LFP battery w/ solar question - Fiberglass RV


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Old 06-06-2020, 06:17 PM   #1
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LFP battery w/ solar question

Assume you have a lithium battery with a low voltage cutoff, such as a Battleborn battery, in a circuit with a solar panel controller. If the battery hits the low voltage cutoff and disconnects itself during the night the voltage will go to 0. When the sun comes up and the solar panels begin delivering power the controller will not be connected to a battery. Since solar charge controller manufacturers always say to connect the battery first, is this scenario an issue?
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Old 06-06-2020, 06:32 PM   #2
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Not an issue, the battery's management system shuts down output, but not input, as long as the input is within the voltage/amperage range of the BMS setting.
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Old 06-06-2020, 07:22 PM   #3
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Thanks Tony. I don't have any schematics of the Battleborn BMS so I was living in ignorance.
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Old 06-07-2020, 09:41 AM   #4
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Assume you have a lithium battery with a low voltage cutoff, such as a Battleborn battery, in a circuit with a solar panel controller. If the battery hits the low voltage cutoff and disconnects itself during the night the voltage will go to 0. When the sun comes up and the solar panels begin delivering power the controller will not be connected to a battery. Since solar charge controller manufacturers always say to connect the battery first, is this scenario an issue?
This has happened a few times with my Battle Born when I worked too late into the night on my energy-hog of a computer. In those cases, I hooked it to the car and got the voltage high enough to get me through the night (without working on the computer). Electrons run without resistance into the BBs, so it only takes about 10 minutes of run time on the car.
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Old 06-07-2020, 11:33 AM   #5
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Assume you have a lithium battery with a low voltage cutoff, such as a Battleborn battery, in a circuit with a solar panel controller. If the battery hits the low voltage cutoff and disconnects itself during the night the voltage will go to 0. When the sun comes up and the solar panels begin delivering power the controller will not be connected to a battery. Since solar charge controller manufacturers always say to connect the battery first, is this scenario an issue?
The Battleborn battery BMS disconnects charging at 25F.

Depending on your controller, you may be able to set a low voltage shut off for the solar. I added the battery temperature sensor to my Victron 100/30 & set a low voltage shut off for 32F.

Discharging can be done to -4F.
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Old 06-07-2020, 11:35 AM   #6
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Not an issue, the battery's management system shuts down output, but not input, as long as the input is within the voltage/amperage range of the BMS setting.
I'm afraid it is the other way around. Battleborn BMS shuts down charging a 25F, but allows discharges down to -4F. Some users have put a heavy load ie microwave on the batteries to warm them up to allow charging...
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Old 06-07-2020, 01:02 PM   #7
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The temperature shutdown is one scenario, however the scenario I assumed is a low voltage shutdown. I have discharged my BB until it shuts down and it goes right to 0 VDC. It must still accept charge because it will recover itself.
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Old 06-07-2020, 01:23 PM   #8
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Sorry about that - I don't know how I got off on the temperature problem. Tony is correct - after shutting down due to low voltage, the battery will charge, but not supply current.
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Old 06-07-2020, 09:51 PM   #9
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There are those who disagree with me, so to be on the safe side, perhaps a little more research on the subject is in order.
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Old 06-08-2020, 11:25 PM   #10
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It's not a danger to the battery (though running it down to the cutoff regularly will definitely shorten its life), but it does have the potential to damage the solar controller. I suspect the slow ramp-up of morning sun reduces the chance of damage compared to a sudden connection.
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Old 06-13-2020, 04:04 PM   #11
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I accidentally ran mine down to shutoff. It wouldn't register on the Victron 700 and wouldn't even run a tiny LED. But it still registered over a volt with my multimeter. It charged up immediately. I didn't try to charge it with a solar system though.
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Old 06-13-2020, 04:15 PM   #12
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Some converters will not charge a dead battery. In that case, a short time on a standard battery charger or jumper cables from your tow vehicle will raise the voltage enough that the converter can take over. Be careful using jumper cables from the tow vehicle alternator - the lithium battery will take all it can & may overheat the alternator. I don't know if there is a problem with a solar controller charging a dead battery.
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