Trickle charging with solar...

Hi there,

I am getting a 5w solar panel to trickle charge my 100amp/hr battery. The panel will put out 17v / 0.3amps - will I need a regulator for this? I usually use my gennie with a 240v charger, but I though this could be another option.

Thanks,
Bomber.
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Reply By: rooster350 - Monday, Apr 02, 2012 at 12:40

Monday, Apr 02, 2012 at 12:40
NO.....a bigger panel would probably be more useful , with a regulator it still would not over charge it and would give you useful input if and when needed. I run a 5w panel on a 40ah battery that runs my water pump and do not use a regulator on it. I have a 80w panel to charge the 160ah van battery and use a regulator on that, both systems work very well.
AnswerID: 482156

Reply By: Battery Value Pty Ltd - Monday, Apr 02, 2012 at 13:04

Monday, Apr 02, 2012 at 13:04
Hi Bomber,

if your battery is VRLA (gas recombination), the small 5W panel will wreck it regardless of solar regulator or not.

cheers, Peter
AnswerID: 482157

Follow Up By: Bomber_WA - Monday, Apr 02, 2012 at 13:35

Monday, Apr 02, 2012 at 13:35
I'm not too sure what a VRLA battery is. Mine is a sealed ACDelco..
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Follow Up By: Battery Value Pty Ltd - Monday, Apr 02, 2012 at 14:03

Monday, Apr 02, 2012 at 14:03
Bomber,

valve regulated lead acid batteries are comprised of AGM and GEL type batteries.
Yours is a wet cell type, with some antimony in it.

So you can use the small solar panel, but the battery may gas a little during peak sun, so a solar regulator set to 13.6V is still recommended in this case.

cheers, Peter
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Follow Up By: Bomber_WA - Monday, Apr 02, 2012 at 14:07

Monday, Apr 02, 2012 at 14:07
Thanks Peter, good info.
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Follow Up By: Member - nick b - Tuesday, Apr 03, 2012 at 06:45

Tuesday, Apr 03, 2012 at 06:45
Peter : can you explain what is meant by wrecking VRLA battery ....
Cheers Nick b
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Follow Up By: Battery Value Pty Ltd - Tuesday, Apr 03, 2012 at 08:03

Tuesday, Apr 03, 2012 at 08:03
Sure Nick,

both negative and positive electrodes inside a cell carry some charge.
In order to increase the charge in both cells, an 'overpotential' needs to be applied - otherwise no charging current would flow.
That's why charging voltages are always higher than discharging voltages.

In a wet cell battery, the overpotential is split evenly between the two electrodes.
The moment you drive charging current through the cell (even small currents), overpotential starts to form on both electrodes.
The formation of overpotental either means the cells increase their stored charge, or the electrolyte starts breaking down towards the end of the charging process (gassing).

Now looking at VRLA batteries, there's this additional gas recombination cycle which disturbs the even distribution of overpotential between the electrodes.

The gas recombination happens along the negative electrode. Because hydrogen forms the building blocks of this electrode's overpotential, and it gets eaten away by oxygen ions drifting over from the positive electrode, the overpotential on the negative side will always be lower than on the positive electrodes.
At very low float charging currents, there aren't enough hydrogen ions left to form an overpotential at all.

And an electrode losing its overpotential during float charging has the same effect as discharging it.

One way to ensure this can't happen, is to keep the float charging current high enough to guarantee at least a small amount of overcharge on both electrodes.
In a VRLA 12V battery, sufficient float charging current can be assumed when the battery terminal voltage is between 13.6 and 13.8V.
The steady state current at this voltage is age and temperature dependent, and can be as high as 100mA in a 100Ah battery.

A 150mA rated solar panel supplies less than 100mA for most of the time, allowing negative plate sulphation to sneak in.
And because sulphation doesn't happen in all cells at the same rate, cell imbalances will form in the 6 cell series string, which is bad news in itself.

cheers, Peter
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Follow Up By: Member - nick b - Tuesday, Apr 03, 2012 at 08:35

Tuesday, Apr 03, 2012 at 08:35
Thanks for your reply ...very good ....always getting good info here ...

cheers nick
Cheers Nick b
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Follow Up By: Allan B (Member, SunCoast) - Tuesday, Apr 03, 2012 at 08:45

Tuesday, Apr 03, 2012 at 08:45
Peter, it seems the more I learn about lead-acid batteries, I come to realise how much more there is to learn!

It seems that virtually every installation of lead-acid batteries is abusive in some way and compromise prevails. The secret is of course to identify and accept the most reasonable compromise for one's own situation. Not easy!

Cheers
Allan

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Follow Up By: Battery Value Pty Ltd - Tuesday, Apr 03, 2012 at 09:55

Tuesday, Apr 03, 2012 at 09:55
pleasure Nick.

And well said Allan.

That's why multistage charging was introduced which is capable of looking after the needs of lead acid batteries pretty well.

Problems arise, when operators don't select multistage charging gear, and on top of that, ignore what's written in the battery specs, and sometimes on the battery itself.

And the other problem is that a great majority of battery sellers don't really know how batteries need to be treated in order to go the distance, and why would they care anyway.

cheers, Peter
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Follow Up By: Member - John and Val - Friday, Apr 06, 2012 at 07:43

Friday, Apr 06, 2012 at 07:43
Peter,

Very interesting indeed. I take it then that you shouldn't leave a gel or AGM battery sitting on float for extended periods???

Cheers

John
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