Testing/adjusting amperage output

[maok]

On 9/8/2023 at 12:46 PM, CarlN-NDC said:

Hey @keithb7, I was re-watching the segment of your video where you demonstrated a few tests with your clamp-style amp meter.  I've probably watched that video alone a dozen times since you've posted it, but I always notice some additional detail every play-through!

 

You had mentioned you weren't able to get an amp reading from the battery cables while cranking over your engine.  I hope I'm not pointing out the obvious here, but could it be because the UNI-T UT210D's limit is 200A DC?

 

Just thinking about how automotive batteries are rated (Cranking Amps and Cold Cranking Amps), they are easily rated to output 3 to 4 times the UNI-T's testing range!  We know these stock 6-Volt system can draw quite a bit of amps (OHM's law) through the wires.  I know in a separate video you had stated you replaced the battery cables in your '38 Plymouth with 2/0 cables.  That got me thinking... I wonder at what size cable would you reach a limit of "diminishing returns"?  Where it doesn't matter how much bigger up in cable size you go, there would become some other limitation, outside of the battery cables, whether it be the starter itself couldn't accept any more amps or something else.

 

Obviously there are many factors at play that can cause a starter to draw more or less amps to get an engine going.  Engine temperature, ambient air temperature, overall condition of the engine (how much compression is it making), condition of the wiring harness and connections, etc.

 

It would be an interesting topic to research further to determine what size cable is the "limit".  I'd love to perform this study myself, but my '48 DeSoto is still in pieces!  Maybe someone on here has already conducted similar testing?

 

 

Carl

 

FYI, current draw is mainly based on the mechanical resistance from the engine to the start motor, ie. engine capacity, compression, accessories attached, etc. Ohms law doesn't work with an electric motor in the circuit, if you replace the 6volt battery with a 12volt battery you will find that the current draw is slightly larger than the 6 volt battery, going against ohm's law.