First Generation Power Relay Board

OK, been working on the circuitry and the actual panel for this silly thing nearly every morning. Right now, the control panel enclosure is being fabricated at a place here in Phoenix called, "Liquid Metal Concepts." The labeling/graphics overlay for the panel is being printed at Sign-A-Rama here in Tempe. They will peel-n-stick the control labels onto the aluminum. The labels are black printed on transparent something-something.

The first edition of the relay PCB that switches the main drive power (24VDC) and the accessories (12VDC) mostly worked OK. I forgot to add a couple of diodes around the relay coils to prevent voltages on the 24V coils when the 12V rail was switched on out-of-sequence. I may require some electrical engineering assistance on this to be sure the power is all OK. The relays are very beefy and to cover the potential current the motors may draw, I put two relays in parallel for the 24V rail.

Here's a picture of the board in testing:

The left relay is the 12V. The other two handle the 24V. To minimize heat, I'm using 6 AWG wire when it comes to the motors and the batteries.

The one thing that concerns me, and from what I'm reading around the web it's expected, is that the coils on the relays are getting quite warm (upwards of 130ºF). I know why, but I don't know if that's normal. I'm not sure that it shouldn't be normal, given the voltage and the current going through the coils, but still, they're too hot to touch for more than a second or so. I think I may put a 24VDC fan on the contraption for added happy fun times. Any thoughts?

I'll post some more stuff shortly.

Andy Frey, Gilbert, AZ, US

My name is Andy and I am a maker. Enough about me. How are you? What did you have for lunch yesterday? Have you made anything cool lately? OK, back to me: I like to make things, with or without purpose. Clocks, shelves, machines that turn themselves off, homemade circuit boards, IKEA chairs with motors, etc. I love to learn how to manufacture stuff myself. I also love to take things apart to see how real-world products are engineered.