Battery charger current draw calculation

Question

Hello Everyone,

Lately I have been trying to figure out how to calculate the current draw of circuits but I ran into a problem with battery charging circuits. My question is whether to plug in the battery to the circuit to obtain a correct reading?

Thank you

D_Hersey · Accepted Answer

Current is measured through a point. Your current meter has a maximum safe value it can measure. If this is greater than the current you anticipate, go ahead and break the circuit and and insert your ammeter and charge the battery through it. This presumes your ammeter is bipolar, otherwise, mind the polarity.

dougw · Answer

It depends where you are measuring the current.

If you measure current to the regulator, you can't tell how much is going into the circuit, how much is going into the battery and how much is coming from the battery. If you disconnect the battery, you can determine current to the circuit, but if the voltage changes when the battery is inserted, the current may also be different.

If you measure at the output of the regulator and battery, it will capture all current to the circuit, but will not indicate how much is being used to charge the battery nor how much is coming from either supply.

You may need to measure at more than one place to know everything.