Start capacitor blew on new a/c motor after second use. What is fix?

Hello,

I have a brand new 1.5hp, single phase, high torque, ac motor. It is dual voltage and it is wired to run at 240v (I have a previous thread concerning wiring the motor at 240v). I hooked the motor up to a 12" metal shaft that has approximately 8 to 10 pounds of chain link attached to the shaft. The links are equally spaced and weight is equally distributed on each side of the shaft (two links on ones side, two on the other equally spaced apart). When I put power to the motor it started fine, got up to speed and ran fine. I shut it off, came back later, adjusted the links to ensure nothing was jammed and started it up again. This time the motor started but I saw a small puff of smoke from under one of the capacitor covers and the cover got hot. The motor started running at speed with no other problems though. The third time I turned it on the motor had a hard time starting and it pulled a huge amount current out of the generator (the generator rpm dropped way down before the motor got up to speed). Once the motor got up to speed it ran fine. I opened the start capacitor cover and noticed the pressure valve popped and it had some liquid leaking out. Okay, starter cap is bad. However, any thoughts on why the capacitor got hot and popped its valve?

The start capacitor is a 300uf 125volt unit. The run cap is 50uf, 250v, 40/80/21 unit.

Any suggestions on how to ensure I do not blow a new capacitor? If that is the correct question to ask that is. Should I maybe get a hard start kit type cap setup? I have never used one but I read some info on it today. I don't think the hard start kit would fit under the cap cover though. Obviously I am learning as a go here. Thanks for any help.

Start caps are pretty junky. Get a new one with a higher voltage since you are running at 220, someone may have replaced it before with a lower voltage one.
Joe

jdavi581 said:

Start caps are pretty junky. Get a new one with a higher voltage since you are running at 220, someone may have replaced it before with a lower voltage one.
Joe

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I suppose it is possible someone swapped it out but it is Brand New from the dealer. I am the first owner and I did not swap it out. That is what is weird. The start cap is 125v and the run is 250v. No range values are listed on the caps at all.

For dual voltage motors, the cap is normally rated foor the lower, and is tapped across one motor winding, In series for high volts, that cuts the cap voltage to the normal rated.

If the connections were messed up, it could have been presented with a too-high voltage, which I would have expected to blow it the first time, maybe the second.

I suspect that your load is too hard to start. Starting circuits are only designed to be energized for a second or two. Any more than that and it lets out the smoke. Next to fail will be the centrifugal starting switch inside the motor, if the load is too great

I would suggest trying to power it from a utility source, after a cap replacement. You generator may be bogging down on startup, or your chains present too much load for the starting circuit to get moving fast enough.

You may need to reduce the load or use a larger motor to prevent failure.

SAF Ω

JST said:

For dual voltage motors, the cap is normally rated foor the lower, and is tapped across one motor winding, In series for high volts, that cuts the cap voltage to the normal rated.

If the connections were messed up, it could have been presented with a too-high voltage, which I would have expected to blow it the first time, maybe the second.

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Which connections are you referring? The electrical cable or the capacitor wiring? Not sure which you meant. The electrical is two hots and a ground. The caps? I have no idea.

SAF said:

I suspect that your load is too hard to start. Starting circuits are only designed to be energized for a second or two. Any more than that and it lets out the smoke. Next to fail will be the centrifugal starting switch inside the motor, if the load is too great

I would suggest trying to power it from a utility source, after a cap replacement. You generator may be bogging down on startup, or your chains present too much load for the starting circuit to get moving fast enough.

You may need to reduce the load or use a larger motor to prevent failure.

SAF Ω

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I can't reduce the load as what is there is necessary for the crusher to work correctly. The equipment is designed to work outdoors off of a generator so I need to make it work in that fasion. My generator is a 6500w continuous and 8500w start. Would a hard start kit help to fix this problem? Or a larger/different start capacitor?

The capacitors should be rated at twice the supply voltage, For 220V use it would be normal to use capacitors that were 400V rated. The voltage rating on a capacitor is the maximum peak voltage the capacitor will stand, and should always be well above the supply voltage to allow for volt spikes which are a charicteristic of AC power lines, and damage capacitors more than anything. A motor designed to operate at 220V should not have a 125V rated capacitor fitted to it! Warranty claim?

Gunny65 said:

Which connections are you referring? The electrical cable or the capacitor wiring? Not sure which you meant. The electrical is two hots and a ground. The caps? I have no idea.

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Sorry...did not include all the info

The use of a 125V capacitor is normal for a 120/240 motor. There are two motor main (run) windings, each made for 120V. The start circuit is across one of them. For 240V, the two windings are in series, and each gets only 120V, so the start circuit also gets 120V, and the capacitor is fine at 125V. That is a "use with" rating, and not an actual voltage rating. It is meant to be used at 120VAC, and will work with a normal dual voltage motor

Your failure was not very spectacular, which suggests either an original defect in the part (quite possible), some not-as-bad wiring issue, or, yes, a very long start cycle that heated up the cap and made it fail.

Check the label for made n china. The QC may not be up to the task. HVAC Start cape are better when made Not in china.

Okay, this is what I am understanding.

The 125v start cap is okay because of the two windings in series. So when I hook up 220v the two winding are now running at 120v each. It separates the incoming power rather than having something that switches over when 220v is applied. I am assuming then that when you are running 120v to the motor it only runs on one winding?

It also sounds like I can up the voltage since it is a "use with" function. So both caps can be upgraded to higher voltage abilities? However, as I understand it, I should stick with the 300uf start cap and the 50uf run cap since that is what the motor was designed to use? What are the plus or minus variables for changing the UF capacitors.

Yes, this motor is made in China. For a high torque type motor, it sure is sucking at it. From everything I have read, a 1.5HP motor should easily run the load weight I have connected to it (the 8 to 10 lbs of chain link). My generator should be more than enough as well. At 220v the motor runs a 6.9 amps.

On 120V it runs on both because they get connected in parallel (start, and both run windings are all connected to the same 2 input wires).

You COULD use a higher voltage, so long as the uF rating is he same. A fairly small change, one size up or down in uF will be relatively low impact. Can change the speed of starting and the current drawn at start a bit.

Chinese motors are notorious for being short-lived, and having problems. Even the chinese admit that. Chinese motor, chinese capacitor.... no big surprises. They CAN make decent capacitors, but that one may not have been one of their finest efforts. Get a proper one that was made somewhere else, and if the motor itself is OK, you should be good to go.

What IS this thing? Sounds like some flavor of shredder or pulverizer type device. In that case, it presumably starts with only the chain whirling as a load. How LONG is your 8 lb of chain links? that has a big effect on what the inertia is, how fast the motor can get it started, and whether the motor can get it up to full speed. Air resistance might hold your motor down with the speed lower than the cutoff rpm,and then it's a case of "fire in the hole"..

If the motor stays below the cutout speed too long, it won't matter where the capacitor was made. It won't last very well. Those capacitors are deliberately overloaded, counting on the start taking only a short time. It they were rated for the current they draw on a continuous basis, they would be quite a bit bigger.

I built a rock crusher. Impact style. The chain links are approximately four inches long. They are counterbalanced via the same length of chain on the opposite side of the shaft. You are correct, they chain is the only load on the machine as it starts up. No rocks are inserted until the machine is up to full speed. Well, so far it has not had ANY rocks through it. I am still in the "bug out" phase of the build.

Service factor (SF on the motor badge) will usually give a hint as to the quality of the motor. Higher is better. 1.15 is about as high as they get these days, 1.07 (IIRC) is common, anything less is well, less well built. And no SF listed at all is the worst.

Neil

OK, if your chain is 3 links long (I expect it is longer) then with a 1725 RPM motor, the outer link is traveling about 50 mph at the center of the link. Just the air resistance will be a considerable load, and then there is the inertia effect slowing acceleration.

Rocks are an added load.

Did you mean to say 1.5 HP or 15 HP? Honestly, I think 1.5 HP would have trouble shredding leaves and yard waste, let alone breaking rocks, given my experience. My shredder is 6 HP, and slows down when working on leaves etc.

I will say again, the rated working voltage of the capacitors needs to be twice the maximum voltage of the supply, a 125V rated capacitor is not rated high enough for a 120v supply, it will fail! OH, it did fail, there is the proof! You are running it from a generator? Generators are really good at producing capacitor killing transient voltage spikes!!!

hermetic said:

I will say again, the rated working voltage of the capacitors needs to be twice the maximum voltage of the supply, a 125V rated capacitor is not rated high enough for a 120v supply, it will fail! OH, it did fail, there is the proof! You are running it from a generator? Generators are really good at producing capacitor killing transient voltage spikes!!!

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I did hear you Hermetic and I did buy one that is higher voltage capable. Today. I installed it and had no issues. I also went with a little higher UF rating. The original was 300UF and the new is 400-480UF. We will see how this one holds up. I hope well. Thanks for the assistance.

neilho said:

Service factor (SF on the motor badge) will usually give a hint as to the quality of the motor. Higher is better. 1.15 is about as high as they get these days, 1.07 (IIRC) is common, anything less is well, less well built. And no SF listed at all is the worst.

Neil

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I was a bit worried when I read this but it turns out the motor is a 1.15 rating. Hopefully that means it is good and will last awhile.

JST said:

OK, if your chain is 3 links long (I expect it is longer) then with a 1725 RPM motor, the outer link is traveling about 50 mph at the center of the link. Just the air resistance will be a considerable load, and then there is the inertia effect slowing acceleration.

Rocks are an added load.

Did you mean to say 1.5 HP or 15 HP? Honestly, I think 1.5 HP would have trouble shredding leaves and yard waste, let alone breaking rocks, given my experience. My shredder is 6 HP, and slows down when working on leaves etc.

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No, you are initially correct. 1.5 HP. I put a new start cap in today and it started up with no issues. The cap was a little higher rated voltage and UF so that may have helped as well. I will come back in and let you know how it holds up under a rock load. As is, the links are three links long, on each side of the center shaft. I have four rows of links along the shaft. An acquaintance built one using a 1.0HP motor and it works good. It is just a little smaller than mine though. His was 12 inches in diameter and about 8 inches in width. Mine is 16 inches in diameter and 10 inches wide. Not real big but it will should work well for my load gold mine.

Thanks for all the assistance in figuring out what I should do to get this working again. As of three days ago, I had never messed with a capacitor. After reading on this forum, the internet and the help from all of you I learned quite a bit. Thank you.