Checking Current Draw

hillbilly1 said:
The meter has internal fusing, so the worst that would happen would be the fuse blowing, but a shunt switch could be used for the initial startup.
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I planned on checking before anything is ever turned on, and after it has set overnight. If I have to get in the vehicle to check fuses that might not be under the hood, I will force the door switch closed so the interior light doesn't come on. Then I may wait a while after that to check inside.
 
My truck has what sounds like a pressurization pump that kicks on for a few seconds when you open the door, I think it may be the fuel tank pressurization pump to check the seal. Just put new tires on it, and now the service tire monitor light came on. Tire place probably broke one of the sensors. It’s a big money maker for them. They would do it every time on my previous employers trucks.
 
hillbilly1 said:
The meter has internal fusing, so the worst that would happen would be the fuse blowing, but a shunt switch could be used for the initial startup.
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That's what I mean. Blowing the fuse in my Fluke DMM is not a cheap deal. I'll remain where I'm at with a nice DC clamp meter with 1mA rez. People don't realize all the wake ups cars do, even charcoal pump purges. That can be enough to blow a fuse right there.
 
fastline said:
Again, good luck. There are a lot of capacitors that load up with key on. Consider this an inrush hit of a motor. It's not trivial.
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Which is another reason why you need to wait a bit after connecting to the source, to give any items that only draw current for a short time to do their thing before searching for any load that maybe shouldn't be running. When searching for something that is draining your battery when vehicle is not in use you would not be turning the key on either.
 
Here is a video from South Main Auto that uses the idea of checking voltage drop across fuses - just like the chart that Tom posted above.


This channel is one of the best on the internet (excluding this forum, obvs ;) ). I am sure that some of you may already watch Eric O, from upstate NY, His videos are excellent, funny and informative. Some are purely mechanical - like brake jobs. Some are medium deep dives into the electrical systems in modern cars, like CAN Bus issues. His diagnostic skills and explanations are always really good. And an often fun look at what it's like to own and operate a small independent auto repair business in a small town.

He has several where he diagnoses parasitic battery draw, this is the first I came across with a quick google. He has discussed that chart that Tom shows above in several videos.
 
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