

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