Batteries (again)

Submitted: Wednesday, Feb 08, 2006 at 12:09
ThreadID: 30553 Views:1961 Replies:3 FollowUps:3
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I have a Trojan 105 amp hr deep cycle in the CT. If I add another battery when I set up the solar panels will it need to be the ientical battery?
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Reply By: flappa - Wednesday, Feb 08, 2006 at 13:36

Wednesday, Feb 08, 2006 at 13:36
Does it NEED to be identical . . . No.

Is it best to have it identical . . . Yes.

ANY battery will work , but to get best use out of the system , an identical battery including one of the same age is the best way.

Why ? Charge rates are the same . . . One isn't trying to outdo the other , they will last longer , good when you pay a few bucks for a DC.

The actually nitty gritty as to why they should be the same , I'm not a 12v expert and wont try to explain it. I'm sure a few of the local experts will be along shortly to expalin why.
AnswerID: 153835

Follow Up By: V8troopie - Wednesday, Feb 08, 2006 at 17:20

Wednesday, Feb 08, 2006 at 17:20
Here's a bit of practical experience from a boat. I had two unused 130AH Trojan's but one was about 2 years younger than the other. Both were maintained.
I did parallel them up to run a small Engel fridge plus the few boat electrics. Charging was from 44W solar panel + a 30Amp DC only genny on many days when the voltage was getting low.
This was intermittant heavy use, totalling maybe 6-8 weeks/year, the rest of the time the batteries were trickle charged when the boat was parked.
The batteries lasted not very long, I guess one of them never got fully charged as it died before the other, got maybe 2 years use out of it, the other lasted another year.

In my experience these batteries take a very long time to fully charge once they have been run down to 50% or so. Certainly, running the tank dry on the genny (about 3 hours) did not do the job, part of the problem being the genny's regulator cutting back the charge from full 30A to 1/3rd or less after a short time. These batteries apparently preferred to be slow charged or having some kind of smarter charger instead the one my Honda genny has built in.

I also found that my Trojans were rather thirsty despite being fed with well regulated charge inputs. I now use sealed ACdelco's and had no problem so far (4 years).
FollowupID: 407769

Reply By: Mainey (WA) - Wednesday, Feb 08, 2006 at 14:21

Wednesday, Feb 08, 2006 at 14:21
further information required

What capacity is the Solar system ?
Why do you need to add another battery ?
Do you actually run your 105a/h battery flat often ?
AnswerID: 153841

Follow Up By: Member - Ray - Wednesday, Feb 08, 2006 at 23:48

Wednesday, Feb 08, 2006 at 23:48
I am looking at a Unisolar twin 65w system from the 12 volt shop.
Had a problem on our last trip to Shark Bay with the small genset not keeping up the charging.Battery ended up flat and had a problem for a while. Just thought a second battery would enhance the system.If we are not camped out for more than a night or two we are okay.
FollowupID: 407883

Follow Up By: Mainey (WA) - Thursday, Feb 09, 2006 at 00:44

Thursday, Feb 09, 2006 at 00:44
Ray, do I understand you have a 105 A/h Trojan Deep Cycle battery and "the small genset could not keep up the charge to the battery"
How "small" is it??

I would first talk with Tony at 12v Shop and explain your geni can't restore the power to the Trojan, I think it's a battery or generator problem, lack of performance and most possibly not fixed by a solar system!

If the original battery is any less than 100% perfect the new Trojan DC when wired in parallel to the original, will loose power to the faulty original battery when they equalise and you will have two x 1/2 charged batteries.
FollowupID: 407890

Reply By: Member - Collyn R (WA) - Thursday, Feb 09, 2006 at 12:58

Thursday, Feb 09, 2006 at 12:58
Almost all gen sets have a 12-volt dc output that may be labelled 'battery charging'. Their output however is typically 8 amps max at 13.6 volts and this is far too low to charge a battery in adequate time. The output is limited to prevent long-term damage to 12-volt devices driven by thet gen set. (This comment is a generalisation tho - a few can exceed 16 volts! - particularly the Honda inverter range: Honda advised me in writing that is not advisable to use that output to charge a battery beyond 50%.)

This seems most of your problem. The solution is to charge the battery via a 240-volt mains charger (preferably a good quality three-stage unit) from the 240-volt outlet of that gen set.

Unless you do this adding a seond battery is just like opening a second bank account without increasing the money you pay in.

Re paralleling batteries. Should be same type, same voltage and preferably about the same age. However contrary to general belief they can be of quite different Ah capacities. Each draws and delivers charge in proportion to its capacity - and when on charge will both reach the same state of charge in much the same time.
Collyn Rivers
AnswerID: 154061

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