Overcharging Batteries with a Combiner or ACR

[Stu Jackson]

In another forum (C36IA) we were discussing using combiners or ACRs.  Maine Sail, quite properly, corrected my incorrect assumptions.

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Quote:
Originally Posted by stu jackson c34 View Post
Sam, glad you survived. Instead of the ACR you might be better off with an echo charger. The toggle is on the ground line from my combiner to avoid overcharging the reserve bank when motoring for long periods. With the echo charger limiting the charge amperage to the reserve bank to 15A, you won't need one.


Stu,

I am shocked to hear you of all people spout this misinformation about an ACR. This is a misunderstanding and common myth that folks who know little about how electrical systems work, or how batteries charge, feel about how an ACR works. What you stated above, about over charging a start battery, is not possible with an ACR. The only way for this to be possible if you are also over charging the house bank. You can not over charge the start bank with an ACR, or by combining them with the BOTH feature.

Here's an excellent example of why that myth is just that, a myth.

The old start battery on our boat was charged for 2800 engine hours, with a DUMB REGULATED alternator and 5 solid years of solar during a 5 year world cruise. Our friends Norm and Judy did this once in a lifetime cruise on our boat boat before we bought her.. The batteries were purchased at the beginning of the cruise were combined during charging with a Yandina combiner.

When we bought the boat the batteries had been used for five straight years 24/7 with over 98% of the time spent on the hook cruising. That is a LOT more abuse than most boaters do in a lifetime. for the average boater that is 28 years of engine use!!!!! Over charge? The battery banks still worked when we purchased the boat at year six. I retired the house bank but the start battery was still actually fairly healthy so I gave it to my brother for his Mako. It started his boat into the batteries 8th season before finally getting weak enough to be of concern.

That battery was combined every day for five straight years via either solar or the dumb regulated alternator.

The bottom line is that current simply flows where it is needed, batteries will take what they need when batteries are combined, and the voltage becomes equal among the new combined bank. Unless your charger, alternator or solar/wind system is pumping out an incorrect voltage for you bank you will not over charge using an ACR.

A few weeks ago I had a customer over to my shop and was talking to him about an ACR. He regurgitated the same myth you just did. I had two batteries on my bench for equalization and they were both at varying states of charge but both above 80% SOC.

I connected them in parallel and then turned on the charger. I then put my clamp meter on each battery and each battery was taking a different level of current. One battery was near full and was taking just 2 - 2.2A the other battery was taking about 11 - 11.3A. The"combined" bank, both batteries, were at 14.4V but each battery was taking only what it needed. He immediately understood, by seeing it, that the batteries take what they need and only what they need in current.

I see and measure this stuff on a daily basis.. Had a house bank a month ago of Odyssey AGM's taking 120A of charge current from the alt. That bank was combined with a much smaller Odyssey starting battery. It was taking about 1.4A of charge current... All batteries in parallel and the house bank getting 120A and the start getting 1.4A. You don' need an Echo to limit the current the batteries do that on their own..

That said I do have a switch in the neg leg of my ACR. I use it to turn off the ACR so I am not burning amps in "combined" mode when charging off solar and so all the current can flow to my house bank without any "phantom loads".

I will be installing a Sterling ProLatch R soon, which is an ACR with near zero draw when combined, and a very, very low standby current. Once I get to that I won't need the switch in the neg leg...
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-Maine Sail


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I wrote back:

I am chastened.

Interestingly enough, that's the way I use our system. Combiner off when not on the boat using solar to the house bank instead of plugged in to shorepower, combiner on when charging with shorepower (like at marinas for weekends) or the engine.

[lazybone]

Almost unrelated.

My West Marine combiner stoped working this past year after almost twenty years of service.
I wraped it up and returned it to "Yandina" (the maker) who repaired it and sent it back at no charge.
Guarenteed for life is his story.  Not going to find that very often.

[Ed Shankle]

Mainsail, one thing struck me while re-reading your post. Happened when I got the part where you mentioned having a couple of batteries equalizing on the bench; if your world cruising friends spent most of their time on the hook, I assume they couldn't do periodic equalization. If that's correct, how did the batteries fare so well? Does that mean equalization isn't as important to battery life? Just when I think I'm starting to understand....

Ed

[mainesail]

Mainsail, one thing struck me while re-reading your post. Happened when I got the part where you mentioned having a couple of batteries equalizing on the bench; if your world cruising friends spent most of their time on the hook, I assume they couldn't do periodic equalization. If that's correct, how did the batteries fare so well? Does that mean equalization isn't as important to battery life? Just when I think I'm starting to understand....

Ed

Cruisers like everyone else eventually pull into a marina or have a gen set that can do equalization charges. Balmar regs can also do an equalization charge but it is kind of ridiculous to your engine to do it that way unless motoring for a loooong distance. Equalization is less critical with proper charging and charging voltages and should only be done when a cell imbalance is noted. It is often more important in climates where the batts are regularly over 80F....