Thread: Electrical power draw

I feel honoured by your confidence in me but i must admit i didnt think about that untill now, i only know the average current draw with ignition off ... though i'm sure there are differencies from one vehicle to another based on various factors so for you to be 100% on the safe side better measure it cos that's certain... the easyest way would be if you can borrow a clamp meter if you dont have one and put it around the positive lead with engine running, or "invest" in one of these VC3266L+ Mini Digital Multimeter Voltmeter Ammeter OHM Diode Voltage Tester 200A Auto Range AC/DC Test Clamp Meter Tester-in Multimeters from Home Improvement on Aliexpress.com | Alibaba Group cos it's handy to have it within reach

That multimeter linked to the post doesn't clamp dc current, only ac, so its of no use. You need a dc clamp meter.

My guess would be a couple of amps for the engine, cerainly negligible in the scheme of a 120 amp alternator. Other ancillaries certainly draw heaps more. Lights, wipers, heater fan, rear demister, indicators and brake lights all draw far more and would add up to 30 or 40 if everything was on at once - plenty left for additional lighting, etc.

What were you planning on running?

Originally Posted by Vern

That multimeter linked to the post doesn't clamp dc current, only ac, so its of no use. You need a dc clamp meter.

... you are right, sorry, i just linked the first clamp meter i found without reading well the description... i should have thought that a Hall DC clamp meter can't be so cheap but being chinese i presumed that everything is possible.

It's no good putting a clamp meter anywhere near the battery as you would only be measuring the balance of charge current. Not quite sure how a D2 fuse box works but you would have to isolate the input from both the battery and alternator, then measure the load. I'd be looking at fitting a 100A current shunt in the fuse box feed and measuring the current through that. I wouldn't be surprised to see 15-20 amps load including the varying duty cycle of the injectors, the fuel pump, various control valves etc.

DC 6.5-100V 100A/20A Digital Power Meter Monitor Power Voltmeter Ammeter Shunt | eBay

The OP wants to know the draw with engine running to not exceed the alternator's output with some add-ons so IMO a clamp around the battery lead (leaving the wire from alternator to battery out) is OK

Thanks chaps.

Thermo fans, cabin fan, head and tail lights, fuel pump in the order of 15 amps each I would think. Wipers, indicators, brake lights, rear demister I'd guess 5 each. Stereo about 10. So my guess is a total up around 90 amps.

In addition I am already running spotties/flood lights (15 amps), a second battery (? amps) with fridge (5 amps) and various low current outputs.

Am building a drying box for snow gear which will pull up to 25 amps off the second battery.

So my estimation is that the drying box will draw down the second battery at about 10 amps.

Am I close?

Originally Posted by ballbag

Thanks chaps.

Thermo fans, cabin fan - 5 amps, head and tail lights, fuel pump - 5 amps in the order of 15 amps each I would think. Wipers, indicators, brake lights, rear demister I'd guess 5 each. Stereo about 10 - 2 to 3. So my guess is a total up around 90 amps.

In addition I am already running spotties/flood lights (15 amps), a second battery (? amps) with fridge (5 amps) and various low current outputs.

Am building a drying box for snow gear which will pull up to 25 amps off the second battery.

So my estimation is that the drying box will draw down the second battery at about 10 amps.

Am I close?

Remember that you would rarely - if ever, use all of that at once. The maximum demand of the vehicle would be around 50 amps leaving plenty up your sleeve. Even if you occasionally run over 120 amps for a short time (which I would doubt) it isn't going to hurt anything (as long as all your wiring is in good condition) but just draw down your battery a few amps - and that's a big if IMO - I used to max out my old 35amp alternator on my Subaru occasionally on a cold wet night with my upgraded headlights and spotties on - the charge light would glow but I could still drive it the 45 minutes home from work after afternoon shift and start it again fine the next day.

I wouldn't worry about the alternator size at all - just make sure the wiring to the high load devices you are adding is up to scratch.