4 Wire Method Power Supply

Hey All,

I want to measure the resistance of a BLDC I have using the 4 wire method but I don't have a constant current power supply.

My thought is to use an old cell phone charger for the constant current supply but I'm not sure if it's suitable (rated at 4.75V @ 0.55A). My second thought is to use a cell phone charger to power an LM317 circuit set to about 1A.

Any thought or suggestions?

Cheers!

mclovin said:

Hey All,

I want to measure the resistance of a BLDC I have using the 4 wire method but I don't have a constant current power supply.

My thought is to use an old cell phone charger for the constant current supply but I'm not sure if it's suitable (rated at 4.75V @ 0.55A). My second thought is to use a cell phone charger to power an LM317 circuit set to about 1A.

Any thought or suggestions?

Cheers!

Click to expand...

I would use the LM317 as constant current source :wink:

the 4 wire method is also called kelvin measurement method :wink:

But wait a minute... what is important for your precise resistance measurement with kelvin method is not really having a constant current source.. :wink: but just to know precisely the current and voltage across the winding lead.. :wink:

so using a little resistor or a car lightbulb in serie with the cellphone power supply would make you a current limiting device.. than you just have to measure current and voltage on the winding :wink:

Doc

If you have an iCharger, you can set it to hot-wire cut mode, and it will behave as a constant current source.

If you were close I would let you borrow any of my constant current supplies, I have at least 10 of them all the way to 400amps constant.

Once I get the resistance measured do I just use the average of the three phase resistances for my motor calcs?