Mixing Batteries on Float-- Mex Test Update 2

[BFL13]

UPDATE 1 on 23 Dec post
UPDATE 2 on 25 Dec post
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Mex is driving me crazy! He said do not mix my used 12s (Scrubber batteries, he calls them--humph! They are respectable golf car batteries I'll have you know. Humph!) with my regular bank of 6s or they would evilly interact, and I would ruin my good 6s. I asked if that were still true if they were all on a Float charge.

Mex said they would still have evil interactions even when all on a Float. So I have gone ahead at some inconvenience to keep the used 12s and the good 6s apart.

Now all of a sudden, Mex pipes up in another thread with this!!!

MEXICOWANDERER wrote:
Batteries should be separated after the charging protocol. Connect all batteries together and apply 1 nominal 14.2 charging volts and there is no way any of the batteries can detect it one battery or a hundred are online, or the chemistry of any of them. The only requirement made of a charging system is that it not under or overcharge the battery. Voltage requiments for flooded 5% antimony batteries and pure lead AGM is similar enough for multiple warhead work.

It's when the charging ceases that the problems arise.

So go ahead and use a smart solenoid to parallel charge the batteries. I have done this too many times to count.

What is going on here? Are there evil interactions or not as long as they are charging or on a float? Does this leave the time they are discharging together as when the evil interactions get going?

If they are banked on solar, they discharge at night and charge during the day. So the evil interactions come out after dark? Can I just call Ghost Busters?

[LScamper]

A few observations about parallel batteries on float charge or just left connected in parallel. First assume that both batteries are in good shape and full charged. Mex said less than .1V after four or five days no problem.

Seems like you could measure how one battery charges or discharges the other. Measure the current in the parallel connection between the two batteries. If they are at the same voltage there will be no current flowing from one to the other and the two batteries will not know they are connected together. If one is lower than the other you could measure the current and from that calculate the Amp hour discharge of the better battery.

While in float charge if one battery has an open cell it will not draw any current from the charger and only the good battery will charge. If one battery has a shorted cell it will draw all or most of the current from the charger and may draw current from the good battery discharging it. I can’t think of any other interaction off the top of my head.

Do you float charge or leave connected two six-volt batteries in series? If you do it seems that there is all most the same problem as two twelve-volt batteries in parallel. If left connected but not on a charger there is no problem.

If one cell is open when float charging there will be no current and neither battery will charge. If one battery has a shorted cell all the good cells will over charge.

Should you worry about either case? How often will a good battery go bad when it is left on a float charge or just left alone?

[mena661]

If I knew what I was doing next weekend, I'd join ya on this experiment. Probably won't be camping next until early Feb.

[BFL13]

It's not very exciting, but at least it is something to do with batteries! 🙂 Mex says the low cell sucks from the others. I am waiting to hear how come all the 1.275 cells in Battery B are sucking from that one 1.300 cell, but its SG keeps getting higher!

I'll do another report on Monday and that should settle this whole crazy T-1275 saga one way or another. (So far they seem at least as good as any of the pairs of 6s I have)

[mena661]

Cool! Thanks for doing this!

[BFL13]

After one day, voltages have dropped to 12.93 and 12.90, maintaining that 0.03v difference while losing some surface charge.

Mex says that a tenth of a volt is significant for this difference after four or five days, so unless this difference becomes greater than 0.03v in the next few days, it must be "insignificant?"

[BFL13]

Decided to try out Mex's tests on my two "previously enjoyed" T-1275s where I have noted before that one seems to be in better shape than the other based on higher average SGs, although each has variations among its cells for SG.

This should tell whether they can be left in parallel safely for a long term float on one charger, or need individual floating with two chargers.

MEXICOWANDERER wrote:

...........
Here's a tip to understand the reality of same type of battery has different chemical attributes according to its state of charge or age.

Fully charge all batteries

Wait 4 or 5 days, then measure the voltage potential of each battery

Take a hydrometer reading then reconcile it to voltage of each battery.

A tenth of a volt is significant, two tenths is worrysome when you are trying to balance batteries.

To amplify the test, apply 14.8 volts after fully charging the batteries. Note that the cells with the lowest gravity and lowest initial voltage boil first.

Cells that droop after charging, actually CONSUME power. Roaches check in but they don't check out, time. The worse the cell the hungrier they get. Some are the eqvt of a 20 watt load on the other cells in the bank.
............

.

So to get started, where they have been on individual floats for a while at different voltages (13.5, 13.4) been watered a little in some cells after last overcharge(affecting SGs), I put them in parallel, gave them a quick overcharge at 15v for an hour, and got , while still being charged, 14.94v each.

I watched as they started to show bubbles, but did not see anything obvious which cells started to bubble first. Not boiling anyway, just small bubbles coming up in strings.

So next step is disconnect everything and let them sit for four or five days and check voltages and SGs. Meanwhile, after an hour I took an initial set as a benchmark sort of with surface charge still present:

Battery A (the good one?) 13.43v
Battery B (the also ran) 13.40v

Battery A 1.275, 75, 70, 90, 75, 75
Battery B 75, 75, 1.300, 75, 75, 75

So now must wait a few days and see what happens.

Mex says a low cell draws from the others. Battery A has that lower cell at 70 there, which is always the low cell when taking SGs. Battery B has that crazy high SG cell, which is always high like that.
Not a clue what that might mean, can't fix it, it just is!

If Mex is reading, is this a proper start? Do I check daily or just wait four days? (I doubt all the surface charge will be gone in only four or five days, but we'll see)

[mena661]

MEXICOWANDERER wrote:

Cells that droop after charging, actually CONSUME power. Roaches check in but they don't check out, time. The worse the cell the hungrier they get. Some are the eqvt of a 20 watt load on the other cells in the bank.

Thanks for saying this as it explains some behavior I noticed when I had the broken wire (and even after I fixed the wire).

[BFL13]

Thanks Mex, I am seeing it now. I know you try to be careful in your advice so people like me don't get the wrong idea and do whatever they like.

[MEXICOWANDERER]

BFL13, Like William Jefferson Clinton quipped "It depends on the meaning of the word 'is'"

Your usage description got a little dizzy spinning round in my head. "Paralleled For Charging " is different than "Paralleled For Float" or "Paralleled For Cycling"

Somehow I got it into my head for the initial question that you intended on using the batteries, then recharging them until they floated then maintaining them on float.

But for how long a time?

A very long term float after all batteries have been fully charged is a heck of a lot different than a short term float after the batteries are "sorta recharged"

Time spent at "maximum absorbsion voltage" is critical.

Here's a tip to understand the reality of same type of battery has different chemical attributes according to its state of charge or age.

Fully charge all batteries

Wait 4 or 5 days, then measure the voltage potential of each battery

Take a hydrometer reading then reconcile it to voltage of each battery.

A tenth of a volt is significant, two tenths is worrysome when you are trying to balance batteries.

To amplify the test, apply 14.8 volts after fully charging the batteries. Note that the cells with the lowest gravity and lowest initial voltage boil first.

Cells that droop after charging, actually CONSUME power. Roaches check in but they don't check out, time. The worse the cell the hungrier they get. Some are the eqvt of a 20 watt load on the other cells in the bank.

Let's say, a mixed bank were the be used for camping. Parallel the batteries, charge as much as possible, use the bank then recharge as soon as possible. This would have the least effect on the good cells.

I have seen a new, good battery destroyed in 6 months when paralleled 100% of the time to a bad battery.

But to put a point on the question "How about when the batteries are floated?"

Connect the charged batteries in the form of a bank. Apply a flat current. The good batteries will stay good until the bad batteries degrade to the point where they Bogart all the wattage, the float voltage sags then all the cells die.

Looking at this again, I must have been so conditioned by BFL's oft stated camping agenda the thought of a simple, continued float-only regimen did not occur to me.

[BFL13]

Pipeman wrote:
Quoting Mex "It's when the charging ceases that the problems arise." I get charge them together and then disconnect them from one another after charged!!!!

Yes but that isn't much use when you are still camping and want them still banked. Ok at home on a float with more than one float charger.

I would like to clarify what it means for camping. I will do the float separately, that's easy. Is there a time factor for how many times camping you can get away with it for instance?

[BFL13]

OK so I continue to have them separated for recoveries and floating at home.

But I am just not seeing where having them separate at home, then going camping (no solar) for four days with them banked doing say three 50-90s, then returning home and separating them, is going to end up with one set eating the other.

I would likely do that three times by mid-April, then it is on to the seasonal off-grid site with solar.

I always have a "less than optimal" battery set-up. Seems like a case of "perfection being the enemy of good enough?"

[Pipeman]

Quoting Mex "It's when the charging ceases that the problems arise." I get charge them together and then disconnect them from one another after charged!!!!

[pianotuna]

Hi mena,

No, it doesn't matter if the batteries are all new. In an ideal world they need to be as near twins of each other as possible. Mixing a 6 volt bank, with 12 volt jars simply is not optimal.

[pianotuna]

Hi BFL13,

It may help to think of alternator charging at the end of a long wire. The alternator tends to "see" the chassis battery--and shuts down leaving the battery on the long wire less than fully charged (or even not doing any charging at all).

A similar process may be going on with dissimilar chemistries and voltages. The six volt in series, because of their external series link needs must always have slightly lower voltage due to increased resistance from the connections, so charging voltage, for them, needs to be "tweaked" upwards to overcome the resistance--but that means the 12 volt jars would be receiving higher than optimal voltage and possibly tending towards overcharging.

It was interesting to see my house batteries being "thirsty" after 4 days of 13.2 volts in cold weather (-20 to -30 C), with little in the way of solar charging. I did remember to push the button to get to 14.4 a couple of times, but mostly I forgot.

[mena661]

MEX meant that your bad batteries would prey on your good one's. That's why he saying not to connect them together. I think if your T1275's were new they would be ok to connect together while camping. There is interaction between them especially when they're on float. I saw this for myself recently when I found the bad wiring connection and one of the 6V wasn't getting fully charged. One battery was at baseline, two were above baseline and the not fully charged one was showing just that. Fixing the bad wire didn't allow a full charge on that low battery either with them all connected together (believe me I wasted a week on trying to do just that). I had to separate them all and charge that 6V individually. OT, it seems that topping them off (finish charging) individually is a pretty fast process.