Why do battery needs a float current?
I mean, when it's full, floating and there are no loads? To fight the self-discharge, alright. But it draws a bit more than self-discharge would require. I have 300 AH AGM bank, self-discharge ...
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Mex, give me a break... Manganin shunt and precision DMM in Baja, sure... Besides, +/- 0.1A accuracy of my crude measuring device, namely the controller display, was enough to notice 0.3A current where in theory there should be 0.14 A (total of controller internal consumption and self-discharge). Not that Trimetric is more accurate, same +/- 0.1A.
Heat loss in poor contacts and booster cables must be the reason. Controller is maintaining the battery voltage at the right level due to thin voltage sense wires, but the power loss in power cables and contacts (or voltage drop, whatever) causes controller to increase the output so that wouldn't be a voltage drop on the battery end. Which in turn creates those extra currents. Or the currents cause controller to increase the output. Whether it was egg or chicken first, heat means current.
Don't know if it's a pure copper, but the booster is a cheap Walmart junk, jaws are falling out already. Yes, jaws have little contact with bare wire, and the copper-ish metal on them is more green than yellow :)
Yesterday put up the batteries to real service - connected to trailer DC wires. With circuits of LP fridge, bulbs not yet converted to LED, pumps and all. This morning batts went into Absorption at 10 am, into Float at 11 am (3A Float setpoint), and at sunset were still floating at 0.7A. Worse than 0.3A previously observed after a week of pure floating, but this was to be expected. Current with trailer loads was 1.3-1.4A, but fridge circuits and other parasites draw 0.6-0.7A on the average, so this leaves 0.7A for battery. Hopefully things will improve with proper wiring. No time even to go fishing, dammit...
Heat loss in poor contacts and booster cables must be the reason. Controller is maintaining the battery voltage at the right level due to thin voltage sense wires, but the power loss in power cables and contacts (or voltage drop, whatever) causes controller to increase the output so that wouldn't be a voltage drop on the battery end. Which in turn creates those extra currents. Or the currents cause controller to increase the output. Whether it was egg or chicken first, heat means current.
westend wrote:
Is that #8 battery booster cable copper coated aluminum or stranded copper? I just bought some 4 AWG booster cables, got them home, and found out they are copper coated aluminum. Also, those jaws are about the worst connector to a bare wire when you look at the amount of surface area in contact.
Don't know if it's a pure copper, but the booster is a cheap Walmart junk, jaws are falling out already. Yes, jaws have little contact with bare wire, and the copper-ish metal on them is more green than yellow :)
Yesterday put up the batteries to real service - connected to trailer DC wires. With circuits of LP fridge, bulbs not yet converted to LED, pumps and all. This morning batts went into Absorption at 10 am, into Float at 11 am (3A Float setpoint), and at sunset were still floating at 0.7A. Worse than 0.3A previously observed after a week of pure floating, but this was to be expected. Current with trailer loads was 1.3-1.4A, but fridge circuits and other parasites draw 0.6-0.7A on the average, so this leaves 0.7A for battery. Hopefully things will improve with proper wiring. No time even to go fishing, dammit...
