Compressor Electrikery

[mr haynes]

Fixing up my old single phase compressor...

It kinda still runs with a bit of a push start

Anyone able to advise on the capacitors?
Unfortunately on one the markings have gone
Don't know if it's the run or start.
Probably going to replace both anyway so any thoughts appreciated, especially what size the one without markings would be.

Markings i do have:

 

[Al Strachan]

what uF value is the one in the photo.? if its 36uF/30uf its likely the start one. the run will have a higher value and possibly physically larger. Run's tend to be 450v also, and starts are ok at 250v.

do you have a multimeter with capacitor function to check both values?

 

[Seadog]

It looks like 3.6µF at 250V.

 

[mr haynes]

what uF value is the one in the photo.? if its 36uF/30uf its likely the start one. the run will have a higher value and possibly physically larger. Run's tend to be 450v also, and starts are ok at 250v.

do you have a multimeter with capacitor function to check both values?

3.6uf to my eyes. From memory both were physically similar size.
Yes i can measure capacitance and will do later, didn't have my meter to hand at time of pics.

 

[mr haynes]

More pics of capacitors

 

[Al Strachan]

should also be quite easy after a poke around with a multimeter to do a quick wiring diag and also determine which is the start cap since it will go through the centrifugal switch.

 

[carbon]

I have only seen start caps that have higher capacitance than the run cap, but don’t see many on pressure washers. The start caps I’ve seen have been in the 200-300 uf range if the run cap was 40-70uf. But 3.6uf seems low for a 3hp motor if I’m reading that correctly

 

[mr haynes]

I have only seen start caps that have higher capacitance than the run cap, but don’t see many on pressure washers. The start caps I’ve seen have been in the 200-300 uf range if the run cap was 40-70uf. But 3.6uf seems low for a 3hp motor if I’m reading that correctly

I don't know which cap is which. Other cap unfortunately the markings have rubbed of.
My best guess was the 3.6 was the run cap

 

[carbon]

Is it a 3hp motor?

Are the caps wires in parallel?

 

[mr haynes]

Is it a 3hp motor?

yes

 

[mr haynes]

Is it a 3hp motor?

Are the caps wires in parallel?

RE the caps, a good question, will have to check.
Not at the machine just now

 

[Lewis_RX8]

I have only seen start caps that have higher capacitance than the run cap, but don’t see many on pressure washers. The start caps I’ve seen have been in the 200-300 uf range if the run cap was 40-70uf. But 3.6uf seems low for a 3hp motor if I’m reading that correctly

My 3hp has a 14uf i believe however may be diffrent . Maybe look up the motor and see what is reccomended

 

[Seadog]

Someone has liberally sprayed paint on the caps. See if some warm water and detergent will shift it. The numbers are under there just waiting for you.

 

[mr haynes]

Will try and get a closer look tomorrow

 

[mr haynes]

Someone has liberally sprayed paint on the caps. See if some warm water and detergent will shift it. The numbers are under there just waiting for you.

No joy with cleaning, nothing to be seen under the crud.

Have now measured the caps though:

The 3.6uf measured at 14.91uf so safely say not good.
The unknown measured at 31.11 uf

 

[carbon]

Ive never seen a motor cap that the capacitance increased when it failed.

 

[mr haynes]

Is it a 3hp motor?

Are the caps wires in parallel?

Ive never seen a motor cap that the capacitance increased when it failed.

Measured each half dozen times all ways across terminals

 

[mr haynes]

Is it a 3hp motor?

Are the caps wires in parallel?

 

[carbon]

I wasn't disputing the reading. Also seems odd to have two different valve caps in parallel, could they have been aiming for 35uf. On my old compressor 2800 rpm 2.2kw motor it had a single 40uf cap

 

[mr haynes]

Bit of a burn found once opened up motor.
Opinions anyone?