What's Going On With These Batteries?

[Tikka]

chemical cells are always different measured individually, there is nothing wrong.
- the only reasonable and meaningful reading is with the load , at least 5A.
- having them paraller permanently is bad anyway, if one bat. is weak, pull down the others. Now you have job, to eliminate which one is the one,

[pcmm]

Originally Posted by CapnCrunch

Update, etc.:

I should maybe have specified that the voltage values I initially gave were taken as each battery was first disconnected from the bank and then, again, when all the batterys were reconnected. I checked them again this morning and all read around 12.84. It looks like maybe I just didnt give them time to equalize after re-connecting. (BTW: pcmm was right. The bank is connected to the panel at battery A However, I had turned everything off, so i dont know where any drain could have come from)

The next thing I dont understand is why my BMV 702 shows 11.9v when the bank reads 12.84 with the multimeter, unless the difference is caused by my fridge (which draws about 5.5A, according to the BMV).

An easy fix for this would be to extend the negative lead so that it connects to the bank at the farthest negative terminal from the positive (opposite end of the bank) this will force the voltage drop to occur more equally across all the batteries.

The way they are connected now, the first battery takes all the abuse and will always show lower readings than the other ones in the string.

[GrowleyMonster]

Originally Posted by pcmm

An easy fix for this would be to extend the negative lead so that it connects to the bank at the farthest negative terminal from the positive (opposite end of the bank) this will force the voltage drop to occur more equally across all the batteries.

The way they are connected now, the first battery takes all the abuse and will always show lower readings than the other ones in the string.

Yup. +1. Just use nice heavy cables.

[pcmm]

Originally Posted by Tikka

chemical cells are always different measured individually, there is nothing wrong.
- the only reasonable and meaningful reading is with the load , at least 5A.
- having them paraller permanently is bad anyway, if one bat. is weak, pull down the others. Now you have job, to eliminate which one is the one,

That seems to be counter to all the literature out there. The only reasonable way (accepted) is to fully charge the battery(s) then leave them disconnected from everything for 12 or more hours, then take the voltage reading. Having them all in parallel is the ideal setup as long as the pos an negative feeds are connected to opposite ends of the bank. Having them in parallel reduces the depth of discharge per battery extending the life of the bank.

[Tikka]

pcmm, sure parallel set up is ideal as you mention,
I should mention as long as there is / at least small charge or discharge / ,
than self discharge not happening .

simple test of cables, all bat. connected parallel , turn on some load, Nav. lights, fridge
now measure voltage drop ocross cables.
....not between plus - minus , but between first minus buss bar main distribution panel and individual minus battery posts, secondly the same for plus bus bar .
if there is any unwonted resistance , verify by increasing the current flow.
this is easiest way how check quality connection to on device across the boat, as long as there is a current flow through circuit.
it save you time and money, changing or modifying stuff if not need it.

[CapnCrunch]

Originally Posted by pcmm

That seems to be counter to all the literature out there. The only reasonable way (accepted) is to fully charge the battery(s) then leave them disconnected from everything for 12 or more hours, then take the voltage reading. Having them all in parallel is the ideal setup as long as the pos an negative feeds are connected to opposite ends of the bank. Having them in parallel reduces the depth of discharge per battery extending the life of the bank.

I disconnected the bank from the load and brought it up to full charge. (my charger enters acceptance mode at 14.2 and floats at 13.3). The bank has been "resting" for 14hrs and all batteries read 12.99.

I'm still fairly new to the issues of DC power management and (at the age of 66) sometimes forget what I have learned. So, I'm going to sort of start over and ask some seemingly stupid questions.

First question: Is 12.99 an acceptable charge level for a 6-battery (I added one), wet cell, bank "rated" at 720 amps that is supporting an offshore cruising sailboat?

[pcmm]

Originally Posted by CapnCrunch

I disconnected the bank from the load and brought it up to full charge. (my charger enters acceptance mode at 14.2 and floats at 13.3). The bank has been "resting" for 14hrs and all batteries read 12.99.

I'm still fairly new to the issues of DC power management and (at the age of 66) sometimes forget what I have learned. So, I'm going to sort of start over and ask some seemingly stupid questions.

First question: Is 12.99 an acceptable charge level for a 6-battery (I added one), wet cell, bank "rated" at 720 amps that is supporting an offshore cruising sailboat?

100% fully charged (at rest for FLA) is 12.7 so you're still reading some risidual charge, I'd say your good. If you want to be hyper accurate, you can measure the 6v readings for each battery. or use specific gravity readings.

[CapnCrunch]

Originally Posted by pcmm

100% fully charged (at rest for FLA) is 12.7 so you're still reading some risidual harge, I'd say your good. If you want to be hyper accurate, you can measure the 6v readings for each battery. or use specific gravity readings.

OK. That is (i'm pretty sure) the first time i've seen an "acceptable number" for a "fully charged" battery - thanx

Next question: I have now reconnected the loads to the bank which still reads 12.88, but my Victron 702 reads 12.66 until the fridge (which is the only thing turned on and draws 5.5-6A) kicks on. Then the BMV reading drops to 11.68v. Does this make sense?

[pcmm]

Originally Posted by CapnCrunch

OK. That is (i'm pretty sure) the first time i've seen an "acceptable number" for a "fully charged" battery - thanx

Next question: I have now reconnected the loads to the bank which still reads 12.88, but my Victron 702 reads 12.66 until the fridge (which is the only thing turned on and draws 5.5-6A) kicks on. Then the BMV reading drops to 11.68v. Does this make sense?

Check the voltage at the shunt if your multimeter reads higher than the bictron, it may need some calibration.

For the voltage drop when the fridge turns on, yes that's normal. when the fridge stops the voltage should climb back up to its resting voltage.

the "accepted voltages" for fully charged FLA are all over the interwebs, just google it. Have a look here:

https://4.bp.blogspot.com/-qK1kkxuMQ...y%2Bcharge.jpg

Lots of great articles on the web. First thing you should do is get yourself a copy of Nigel Calders "Boatowners mechanical and electrical manual" it literally covers everything you need to know!

[Tikka]

this is a table of state of charge, regardles how many batteries are connected,
the is correct indication when battery / ies are under load.

[a64pilot]

[QUOTE=CapnCrunch;2673841 First question: Is 12.99 an acceptable charge level for a 6-battery (I added one), wet cell, bank "rated" at 720 amps that is supporting an offshore cruising sailboat?[/QUOTE]



Which batteries, if Lifeline AGM which I suppose cause your absorption and float voltages are very close to them, then yes 12.99 is good, others maybe not.

[CapnCrunch]

Originally Posted by pcmm

For the voltage drop when the fridge turns on, yes that's normal. when the fridge stops the voltage should climb back up to its resting voltage.

the "accepted voltages" for fully charged FLA are all over the interwebs, just google it.

I understand that battery soc would drop when subject to a load. It just seemed weird that the BMV would show a drop in excess of one volt when the multimeter reading of the batteries during that same load would only drop a few hundredths of a volt?

I searched the net and was finding info like "When batteries reach 14.2v....or....13.5v..." I was aware that voltage would taper off after charging ceases, but I just couldnt seem to find a definitive number for after the batteries had fully "rested."

a64: I'm embarrassed to admit that the batteries are all Wal-Mart Marine Deep Cycles rated at 122Ah capacity. They were all I could afford when I needed to replace the old ones. I figure I can replace them with good ones when we get ready to head out next summer.

BTW: someone had asked what my cableing was - it is 2AWG.

[pcmm]

Originally Posted by CapnCrunch

I understand that battery soc would drop when subject to a load. It just seemed weird that the BMV would show a drop in excess of one volt when the multimeter reading of the batteries during that same load would only drop a few hundredths of a volt?

I searched the net and was finding info like "When batteries reach 14.2v....or....13.5v..." I was aware that voltage would taper off after charging ceases, but I just couldnt seem to find a definitive number for after the batteries had fully "rested."

a64: I'm embarrassed to admit that the batteries are all Wal-Mart Marine Deep Cycles rated at 122Ah capacity. They were all I could afford when I needed to replace the old ones. I figure I can replace them with good ones when we get ready to head out next summer.

BTW: someone had asked what my cableing was - it is 2AWG.

Nothing to be embarassed about. The maker of walmarts batteries is the same one that makes West Marine;s Deep cycle batteries, and the Deka 6v golf cart batteries. All made by East Penn.

The voltages you are quoting are the charger float voltages not that battery rest voltages.

[CapnCrunch]

Originally Posted by pcmm

Nothing to be embarassed about. The maker of walmarts batteries is the same one that makes West Marine;s Deep cycle batteries, and the Deka 6v golf cart batteries. All made by East Penn.

The voltages you are quoting are the charger float voltages not that battery rest voltages.

Well, at least I got something half-way right LOL. It was odd that I found 3 or 4 sites that talked about bulk transition voltages, absorption transition voltages and float points, etc., but did not say what fully charged resting voltage should be. So, thanx for clearing that up for me.

As for the BMV, I was wondering if there is a way to calculate/estimate how much "apparent" voltage drop to expect from any particular load. It's a bit scary to see your voltage reading 11.68v, and not knowing if that's the "actual" voltage of your bank or it's just your fridge running. Or maybe I just worry too much LOL

[a64pilot]

You may want to try to find out what your batteries charging voltages are, your voltages are almost dead on for Lifeline and they usually for whatever reason run low voltages.
The bank voltage drop when the fridge kicks on should be nearly nothing, not much at all. If it drops much it likely means a loose connection somewhere.