Starter cap voltage?

[®smpr_fi_mac®]

I don't have the original cap on my DC motor, but replaced it with a 400-480mF 125V. I remember getting the mF rating from the old cap but don't remember what the voltage rating was.

The motor is a 240V 3hp.

I think I need to replace it with a 250V rated cap. Am I wrong?

It starts, but seems slow in getting going.

[TDKPE]

I don’t know if it’s a dual-voltage motor or single, but 120 or 125V sounds low, especially since 120V power actually has voltage peaks of 170V.  The original was probably 250V or 330V or thereabouts.  Also, if the cap has a lower voltage rating than what it experiences it won’t hold as much charge which will limit current through the start winding, and likely deteriorate early.

[jteneyck]

I don’t know if it’s a dual-voltage motor or single, but 120 or 125V sounds low, especially since 120V power actually has voltage peaks of 170V.  The original was probably 250V or 330V or thereabouts.  Also, if the cap has a lower voltage rating than what it experiences it won’t hold as much charge which will limit current through the start winding, and likely deteriorate early.

Please educate me.  I thought DC motors didn't require a start capacitor, only AC ones.  I know capacitors are used in some DC motors but I thought it was for some other reason.  

John

[TheCabinetmaker]

If the motor is truly 3ph (and not 1ph ) then it wouldn't have a starter cap as 3ph motors don't have a starter winding (at least none that I have seen). Now it you are using a starter cap as part of a static converter (to allow a 3ph motor to start on 1ph) then would have both a starter cap and a run cap.

[TDKPE]

The OP said his “DC motor”, which I assumed to mean dust collector as that’s how it’s commonly used.  Also, 240V and 3hp, both common dust collector motor values. I didn’t see a mention of three-phase though.

[TheCabinetmaker]

I see I misread the post, sorry about any confusion.

[®smpr_fi_mac®]

Sorry, folks, single phase dust collector motor. It's a single voltage motor. For some reason I thought that voltage rating doesn't matter but looked it up and found that it should, but just wanted a live person to back that up.

And yeah, I think several months of running it at too-high voltage has damaged the cap; it started leaking today. I'll replace it.

Thanks!

[Roly]

Sorry, folks, single phase dust collector motor.  It's a single voltage motor.  For some reason I thought that voltage rating doesn't matter but looked it up and found that it should, but just wanted a live person to back that up.

And yeah, I think several months of running it at too-high voltage has damaged the cap; it started leaking today.  I'll replace it. 

Thanks!

It won't last much longer now,  better get one soon.   Roly

[TDKPE]

It won't last much longer now,  better get one soon.   Roly

And minimize the number of starts until you do.  Leave it running between operations if you can, and close all the blast gates to reduce the motor load and therefore motor current if you like.  You only have so many starts left in a bulging cap, so probably sooner rather than later it’ll pop and you won’t have any starts left.

[®smpr_fi_mac®]

Oh, I didn't use it any more once I realized I had a problem and ordered a new cap as soon as you guys verified what I needed. The new cap is in and I'll install it later today.