Das_Wookie
Aluminum
- Joined
- Jan 11, 2008
- Location
- Austin, TX
TL;DR; - 10hp self starting RPC build is using 490uf run caps, still not starting well, and runs hot.
I'm upgrading my 3hp RPC due to a new VMC purchase, and am running into an issue and am trying to diagnose what might be the problem.
For reference, my existing 3hp motor is an old 1940-somthing motor from a retired Monarch lathe. I have 110uF worth of run caps (a 50uF and 60uF run in parallel) and it starts right up, no issues. Voltage is fairly well balanced at around 265v on my L3 generated leg and the L1 drive leg. L2 is my regular line voltage which here in central rural Texas always runs a little hot where my 110v is usually somewhere around 126v to 134v and my 220v tends to run around 250-270. Not knowing exactly how much in the way of capacitance I'd need for the new 10hp motor, I purchased a varying array of run capacitors so I could mix and match to find the value I'd need.
My new RPC motor is a used Baldor purchased from a shop that was shutting down. I was told the motor was taken out of service because they upgraded their dust collector, and needed a larger motor for it, so they retired the 10hp and put in a new 20hp motor for their collection system. I tested all wires to the chassis, and all looked good. I wasn't able to test the motor under power tho. I figured these things are damn hard to kill, so purchased it anyway. That was almost 3 years ago. We all know how it goes. Projects only advance when they have to. {shrug}
So, setup with my used Baldor 10hp motor, I started to bench setup the new RPC in a self starting configuration. My reference was my 3hp motor, and 110uF, so that was ~36uF per HP. So, I assembled a chain of run caps with a value of 360uF total, verified the capacitance with a multimeter, wired everything up, and threw the switch. All the motor did is buzz with the shaft moving very slightly back and forty. Shut it off, and added another capacitor. Lather, Rinse, Repeat as necessary. Eventually I had used up my full assembly of caps, so I stole the caps off my 3hp RPC, and added those to the chain as well. By this time, I was at 490uF, and the motor would start, tho not crisply. It would sometimes buzz, other times it would start to slowly rotate, and after 2-3 seconds it would then snap up to full speed. My generated leg is running just over 300v. This seems very high to me, and might be what's contributing to my motor getting as hot as it does as quickly as it is. To investigate, I pulled the back side cover of the housing, and the bearing didn't look great. Not horrible, but not great. So I decided, a bearing swap was in order. No time like now given it's going to get setup and (hopefully) ignored for who knows how long!
My problems:
1) I'm well north of the anticipated MFD - tho this might be expected given it's a newer motor and I just have to keep adding until it starts crisply.
2) When the motor DOES start, it's getting hot, and I mean HOT! Like, the case of the motor got almost too hot to touch in about 20 seconds of running hot. After I checked the voltages, not wanting to damage anything, I went ahead and just shut it all down, and figured I'd post on PM and see if I'm just being stupid.
3) I don't know how much more MFD I might need, or if I'm chasing things the wrong direction here and maybe have too MUCH capacitance maybe???
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Motor Specs:
10hp Baldor - Model M3313T - M3313T - Baldor.com
Wired for low voltage / 220v - This has been verified multiple times, both by myself and independently by a buddy who was giving me a hand.
Front Bearing - 6307ZC3
Rear Bearing - 6206Z
Rotor - It has a little surface rust on one side, likely just from humidity, but otherwise looks to be in good condition. There is no signs of it rubbing the windings or anything like that.
Stator - The windings have their share of dust and a few cobwebs, but otherwise everything looks pretty good in there. No signs of rust, rubbing, or any shorts / scorch marks.
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My thoughts for where to go next for further debugging: I've ordered some 100uF run caps to both consolidate the the number of caps being used down, as well as give me more range of MFD to play with. I've also ordered the new bearings, and will press those on before putting everything back together. While the rotor was out, I cleaned up the rotor shaft by putting it between centers on the lathe and just ran a (very used) foam sanding pad over it in the spots where there was surface corrosion and/or dried on grease. I'm considering doing the same to the rest of the armature, but the initial priority was cleaning up the shaft so I can get the new bearings on when they arrive later this week.
I haven't ever built a RPC of this size tho, so I'm open to ideas and explanations as to what I'm dong wrong.
I'm upgrading my 3hp RPC due to a new VMC purchase, and am running into an issue and am trying to diagnose what might be the problem.
For reference, my existing 3hp motor is an old 1940-somthing motor from a retired Monarch lathe. I have 110uF worth of run caps (a 50uF and 60uF run in parallel) and it starts right up, no issues. Voltage is fairly well balanced at around 265v on my L3 generated leg and the L1 drive leg. L2 is my regular line voltage which here in central rural Texas always runs a little hot where my 110v is usually somewhere around 126v to 134v and my 220v tends to run around 250-270. Not knowing exactly how much in the way of capacitance I'd need for the new 10hp motor, I purchased a varying array of run capacitors so I could mix and match to find the value I'd need.
My new RPC motor is a used Baldor purchased from a shop that was shutting down. I was told the motor was taken out of service because they upgraded their dust collector, and needed a larger motor for it, so they retired the 10hp and put in a new 20hp motor for their collection system. I tested all wires to the chassis, and all looked good. I wasn't able to test the motor under power tho. I figured these things are damn hard to kill, so purchased it anyway. That was almost 3 years ago. We all know how it goes. Projects only advance when they have to. {shrug}
So, setup with my used Baldor 10hp motor, I started to bench setup the new RPC in a self starting configuration. My reference was my 3hp motor, and 110uF, so that was ~36uF per HP. So, I assembled a chain of run caps with a value of 360uF total, verified the capacitance with a multimeter, wired everything up, and threw the switch. All the motor did is buzz with the shaft moving very slightly back and forty. Shut it off, and added another capacitor. Lather, Rinse, Repeat as necessary. Eventually I had used up my full assembly of caps, so I stole the caps off my 3hp RPC, and added those to the chain as well. By this time, I was at 490uF, and the motor would start, tho not crisply. It would sometimes buzz, other times it would start to slowly rotate, and after 2-3 seconds it would then snap up to full speed. My generated leg is running just over 300v. This seems very high to me, and might be what's contributing to my motor getting as hot as it does as quickly as it is. To investigate, I pulled the back side cover of the housing, and the bearing didn't look great. Not horrible, but not great. So I decided, a bearing swap was in order. No time like now given it's going to get setup and (hopefully) ignored for who knows how long!
My problems:
1) I'm well north of the anticipated MFD - tho this might be expected given it's a newer motor and I just have to keep adding until it starts crisply.
2) When the motor DOES start, it's getting hot, and I mean HOT! Like, the case of the motor got almost too hot to touch in about 20 seconds of running hot. After I checked the voltages, not wanting to damage anything, I went ahead and just shut it all down, and figured I'd post on PM and see if I'm just being stupid.
3) I don't know how much more MFD I might need, or if I'm chasing things the wrong direction here and maybe have too MUCH capacitance maybe???
----------------------------------------------------------------------------------------
Motor Specs:
10hp Baldor - Model M3313T - M3313T - Baldor.com
Wired for low voltage / 220v - This has been verified multiple times, both by myself and independently by a buddy who was giving me a hand.
Front Bearing - 6307ZC3
Rear Bearing - 6206Z
Rotor - It has a little surface rust on one side, likely just from humidity, but otherwise looks to be in good condition. There is no signs of it rubbing the windings or anything like that.
Stator - The windings have their share of dust and a few cobwebs, but otherwise everything looks pretty good in there. No signs of rust, rubbing, or any shorts / scorch marks.
----------------------------------------------------------------------------------------
My thoughts for where to go next for further debugging: I've ordered some 100uF run caps to both consolidate the the number of caps being used down, as well as give me more range of MFD to play with. I've also ordered the new bearings, and will press those on before putting everything back together. While the rotor was out, I cleaned up the rotor shaft by putting it between centers on the lathe and just ran a (very used) foam sanding pad over it in the spots where there was surface corrosion and/or dried on grease. I'm considering doing the same to the rest of the armature, but the initial priority was cleaning up the shaft so I can get the new bearings on when they arrive later this week.
I haven't ever built a RPC of this size tho, so I'm open to ideas and explanations as to what I'm dong wrong.