5Hp Air Compressor Overheating?

[madosta]

So I updated a buddy's compressor with a new pump that is rated with either a 5hp or 7.5hp motor. He had a 5hp motor and about the same size pump with PSI and CFM.

He has been running it but recently with a DA it was running for over 30 minutes and shut off due to the thermal push button switch. He thought it was the caps, but I tested them fine and jumped the thermal switch to get it running and it runs fine, but is drawing 36A per leg and is a 22FLA motor.

He was thinking maybe the belt was tight or loose, but it seems the motor is pulling a lot more than it should be. Why?

Might be looking at a new motor - maybe it's "tired"? Any ideas?

 

[madosta]

And yes, the thermal push button switch would not reset thus I jumped it...

 

[wyliesdiesels]

Sounds like the new pump may be too much of a load for the motor. Are u sure the pump is the right size for the motor? U mentioned the pump might be for a larger motor, which would cause the motor to work too hard/draw to many amps causing it to overheat! Did this motor work fine with the old pump, before u replaced it? During the 30mins it ran for, did it ever reach cut off pressure and keep running, meaning the pressure switch is bad? Are there any leaks in the system? How heavy of an air tool(s) was he using? Need more details!!!

 

[justsam]

Are you running the compressor at the rated RPM for a 5 HP application?

May need to use a smaller motor pulley.

 

[G_P]

So the motor is supposed to draw 22a max but is drawing 68a??

Why is this not tripping the breaker?

Sent from my C5120 using Tapatalk 2

 

[madosta]

Sounds like the new pump may be too much of a load for the motor. Are u sure the pump is the right size for the motor? U mentioned the pump might be for a larger motor, which would cause the motor to work too hard/draw to many amps causing it to overheat! Did this motor work fine with the old pump, before u replaced it? During the 30mins it ran for, did it ever reach cut off pressure and keep running, meaning the pressure switch is bad? Are there any leaks in the system? How heavy of an air tool(s) was he using? Need more details!!!

He was running two DA sanders at the same time (well he and another guy). The motor ran fine, the pump just went bad. There's a new pressure switch that is 125-170PSI an is working, but the air demand was so high the motor never turned off.

Are you running the compressor at the rated RPM for a 5 HP application?

May need to use a smaller motor pulley.

Hmmm, this makes the most sense. I'll take a look at what I can find. The pulley on the motor now is fairly large.

So the motor is supposed to draw 22a max but is drawing 68a??

Why is this not tripping the breaker?

Awww c'mon man, it's plugged into a 50amp welder receptacle that's why and 36 < 50!

 

[hidollartoys]

You need to size the motor pulley so the current draw is just below the FLA of the motor. Measure the FLA with a clamp-on current meter.

 

[wyliesdiesels]

So the motor is supposed to draw 22a max but is drawing 68a??

Why is this not tripping the breaker?

Sent from my C5120 using Tapatalk 2

I dont think u read his post clearly. He said its drawing 36a NOT 68a!!

He was running two DA sanders at the same time (well he and another guy). The motor ran fine, the pump just went bad. There's a new pressure switch that is 125-170PSI an is working, but the air demand was so high the motor never turned off....

What is the duty cycle of the motor? And is the pressure switch the same specs as the old one? 175psi seems like a real high cut off for a medium size air compressor. Our large compressor at work doesnt even have a cutoff that high!(125psi is when it shuts off) And yes, what about the pulley? Is it the same one from the old pump or did it come with the new pump? Maybe its the wrong size...can u use the pulley off the old pump?

 

[Kevin C]

Are you running the compressor at the rated RPM for a 5 HP application?

May need to use a smaller motor pulley.

Thats what I would guess....

The old pump was probably rated for 5hp, and at a higher RPM than the new pump and ...or the new pump has a smaller large pulley.

The installation instructions for the new pump should have had a RPM vs HP chart. My guess is that by using motor pulley from the old setup your spinning the new pump too fast.

You either need to slow the pump down (smaller pulley on the motor) or get a larger motor.

 

[madosta]

Yikes it has a 6.5" motor pulley.

Old 5hp pump: 14.5"
New 5-7.5hp pump: 13.5"
Belt: 63"

Man you guys are smart. The "great" place I ordered this from sent a whole lotta nothing!

Now to do some more research for the proper size and shorter belt.

 

[larry_g]

A bit of math

22a/36a * 6.5"= 3.97". I would suggest that you try a 4" pulley on the motor and back off the cutout pressure back a bit or a 3.75" pulley and leave the pressure as is.

lg
no neat sig line

 

[Kevin C]

http://www.abac-support.co.uk/pumps/Acrobat/b5900.pdf

My estimate assuming the pump is a B5900 ( Is this is the pump from another post that had a problem with the air fitting?).

That pump is rated at 5.5 HP @ 1370 pump RPM with a pressure of 174 PSI. Right now your running at 1700 RPM.

The pump pulley should actually be 13.75". You want to run a bit less than 1250 RPM for a max pressure of 174 PSI with a 5 hp motor.

If you have a 3600 RPM motor and a 13.75" main pulley you want a pulley ratio of 2.88. It should work out to ---- 13.75 / 2.88 = 4.74" motor pulley. 3.75 would be safe, 4.75 should be a good match. I would go for 4.5" ... In any case, measure the draw.

 

[madosta]

Yes it's a B5900. You guys rock. I'll see what size pulleys I can source locally and go from there.

 

[madosta]

I finally got the correct pulley, went with a 4" - guess what!? 19 amps per leg. Woot! Thanks guys.