Motor start capacitor question

[Jason White]

Since my bandsaw motor is still in pieces all over my workshop, I'm thinking I'll go ahead and replace the start capacitor even though it's still working. My guess is that it's original to the motor (about 20 years old), and you know what they says about "Murphy's Law"..... :rolleyes:

Can I replace the existing capacitor with one that's a little smaller (dimensionally-speaking)? I threaded a new Romex clamp into the housing for the switch cable and it isn't leaving me much room to put the old capacitor back in.

Jason

[Lee Schierer]

It is important that you have the correct size in terms of microfarads and voltage. Go to a local motor shop and they should be able to help. BTW just because it is 20 years old doesn't mean it is likely to fail. There are no moving parts and it will depend upon how often you start the motor as to what sort of work the capacitor will be doing.

[Charles Lent]

You can replace the capacitor with a different size capacitor if the replacement capacitor's MFD rating is close (within 5%) to the original rating, it's an AC rated capacitor, and it has a working voltage equal to or greater than the original capacitor. It's physical size isn't important, as long as it will fit in the capacitor housing. If it fits loose you may need to shim it to keep it from moving around and to keep it's contacts from shorting. Phenolic is an ideal shim, but wood will work OK too.

Charley

[Josiah Bartlett]

I would use foam weatherstripping as a shim instead of wood- you don't want to dent the capacitor housing.

Capacitors last indefinitely if they aren't overheated, but they also have a shelf life.
Capacitors can fail just as badly from not enough use as they can from heavy use. Some capacitors use an electrolyte as an insulator, and they rely on an electric field to plate the insulating material on the electrodes. Those tend to leak electrons across the plates if they aren't used enough, and this causes them to overheat and explode. Oil impregnated capacitors can eventually have enough oil seep out that they don't work.

In my opinion, 20 years is about as long as you could ever expect to get from one, and you should replace it with a new one. There are some that last longer- I have a 1950's vintage Atlas motor that still has its original cap, but I expect it to fail at any time.

[Jason White]

I guess I'll be replacing the starter cap after all! I put the motor back together tonight and fired it up. Was running fine for a few seconds and then smoke started pouring out. I pulled the cover off and it appears that the capacitor overheated and melted!

My guess is that the new bearings in both the saw and motor caused just enough extra resistance to cause the starter cap to go "poof!". The motor still runs great, as long as I give it a spin by hand to start it.



I would use foam weatherstripping as a shim instead of wood- you don't want to dent the capacitor housing. Capacitors last indefinitely if they aren't overheated, but they also have a shelf life. Capacitors can fail just as badly from not enough use as they can from heavy use. Some capacitors use an electrolyte as an insulator, and they rely on an electric field to plate the insulating material on the electrodes. Those tend to leak electrons across the plates if they aren't used enough, and this causes them to overheat and explode. Oil impregnated capacitors can eventually have enough oil seep out that they don't work. In my opinion, 20 years is about as long as you could ever expect to get from one, and you should replace it with a new one. There are some that last longer- I have a 1950's vintage Atlas motor that still has its original cap, but I expect it to fail at any time.

[Chip Lindley]

...and you know what they says about "Murphy's Law"..... :rolleyes:

Can I replace the existing capacitor with one that's a little smaller (dimensionally-speaking)?

By all means, replace that capacitor Jason! Physically smaller is always doable. Larger is a no-no! Why not purchase a spare capacitor, just in case Murphy pays another visit!

[Charles Lent]

Double check the centrifugal start switch in the end housing of the motor. It may be the cause of your capacitor going up in smoke. The weight mechanism on the shaft needs to move freely and the springs need to be in place. The switch contacts need to be clean and in contact with each other (they open when the motor comes up to speed, removing the capacitor and start winding from power. If they don't open either the start winding or the capacitor can be destroyed. Wiggling the terminals of the capacitor while connecting / disconnecting the wires may have damaged it. Also, make sure that you connected the wires correctly when you put the motor back together. It's a strange coincidence that the capacitor went bad the first time that you applied power after after putting it back together.

Charley

[Jason White]

I had the same thoughts.

The centrifugal switch seems to be working from what I can visibly see with the motor running. The motor gets up to speed and then the switch flies open and disengages. It then springs back the other way as the motor starts slowing to a stop. haven't checked anything with a multimeter to see if it's "really" disengaging however.

All the wiring appears to be correct. The motor still powers on and off when I flip the switch. It starts humming and then I give the pulley a turn by hand to get it running.


Double check the centrifugal start switch in the end housing of the motor. It may be the cause of your capacitor going up in smoke. The weight mechanism on the shaft needs to move freely and the springs need to be in place. The switch contacts need to be clean and in contact with each other (they open when the motor comes up to speed, removing the capacitor and start winding from power. If they don't open either the start winding or the capacitor can be destroyed. Wiggling the terminals of the capacitor while connecting / disconnecting the wires may have damaged it. Also, make sure that you connected the wires correctly when you put the motor back together. It's a strange coincidence that the capacitor went bad the first time that you applied power after after putting it back together. Charley

[Jason White]

So, this morning I got to thinking...

My old motor is 27 years old and was made in Taiwan. I can see a lot of wear inside from the rotor rubbing against the windings (I assume this is because the old bearings were shot).

Some of the wiring inside the motor also looks suspect. Parts of the insulation are nicked or frayed and I wouldn't be surprised if the starter windings have a short in them, too (which might be why the start capacitor blew up).

I've already spent $20 on new bearings for this thing. A new starter cap is probably another $20 or so. Rather than throwing more good money after bad, I went ahead and ordered a new motor :o

I found a 1HP TEFC continuous-duty motor on Amazon (made by Grizzly) for pretty short money. It appears to be slightly more powerful than my old motor (higher amp draw). Also, because it's a TEFC motor, I won't have to worry about sawdust causing problems inside the motor.

I guess the case of the exploding starter cap will forever remain a mystery... :D



I had the same thoughts.

The centrifugal switch seems to be working from what I can visibly see with the motor running. The motor gets up to speed and then the switch flies open and disengages. It then springs back the other way as the motor starts slowing to a stop. haven't checked anything with a multimeter to see if it's "really" disengaging however.

All the wiring appears to be correct. The motor still powers on and off when I flip the switch. It starts humming and then I give the pulley a turn by hand to get it running.

[Britt Lifsey]

Hey Jason,
Which motor model did you order? Even after replacing start capacitor on my TS it still is not right. I was looking at the motors on Grizzly site after reading your post here. I'm wondering what the difference between the G2533 ($124) and H5380 ($149) is. They both look to be 3450RPM, 1HP, 110/220V, NEMA 56 frames and TEFC. Anyway, I'd be interested in how satisfied you are with motor, delivery time, etc. THANKS and hope new motor works out great for you!

[Jason White]

I bought the 1725 rpm, 1hp tefc motor. I actually received it today and hooked it up. Quite a bit quieter and it does seem a tad more powerful. Seems to be a terrific motor for the money. I imagine I'll get at least 20 years out of it with only occasional use v


Hey Jason, Which motor model did you order? Even after replacing start capacitor on my TS it still is not right. I was looking at the motors on Grizzly site after reading your post here. I'm wondering what the difference between the G2533 ($124) and H5380 ($149) is. They both look to be 3450RPM, 1HP, 110/220V, NEMA 56 frames and TEFC. Anyway, I'd be interested in how satisfied you are with motor, delivery time, etc. THANKS and hope new motor works out great for you!

[Britt Lifsey]

Thanks for update! That was quick delivery.

[Jason White]

Yeah, I think I had it in two days.



Thanks for update! That was quick delivery.

[Britt Lifsey]

Thanks for posting this topic! The motor for my table saw arrived today and works like a champ.