Daisy Chaining Relays For Motor Reversing

Thread Starter

Brian Fuller

Joined May 9, 2019
2
I'm designing a power window switch that will use two SPDT relays to reverse the motor for up/down. I have the whole system wired and and testing properly, but I need to optimize the design for the small space in which it will be installed.

Can I daisy chain the 12v+(87) together and the grounds (87a) together? I believe the answer is 'yes' because the way I've wired my switches means that only one relay coil can be activated at a time (and even if both were activated, nothing would happen because neither motor terminals would see ground); however, google has been stubbornly refusing to confirm my theory. I'm (obviously) not an expert, so I'm worried I may be missing something.

The wiring conceptually follows the diagram below. The relay coils will be wired to switches differently, but that's not relevant to the question at hand. My question is only about the 87 and 87a terminals. Can I daisy chain the 87 terminal on the first relay to the 87 on the second relay, and similarly daisy chain the 87a terminal on the first relay to the 87a on the second relay?

motor_reversing.jpg

I'm short on space, so a power distribution block is not ideal. Running independent lines back to a power source is not ideal either. The wires will be sized to the appropriate current, and the circuit is fused, so I'm safe there.

Thanks in advance for helping me solve the last piece to this puzzle!
 

Thread Starter

Brian Fuller

Joined May 9, 2019
2
Should be no problem, the relay coil current is not that high.
Max.
Thanks for the quick reply @MaxHeadRoom! However, the second part of your response "the relay coil current is not that high" makes me think that either I'm misunderstanding your response, or you're misunderstanding my question. My question is about the 87 and 87a terminals, not the coil terminals. Thanks!
 

MaxHeadRoom

Joined Jul 18, 2013
21,403
Thanks for the quick reply @MaxHeadRoom! However, the second part of your response "the relay coil current is not that high" makes me think that either I'm misunderstanding your response, or you're misunderstanding my question. My question is about the 87 and 87a terminals, not the coil terminals. Thanks!
Of course, :oops:
But still, if the conductors can carry the current then it should be no problem.
Max.
 
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