Different current from house bank batteries

[DeepFrz]

Originally Posted by rotorman

I can not paste image here. No. I have 2 posts (+ and -) outside the batteries. To this post all batteries are connected with the same length with very heavy cables. All connections are in very good condition.
This configuration is different from the image you have pasted but I struggle to understand why the connection you suggested is better.

Your set up is just fine although it uses more cable. For one thing it allows you to check the output of each battery in the bank. I think you need to disconnect battery #2. You could try a few stand alone charge/discharge cycles to see if you can bring it back to life.

[hzcruiser]

Originally Posted by rotorman

I can not paste image here. No. I have 2 posts (+ and -) outside the batteries. To this post all batteries are connected with the same length with very heavy cables. All connections are in very good condition.
This configuration is different from the image you have pasted but I struggle to understand why the connection you suggested is better.

What size (Ah) are your batts?
If the charge current is or was quite high and the three are touching, there is a chance the middle one couldn't get rid of the heat as well as the others.

One way to find out is to charge them up to what you think is full, or close to that, and disconnect them all. Then check the voltage very few days.

If that's not feasible because you have to rely on them, just disconnect #2 and leave the others on, checking the self-discharge on #2 every few days.

[rotorman]

The batteries are 3 x 220AH

This morning I have measure the voltage after disconnecting everything and let them rest for half hour.

1. 12.47V
2. 12.44V
3. 12.47V

Then switched on some continuour loads on the boat and connected the batteries each one by one. The load was around 16A. Measured voltage after 20 seconds (that's when it seems to be stabilized - not dropping any further fast any longer)

1. 12.04V
2. 11.93V
3. 12.08V

[hzcruiser]

Originally Posted by rotorman

The batteries are 3 x 220AH

This morning I have measure the voltage after disconnecting everything and let them rest for half hour.

1. 12.47V
2. 12.44V
3. 12.47V

Then switched on some continuour loads on the boat and connected the batteries each one by one. The load was around 16A. Measured voltage after 20 seconds (that's when it seems to be stabilized - not dropping any further fast any longer)

1. 12.04V
2. 11.93V
3. 12.08V

12.47V in the morning sounds ok, according to:

Measuring State-of-charge - Battery University


That's above 60%. If they don't get drained further during the day you should be allright.

The #2 does sag more which supports your doubts. To what voltage did they recover after you took the load away? A difference of 0.1V on #2 could pull down the other two batts if there is no charging source.

The good news is that #2 was still able to deliver 16A, hence you could continue for now.

I would still consider to swap #2 with one of the other batts and after a few days check if that changes anything.

[rotorman]

Thanks!

Originally Posted by hzcruiser

I would still consider to swap #2 with one of the other batts and after a few days check if that changes anything.

Sorry what do you mean?

[DeepFrz]

The way you have them wired up there is really no need to re-cable but #2 was badly discharged. Try an equalization charge and see if that helps. If not then time for replacement.

[smac999]

Originally Posted by Cadence

I don't by the wiring. Paralleled batteries are electrically the same no matter where the taps are. As long as the wire ga. is sufficient connecting them.

in theory yes. most of physics is theory and is slightly wrong in real life when you add air resistance instead of in a vacuum....

actulal testing proves it is not the same. after many years. the close battery will be weaker (more worn out) then the far one. as it's taking more load. and the back one is filling it back up.

[smac999]

Originally Posted by rotorman

I can not paste image here. No. I have 2 posts (+ and -) outside the batteries. To this post all batteries are connected with the same length with very heavy cables. All connections are in very good condition.
This configuration is different from the image you have pasted but I struggle to understand why the connection you suggested is better.

yours is better then the one posted. just less common as more $ and space. leave as is

[hzcruiser]

Originally Posted by rotorman

Thanks!


Sorry what do you mean?

If #2 is wedged between #1 and #3 it would get warmer than the other two during high charge and discharge currrents.

If #2 has been damaged due to heat, it might be too late to physically swap them, so that #2 is on the outside. Or add a spacer between the batts to increase air flow/cooling.

[john61ct]

Separate them, fully charge then do a proper 20-hour load test on each.

If residual capacity is over 70-75% on all, and they are within 5-10% of each other, carry on, maybe improving wiring and spacing.

Otherwise I'd reduce to two good ones, or scrap and replace all at once.

[Zil]

Back to your OP. It is not unusual for 5 year old battery to be done. Your configuration is the best to keep batteries balanced. Your connections are clean and tested for voltage drop. Then the only answer is a bad battery. Disconnect the bad battery. Plan to replace the whole bank when you can. You could keep the bad battery charged, but don't connect it into the bank.

[Cadence]

Originally Posted by smac999

in theory yes. most of physics is theory and is slightly wrong in real life when you add air resistance instead of in a vacuum....

actulal testing proves it is not the same. after many years. the close battery will be weaker (more worn out) then the far one. as it's taking more load. and the back one is filling it back up.

If you believe that theory OK. It is DC fundamentals not physics. The problem is when one battery is shot which is what it sounds like he has. I'd cut it loose to avoid damaging his two remaining batteries.

[rotorman]

Thanks all, I have disconnected the middle battery. I still need testing but morning voltages are now higher. I only have one more month to survive which will be ok with the reduced Ah, before putting the boat on the hard for 6 months. Will replace all when I get back

[rom]

Originally Posted by ZULU40

not tested the idea myself, but the views on this page are now commonplace. If your connections are as in the first illustration, change them

SmartGauge Electronics - Interconnecting multiple batteries to form one larger bank

That how I did it, 4 batteries, "Method 4". The only proper way to connect batteries IMO.

OP has 3 batteries, in this case I would use "Method 3", if possible, or fallback to the more classical "Method 2" already shown in this thread.

[ZULU40]

Originally Posted by rom

That how I did it, 4 batteries, "Method 4". The only proper way to connect batteries IMO.

OP has 3 batteries, in this case I would use "Method 3", if possible, or fallback to the more classical "Method 2" already shown in this thread.

Its definitely more complicated for fout batteries. I have three batteries too, and Im presently fitting a xantrex charger to the boat.

I had been considering either just connecting the centre battery (two) or the next positive and the next negative on batteries one and three, but now Im not so sure.