View Single Post
Old 03-27-2019, 01:23 PM   #38 (permalink)
Ecky
Master EcoModder
 
Ecky's Avatar
 
Join Date: Dec 2011
Location: New Zealand
Posts: 5,096

ND Miata - '15 Mazda MX-5 Special Package
90 day: 39.72 mpg (US)

Oxygen Blue - '00 Honda Insight
90 day: 58.53 mpg (US)
Thanks: 2,907
Thanked 2,572 Times in 1,594 Posts
Quote:
Originally Posted by redpoint5 View Post
Does measuring alternator output reliably tell you accessory draw? I used battery draw only since I know it's reliable and will only output what is being consumed. With an alternator, you don't know if it's feeding the battery, or supplying a load.

I suppose if you take a baseline measurement with the car running, you can subtract it from whatever the reading is when an accessory is turned on. Still unsure of accuracy since alternators can vary output depending on the load it senses and bump up voltages.

I've got a decent DC clamp meter that goes up to 400A that I use to measure starter draw.
Mine is wired:

"Alternator* -> Battery/capacitors -> Car

So, I just clamp between the battery and car on the positive and I have an accurate reading. You're right in that in most vehicles, the alternator isn't a great place to measure instantaneous current, but the average should still be correct.
  Reply With Quote