Would charging my 110ah agm from multi sources cause instability

Submitted: Tuesday, Nov 17, 2015 at 14:08

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Joan K

Hi all, I have a question for the techies please.
I have a 110 ah AGM battery installed with isolator in the boot of my car. When camping it is charged with either a 100w or 140 portable solar panel. One has a 10a controller and the other has a 15a controller. I suspect the current from each would not be equal. Would combining any of these 3 charging sources (car idle, 100w and 140w) cause instability in my battery? Thanks for your help. Joan

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Reply By: Mick O - Tuesday, Nov 17, 2015 at 14:36

Reply By: Member - Boobook - Tuesday, Nov 17, 2015 at 14:55

Tuesday, Nov 17, 2015 at 14:55

Joan, the good news is that your battery will be fine, and given the battery is a fair way from your alternator, you could use one of the portable panels or even both, BUT they will not work at full capacity.

The bad news is that unless you have ( expensive) controllers, of the same brand and type, they won't work at full efficiency, and one or both will almost contribute nothing most of the time. You can measure this with an ammeter. One will work hard and the other will think the battery is charged and go to float mode.

For many reasons, you are better off removing the individual regulators and buying a bigger MPPT one and feed the inputs to that ( with blocking diodes). Going to MPPT will give you 20 - 25 % more output from your existing panels, and they should be installed next to the battery, not the solar panels.

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Follow Up By: Mick O - Tuesday, Nov 17, 2015 at 22:43

Tuesday, Nov 17, 2015 at 22:43

I wish I'd said that ;-)

Now that's a good answer.

Cheers.

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trip would doubtless be attended with much hardship.''
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Follow Up By: Nomadic Navara - Thursday, Nov 19, 2015 at 01:57

Thursday, Nov 19, 2015 at 01:57

Quote "The bad news is that unless you have ( expensive) controllers, of the same brand and type, they won't work at full efficiency, and one or both will almost contribute nothing most of the time. You can measure this with an ammeter. One will work hard and the other will think the battery is charged and go to float mode."

Both controllers and panels will work to their maximum capacity when the battery voltage is down. As the battery voltage rises with the charging you will get to the point where the controller with the lower set voltage will commence to close down, that does not matter much as the remaining working panel is capable of doing the absorption charging on its own.

The charge controllers supplied with portable kits are generally of poor quality and do not switch to float voltage when the battery is charged. This may overcharge your battery if you leave them connected to your battery for a few days when you not using it so be careful.

The other thing is that if you have one of the new vehicles with a smart alternator, the alternator will control the battery charging voltage if you are using it to charge the battery when you have the solar panels connected. If your panels are capable of charging the battery with a higher voltage than the alternator system voltage the alternators regulator will reduce the alternator output in an attempt to restore the system voltage at that lower level. This will mean that the panels will be running your vehicles electrical system and that power will not be charging your batteries. That will mean it will take longer to charge your batteries.