battery voltage drop

[Ken Heyman]

I have a two bank system consisting of 4 T105s . Each bank is 2 T105s connected in series and then paralleled at the switch for engine/ alternator charging. I generally use either bank 1 or bank 2 for normal electrical loads (lights, refrigeration, navigation lights etc) Accordingly after a  cruise there could be a difference in the measured voltage of bank 1 vs bank 2(assuming I didn't switch periodically to the other bank).

when batteries are paralleled, the weaker battery brings down the stronger battery (I'm told).-- so hypothetically, if I have one unloaded bank measuring 12.6v and the other 12.2V and I now combine these banks at the 1-2 switch (the All position), how long will it take before the stronger bank ebbs to the level of the weaker battery.

thanks,

Ken

[Mike and Joanne Stimmler]

Hi Ken,
Normally, this is only a problem if one of your banks has a battery with a bad cell. If both of your banks are healthy, they will simply equalize. You probably will want to wait until after you start the engine or plug into shore power to make the switch so that they will both charge.
As far as the time it takes to equalize, I don't know if there's a formula for that, maybe one of the other folks on the message board will have an idea.

Of course in San Deigo, we don't have these problems. Perhaps you should consider
moving your boat here!     

[mainesail]

Ken,

If you use both of these banks for house loads you will get a longer cycle life out of one large bank not two smaller banks. These batts will only accept about 25% of the Ah rating so 225 amps per bank @ 25% is about 56 amps BUT as these two voltages get closer to one another the process slows down. It can take a while to fully equalize, just as it does to charge, but you will & can still see a hefty load being transferred from the full bank to the low bank.

I would combine all four 6V's into one bank and add a single reserve battery as this will reduce your cycle depth and can increase the battery life. You may also want to consider an ACR or Echo type charger so you don't have to manually "switch" to top up both banks..

[Stu Jackson]

Rod, I've been trying to get Ken to do just that for the past three years!   I did get him to do the wiring harness upgrade.  One down, one to go!

[Ken Heyman]

thanks all. I agree that a dedicated starting battery would be ideal. I'm into my fifth season with the T105's and third season with a Sunsei solar panel  (22.5 watts) used to trickle charge. I'm able to maintain "adequate" battery health even though we are on a can and only have access to shore power when we cruise to different Marinas. I am somewhat judicious in the use of the Adler Barbour frig although we allowed it to cycle over the hot Chicago 4th of July holiday with no adversity. In short, for the way we use the boat I'm satisfied. I do bring a "quickstart" pack (just in case) when we cruise but have never depleted the batteries to require its use. BTW when we talk about the batteries equalizing, are we talking about regression to the mean or simply regression to the lowest bank voltage level. In our hypothetical with banks at 12.6 vs. 12.2, when paralleled (with no loads on ) to we end up at 12. 4 or 12.2 (which is what I had thought)

thanks again,

Ken

[Stu Jackson]

Battery Management 101:  Ken, you really shouldn't need to ever need to parallel the two house banks you have UNLESS you are charging with shorepower, given the small size of your solar panel.  Ken's advised me, IIRC, that he charges one bank at a time with his solar panel when he's away from the boat on the mooring.

We also need to be careful with nomenclature.  Equalization means "overcharging" by higher voltage deliberately, rather than paralleling the banks.  I'm sure Ken knows that, but many may not, so I thought it would be helpful to be clear. 

For really good battery information, I highly recommend reading the Ample Power Primer, available at www.amplepower.com, tech tab, download, save and read --- and reread over and over again.  It's one of the very best pieces of battery information I've ever found.

[Ron Hill]

Ken : I think that I can answer some of your questions.  
BTW, a 22.5 W solar is NOT a trickle charge unless you have a solar V regulator.

Don't use the Adler Barbour "sparingly".  Like any other appliance it needs to be used.  Just remember that if you have good battery to starter cabling and soldered connection that you are only starting a 23 HP diesel NOT a 230 HP diesel.  

On battery equalization - I'd look at Google, as it's easier than trying to explain on this form.  
A few thoughts

[Ken Heyman]

thanks Ron,

I do have a solar regulator.

Also,I used the term "equalization" because it was used by Mike in the above responses. More specifically, I'm just curious if voltage of the lowest bank is increased at all when paralleled with a higher voltage bank. I've always read that the better bank is simply pulled down by the lower bank.

Ken

[Mike and Joanne Stimmler]

I'm sorry guys, I did use the term equalize improperly. What I was trying to say was that I think they would average each other out. In Kens example of one at 12.6 and one at 12.2 they should both wind up at 12.4 but I don't know how you could calculate how long it would take.
It sounds like what you're doing is working for you if your 105's have lasted five years and still going strong,

Mike

[Stu Jackson]

...I did use the term equalize improperly. What I was trying to say was that I think they would average each other out. In Kens example of one at 12.6 and one at 12.2 they should both wind up at 12.4 but I don't know how you could calculate how long it would take...

Sorry, nope.  The lower bank would draw the higher one down.  They will NOT average.

What Ken is describing is the very basic use and management of a two equal bank battery system.

There is no one right answer to electrical systems, although I've been a proponent of the largest house bank you can have with a small backup reserve bank.  Ken's works for him and can be used by anyone, as long as they understand, as Ken does, how to manage them.

What's happening is that Ken is measuring his Day 2 bank at the end of Day 2.  Of course his Bank 1 will be higher.

Let's simply be careful about using the right terminology and definitions.

Both Calder and Ample Power discus the different types of house bank setups that can be used.  Instead of retyping all their advice, I suggest you simply read them --- again.

[Ken Heyman]

Thanks again guys,

The above does confirm my understanding. One observation does trickle up from the discourse. If I leave the boat for a few days with the solar panel only charging one bank ----return to the boat where there is now a difference in voltage between the two banks-prepare for departure-turn the selector switch to the ALL position ( in order to charge both banks while under power)-----I have just nullified any benefit of charging only one bank. In short, I should keep the banks as close as possible to each other which I generally do(or of course break down-buy the dedicated starting battery and get the ACR or Echo type charger).

Happy summer sailing,

Ken

[Stu Jackson]

...return to the boat where there is now a difference in voltage between the two banks-prepare for departure-turn the selector switch to the ALL position ( in order to charge both banks while under power)-----I have just nullified any benefit of charging only one bank.

Because of the very short time between turning to Both just before you start your engine, that shouldn't be a problem.  'Cuz then you're starting to charge immediately with the alternator.  Ken's AO is wired to his 1-2-B switch.

It's only when the engine is off, with no shorepower charging, that the higher bank will drain into the lower bank if you keep it on B for an extended period of time.  Your judicious use of an equal two house bank system would preclude that by switching between banks on a daily basis.

[mainesail]

equalize -

v., -ized, -iz·ing, -iz·es. v.tr.

1. To make equal: equalized the responsibilities of the staff members.
2. To make uniform. To constitute or induce equality, equilibrium, or balance

"A Combiner can't make the voltage on one battery get higher than the other,  it can only make them equal."

Quote above from the president of Yandina the folks who invented the automatic battery combining relay.


Stu,

When you combine two banks together they will eventually become equal, reach equilibrium or equalize at an over all lower state of charge than the higher charged battery had been. The low battery will come up some from taking a charge from the higher bank and the high battery will go down some until the become equal in voltage and the amp transfer ceases. At this point the batteries are equal, equalized or have reached equilibrium. If you watch this on a bench, with battery monitors or ammeters monitoring amps and voltage, you will see that as the battery voltages get closer together the slower the equalizing and amp transfer becomes. It starts out rather fast with wets but then slows. More than one definition for the word equalize...  

A battery equalization charge is basically correcting and equalizing specific gravity across the cells inside a battery. Seeing as these cells are 2v batteries and you are making them equal in voltage again the word has many meanings but the context of the conversation is what is important. We were discussing batteries becoming equal via the act of combining them via a switch into one large bank. By combining two batteries in parallel you eventually cause them them to become equal in voltage and by supplying a controlled overcharge voltage you can equalize the individual cells of a battery. Many meanings for the same words..

[Mike and Joanne Stimmler]

Thank you Mainsail

[Stu Jackson]

It certainly appears that we are now all equalized!    Thanks, guys.