2 Bank Battery Chargers, and a Combiner

[Dan Hayes]

Hi There All -

My Not Mechanically Gifted Question of the Week is this... I have something called a Battery Combiner hooked up to my batteries. This thing is supposed to equalize the charge from the alternator when the engine is running and charging the batteries (I think). So each battery gets the correct amount of charge (or so I've been told). However, what about when I hook up a battery charger at the dock, and want to charge the batteries - do I leave the combiner hooked up? Should I disonnect it, and charge them one at a time? That's what I've been doing.
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Am I better off buying a two bank charger?
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My second part to this question is - do you guys leave a battery charger hooked up to your boat? The PO of my previous boat said to never do so - that to do so invited electrolysis. I'd like to do a few things around the boat, play the stereo, run the lights, etc. and then have the batteries fully charged when I go to the boat next time. Will I be subjecting my prop and shaft to the horrors of electrolysis if I hook up a charger all the time? Year in and year out, it's OK?

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Your esteemed opinions are greatly appreciated. Thanks!


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[rgoff]

Get a small solar panel ($100 or so) and leave it hooked up all the time to both batteries. That's what I've done for 20 years (same panel) and I always have fully charged batteries each visit. Of course, this depends on if you live where the sun shines.

 

[NateHanson]

My second part to this question is - do you guys leave a battery charger hooked up to your boat? The PO of my previous boat said to never do so - that to do so invited electrolysis. I'd like to do a few things around the boat, play the stereo, run the lights, etc. and then have the batteries fully charged when I go to the boat next time. Will I be subjecting my prop and shaft to the horrors of electrolysis if I hook up a charger all the time? Year in and year out, it's OK?

You're correct that leaving the shore power cord hooked up all the time invites stray current corrosion between the bonded underwater metals of your boat and the boats near you that are also pluged in. The ground wire provides the electrical connection necessary to make a battery out of you and your neighbors.

You can get around this with a galvanic isolator or an isolation transformer ($$). Nigel Calder describes the problem and possible solutions in his book. Definitely worth a look.

Nate

 

[Geoff Johnson]

The combiner merely parallels the batteries when the voltage rises 13.5 volts or so. I don't use one becauser I charge my batteries only off the engine and leave the switch in the "BOTH" position (I have a separate starting battery). My boat is on a mooring so I too use a small solar panel but not with a combiner because the combiner uses at least .15 amps, which is a major hit opn a small solar panel. I alternate the panel between batteries every week.

 

[chaco]

Two-Bank Charger

As you have a two-bank battery system you will need a two-bank charger
for automatic equal charging of each battery. A one-bank charger will get
feedback from the battery that is charged first and back off the charge.
You would have to charge each battery manually with this arrangement.
Check out Xantrex (www.xantrex.com) they make a whole range of
automatic multi-bank chargers with galvanic isolators BUILT-IN.
I have the dual 10A model for (2) 80AH Deep Cells....works great.
You need to have some sort of charging of batteries at all times.
Batteries will go dead just sitting there without use.
Be it solar or shore power, you need power for your bilge pump for those
little emergencies. I manually "combine" my batteries with a
4-way switch for starting-both / charging-both / using-1 or 2.
Will upgrade to external regulated alternator / electronic controller with
two-bank output ( (2) House / (1) Start battery).....no need for a combiner.

Happy Battery Bank /) /)

 

[u079721]

I've wondered that too....

My boat also had a two bank modern 3 step charger, AND a battery combiner in the set up. As mentioned above you don't really need a combiner, but I liked the foolproof simplicity of it, not having to remember to switch the batter bank switch from 1 to ALL and back again.

In my case I kept the combiner installed for use while cruising. Most of the season while at the dock I would keep the combiner disconnected, and just use the two bank charger. But I would only use that every other weekend or so, not all the time, since there was no need. But while cruising (away from shore power) I would hook the combiner back up. That way I could just leave the battery bank on House and forget about whether the engine back up battery was topped off or not, and also didn't have to worry about accidentally drawing down the engine battery as well.

I'm not sure what happens if you have the combiner hooked up at the same time as the charger. I've done it, and nothing catches fire or anything, but it may not be the best way to do it. That's why I only hook up the combiner when cruising away from shore power. (To disconnect it just undo the groud connector.)

And if you haven't noticed by now....if there are 10 boaters around, there will be at least 10 (if not 11 or 12) ways suggested to rig up your battery system!

 

[Dan Hayes]

Yes, lots of opinions, but lots of great ideas, too. I think your solution sounds perfect for me, as a two bank charger just used while I am tied up to the dock sounds like an elegant solution to me. The things I use at the dock are primarily 12 volt - radio, cabin lights, etc., but I don't like to run down the battery. And, I don't like the idea of leaving my shore power cord connected all the time (for the reasons indicated above). So, I can easily disconnect the combiner while using a two bank charger, and not have to buy a galvanic isolater, and be done with it. Unfortunately, I recently bought a new high tech three stage single battery charger, which can now live in my garage...
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One quick question - are there any issues with running lights and a stereo while hooked up to a battery charger?

 

[u079721]

One quick question - are there any issues with running lights and a stereo while hooked up to a battery charger?

No problem at all. It just takes a bit longer to bring the batteries up to full charge if you are draining them at the same time.

 

[Tom Metzger]

... Unfortunately, I recently bought a new high tech three stage single battery charger, which can now live in my garage...
QUOTE]

Dan - Keep in mind that a lot of the ideas that you get on the net are worth exactly what you pay for them. Have you ever noticed that almost everyone says that the product or system they have is the greatest? It's human nature, but that doesn't make it true.

Why would you be willing to take out a brand new charger that has one output to put in a new charger that has one output split to two terminals? You already have a combiner to do the splitting. Not too smart IMHO.

If other people in your marina are burning through zincs you can take a hundred of the dollars I just saved you and invest in a galvanic isolator. Defender has them for $95. http://www.defender.com/category.jsp?path=-1|328&id=303336&start=11&results=1&sort=products

And to those of you switching out combiners while using a multiple output charger, you are wasting your time. Your charger has only one regulator so both batteries see approximately the same voltage. A fully charged battery does not tell a charger to shut down if the other battery needs a charge. Charge currents a split according to need.

"My humble opinion" is based on several years of engineering experience including designing battery systems.

 

[Loren Beach]

Isolating those galvanics...

Yo Tom,
If money were, um, less of a concern...
would you install the galvanic isolator or an isolation transformer?

Just curious...

Thanks,
Loren in PDX

 

[Tom Metzger]

Yo Tom, If money were, um, less of a concern...
would you install the galvanic isolator or an isolation transformer?

Loren - I assume that when you say that money is not the motivator you are talking about your 75 foot Oyster.

An isolation transformer is more reliable than an isolator. Also more weighty, and larger, and more expensive. All of these items decrease in importance as the size of the boat increases.

The cheapest 30 amp isolation transformer At Defender costs four times what the galvanic isolator costs and weighs 60 pounds, vs 1 pound.

 

[ted_reshetiloff]

I am with Tom here. I use a Xantrex True CHarge 20 with a combiner. I have feeds from the AC charger going to both banks (house and start). The combiner is for when I am charging off the engine as my alterator output goes straight to my house bank, but one feed to the house bank with a combiner to get to the start battery would be fine. I use a blue seas panel which has a key type switch for emergency parralleling. My starting battery is connected to one thing: the starter, only feed off the starter is the engine panel. Most systems have the alternator output going to the starter then back to the battery switch. This topic of isolating staring batteries has been covered in other threads but the jist is just what Tom said. AC charger with a combiner to charge the starting battery is fine. Again to Toms point all this is just MHO...

 

[Tom Metzger]

Please don't interpret what I said as a recommendation of the optimum system, or even a good system. I was just commenting on the equipment mentioned. Different use patterns require different equipment, and there was no mention of this.

 

[Dan Hayes]

OK, guys, so let me get this straight... I can plug my single bank multi-stage charger into one battery - and it will charge, through the combiner, both batteries? That would be good news. I was under the impression that it might short something out, or be unable to determine that one battery was full, and so would overcharge the first battery.

So, do I leave the battery switch on One, Two, or Both when I am using my single bank charger?

Again, thanks to all of you - all this discussion is great, as I am learning a lot from this (as, I'm sure, are a lot of other owners).

 

[Geoff Johnson]

All the combiner does is to put the attached batteries in parallel when a certain voltage is reached (e.g. 13.5 volts). You don't need to touch the battery switch. The combiner should be able to handle a charging current of at least 20 amps.

 

[Jeff Asbury]

Guilty! Gross Polluter of Electrolysis Here!

For what it's worth, I am at the same Marina as Dan. I have a 3 stage charger on all the time with a parallel bank of two deep cycles and a separate bank single starting battery. No Isolator. I have been at this Marina for four years and only have had to replace my zincs 3 times. I have inspected my strut, shaft and prop annually and have found no problems. Am I just lucky or am I still looking for trouble? I have noticed that most boats I see do have their shore power connected all the time. Especially the live aboards. Am I going to hell?

I do have a 5 watt Solar trickle charger that I only use when I am sitting at anchor. :eek:

 

[rwthomas1]

This is very interesting as everyone I see is plugged in to shore power all the time and I have never heard of anyone at my club having any problems. Most of these folks are powerboaters with fridges, AC, etc. running all the time in summer but the sailboats are all plugged in too. RT

 

[ted_reshetiloff]

Jeff have you checked your heat exchanger zinc? These are pretty small usually and dont last nearly as long as a big shaft zinc. Wait a minute you probably have no heat exchanger and run an A-4?

 

[Jeff Asbury]

Nope, No heat exchanger on my little sea water cooled 1GM10 Yanmar Diesel. I do have a internal zinc in the engine and I changed it out about 3 months ago. It appeared to be completely un corroded. The Yanmar manual said to scratch it with a wire brush to test it. If less than 50% remained, replace it. Well I scratched it and it completely crumbled. So I replaced it. This is something I will also check annually. It was a real son of a #@%! to get to. Had to take the alternator off.

 

[ted_reshetiloff]

Spoke with a marine electrician I know and he said those engine zincs rarely last more than 3-4 months because of their size and because so many people leave their boat plugged in to AC all the time. Mine did not last a year either.