Delta Dust Collector Motor Issue

What to do when a bad capacitor keeps a motor from starting properly. April 18, 2011

My model 50-850 collector, wired for 110 volts went out yesterday. As it tries to start the motor mounted breaker kicks out, as it's drawing too many amps. Is this a capacitor gone bad? There are two, one in the switch box and one on the exterior. Any thoughts?

Forum Responses
(Cabinetmaking Forum)
From contributor L:
I used to have one of those and it was capacitor in the housing. It's a great collector and did a great job. You might just want to take it off and take it to a motor shop. We just took a 10hp Baldor in for one of the collectors for new bearings and itís a totally different sounding machine.

From contributor B:
I had a capacitor go out on mine (same model) about five years ago and I seem to recall the symptoms were the same. I got a replacement directly from Delta. Give them a call - they're typically very helpful.

From contributor I:
The motor has a start capacitor and a run capacitor, it sounds like the start capacitor is bad (normally mounted directly on side of motor under a cover). Very often when bad they will seep out a liquid substance. Remove cover and capacitor will have two wires going to it, disconnect them and you can pull the capacitor. Capacitors arenít expensive. Replacement is easy as it does not matter which way you wire up the two wires. Size and type of capacitor is important (should be marked on side, i.e motor start capacitor cap 300mfd 125 vac). Itís easier to replace in place than remove the motor.

From contributor T:
Check the simple things first. Do a quick check on your circuit. Plug another high current-drawing devise into that circuit - an air compressor would be good. Measure the voltage as you put power to the motor - if you starve a motor for voltage, it will try to make up for it by drawing more amps. You may have a high-resistance connection, an arced contact on your start switch, etc. I've never heard of a "run capacitor", but normally a motor will hum and attempt to run when the start cap is bad. If you are instantly tripping the reset, I doubt it's due to a bad start capacitor.

A start capacitor would have to be a dead short to cause an instant trip of the reset - normally when a capacitor goes bad, it "opens up", rather than melt into a dead short. The extra cap at the start switch is also a new one on me. I suspect it is simply an additional start capacitor - or maybe its function is to minimize contact arcing on the start switch itself. It could also be a defective reset button - you need to try to measure the current draw to know for sure. The reset button also provides thermal protection, and that feature may have nothing to do with amperage draw. In other words, a reset button can fail in two different, non-related ways. If you can get to the backside of the reset button, you can jump across it with a wire and bypass it.

A capacitor stores electricity, and in your case 110 volts. Before touching the wires on a capacitor, always discharge the capacitor with a screwdriver by shorting the two terminals together. Most of the time, a capacitor will discharge on its own - but if not, and you don't short it out, you risk banging your elbow. It's a fun, yet (sometimes) aggravating process of elimination.

From contributor T:
I just Googled run capacitor. These caps are used to make a motor more efficiently, not normally a concern with most consumer grade tools. I suppose it could be used to slightly increase horsepower rating - always a plus for the marketing department. But if marketing is using amperage draw as a selling point (more is better), then certainly there is no incentive to make a motor more efficient.

Making a motor more efficient is, however, advantageous for equipment such as HVAC and refrigerators, where operating costs are scrutinized, measured, and rated. (The American consumer is a funny critter)!

So if you understand what an AC sine wave is, then it would appear the run capacitor charges at the peak of the sine wave, and discharges as the voltage approaches the datum line - they're tricking the motor and making it work more like a three phase motor, or a DC motor.

Interesting - I wouldn't have guessed the gain would be worth the pain (cost). Regardless, as applies to your dust collector, I still think either cap would have to be at dead short to cause an instant reset trip. Pull a wire off the cap and check for continuity with your voltmeter. If the needle on your meter jumps up, then slowly drops back down, the cap is likely good. If you show steady continuity, you have a dead short. If you get no needle movement at all, the cap is likely fried open (defective).

From the original questioner:
To all who responded: the run capacitor mounted on the motor exterior tested bad. I ordered a new one for $30 with shipping and now it runs fine. Thanks all.