T 105 trojans

[adamant]

 picked up 5 used t 105's that i would like to add to my battery bank that includes 2 t 105's that are about 3 mo. old.

the 5 batterys that i picked up used each read 6.70 volts each.

would it be ok to add them to my bank of 2 t 105's that i got new few mo. ago?

what i use them for is to power up my cabin's 12 volts lights...

http://community.webshots.com/user/adamant117

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[adamant]

see link below

http://community.webshots.com/user/adamant117

[bill541]

Most of the time, you want to have all the batteries the same age and type. This is mainly true when you have large series strings of batteries.

For your 12V bank, just match pairs of batteries that are the same age and condition. Then place these in parallel to your existing bank.

I did this with a bunch of used T-105s in the past and it worked fine for a 12V bank, however it was totally unacceptable for a 48V bank. One weak battery in the series string ruins the whole string.

Use the open circuit voltage to match the batteries in pairs. Then during charge and discharge, measure the voltage across each batteries series, if they read the same voltage within a couple 10ths, then they are a good pair and should be fine.

-Bill-

[thunderhead]

Did you try using some sort of equaliser circuit on the batteries?  I know that EVers use an equaliser across each battery in a chain, to make sure that they all reach charge endpoint.  That tends to cancel out the problems of a weak battery, since it has a chance to recover.

[adamant]

equaliser circuit on the batteries....

can you tell me more about this?

[bill541]

Equalizing circuits are sometimes used in very large series strings where the DC voltage is 90 volts or more. This is fine during charging, but does nothing during discharge.

If you have a weak battery in a series string. During discharge, this weak battery will drop to a very low voltage even while the other batteries in series are still near full voltage. This causes the capacity of the series string to drop to the value of the weakest battery.

I wouldn't worry about it too much in a 12V system, as you will only have two 6V batteries in each series string. As long as the two batteries in series are well matched, they will share the load evenly during charge and discharge.

When I was sorting out all my used batteries, I fully charged each one and then let them sit unconnected for 4 hours. Then I took hydrometer readings on each battery. Then I matched batteries in pairs. Each pair had similar hydrometer readings. Then I load tested the whole bank (about 500 watts)and measured the voltage drop across each battery. It took a while, but after reorganizing the batteries a couple of times, I was able to match them up.

This is why it is usually recommended to buy all the batteries at the same time and in the same condition, less testing and swapping that way. But if you have the time, you can do it and end up with a good bank. I would suggest putting numbers on each battery so you know when they went into service and can keep records on them.

-Bill-