paralleled start capacitors?

[mdr]

Hi all,
2 hp Leeson motor, wired for 220v. It's having trouble starting, so I'm replacing the existing starting capacitor(s). No run cap on the motor.

Existing setup has 2x 60 mf caps in parallel for 120 mf.

Any reason why I can't go for a single 120mf cap? Any ideas why they used two caps? The existing caps are giant, 2" dia, 8" long.

Thanks,

M

 

[rlitman]

Capacitors in parallel have additive capacitance, and maintain their voltage rating. Yes, you could substitute a single one.

 

[dogdog]

you might have one of those dual run/start caps... ?

Both of them are connected to the start winding eventually, one connects straight to the start winding the other goes through a centrifugal switch.. that gets disconnected after motor spins up to speed.

are you sure you don't have a run cap?

 

[Lightning rod]

like DogDog said

what model number of Leeson Motor
you can look it up and know for sure

or post pics

 

[Bert_]

If it fits it's fine.

It's pretty common to use multiple on larger motors. I work on lots of baldors. The 7.5 and 10hp 1 phase use (4) 216-259 MFD capacitors in parallel. I carry a close to a dozen in the truck. I've found you can substitute some multiple of those capacitors in a lot of motors.

 

[American Locomotive]

Potential reasons for parallel caps:

- Cost: Maybe 2 smaller caps is cheaper than 1 larger.
- Packaging: Maybe they couldn't find a capacitor in the capacity they needed that would fit in their box
- Peak Current: Perhaps they couldn't find a single capacitor capable of delivering the peak current they needed.
- Heating: Perhaps two capacitors can more efficiently dissipate heat from start up compared to a single large cap.

 

[dogdog]

I am not too sure about the last two points....

Never thought to associate capacitor with current... Inductors maybe.

I guess the OP needs to post the make / model of that motor in question to solve this mystery...

Yes cap in parallel adds capacitance, cap in series decrease just the same formula as the resistor in parallel...

 

[Innovate1]

Capacitors definitely have a current limitation. Not sure if it is a realistic issue for this type of cap (capability may exceed most uses for this use case). Current creates heating as no capacitor is ideal with zero resistance. Heating causes bad things to happen if it gets high enough even if it's just shorter life.

1 larger cap is usually cheaper than two of half the size so there is likely some reason they went with two. Could be availability, physical size/shape limitations, current, etc.

 

[mdr]

Thanks all.
Doofus moment in that I didn't even look at the nameplate, which shows a 120mf capacitor. So whichever motor shop hooked it up used 2 x 60. Strange thing is that the 60mf are huge (2"dia x 8" long). Anyway, I'll probably replace with a 120mf single.

 

[nadogail]

Sometimes you need to just have to go with what you can get when a production line or machine is down. More than once I have made a piece of equipment work with "alternative" parts.