24v Charging

Submitted: Monday, Jan 16, 2012 at 12:57
ThreadID: 91238 Views:1141 Replies:3 FollowUps:3
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Hi all. Son has a bus motor home with a 2x24v battery banks - 1 for bus and 1 for auxilaries. Wants to add a third system using some additional solar panels for charging. He has two new 6 volt wet batteries he can use and is thinking of buying a 12v battery to make up the 24v system. Can we mix 6v and 12v batteries together off the one 24v solar controller? Would also think new battery would need to be a wet battery similar to existing to limit gassing problems.
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Reply By: oldtrack123 - Monday, Jan 16, 2012 at 13:12

Monday, Jan 16, 2012 at 13:12
The hurdle are :
[1]When connecting batteries in series to get a higher vottage THEY SHOULD be the same type & amphr capacity

[2]You cannot have different voltage battery banks directly connected to any charging source
The total voltage of each bank MUST be the same

AnswerID: 475081

Follow Up By: mepvic - Monday, Jan 16, 2012 at 16:08

Monday, Jan 16, 2012 at 16:08
Thanks Peter. The two 6V and the 12V batteries would all be in series to make the one new 24V system with its own 24V regulator.
FollowupID: 750047

Reply By: Robin Miller - Monday, Jan 16, 2012 at 13:17

Monday, Jan 16, 2012 at 13:17
It can be done Mepvic , but I would not do it because of the uneven charging.
In fact I wouldn't even put the 12v in series to make 24vdc unless they were the same batteries and were in known good condition.
Robin Miller

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AnswerID: 475082

Reply By: Battery Value Pty Ltd - Monday, Jan 16, 2012 at 14:43

Monday, Jan 16, 2012 at 14:43

as has been said, using your single 24V charging source (solar regulator), then that's not recommended on a series string of different batteries.

But there's a workaround:

using two independent solar regulators, each wired to its own solar panel, and battery - then this will work because any battery imbalances won't matter now.

And if you select true MPPT solar regulators, they'll run most efficiently with their individual 24V panel, to charge the 12V battery connected to them.
Each battery in the 24V string will be perfectly charged.

For any other questions, you can get in touch with us by following the link below.

cheers, Peter
AnswerID: 475091

Follow Up By: mepvic - Monday, Jan 16, 2012 at 16:04

Monday, Jan 16, 2012 at 16:04
Have I got this right? If we kept our two 6 volts in series connected to one of our solar panels (130W) via a regulator and connected our other 130W solar panel through another regulator dedicated to a new 12V battery I could then series all batteries to make a 24V system. Each of the 12V banks would have their own solar panel and 12V regulator but I would have a functioning 24V system.
FollowupID: 750046

Follow Up By: Battery Value Pty Ltd - Monday, Jan 16, 2012 at 16:13

Monday, Jan 16, 2012 at 16:13
yep, that's correct.

All you have to ensure is that the panels have to be rated 12V when using an ordinary PWM solar regulator.
On the other hand, using a true MPPT solar regulator allows you to select a 24V rated panel for an overall efficiency gain of ~20%, so you can actually expect close to 130W from your panel under ideal operating conditions.
PWM regulators can't make available the top 20% of panel power under the same conditions.

cheers, Peter
FollowupID: 750048

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