Puls width modulator fish finder interference?

[DanielG]

I have an all electric boat. Just a couple of minn kotas on a lake I live on. I recently installed a pulse width modulator on one of the motors for better control. When I run it the fish in the fish finder never appear. Sometimes the bottom will look like a lot of little spikes too but not all the time. If I turn it off and run the other motor that is not on the PWM the fish return. Anyone have a setup like this and ever notice an issue? I'm thinking of maybe faraday caging the unit in the console.. you know putting it in a metal box thinking this might solve the problem. Anyone ever have this issue or know if my solution might be a good one? Other than that the PWM is performing really nicely and I'd like to keep it.

Thnx.

[Tennessee Boy]

Is your fish finder and trolling motor connected to the same battery or to a battery connected to the same onboard charger?

[DanielG]

1 hour ago, Tennessee Boy said:

Is your fish finder and trolling motor connected to the same battery or to a battery connected to the same onboard charger?

Yes, but for a couple of years now never an issue before the pwm and not an issue when using the non pwm motor. Just when I turn on the pwm. The charger only charges when I plug it in at the dock. It's not connected to an engine that charges it. No gasoline motor on board.

[Tennessee Boy]

You hear a lot of people say that having a fish finder and trolling motor on the same battery causes interference and this is almost always the cause of interference.  However, I ran multiple fish finders on the same battery as my trolling motor for years on my first boat without ever having an interference problem.  I think it depends on the trolling motor.  I've never had the problem you are experiencing but I would be willing to bet that the solutions that fix trolling motor interference will solve the problem.  I would try separate batteries if you have an extra.  Many people fix interference by properly grounding the trolling motor.  Doing the same with PWM might fix it.

[DanielG]

I'll give it a try, but it works good with the trolling motor connected to the same battery that doesn't use the PWM. Only when I turn the PWM on.....

[Tennessee Boy]

I guess what I'm really trying to say is I think the PWM is causing interference like some trolling motors do. I would try to fix it the same way.  I think the interference is coming through the power cables not through the air so I don't think a faraday cage would help.  If you have an extra battery you could test this very quickly.

[MN Fisher]

1 hour ago, Tennessee Boy said:

I guess what I'm really trying to say is I think the PWM is causing interference like some trolling motors do. I would try to fix it the same way.  I think the interference is coming through the power cables not through the air so I don't think a faraday cage would help.  If you have an extra battery you could test this very quickly.

If it is the the PWM - putting a rectifier circuit before the fish finder may clear it up.