Battery voltage uneven???

[gambit1982]

Hi there, I have a battery bank consisting of 6 golf cart batteries, two wired in series to make a 12 volt system, and then parallel. Each set of batteries were not purchased at the same time. I would say each set were purchased one month apart from another. Anyways, the problem that I notice is when the charge controller is charging the batteries during the day time, when I measure voltage from each battery on a string of two, I notice there's a big difference in voltage between the two batteries. For instance, the charge controller is set to charge at 14.6Volts, but when I measure each battery in one string, it'll read something like 7.00 volts and 7.60 volts. And another string would read 7.15 volts and 7.45 volts. But only one string had voltages that were very close within range, something like 7.29 volts and 7.31 volts. So I'm a little concern. So is this perfectly normal or should I take the batteries back to Costco and exchange them? I tried equalizing the batteries and it didn't seem to help. I have a morningstar TS-45 charge controller if anyone know what range I should set it to in order to fix this dilema. Oh yeah, just want to point out one more thing. On two of the uneven strings, 2 batteries were manufactured 08/06, one 09/06, and the other 11/06. One pair of string consisted of 08/06 and 09/06 and the other string consisted of  08/06 and 11/06 battery. And the perfectly even strings had the same manufactured date of 08/06. I had to buy them this way because Costco didn't have more than two in stock during the time. Could it be because one battery sat a month or two longer than the other, so it had a bigger discharge? Please if anyone can help me I would greatly appreciate it. Thanks in advance.

Steven

[ghurd]

I will wait with you for better information, but I have the same problem.

It seems to have had no ill effects on 6V batteries we have used for several years.

It shows up with several pairs, or only one pair.  The difference can be quite shocking.

G-

PS- A Good Question!

[wpowokal]

Steven how long did you equalise them for and do you have a good quality hydromiter, not a dollar special. That will be your best indication of each batterys state of charge.

I find with a digital multimetre that it is possible for the probe to make a bad connection, wiggle it a little.

allan down under

[Nando]

The voltage difference WHILE being charged should not differ by more than 0.3 volts.

If greater differential voltage, the batteries need equalization and some time a bit hard equalization to bring them to equal charge.

The are not old in fabrication, but some "film" sulfation may have occurred, also fabrication batches may have some chemical differences.

Check the hygrometer readings. prior the charge cycle and immediately you stop the charge cycle, them about one hour later -- record all the values to see how the readings varies.

Nando

[gambit1982]

I equalized them yesterday for about 1 1/2 hour. I decided to stop the equalization process after not seeing the voltage of the two batteries equaling out. What I measured right after turning on the equalization mode is one battery's voltage would measure 7.85volt or something and the other would be somewhere like 7.20volt. These aren't exact numbers, just something I recall but didn't write down. BUt the gap between the two was that much. So I stopped the equalization process fearing I might fry the batteries. But the string of battery that had similar voltage still had close reading within one another, maybe .1 or .2 volt difference. So would it be safe to start the equalization process again and let it complete? Seems like one battery is hogging all the voltages in that string and not letting the other battery charge to a full level. Unfortunately, I have one of those dollar special hydrometer, the one with the floating balls. It shows that all of the batteries are at full, with all 4 balls floating. I know...I'm going to buy a better hydrometer today. Do you know if this one is decent?

http://www.acehardware.com/product/index.jsp?productId=1292142

Thanks you for everyone's comments and advices. I'll try to equalize them again and see what my results are. No sunshine today though. Forecast is showing a sunny day on Monday. So I guess I'll have to wait till then.

Steven

[Flux]

You could try linking the centre point of the 3 strings for a day or two and see if that sorts things out.

Ideally you need a supply capable of equalising the low batteries individually at 6v to see if you can get them up.

You might even try connecting a lamp across the high volt ones to force more current into the low ones, something like car headlamp bulbs.

Flux

[wpowokal]

Steven, I have assumed these are flouded lead acid batteries, and therefore in my experience they need at least 4 hours equalisation.

Paramiters here are 10% average of amp hour rating(or they may get hot)

Give them a serious bubbling then add distilled water if necessary, some days my batteries are floating at 31-32 V for hours (24V system). But then neither my batteries nor me fit the mould.

Are any two people the same? Read the volts but don't stress over slight differences, yes you should be able to get their voltages closer but if not so what.

Some reading,http://www.sandia.gov/pv/docs/BattIntro.htm

allan down under