Car battery overcharge risk

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Ray asked Dec 7, '18

Car battery overcharge risk

I have a smart solar 100/20, 300watt pv and 2 x 66ah Optima batteries in or on the vehicle. When running in full sun with 14.7volt absorb voltage set, in bulk mode the regulator supplies the full 20 amps to the batteries and loads because alternator voltage is about 14.3 only. After a few minutes it settles to absorb mode and 14.5v at 10amps.

Will this setup be likely to overcharge the batteries, especially in hot conditions because the smart battery sense does not work from the engine bay, it is inside the vehicle cabin on extended leads at present and sends correct voltage not correct temp.

Smart Battery Sense

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Answer 1 · 2018-12-07T08:14:27Z

JohnC answered · Dec 07, 2018 at 08:14 AM

Hi Ray. Suspect you're from my country, the 'bigpond', eh. So G'day.. :)

Reached 40C for me today, and was happy to see Victron algorithm max me at 14.1V with legit temp comp.

For me, 14.7V is too much, even in winter, when even Victron won't get that high. And I'll add that I view that those Victron levels as well-considered.

Personal choice for you of course, but your concern I believe justified. Up to you, but I'd lower em. Good luck mate.

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Ray commented · Dec 08, 2018 at 05:13 AM

Thanks JohnC, The current flow does reduce with run time so I will test current flowing into start and aux batteries as voltages rise (if they rise). I like the fact that solar is input while the engine is running, as long as it is not too much. Also good that the reg is so configurable voltage wise and the voltages can be reduced.

From NSW

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Ray commented · Feb 22, 2019 at 03:47 AM

Further to the above the 100/20 regulator is at the rear of the vehicle and measures its ambient temp.

I have increased the temp compensation to the maximum -30mv/degree and have noted when engine bay temp is about +65 c. Battery max voltage sits at 14.5 v (better than 14.7) but when the engine bay is cooler the battery reaches 14.8 v, this could lead to overcharging I think. What settings should I use to provide correct charging at say zero centigrade while parked and up to +65c when driving.

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