Dave in AZ
Solar Enthusiast
This thread is just for reference for those looking to use excess alternator capacity to charge a battery. Other cars should have similar loads to this Tacoma for lights, airco, radio, etc.
21 Tacoma OffRoad, 130A alternator, 9k miles, running perfect, zero issues battery or alternator. I decided to test how much of my alternator output capability was being used, before I came up with a plan for a dcdc charger off the alternator to charge a 2nd house battery.
I used a Klein tools clamp ammeter, the one Will Prowse recommends. It has been tested and verified for good calibration, using Kill A watt meter and cross checking ac and dc amps for devices both.
I tested on the main negative battery cable. The positive starter battery terminal has 2 cables to it, one from alternator and one to fuse box. At idle, alternator charging tested on alternator to battery positive was only 4 to 5 A. I was surprised the positive to the fusebox showed -4A, which I didn't understand, thought all the power from battery would flow through that to fusebox. However, the main negative battery cable was the highest readings and seemed correct, and I know the SmartShunts go there also, so... The battery negative to chassis ground cable was about 4A less than the main negative.
Truck running idle, nothing on, 11.2A
+ lowbeam 55w ea +11.1A 22.3A
+ door open light and dome +1.2A 23.5A
+ air-co full cold and fan +10A 33.5A
+ fog lights, only avail on lowbeam 19w +3.4A 36.9A
+ turn signal, 21w x 2 +1.6A 38.5A
+ highbeam headlights, 65w ea 45.5A
(+7A from lowbeam&fog to Hibeam)
+ Qi pho e charger +0.2A
+ radio full loud +3A
Bed lights +0.4A
Likely driving setup Snapshots:
Truck alone 11.2A
Lowbeams 22.3A
Full draw: Hibeams, full airco, turn signal, full radio 46.5A
With Inverter: 125v measured, supposedly 400w in park and 100w in gear. Should be 31.2A of 12.8v at battery. However, tested way lower.
+ 465w pull on 400w inverter, +22A
--- In Lowbeam, dome, full airco, 33.5A without inverter, 465w on inverter 55.0A
--- In Full Draw (hibeam, full airco, full radio) 46.5, with 465w on inverter 65.5A
Conclusions: test was done parked in idle, normal driving 2500rpm load unknown.
130A alternator appears able to support 400w inverter full time. With all loads off but inverter, amps are 33.2A. Driving with lowbeams and turn signal gives +12.7A for approx 55A. This is a safe setup for driving, at 42% alternator stated max.
Most I could load truck in idle WITH inverter, 65.5A. This is 50% of alternator stated max.
If running full 400w while driving, can reduce alternator load by turning off devices, 11A for lights, 10A airco, 3A radio.
21 Tacoma OffRoad, 130A alternator, 9k miles, running perfect, zero issues battery or alternator. I decided to test how much of my alternator output capability was being used, before I came up with a plan for a dcdc charger off the alternator to charge a 2nd house battery.
I used a Klein tools clamp ammeter, the one Will Prowse recommends. It has been tested and verified for good calibration, using Kill A watt meter and cross checking ac and dc amps for devices both.
I tested on the main negative battery cable. The positive starter battery terminal has 2 cables to it, one from alternator and one to fuse box. At idle, alternator charging tested on alternator to battery positive was only 4 to 5 A. I was surprised the positive to the fusebox showed -4A, which I didn't understand, thought all the power from battery would flow through that to fusebox. However, the main negative battery cable was the highest readings and seemed correct, and I know the SmartShunts go there also, so... The battery negative to chassis ground cable was about 4A less than the main negative.
Truck running idle, nothing on, 11.2A
+ lowbeam 55w ea +11.1A 22.3A
+ door open light and dome +1.2A 23.5A
+ air-co full cold and fan +10A 33.5A
+ fog lights, only avail on lowbeam 19w +3.4A 36.9A
+ turn signal, 21w x 2 +1.6A 38.5A
+ highbeam headlights, 65w ea 45.5A
(+7A from lowbeam&fog to Hibeam)
+ Qi pho e charger +0.2A
+ radio full loud +3A
Bed lights +0.4A
Likely driving setup Snapshots:
Truck alone 11.2A
Lowbeams 22.3A
Full draw: Hibeams, full airco, turn signal, full radio 46.5A
With Inverter: 125v measured, supposedly 400w in park and 100w in gear. Should be 31.2A of 12.8v at battery. However, tested way lower.
+ 465w pull on 400w inverter, +22A
--- In Lowbeam, dome, full airco, 33.5A without inverter, 465w on inverter 55.0A
--- In Full Draw (hibeam, full airco, full radio) 46.5, with 465w on inverter 65.5A
Conclusions: test was done parked in idle, normal driving 2500rpm load unknown.
130A alternator appears able to support 400w inverter full time. With all loads off but inverter, amps are 33.2A. Driving with lowbeams and turn signal gives +12.7A for approx 55A. This is a safe setup for driving, at 42% alternator stated max.
Most I could load truck in idle WITH inverter, 65.5A. This is 50% of alternator stated max.
If running full 400w while driving, can reduce alternator load by turning off devices, 11A for lights, 10A airco, 3A radio.