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| SLA floating in a car |
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| viperidae:
I'm putting a computer in my car, and to get around the issues of battery draining if something goes wrong and surviving engine cranking I though I'd use a 7.2Ah SLA battery I have laying around from an old UPS. I figure I can run the computer from the SLA battery and connect the SLA to the switched car supply via a diode. My theory is it will be kept at half a volt lower than the flooded lead acid battery in the car. so shouldn't suffer too much from the ~14V when the alternator is going. Anyone see any flaws in my plan? I'm a bit paranoid about having something go wrong and returning to a car after work with a dead battery. In terms of power delivery, I'm expecting no more than 20W peak. |
| cs.dk:
Why not a relay driven of the D+ signal (engine running). That way, if the little battery fails, it can't drain the main battery, and it will recieve a proper charge. |
| viperidae:
I didn't think the SLA would like being effectively float charged at the 14+V of the alternator when it's charging the car battery, hence the diode. If I power the set up via a circuit that is only power when the ignition is on, I will never have to worry about a flat car battery |
| cs.dk:
--- Quote from: viperidae on July 24, 2019, 08:17:28 am ---If I power the set up via a circuit that is only power when the ignition is on, I will never have to worry about a flat car battery --- End quote --- Thats why i suggested a relay or other circuit running of the D+ signal, instead of KL.15 (ignition). Thats how most european campers are made. You can still install a diode in series if you want. If the second battery is flat in a camper, and you turn on the ignition, it can drain the main battery. If the relay first pulls in when the engine is running, the alternator is there to help you out. |
| viperidae:
I'm not aware of a signal for "engine running" in my car. It's a gen 7 JDM Honda Accord. There is canbus data that can tell me that but I don't think there is a wire for it. |
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