How do i fuse a wiper motor?

366 Views 3 Replies 4 Participants Last post by corey872, 23 d ago

barryabrams

Discussion Starter · 24 d ago

I'm building a simple animatronic using a single wiper motor connected to a speed controller (similar to this one fright props sells). It's hooked to a 12v 5amp power supply, and being controlled through a relay. I'm not using park, just driving it clockwise and counter clockwise. The motor just moves a set amount of degrees until it hits a limit switch, waits for input and then moves the reverse direction until it hits another limit switch.

Yesterday, when I was testing it, I forgot that I had the armature locked in a safety position and the motor tried it's hardest to move but couldn't. After 5 or so seconds, the power and ground wires from the power supply to the speed controller smoked and melted. After replacing those two wires, everything still works so no real damage. Granted, those two wires were 22 or 24 gauge, while everything else is heavier in the 14-18 range.

To prevent this from happening in the future—or more likely something getting stuck under the animatronic before it can hit it's limit switch—I should just put a fuse between the power supply and speed controller, right? Is there a good way to figure out what value fuse i'd need? Or perhaps there's something else i'm missing.

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derf63

· #2 · 24 d ago

barryabrams said:
I'm building a simple animatronic using a single wiper motor connected to a speed controller (similar to this one fright props sells). It's hooked to a 12v 5amp power supply, and being controlled through a relay. I'm not using park, just driving it clockwise and counter clockwise. The motor just moves a set amount of degrees until it hits a limit switch, waits for input and then moves the reverse direction until it hits another limit switch.

Yesterday, when I was testing it, I forgot that I had the armature locked in a safety position and the motor tried it's hardest to move but couldn't. After 5 or so seconds, the power and ground wires from the power supply to the speed controller smoked and melted. After replacing those two wires, everything still works so no real damage. Granted, those two wires were 22 or 24 gauge, while everything else is heavier in the 14-18 range.

To prevent this from happening in the future—or more likely something getting stuck under the animatronic before it can hit it's limit switch—I should just put a fuse between the power supply and speed controller, right? Is there a good way to figure out what value fuse i'd need? Or perhaps there's something else i'm missing.

I would strongly suggest an inline fuse on the positive side of the power supply. I'm doing this from memory so anyone feel free to jump in and correct me, but I think I'm pretty close on my estimates. It's not surprising the 22-24 gage wire melted first. It would only be able to take maybe 5 amps max of load depending on the number of cores before heating up, and a jammed wiper motor would be attempting to pull way more than that.

As a general rule single core wire can handle more load. For example; 12-14 gage wire stranded can typically handle 10-15 amp, and single core 25-35 amp load. So a lot depends on the quality/type of wire used. I would look at the output rating of your power supply and adjust the fuse rating to that so you don't accidentally cook your PS.

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Jekyll-labs

· #3 · 24 d ago

Wiper motors come from cars so I use automotive fuses. You can buy fuses for however many amps you like. I have it on the positive lead of my power supply. Not sure if it’s better to have it closer to motor. I’d be interested in other people’s thoughts.

I use 7.5A ones similar to these (I can’t remember which supplier).

5 Pack 12 AWG Inline Fuse Holder - Automotive Replacement Fuse Holder with 60 Pcs (2A, 3A, 5A, 7.5A, 10A, 15A, 20A, 25A, 30A, 35A, 40A, 50A) ATC/ATO Standard Blade Fuses https://a.co/d/5wYBom4

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corey872

· #4 · 23 d ago

Welcome to the forum. Several ways to skin this cat. Several good ideas mentioned above.

In considering simplicity and robustness, I would ask does your power supply not already have a fuse? ...or current limiting? If it does, then possibly the simplest thing to do would be to wire the circuit to comfortably take 5 amps.

If you do go with an add-on fuse, I would still design the circuit to be fairly robust - if the supply is rated at 5A, and the speed controller can handle it, then maybe use wire and a fuse around 7.5 - 10A. That way you only blow the fuse in a 'real' emergency... shorted wires or similar.

The other tidbit of advice might be to look for a 'resettable' fuse / breaker. This would be something where a tripped circuit could be reset with the press of a button or even just some wait/cool down time.

The last thing you want on the big night is having to run around in the dark with a bag of 'one shot' fuses and continually replace/restart props. Or be like me and buy a big bag of fuses, then forget where you stashed them! (32 channels of lighting, each with an independent 5A fuse is a lot of chances to blow!)

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