Hi folks, I have another project on the go. This time for work.
I have bought a cheap eBay PWM controller and power supply for the purpose of testing automotive components. So far no issue testing electric motors at variable speeds.
I’d also like to try using this setup to test solenoids and servo motors.
From reading online I understand a diode is needed to prevent emf feedback when the solenoid coil field collapses and I now have a couple questions;
1) Do I need to use a freewheeling diode or can I just use a rectifier diode? (have some alternator rectifier diodes left over from previous project)
2) If the maximum current will be 30 amps in this circuit then will a 30amp diode suffice or should I go higher?

many thanks in advance

 

Though you're talking about 30 amps - a BEMF diode (Back EMF) doesn't need to be concerned with conducting that much current as it will be a very short blast of current and very quickly drop off. Still, I'd opt for a diode that can handle that much current so you're not over stressing it - albeit brief as heck. The darn thing's GOT to degrade over time. Best engineering practice is to build for 33% over the rating you intend to see.

I'm sure someone here can recommend a good diode for this case. I've used heavy duty diodes that came out of scrapped welding machines - the kind that deal with 100's of amps. One end of the diode is a screw base and the other end is a wire rope welded to a terminal and crimped into the body of the diode. Big snot stuff.

Without knowing what kind of servo's you're talking about:

I’d also like to try using this setup to test solenoids and servo motors.

I wouldn't think there'd be a whole lot of BEMF from a servo.

 

Though you're talking about 30 amps - a BEMF diode (Back EMF) doesn't need to be concerned with conducting that much current as it will be a very short blast of current and very quickly drop off. Still, I'd opt for a diode that can handle that much current so you're not over stressing it - albeit brief as heck. The darn thing's GOT to degrade over time. Best engineering practice is to build for 33% over the rating you intend to see.

I'm sure someone here can recommend a good diode for this case. I've used heavy duty diodes that came out of scrapped welding machines - the kind that deal with 100's of amps. One end of the diode is a screw base and the other end is a wire rope welded to a terminal and crimped into the body of the diode. Big snot stuff.

Without knowing what kind of servo's you're talking about:
I wouldn't think there'd be a whole lot of BEMF from a servo.

Hi there, thanks very much for the reply.
That sounds good, I think I’ll go for a 50amp diode just to be sure.
Servos are just another purpose I’m thinking of trying this system out with, I will also try dc motor driven throttle bodies and maybe even evap system purge valves but the main purpose of the question was about anything with a magnetic coil that I intend to test like oil flow solenoids in variable valve timing.

The system I bought has a capability of supplying up to 30 amps although to be honest I think most of the motors and solenoids I’ll be testing won’t be over 15 amp continuous.
But I’d like to have the system ready to run at capacity problem free if required. It will only be under use for short term testing so I don’t expect to run anything for any real length of time. Just long enough essentially to establish if the device can be operated properly and throughout its normal range without malfunction. So likely just a few minutes at a time.

thanks