Using Solid state relays for motor control

[RancidWAnnaRIot]

Hello,

so i'm using 4 Solid state relays to control two DC motors...

i must be doing something wrong.. the motors are turnign suuuuper slow.. and i'm getting 10A of current going through ground!!!!!! it melted my wires!!!

i checked the wiring over and over. and i'm sure it's right.. so i'm asking you guys. do you guys have any schematics or websites i can check up with.. to double check how i'm wiring that damn thing??

 

[mattg2k4]

You might start by telling us how you connected it. I'm not quite sure why you'd want two relays on each motor, you can use one for simple on/off control and four for an h-bridge (forward and reverse), and I can't think of a useful way to use two relays. If you want any of the schematics I mentioned, they can probably be googled "motor control schematic" or "h-bridge schematic".

If you were using an h-bridge, I would say you have inadvertently turned on the wrong two relays, or more than two relays, and are conducting straight to ground, with only a bit of current going through the motor. I'm not very familiar with SS relays, do they require any sort of pulldown resistor to make sure they're off? That might cause the problem I mentioned.

There are some simple questions about the motors that must be gotten out of the way, as well. Are they under heavy load? Are they designed to draw 10A? Do they turn faster when not using the relays?

And lastly, have you considered using mosfets? They stand a good chance of being cheaper while providing for all of your switching needs.

 

[RancidWAnnaRIot]

You might start by telling us how you connected it. I'm not quite sure why you'd want two relays on each motor, you can use one for simple on/off control and four for an h-bridge (forward and reverse), and I can't think of a useful way to use two relays. If you want any of the schematics I mentioned, they can probably be googled "motor control schematic" or "h-bridge schematic".

If you were using an h-bridge, I would say you have inadvertently turned on the wrong two relays, or more than two relays, and are conducting straight to ground, with only a bit of current going through the motor. I'm not very familiar with SS relays, do they require any sort of pulldown resistor to make sure they're off? That might cause the problem I mentioned.

There are some simple questions about the motors that must be gotten out of the way, as well. Are they under heavy load? Are they designed to draw 10A? Do they turn faster when not using the relays?

And lastly, have you considered using mosfets? They stand a good chance of being cheaper while providing for all of your switching needs.

I can't tell you how they're wired right now as i have to do to class.. but...

yea i'm trying to wire them like a H-bridge. So you would need 4 right? I believe they do requier a pull down resistor. So what i do is just ground the input.. at the moment they are not under Micro processor control.. i'm just trying to do initial testing by connecting some contacts and stuff...

i'm definatly gonna have to check the wiring

so i guess it's considered good practice to wire SSRs in an H-bridge?? cause i just kind of assumed you can do it.. i knwo you can do it with electromechanical relays..


one of the relays can handle 10A.. the other 3 can handle 5A.. the motors are 7.2V motors.. but i'm applying 5V.. cause that's all i need

 

[mattg2k4]

Ah, it is an H bridge. I though you were using 4 relays total, not for each motor.

Your problem is almost definitely that you have the wrong two SSR's, or more than two, conducting at the same time, that way instead of current flowing one direction or the other through the motor, most of it flows straight through the relays to ground, with only a bit going through the motor.

You can wire logic circuits to the appropriate pairs of relays so that only the correct pairs can ever be on at one time. I can't recally any offhand, but I'm sure you can locate them with google.