Need help with capacitor for gear motor...

Hey guys,

I just bought a bodine gear motor for my mill. My 40 in/lbs motor from surpluscenter.com didn't have enough torque.

I'm waiting to get the motor, but I contacted bodine electric to get specs on the capacitor. I was told it needed a 2.7 MFD/250VAC capacitor.

I'm wondering if this is an error. I mean, my old motor had a 20mfd/250vac capacitor. It looks like THIS

A 2.7 MFD/250VAC capacitor looks like THIS

Looks like a stereo part or something.

The motor is new, but is obsolete. So he had to dig into an old catalog. I'd like to get the capacitor ordered without waiting another week for the motor to arrive.

A second issue is that he also said it needs a 300ohm/20 watt resistor. I've no idea why this is needed or how to install it. There seem to be several kinds.

Any help is greatly appreciated. Hmmm.... Should this posted in the electrical forum?

You can find Bodine caps HERE.

It looks like the caps are made with a blade terminal package that would go into a slot in the motor. If that's how the motor you ordered is, then you'll have to find one that fits.

As for size, it does seem a little small. Their 100 lb-in motor uses a 10 MFD cap, and their 40 lb-in uses a 4 MFD cap.

I don't know why you would need a resistor, their current motors don't show that they need one. You may want to wait until you get your motor and go through the documentation that comes with it.

Where did you get the motor?

milldoggy said:

Where did you get the motor?

Click to expand...

I got the motor on ebay from a surplus store in Wisconsin. It had the motors specs, which looked good for a mill, IMO. 75RPM, 130 in/lbs torque. 2 New motors. It was a pretty good deal, $110 for 2 motors.

But their store happened to be closed Tuesday (day I bought it) and Wednesday. So even though I called and emailed to try and find out the specs for the capacitor, they didn't answer. They did ship the motors right away, though.

bakeup said:

You can find Bodine caps HERE.

It looks like the caps are made with a blade terminal package that would go into a slot in the motor. If that's how the motor you ordered is, then you'll have to find one that fits.

As for size, it does seem a little small. Their 100 lb-in motor uses a 10 MFD cap, and their 40 lb-in uses a 4 MFD cap.

I don't know why you would need a resistor, their current motors don't show that they need one. You may want to wait until you get your motor and go through the documentation that comes with it.

Click to expand...

Thanks for the reply. I was hoping to get the capacitor ahead of time so I could test it right away. They have a 7 day return policy, so if I can't get the right capacitor or something (the motor's new, but isn't made anymore) I wanted to be able to return it.

I asked customer service at Bodine Electric to double check those specs and they confirmed they were correct. It's a "stepper" motor, which I understand just to be about how the gears work, but I don't understand it well. I confirmed with Bodine that it doesn't need a controller.

Unfortunately, it's an outdated motor they don't make anymore. So it's been a lot harder to find out about than I thought.

The cap at the stereo store isn't the same type of cap, you need a motor cap. That's why they look different. Grainger, McMaster, or surplus center have motor specific caps you can buy. ie. http://www.surpluscenter.com/item.asp?item=22-1161&catname=electric
Not sure if it's a run or start cap though, you'll need that information to know which one you need. A run cap will need to be larger to handle the heat of constant use - whereas a start cap of the same charge is going to be smaller because it gets switched out of the circuit once the motor is running.

I'm not sure of the size of your motor but to explain if you have two capacitors on your motor then one is a starting cap and the other a running cap. The running cap is there to even out the magnetic field in the primary windings of a single phase motor. If you only have one then is it is the starting capacitor. The starting cap is there to provide the necessary phase shift for the starting windings of a single phase motor to start it rotating before being switched out of the circuit once the motor reaches 75%.

As for the resistor it is there to limit the amount of current flowing through the primary windings while at speed or through the starter windings while starting so it has two possible configurations. Most likely in the starter windings. An AC motor at start up is a dead short until back EMF from the rotating magnetic field limits the current in the windings. As the starter windings are taking up space on the motor and aren't used accept to kick things off they are kept as small as possible hence the need for the resistor. If I knew the size of your motor I could calculate it current draw and based on the size of the resistor we could figure out where it has to go (99% sure it is for the starter windings).

How many caps does your motor have

Clem

I really appreciate the replies. At this point I have to wait until the motor arrives on Monday or Tuesday to see the documentation for the capacitor. The guy at Bodine gave me those specs, but did not say whether it is a run capacitor or a start capacitor.

But as to the resistor, how is that wired up? It almost seems like it needs to be soldered on, no?

The motor arrived today, much earlier than the delivery date of Monday. Unfortunately, I realized right away there was a mistake. It was tiny!

Checking the label, I see that it was inaccurately described. This motor has 140 in/OUNCES of torque, not the 140 in/LBS that was listed in the ebay ad.

I called the seller and he agreed to a full refund plus return shipping.

I just made an offer on another motor that should work. The motor's specs label says has nothing listed in the Uf portion. I assume that means no capacitor is required??

Thanks.