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Gasnets
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# Posted: 23 Mar 2020 05:25pm
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I have 200 amp HR battery for power backup. Cpap machine and tv for a few hours charged with 40 amp marine charger. (a separate power outage system)Also have 100 amp HR battery charged with 300 watts solar. (Used for lanscape lighting)2 separate systems. My question is when power goes out can using jumper cables from the 2 batteries increase the time I get from the power inverter hooked up to the 200 amp HR battery. Especially during the day when 100 amp HR battery is being charged from the sun. This jumper would be temporary. Would it help my runtime? Both batteries are sealed lead acid!
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FishHog
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# Posted: 23 Mar 2020 05:41pm
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it will be fine, don't charge them hooked up, but a light load discharging them will be OK.
Is it perfect? No, but unless you have a high demand load which your cpap isn't, it will work fine.
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Gasnets
Member
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# Posted: 23 Mar 2020 06:02pm
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my max load would be 400 watts on the inverter. So running a jumper from the 2 batteries would be fine? Even charging them with solar at the same time? Anyone else like to weigh in?
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FishHog
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# Posted: 23 Mar 2020 07:15pm
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No do not charge at the same time. Charge separately.
Ideally you don't want to connect two different size or age batteries, but to do it during light usage won't damage them.
Charging them together will do more harm than I'd accept.
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Gasnets
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# Posted: 23 Mar 2020 08:01pm - Edited by: Gasnets
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I only charge the 200 ah once a month for 24 hrs, as i never use it. Only emergency. Perhaps during power failure i should connect my solar. charge controller to the Bigger Battery only. If sunny out i can utilize the 15 amps of solar charging. If i night then use the jumper method. Hows that sound? Yes 15amps is not nearly enough for a 200 ah battery, but if i can get extra run runtime it would be great.
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ICC
Member
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# Posted: 23 Mar 2020 08:39pm
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If the two batteries of different capacities are parallel connected and power is drawn from them nothing bad should happen until the 100 AH battery is drawn down to its minimum capacity. At that point the 100 AH battery will have a lower voltage than the 200 AH battery. If power is continued to be drawn the 100 AH voltage will likely fall into the lower ranges that are going to damage that battery.
If power draw was stopped and the 2 batteries left connected then the 200 AH battery will be at a higher voltage than the 100 AH battery and power will flow from the higher voltage to the lower voltage. There could also be some trasfer of power from the 200 AH to the 100 AH battery while the pair are connected and power is being used. It's just hard to tell what will be happening for sure.
If you charge them when parallel-connected the 100 AH battery should reach full charge before the 200 AH battery. That means the 100 AH would be overcharged continuously until the 200 AH was full.
Why not run the load off one battery until it needs recharging and then swap to the other battery. While using one battery the other can be safely recharged by itself.
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Brettny
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# Posted: 24 Mar 2020 07:38am
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If you don't use that battery much make sure you check the water level and run a desulphate charge on it.
Usually you want 10* of the 20hr AH rating for amp in a charger. So at 200ah your pretty close with 15a.
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