![]() ![]() ![]() I would want to trigger both at the same time with 24V and would put the coils in series. I kept looking for a suitable relay and came up with the idea of using two 12V single-pole double-throw (SPDT) relays. I quickly found out that these relays are expensive for a 40A load. What if I effectively modulated the input voltage for speed control but switched my motor wires when I wanted to go backwards? This is where I cut out three SSRs per motor and wanted to add a 24V DPDT relay. The third idea came while I was waiting for the SSRs to arrive from China where I saved $4/ea versus ones already in the USA. I then placed an order for 10 SSRs from the wonderful Ebay. You can also feed them a PWM signal to control the speed of the motor. SSRs have internal circuitry/magic that makes it possible to use 5VDC to trigger 24VDC. My second idea, was using solid state relays (SSRs) in an H-bridge configuration. I was kind of lazy and making circuit boards can be expensive. I didn't want to design a circuit board and go through the additional complexity of driving MOSFETS. This is where a charge pump comes in, but that is where I took a detour. I found out that you can't use 5VDC to trigger 24VDC on the high side of the bridge. I first tried building an H-Bridge using N-channel MOSFETS. When you have success you will know where it came from instead of saying "I don't know it just works now!?" This makes it easy to identify your mistakes so you can turn around and have a success that you learned something. Everyone gives me a look when I tell them to set themselves up for failure before success! In short, take notes on what you are doing, changing, or breaking. ![]()
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