Hi,

I'm currently working on a project that utilizes an AC single phase motor and an 8051 uC. The uC turns the on the AC motor through a relay. The board which the uC is on and the AC motor are effectively electrically isolated.

When the motor is turned on I have seen, on the scope, what looks like transients. I have disconnected the AC motor and tested to see if the relay was causing these transients but they no longer occur.

I do not know much about AC motors as we didn't go over them in detail at school. I've started reading as much about AC motor theory I can but my boss is really busting my balls to getting this working.

Currently my working theory is that when the AC motor turns on it causes such a heavy load on the AC line that for a short instance my DC power supply is lowered. However this doesn't explain why I get transients that are +-8V on my DC.

I am wondering if there is something I can use so that I can guarantee a stable 5V on my rails while the AC motor starts. I am just confused as to how transients from my AC motor are appearing on my DC line. The two are isolated through a transformer.

I'd greatly appreciate any help on this

Thanks,
Roque