Battery & Alternator Amps
 

Used a clamp on DC amp meter to read my D1 battery values, posting for general reference, your exact values will vary.

Engine off, battery drain:

Dome lights on - 0.8 amps ( I have two LED, and a third regular one that I haven't swapped out yet, was about 2 amps when all three were regular bulbs) - LEDs draw a bunch less, good for camping, etc.

Parking lights on - 5.6 amps

Head lights on - dim 14.2, high 15.6 amps. I have no front fogs.

Crank starter - 378 amps max (very short time - about 65 F) - this is why you need a high CCA rated battery.

Engine running:

Idle, no lights or other items - 18.9 amps from alternator, 4.3 of that to recharge battery. As battery charge returns after starting the amps to battery decrease. So if your alternator died and you were running on battery reserve only, about 15 amps drain, more depending on other accesories. 14.06 volts on battery.

AC on and fan on high - 52.3 amps, battery still being charged at 3.3 amps, 13.88 battery volts

Head lights on - 79 amps - battery charge at 3.5 amps, 13.83 battery volts - if alternator had a blown diode inside, it would not make this many amps, and battery would actually supply some of the load and go dead eventually as you drive down the road. Battery warning light is good, volt meter is a plus. Not sure if battery volts appears as a moniored value on OBDII for D2, it does not on the D1. On my Kia battery volts show up on the scanner as a value. Good thing for those guys with Ultra Gauge to monitor.

Wipers, hazard flasher, rear wiper - 75.5 - 84.5 amps (load varies), battery charge down to 2.0 - 3.0 amps as it has recovered from initial cranking discharge. So if you have multiple fogs / driving lights - here is where you start to run out of amps. 13.8 battery volts.

End of test, engine warmed up, crank again, 287 amps.

scan guage 2 monitors voltage as well.

Great. I'm not sure why my el cheapo Actron doesn't, except when it is a measured value broadcast by the ECU. After all, the scanner gets 12 volt operating power from the OBDII port, pin 16.

Wow, that's a lot more than I thought it would be for a petrol engine.
Thanks for the info!

It monitors stater voltage? :eek:

In any case, the values can be useful for OBD1 Rovers. :)

Tom, I think that the clamp on meter may well have some "math" issues, the reading I got was from the "min/max" setting which captured the data while I just turned the key. And it may well be the absolute peak of the waveform, as opposed to the "average" value over that short time. What prompted this was another post where the parts store test said starter current was low, 1.8 amps. That's low, but highly illogical. I would bet that current is more likely 100 - 200 amps.

And you are right, the diesel starters do draw a lot more because of the compression ratio. I went to a rebult gear drive starter for a 78 John Deere tractor I have, and what a difference!

Yeah, start up draw is peak and will be higher than actual cranking amps. Just like winch motors. I think I read the Warn 8274, which has a stall draw of 450a, can draw up to 650a at start up.
And yeah, a 1.8a draw would mean an exceedingly efficient starter. ;)