### BenFranske: Help using bridge rectifier instead of voltage divider

This post was moved from the old forum:

BenFranske:

Hello! I'm trying to create a circuit to measure current used by a motor with an Arduino using a current transformer and a bridge rectifier. I'm afraid it's been too long since I've done AC circuits or calculated RC values so I'm having some difficulty making sense of the numbers I'm getting, any help would be greatly appreciated.

My specific hardware, with links to the datasheets where applicable:
CR Magnetics CR8410-1000 Current Transformer
Fairchild DF02M DIP Bridge Rectifier
Currently using 200 ohms of burden/load resistance on the AC side of the rectifier for the CT
Currently using 100uF capacitor from the positive output of the rectifier to ground
Currently using 10K resistor in parallel with the capacitor
Measuring across the dc side of the rectifier

Based on the datasheet for the CT I thought I should be using a 100 ohm burden resistor but the voltages across it that I'm seeing when the motor runs (it's on a sump pump either 1/4 or 1/3 HP I think) are lower than I expected based on my calculations (all well below 1V) so I bumped the burden resistance up to 200 ohms to raise the voltages. With a multimeter I'm now measuring voltages around 1.4 Vdc when the motor is running, this still seems a little lower than I'd expect...

One of the things that's somewhat important to me is getting an accurate run duration (being able to detect when the motor starts and stops with reasonable accuracy, say 1/2 second or less) and I'm somewhat concerned that the capacitor is causing a delay in detecting the stop time. If I'm thinking correctly I could reduce this lag by reducing the capacitor size however the only other capacitors I have on hand are a couple non-polarized 1uF and some tiny ceramics. If I were to order another size capacitor what would be ideal.

The circuit itself is a dedicated 20A circuit so ideally I would be able to measure up to 20A but realistically I expect the motor draws somewhere around 10A. I'm located in the US so this is 110/120v. Again, any help is greatly appreciated!