Would charging my 110ah agm from multi sources cause instability

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

Tuesday, Nov 17, 2015 at 14:36
Joan, I'm no techie but I'd suspect that the two solar panels could be combined although I'm not sure of what the difference in controllers would mean (very little I suspect). I believe that they could not be combined directly with the input of the vehicle alternator though (I'm sure I'll be corrected shortly lol ;-) which is a much higher input rate.

The best option would be a DC-DC charger connected to the battery and have that accept and prioritise the best charging options for the battery. You could connect one or both of the panels to the DC-DC charger as 'open circuit' meaning you bypass the built in solar panel controller and just pump the raw output of each panel into the DC-DC charger. It will regulate it appropriately and charge the battery in the way it should be charged.

Cheers

Mick

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Follow Up By: Bonz (Vic) - Thursday, Nov 19, 2015 at 18:29

Thursday, Nov 19, 2015 at 18:29
Im a techie and Mick you're surprisingly accurate
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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.
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Reply By: Robin Miller - Tuesday, Nov 17, 2015 at 14:57

Tuesday, Nov 17, 2015 at 14:57
No it won't Joan, if one has higher output than the other then it will automatically supply more power and overide the others without harm.
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Reply By: HKB Electronics - Tuesday, Nov 17, 2015 at 16:27

Tuesday, Nov 17, 2015 at 16:27
There will always be some sort of interaction when using multiple once the battery reaches a point where one of the chargers switches from cinstant current charging to constant voltage charging, this will generally occur when the battery reaches a state of charge of around 80% unless the chargers are specifically designed to load share.

It is not good to idle the car for long periods of time so unless you have no option I would steer clear of that and stick with solar when camping. If the battery is deeply discharged, with your panels both solar charges will happily share the load until such time as the state of charge of the battery reaches a point where one charger can swap from constant charge mode to constant voltage mode, at that time some hunting may occur but if it does and this worries you then simply you simply turn of one charger.

It would be better if both panels were connected to a good MPPT charger as it would be more efficient than two controllers but don't be misled by the claimed increase in power these devices supposedly give as in many cases very little improvement is seen when the whole system has not been designed to make optimum use of the MPPT charger.

In the case of the car being connected too, same applies.

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Reply By: Joan K - Wednesday, Nov 18, 2015 at 09:34

Wednesday, Nov 18, 2015 at 09:34
Thank you everyone. Your info is really helpful. It's good to know that connecting the 2 panels won't harm the battery. However I will keep the car idle charging separate... and to a minimum...and only use it when all else is exhausted (it's noisy and smelly anyway ). I will test the 2 panels together as they are for now, and see how they fare. In the meantime I will research the most suitable MPPT charger and install it in the boot. I will possibly need 2 of these MPPT chargers as I use the panels for home power off grid as well. These tiny panels put out each morning have saved me $1000 per year. Cheers.
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Follow Up By: Bigfish - Wednesday, Nov 18, 2015 at 11:28

Wednesday, Nov 18, 2015 at 11:28
How do they save you $1000 a year? At about 10 amps combined per hour for 12 volt $1000 seems odd....
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Follow Up By: Joan K - Thursday, Nov 19, 2015 at 20:24

Thursday, Nov 19, 2015 at 20:24
I use very little.....much the same way as when I'm camping. My major cost is the fridge.
The last bill for the winter quarter was $75.00. The graph on my bill shows that I use only one quarter of the power used by similar households. I'm camping at the moment so I don't have access to my bill to see exactly how many kws I actually use. I will try and follow up when I get back.
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Follow Up By: Bigfish - Thursday, Nov 19, 2015 at 20:38

Thursday, Nov 19, 2015 at 20:38
No worries Joan. I didn't figure that you used the system on a house. It cost me $12,000 for a 6kw system on my house 4 years ago. I normally get a $500 a quarter bill and a cheque for $800 at the end of the year. I have not had to pay for electricity for 4 years (save $2000) and also get a $800 Christmas present. On the 44cent tariff....

cheers
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