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Smoked my 8520 Mill motor today CRAP!

Finster

Active Member
Active Member
#1
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?
 

Reeltor

Active User
Active Member
#3
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.
 

whitmore

Active Member
Active Member
#5
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.
 

Finster

Active Member
Active Member
#6
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.
 

mksj

Active User
H-M Supporter-Premium
#7
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/
 

Finster

Active Member
Active Member
#8
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...
 

darkzero

Global Moderator
Staff member
H-M Supporter-Premium
#9
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).
 

hman

Active User
H-M Supporter-Premium
#10
+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.
 

34_40

Dazed and Confused
Active Member
#11
You were making chips and the motor just stopped? Or, the mill was off and you tried to re-start it?

If it was already running and then just stopped, then the start circuit wouldn't be to blame.
 

Finster

Active Member
Active Member
#12
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).
You were making chips and the motor just stopped? Or, the mill was off and you tried to re-start it?

If it was already running and then just stopped, then the start circuit wouldn't be to blame.
Well, it was running and just stopped. However, I believe the motor was overloaded (to deep a cut) and the capacitor may have been jogging open and closed? I could hear it clicking off and on like a start up but since I know nothing much about motors, I didn't really give it much though.
 

darkzero

Global Moderator
Staff member
H-M Supporter-Premium
#13
As some mentioned, the start cap doesn't like frequent start/stops, especially if it's a cheap cap. That's how mine blew as I was working on a run of multiple parts. My run cap said made in Germany & the start cap said made in China.

When my start cap blew the motor either wouldn't turn or turn very slow and it would get very hot. While replacing the start cap I figured I would just change the run cap as well while I had it apart. They were cheap. I think I paid like $7ea and that's at Grainger plus they had it in stock at my local store.
 

34_40

Dazed and Confused
Active Member
#14
Thanks for the reply Finster. just trying to understand how yours failed so hopefully mine doesn't suffer the same fate. :cool:
 

Finster

Active Member
Active Member
#15
Thanks for the reply Finster. just trying to understand how yours failed so hopefully mine doesn't suffer the same fate. :cool:
Yea, I've been putting this mill through the paces to figure out what it can and can't handle. Guess I got 1 answer anyway. I was cutting a 11" railroad rail to make an anvil for my bench. I don't have a face mill or even a decent fly cutter so I was using a .5" carbide endmill taking about .100 and I think it was to deep and I was feeding to fast. Probably my own fault, lesson learned.
 
Last edited:

woodchucker

Active Member
Active Member
#16
Yea, I've been putting this mill through the paces to figure out what it can and can't handle. Guess I got 1 answer anyway. I was cutting a 11" railroad rail to make an anvil for my bench. I don't have a face mill or even a decent fly cutter so I was using a .5" cobalt endmill taking about .100 and I think it was to deep and I was feeding to fast. Probably my own fault, lesson learned.
.1 with a 8520??? Definitely too much with the rail. Hopefully you just blew the capacitor. I'm thinking you kicked out of run and forced the capacitor to kick in. Which you should have recognized way before you smoked it. I'm taking that 8520 away from you... you can't be trusted with it...:grin:
I've been looking myself for one for a while.
 

Finster

Active Member
Active Member
#17
.1 with a 8520??? Definitely too much with the rail. Hopefully you just blew the capacitor. I'm thinking you kicked out of run and forced the capacitor to kick in. Which you should have recognized way before you smoked it. I'm taking that 8520 away from you... you can't be trusted with it...:grin:
I've been looking myself for one for a while.
Here is one that may be close to you? http://www.ebay.com/itm/132126198615?ul_noapp=true
 

Finster

Active Member
Active Member
#19
Well, it's been a very long day. IT'S FIXED! Thanks for the help everyone. It's a very long story but it turned out to be the starter capacitor like everyone thought. I took it to the motor guy today, he checked it out, put on a new capacitor, fixed a frayed wire, and answered 1000 questions I had. He loves to talk by the way. All of this for $20!!!!!! My GOD! I felt like I ripped him off and even offered him more money. This guy has my business from now on. Beyond that, this motor will do 220 or 110. I had it hooked up for 110 since that's what I have in the shop. He said, "let me show you something". He hooked it up on 220 and flipped the switch. The motor almost flipped over it had so much torque. I left there, headed to Lowes and picked up what I needed for a 220 circuit :D She is up and running on 220 now and it's like a different machine. :cheerful: Probably second hand knowledge to you guys but I know nothing about motors and very little about electricity. It's always been my Achilles heal. Just about anything else I'm competent in however, I'm learning. Things are great now and I'm making chips! :D
 

woodchucker

Active Member
Active Member
#20
Yep, glad it was only the start cap. If you listen to the motor, you will hear when it kicks out of run and goes to start. There's a clicking as the centrifigul switch kicks in and out. Try to listen for when you are overloading it. Keep that machine well oiled. 220 also reduces heat to the motor, since you have more voltage, and less AMPS (heat).
 

Finster

Active Member
Active Member
#21
Yep, glad it was only the start cap. If you listen to the motor, you will hear when it kicks out of run and goes to start. There's a clicking as the centrifigul switch kicks in and out. Try to listen for when you are overloading it. Keep that machine well oiled. 220 also reduces heat to the motor, since you have more voltage, and less AMPS (heat).
Yep, he even told me, "There is nothing wrong with this motor, winding is good, bearings are good, you should get some life out of it yet." I took some more cuts on the rail and it didn't even get warm. It never even though about bogging down either. I'm happy about it, BIG TIME!
 

Finster

Active Member
Active Member
#22
Yep, glad it was only the start cap. If you listen to the motor, you will hear when it kicks out of run and goes to start. There's a clicking as the centrifigul switch kicks in and out. Try to listen for when you are overloading it. Keep that machine well oiled. 220 also reduces heat to the motor, since you have more voltage, and less AMPS (heat).
No problem with oil. I'm a believer in oil. Oil is cheap, parts are expensive. I have oil dripping out of every nook and cranny. ;) In fact, if I'm running it for any length of time I shut things down and re oil the bearings. (just in case) Yep, I'm no stranger to the power of oil.
 

JPigg55

Active User
H-M Supporter-Premium
#24
My 8520 had a bad motor when I got it.
I followed Billy G's example and replaced mine with a 1 HP motor from Grizzly, $190 plus shipping. http://www.grizzly.com/search?q=(motor)+AND+(brand:Grizzly)+AND+(category:Motors)
Bolted right on no mods required, but did require buying a different belt due to larger motor diameter.
I went ahead and replaced both belt since I had it apart. Took a 1/2" x 24" and a 1/2" x 48".
Might consider replacing the motor mounts too, I'll see if I can find where I got them, they're cheap and made a world of difference in vibrations at high RPM..
 

Finster

Active Member
Active Member
#25
So what did he show you ??? What's this secret?
To my untrained novice eyes, he hooked it up to 220, hit the switch and the motor had so much torque just sitting there, it jumped 4 inches off the bench (on 110 it just sat there and ran). That's what the show was. Like I said, to many of you, this is second hand knowledge but to me, it was enlightening . I ran the line, the mill is 220 now! :grin:
 

Finster

Active Member
Active Member
#26
My 8520 had a bad motor when I got it.
I followed Billy G's example and replaced mine with a 1 HP motor from Grizzly, $190 plus shipping. http://www.grizzly.com/search?q=(motor)+AND+(brand:Grizzly)+AND+(category:Motors)
Bolted right on no mods required, but did require buying a different belt due to larger motor diameter.
I went ahead and replaced both belt since I had it apart. Took a 1/2" x 24" and a 1/2" x 48".
Might consider replacing the motor mounts too, I'll see if I can find where I got them, they're cheap and made a world of difference in vibrations at high RPM..
Thanks but I don't have mounts on mine. It's bolted right to the cast. I've had no problems. However, please post a link anyway in case I have problems in the future. Thanks.
 

RJSakowski

H-M Supporter - Premium Content
H-M Supporter-Premium
#27
A 120/240 motor will connect the two halves of the run winding in parallel or in series for 120 volt or 240 volt operation, respectively. If a motor is drawing 10 amps running on 120 volts, there is a drop of 120 volts and a current draw of 5 amps through each half of the winding. Each winding will see a power draw of 5 amps x 120 volts or 600 watts.

If the motor is converted to 240 volt operation, the winding halves are in series so the voltage is divided and each winding sees a voltage drop of 120 volts. The current is half what it would be for 120 volt operation or 10 amps /2 = 5 amps. The power draw for each winding is 5 amps x 120 volts or 600 watts. The same as for 120 volt operation.

The big difference is that the line is only supplying 5 amps at 240 volts rather than 10 amps at 120 volts. This lowers the line voltage drop which provides more voltage to the motor. Motors are particularly sensitive to drops in line voltage and tend to run less efficiently, producing less useful torque and more heat. Because less torque is produced, loading the motor causes even more current to be drawn, dropping the line voltage even more and making the situation even worse.

In addition, loading the motor drops the rpm which increases the chip load on the cutter requiring even more power unless the feed rate is reduced accordingly. All of these factors will come together to create the perfect storm, causing the rpm to drop to the point where the start winding kicks in, drawing even more power and eventually stalling the motor and, if continued, overheating the motor.
 

tq60

Active Member
Active Member
#29
If starting capacitor open try this simple thing.

Place drill chuck in spindle.

Get chunk of rope and some masking tape

Make a flag on ed of rope with tape and grip fly in chuck.

Put mill in lower speed if step pulley.

Wind rope around chuck and give it a pull like a top.

Shift belt on pulleys until you get a good motor spin.

Give it a spin and turn on power while spining.

It it runs cap is bad

If no workie go possible other issues but this is simple and quick.

Many HVAC places have caps.

Sent from my SAMSUNG-SGH-I337Z using Tapatalk
 

K3vyl

Iron
Registered Member
#30
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?
If there is an overload device on that starter,it should be adjusted or possibly changed to protect the windings at the lower current draw. If there is a little dial on the starter it can be adjusted. If it has separate "heaters" they can be changed to protect the windings. There should be instructions for the starter.