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using two momentary switches with DPDT Relay for f/r dc motor control
- Thread starter Magoogle
- Start date
You may be right. That's just what I would do. Of course one operational different with a higher voltage is that the conductor will spark more when it makes or brakes contact. That's what I'm thinking will reduce or cripple the life expectancy. That said, I have never actually used an under-rated relay before so you may be fine. I've just stated my expectation.
@KrisBlueNZ , you have a lot of experience under your belt... what do you think of using a 12V 30A relay to control a 24V 2A device?
@KrisBlueNZ , you have a lot of experience under your belt... what do you think of using a 12V 30A relay to control a 24V 2A device?
Well, that's a +1 ...
If you want to use the PCL rated at 5A and 32V, then the partner relay with the PCL will simply be there to provide or cut power. The PCL will switch the current flow by itself. A diode is required for this method (3rd picture). I still suggest a higher rated relay, but as you mentioned the current limit is far higher than you will be using. I can't say for certain if it's a no-go or not. Hoping Kris give a yay or nay.
- Joined
- Nov 28, 2011
- Messages
- 8,393
I've never tried it. The problem with DC loads is the inductive kick-back from the load (the motor) which causes arcing, especially if the contacts move slowly or don't separate very far. I think this would worsen by a factor of four for every doubling of the voltage.
You should have a 1N540x across each contact that could break the circuit to the load. Is the relay rated for an inductive load? I don't know whether you would be safe. I would buy the right part. You'll need one new relay anyway won't you? Might as well get two SPDT relays with 30V contact rating.
Sounds good Kris, Thank you.
Lets see if the op prefers to use the DPDT relay he's got if if buying two higher rated relay's are acceptable and I'll get him a working diagram.
Shopping list should include:
2x SPDT relays. (should be 5-pins. 2=coil, 1common, 1NO, 1NC)
2x Diodes . Part numbers 1N540X (X is anything, these diodes will protect the relay when they turn off... as the motor will cause a voltage spike)
You already made a partial circuit that actuated the relays, so it seems that the keypad can handle enough current for the relay coils... I don't think you have ever stated if they are momentary mechanical buttons, or the little rubber buttons (like in a TV remote) though.
2x SPDT relays. (should be 5-pins. 2=coil, 1common, 1NO, 1NC)
2x Diodes . Part numbers 1N540X (X is anything, these diodes will protect the relay when they turn off... as the motor will cause a voltage spike)
You already made a partial circuit that actuated the relays, so it seems that the keypad can handle enough current for the relay coils... I don't think you have ever stated if they are momentary mechanical buttons, or the little rubber buttons (like in a TV remote) though.
Well, normally (at least from what I have seen) there is a diode placed on the motor side of the relay that is placed backwards... so that when power is cut from the motor, the back fed power has somewhere to go. With this circuit, the motor side of each relay is bidirectional, so the diode would not work here... And I'm thinking of how it could possibly go on the other side of the relay, and It's not magically clicking into place for me . I'm hopin Kris makes another appearance 
Edit. I built one of these for a replacement window controller in a Toyota 4Runner and didn't use diodes. Has lasted for 2 seasons so far.
Edit. I built one of these for a replacement window controller in a Toyota 4Runner and didn't use diodes. Has lasted for 2 seasons so far.
It will. The Diodes are merely added protection for the relay.
Your welcome. Sorry it took so long to get you a simple answer. I completely missed the rating on the pair of relays you had already :s
