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Old 04-26-2013, 08:18 AM   #1
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6v Series Charging Question / Problem...

Both myself and a friend have recently switched to 2 6v in series for our trailers. We are running the Trojan t-105's. We have external intelligent chargers which produce up to 20 amps and charge the batteries fairly quickly . The Problem / Question is. When charging these batteries one does not charge quite as much as the other. One is just over the 1.265 mark on the hydrometer which is fully charged and the other hovers around 1.250 -1.255 which is about 95% give or take...

I would assume that this is not a problem with the batteries as all 4 batteries are brand new and we are getting the same result with 2 different battery banks. I am assuming the problem is because we are using an intelligent charger and once the combined voltage / resistance reaches the set point for the charger it simply switches to float mode and never finishes off the one battery that is slightly lower. The charger shows the batteries as 100% as it sees it as one.

The current charger does not have a 6v setting so we took those ones back to the store and ordered a 30amp version that has a 6v option so we can manually correct the individual battery if needed.

I am looking for some thoughts / previous experience with this. Is this a common issue when charging in series or am I just being anal? Also I wonder if they are out of sync because they started with different voltages? perhaps they just need to be synced once and then they will stay fairly close? Also all 4 of the batteries are from the same production run so age and batch are the same.

I guess at the end of the day I am curious if other people have tested each battery in their bank with a hydrometer and do they notice different charge levels when fully charged with no other variables such as age, different battery brands etc

Thoughts?
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Old 04-26-2013, 08:27 AM   #2
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Are your cable lenghts the same?
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Old 04-26-2013, 09:26 AM   #3
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yup they are not even in the trailer... They are side by side on my basement floor with one 6guage cable connecting them and the charger is directly connected to the batteries with the same length cable on both the positive and negative.
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Old 04-26-2013, 09:52 AM   #4
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I charge my 6V batteries individually. It might be worth a try.
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Old 04-26-2013, 10:31 AM   #5
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Have you measured the specific gravity between the cells to look for a variance?

A variance between the cells could account for a problem with the battery. If there is a variance of 0.05 or more in the cells in one battery, than try to equalize once or twice.

If there is no variance but all cells show less than 1.25, than the battery is undercharged and will need to be fully charged.
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Old 04-26-2013, 10:38 AM   #6
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To answer your question, I do not recall measuring SG and getting results like that. I run Trojan T-145s in series.
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Old 04-26-2013, 02:47 PM   #7
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Quote:
Originally Posted by Triguy View Post
Have you measured the specific gravity between the cells to look for a variance?

A variance between the cells could account for a problem with the battery. If there is a variance of 0.05 or more in the cells in one battery, than try to equalize once or twice.

If there is no variance but all cells show less than 1.25, than the battery is undercharged and will need to be fully charged.
Yup I did measure between cells and no variance... all is well. I think what I have been reading it looks like there may be a sort of break in period and they may level off over time. Not sure about that. I think I am going to nuke them with a manual charger and see what happens..lol
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Old 04-26-2013, 04:49 PM   #8
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you need to equalize for probably 4-6 hours and test again. seems like one battery had a higher charge than the other when the pair was installed. Once installed, both are charged at the same rate as they are in parallel. Charge current and voltage are used to determine when bulk, absorption, and float states begin. Equalization will saturate the batteries and make your readings more equal.
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