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Old 07-05-2017, 01:40 PM   #61
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Here are some quick references on this issue
Best way to hook up multiple batteries?
https://electronics.stackexchange.co...simultaneously
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Old 07-05-2017, 01:56 PM   #62
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So your first dual sixers have a different capacity than the second sixers, correct. I always thought mixing different capacity batteries was not prudent, when charging the charger may only recognize the lesser battery, thereby you may not achieve 100% charging of all the batteries involved?
We while the amps are in transit from the charger, they are free to negotiate which 12v to go to. How they divide the flow is beyond my understanding. As a practical matter I don't care who goes where and when as long both 12v batteries get filled. They do fill up based on manual voltage measurement with very accurate DVM plus the fact that all the amps that left all returned. It's just simple amp accounting. At end of charge both have identical resting no load voltages, often overnight rest while running tests at home.
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Old 07-05-2017, 02:02 PM   #63
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Another source on charging different batteries
https://www.batterystuff.com/kb/arti...-tutorial.html
the issue is you maybe shortening the over life of 1/2 of your batteries and or your charging system.
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Old 07-05-2017, 03:33 PM   #64
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From what I've read, if you want to use 4 6v batteries and produce 12v output, you wire each pair in series and then to each other in parallel - a "series parallel" arrangement. As long as the battery charging profile isn't remarkably different for each matched pair, the charger will do just fine in such an arrangement.

You would wind up with 12V output but double the amp hours of each pair of 6V batteries. So, if each pair produces for example 220ah, you would have 12V 440ah.

You could even add more pairs to the bank, but of course by that point you're talking too much weight for an Escape.
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Old 07-05-2017, 04:03 PM   #65
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From what I've read, if you want to use 4 6v batteries and produce 12v output, you wire each pair in series and then to each other in parallel - a "series parallel" arrangement. As long as the battery charging profile isn't remarkably different for each matched pair, the charger will do just fine in such an arrangement.

You would wind up with 12V output but double the amp hours of each pair of 6V batteries. So, if each pair produces for example 220ah, you would have 12V 440ah.

You could even add more pairs to the bank, but of course by that point you're talking too much weight for an Escape.
This is exactly how mine are wired. I checked with Lifeline on engagitheg the CT 6 with the CT 4 as per the diagram. No problem they said because battery internals are the same.
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Old 07-05-2017, 04:14 PM   #66
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This is exactly how mine are wired. I checked with Lifeline on engagitheg the CT 6 with the CT 4 as per the diagram. No problem they said because battery internals are the same.
Right. I don't see a problem.
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Old 07-05-2017, 04:50 PM   #67
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They are wired properly but since you are using CT4 220 and CT6 300 a/h batteries, eventually your output will be limited to 440, not the 530 you calculated as the smaller battery will charge out quicker before the bigger battery does, thus limiting your total as if you were using 4 CT4 batteries. Thus your reserve will be about 220 a/h.
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Old 07-05-2017, 05:36 PM   #68
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True, it isn't "optimal" to have two pairs paralleled together with different capacities, but I don't see a charging issue.
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Old 07-05-2017, 06:07 PM   #69
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True, it isn't "optimal" to have two pairs paralleled together with different capacities, but I don't see a charging issue.
Just talked to Lifeline tech support and spelled out how the 6CT and 4 CTs were wired, drawn upon by house devices and charged. He plainly said that this configuration (different bank capacity) is a common method and used everywhere they sell Lifelines. 6CT and 4CT share same chemistry, plates and construction. They are same battery except for one being shorter (thus less capacity). As long as the two 12v ones are in parallel and attached to same house bus bar (as I have done) there will never be degradation as you described. In his words, "I can look at this as one BIG battery". They have accounts consisting of fleets of boats using similar configurations generating real world feedback (empirical data) as well as extensive lab testing over the years.

My guess is that this could be different for wet cell technology.

I am good.
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Old 07-05-2017, 06:10 PM   #70
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The folks at Lifeline are right Santiago. It's not the chemistry that makes the configuration less than completely optimal though, it's the difference in capacity. In effect, you aren't getting the total useable output of the battery pair with the higher amp hours. I think its neglible, and nothing to worry about at all.

I think of it similarly to a PWM solar charger vs an MPPT. The MPPT is optimal because it squeezes out the entire charging potential produced from the solar cells. Even though I have a PWM charge controller, I'm in no hurry to change to an MPPT. Not 100% optimal, but it works fine.

If all 4 batteries had the higher capacity, theoretically you would have more useable power, but I wouldn't sweat it.
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Old 07-05-2017, 06:41 PM   #71
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If all 4 batteries had the higher capacity, theoretically you would have more useable power, but I wouldn't sweat it.
Bryan, you are right in that it's not optimal. I like symmetry and common sense.
Common sense tells me both 12v batteries should be same size. That's optimal.

Whether my set up will be less efficient over time, I suspect it will less efficient because its not symmetrical or balanced. Tests charging from 50% to 100% charge indicates that both charge fully. BUT there is that nagging feeling that the system is not symmetrical. I am glad you and Jim brought this up. I am open to suggestions and advice.

The sizes were chosen to be practical. I purposely limited myself to this capacity after much modeling of usage and charging from various sources, boon docking scenarios, etc. Total weight as well as physical dimensions were also a limiting factor.

By end of year after more travelling real usage data is gathered, I could implement plan B which is to separate the two 12v batteries as I have in the past with rotary marine style switches I have. The charger can simultaneously charge each bank separately. I have a plan C by the way.

Thank you both.
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Old 07-05-2017, 07:08 PM   #72
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I like the idea of the marine switch. Battery array dead? No problem. I'll just switch to another array. If you ever decide to go solar, there are usually two bank connections on the charger as well.

Or just go with "plan C" and wow us. [emoji23]
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Old 07-05-2017, 07:35 PM   #73
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They are wired properly but since you are using CT4 220 and CT6 300 a/h batteries, eventually your output will be limited to 440, not the 530 you calculated as the smaller battery will charge out quicker before the bigger battery does, thus limiting your total as if you were using 4 CT4 batteries. Thus your reserve will be about 220 a/h.
Jim, thank you for your thoughtful input. Advice taken.
Not sure what year "eventually" will start but as I said, common sense dictates same sizes.
Will study usage a bit more to compare to data I forecasted and implement plan B as described above. Thanks again.
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Old 07-05-2017, 07:47 PM   #74
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The way I understand to offset the disparity is to charge each set separately, in other words a charger for the CT4 battery bank and one for the CT6 battery. But this would mean 2 circuits, wiring and a battery selector switch. However we are only talking about 16% differential, so costs need to be evaluated. As we used to say at work, "close enough for government work" where we went after 80% of the tax 80% of the time.
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Old 07-05-2017, 08:00 PM   #75
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The way I understand to offset the disparity is to charge each set separately, in other words a charger for the CT4 battery bank and one for the CT6 battery. But this would mean 2 circuits, wiring and a battery selector switch. However we are only talking about 16% differential, so costs need to be evaluated. As we used to say at work, "close enough for government work" where we went after 80% of the tax 80% of the time.
Yes Jim, its the charge cycle. Fortunately I can charge three banks at same time. The wiring is modular and well documented in my schematic so separating the charging to treat each battery independently is doable and was original plan. I combined the two batteries to have all amp flows run through one trimetric. Not buying a second trimetric so need to see usage in the next few months and decide which one gets it. I realize the trimetric can measure only voltage on a second battery but I like seeing amp-hours. Oh well.
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Old 07-05-2017, 08:14 PM   #76
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They are wired properly but since you are using CT4 220 and CT6 300 a/h batteries, eventually your output will be limited to 440, not the 530 you calculated as the smaller battery will charge out quicker before the bigger battery does, thus limiting your total as if you were using 4 CT4 batteries. Thus your reserve will be about 220 a/h.
If each bank was forced to handle the same current, then there would be a concern... but that's not the case. Each battery bank can reasonably be expected to accept or deliver current in proportion to the size of the cell (total plate area), when given the same charging voltage or connected to the same load, since their construction is the same.

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My guess is that this could be different for wet cell technology.
I don't see any reason for AGM versus flooded construction to change this logic.

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The folks at Lifeline are right Santiago. It's not the chemistry that makes the configuration less than completely optimal though, it's the difference in capacity. In effect, you aren't getting the total useable output of the battery pair with the higher amp hours. I think its neglible, and nothing to worry about at all.

I think of it similarly to a PWM solar charger vs an MPPT. The MPPT is optimal because it squeezes out the entire charging potential produced from the solar cells. Even though I have a PWM charge controller, I'm in no hurry to change to an MPPT. Not 100% optimal, but it works fine.

If all 4 batteries had the higher capacity, theoretically you would have more useable power, but I wouldn't sweat it.
I think that Lifeline clearly said that the difference is capacity is not a problem at all, and more than any parallel configuration, even of completely identical batteries. I don't see any advantage even in ideal theory of matched capacity in the banks.

PWM and MPPT charge controllers work quite differently (when in bulk charge mode), so one is better than the other for a particular application while the other is "good enough"; the way parallel battery banks behave is not different due to capacity differences, other than the obvious proportioning of current which is not a problem.

I don't think there's any reason to think that this is some kind of second-rate setup compared to a series-parallel configuration of four batteries of the same capacity.

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I like the idea of the marine switch. Battery array dead? No problem. I'll just switch to another array. If you ever decide to go solar, there are usually two bank connections on the charger as well.
For the entirely unrelated reason of handling a battery failure, the switch idea makes sense to me. Once separated, the two banks should be equalized in charge before paralleling them again; if charged with separate charger outputs (such as those solar charge controllers) that's done for you.
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Old 07-05-2017, 08:55 PM   #77
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If each bank was forced to handle the same current, then there would be a concern... but that's not the case. Each battery bank can reasonably be expected to accept or deliver current in proportion to the size of the cell (total plate area), when given the same charging voltage or connected to the same load, since their construction is the same.
Brian, both batteries (larger and smaller 12v) are not subject to the same current.
They are both exposed to same charge voltage at each of the three stages.

The key to your explanation is that each battery will accept current proportional to the plate size. Meaning less current to smaller battery/plates than the bigger battery/plates.

I can see this as being the answer. I initially mentioned that I don't know how the current divides into each battery as they seem to do and checked by measuring final charged voltage as proof. Your mechanism of current flow proportional to destination ( plate size ) seems to be the answer. Makes sense.
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