The BEST Way TO Perform a Parasitic Draw Test

[GBJeffOH]

I see a lot of people that have issues with electric troubleshooting.

 

[OrangeKrush]

Thanks for posting.. I did this a while back and can't remember exactly how I went about it.. this will help, I'll save it!

 

[Henro]

I found that video interesting.

In heavy industry, something called a shunt is used to measure high currents in relatively high DC voltage circuitry, like the power connectors feeding high HP motors, that are rated at thousands of HP. As well in DC circuits with lower amp loads in the hundred amp range or less. A voltage drop is measured across the shunt terminals, which is essentially the same as measuring the drop across the fuse.

Never thought of using the voltage drop across an automotive type fuse to estimate current flow through a circuit.

With the charts referred to, this is possible within a range anyway.

Here is a link to a chart similar to what is shown in the video.

https://m.roadkillcustoms.com/wp-content/technical-pdf/Mini%20Fuse%20Voltage%20Drop%20Chart.pdf

Thanks to the OP for posting the video.

 

[GreensvilleJay]

yes, it's a slick,easy way but...and there's always a but...
different makes of fuses may give different readings, might only be small but possible.
in any event NO parasitic drain is good....

 

[Henro]

yes, it's a slick,easy way but...and there's always a but...
different makes of fuses may give different readings, might only be small but possible.
in any event NO parasitic drain is good....

I would certainly expect that such measurements would only be a rough indication. After all, fuses are not calibrated for exact resistance values.

BUT why would anyone even care? Probably because in a day or two they keep finding a dead battery if the vehicle is not used.

So I think this method would be meaningful if one were experiencing a possible unexplained battery drain, for whatever reason.

 

[OrangeKrush]

I would certainly expect that such measurements would only be a rough indication. After all, fuses are not calibrated for exact resistance values.

BUT why would anyone even care? Probably because in a day or two they keep finding a dead battery if the vehicle is not used.

So I think this method would be meaningful if one were experiencing a possible unexplained battery drain, for whatever reason.

This was the reason for my testing, from what I remember everything checked out and I think I had just gotten a bad battery but I wanted to be sure. Warranty got me a new battery since it was only 8 months and haven't had any problems 2 years later.

 

[Whatscooking]

Unhook negative battery cable and put a 12v test light in series, no light no draw.