Smoked my 8520 Mill motor today CRAP!

Finster

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I was making chips today on my 8520 and all of a sudden everything stopped and the motor would just hum. It won't even do that in reverse. Apparently the thermal protection didn't protect very well that motor casing was almost to hot to touch. Well, it's smoked, I'm sure of that. I called a guy about a rewind but he hasn't called me back yet. It's a 3/4 hp Baldor motor. A new shiny one is around $300 I don't know what a rewind will cost. So other than this bad news, I actually have a question. Motors are not my strong point. If I have to go the new motor route, is there any harm in upgrading the horsepower? Say a 2 or 3 horse motor? I'll keep the RPM's the same but I would think with a higher HP motor, it would labor less and stay cooler. Can that damage the machine at all? What are any pro's and cons?
 
You might be able to get a 3-phase used one for cheap from a HVAC contractor who works on commercial A/C's. I'd like to know what the motor shop says, what does it cost to have a motor rewound?
I picked up a 5hp 3-phase off of Craigslist for $25. A buddy made his RPC out of it.
 
Check the starting capacitor, run capacitor, & the centrifugal switch. For minor issues it's usually one of those. I blew a start cap a few years ago (same symptoms as you described), replaced it with one from Grainger (I needed it that day) & all has been well ever since.
 
Check the starting capacitor, run capacitor, & the centrifugal switch. For minor issues it's usually one of those.

I second this; if it hums, the motor windings ARE intact. A short would trip the breaker, and an open
winding wouldn't hum (or get hot). It's likely just a few dollars for a capacitor, but (on woodworking
machines) the centrifugal switch frequently gets sawdust poisoning... for that, you have
to disassemble and use compressed air or toothbrushes.
 
I second this; if it hums, the motor windings ARE intact. A short would trip the breaker, and an open
winding wouldn't hum (or get hot). It's likely just a few dollars for a capacitor, but (on woodworking
machines) the centrifugal switch frequently gets sawdust poisoning... for that, you have
to disassemble and use compressed air or toothbrushes.
Would this be a hardware store item? I live in the sticks so options are limited. Is there a way to check the starting capacitor to see if it's bad? Sorry guys, electrical is my weakest subject.
 
It is most likely the motor capacitor as others have indicated, or possibly a sticking centrifugal start switch. With frequent start/stops the capacitor can go quicker and they also have a finite life span (shelf life). I would pop out the capacitor and look at the specs., lots of online vendors and eBay sell replacements. There are ways of checking it with an ohm meter (usually reads open when it goes). Some multi meters will also read capacitance, and the capacitance usually reads nil.

The issue with a motor replacement is the shaft and frame size, so you would need to check that the new motor has the same mounting (frame size) and shaft dimensions which would make installation easier. You may be able to upgrade to a 1 Hp (see thread below). Ideally a 3 phase motor is probably a better way to go as a direct drop in replacement with the advantages of no start capacitor and smoother power delivery, main drawback is the need for a VFD (or RPC) and cost.
http://www.hobby-machinist.com/threads/need-help-wiring-clausing-8520.18606/
 
So if I check this capacitor for continuity and get continuity, the capacitor is bad? What are the chances this capacitor is juiced up and is going to zap me? lol.... I hate gett'in zapped ... lol...
 
If the cap is good it may still be charged, discharge it before connecting to a multimeter and for your safety. If the cap is bad, you won't get continuity, it will show as open. Sometimes they pop or swell so if you immediately see signs of that you know the answer.

Unfortunately it can't be found at a common hardware store. Mcmaster carries them if you need it next day. If the cap didn't blow up, you should be able to see the value printed on it so you buy the new one (micro farad / μF).
 
+1 on shorting the capacitor (a screwdriver is good for this) before doing anything else. Then disconnect one or both leads. Check with an ohm meter (preferably analog). If it's good, the meter will briefly indicate some resistance value, then go to "open". This is the capacitor accepting the charge from the meter's battery, until it's up to the test voltage. If you swap the leads, it will briefly show "below zero" resistance, then go back to "open" or infinite. This is the capacitor draining off the charge you just added to it.

If the capacitor shows a continuous non-infinite resistance, it's shorted. If it fails to show the initial "spike," it's probably open.
 
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