Generator won't power compressor....ideas?

[Soundguy]

Actually, it draws about 2KW. With efficiency [less than 70%] the motor would be about 1.5 to 1.8HP
larry

yes, good point. my reference was only taking into account draw.. etc.. which was where I was infering the hp guestament..

 

[Wheels2]

6500W at 120V = 54A. 6500W at 240V = 27.5A


Neither one is 4 times the rated amps at the running voltage, but probably plenty to get the compressor started. You just need to get that power to the compressor in a practical way.

Your compressor is listed as 4 HP. But 115V X 16A = 1,840W and that equals 2.47 HP. Many compressors have exaggerated HP figures.

Will your compressor start if you plug it into a 20A 120V household plug with no extension cord?



A 6500W, 120V generator can have a much larger breaker than 20A. A larger breaker to handle the surge amps might be a good method and the generator has the capacity. But the internal wiring in the generator might not handle a larger breaker on that circuit.

If you rewire the compressor for 240V and use a 20A 240V breaker, you'll be doubling the number of watts to the compressor and still be within the generator's watt rating. This would make more sense than a 50A breaker on the 120V side. And it would only require #12 wire. What size breaker is on the 240V generator output?

See if you can find a 12-3 extension cord and 240V plug to match the generator plug. Or hardwire it in. Keep the cord short.

If the generator is permanently mounted near the compressor you could use stranded wire in flex conduit and hardwire it through a switch.

Large capacitor start kits work well on air conditioners. I did it on one one of mine to get my generator to start the unit and it worked. But I have never tried it on a compressor. You can get them at Grainger.

I suggest just altering the motor voltage first and going with a 20A breaker on the 240V output.

During emergency power outages you probably don't need a large compressor. So you could always buy a cheam an electricain and ran apo small one to use for filling a tire or something. Sears makes a 1hp oil lubed unit with an iron compressor that can be had for $100. on sale. I have had one for years and they are great. Paid $69. for it at some blowout sale and felt like I was stealing. There's no way my 5 HP compressor will ever run from my 2000 watt diesel emergency generator. And that's OK.

Don't make this complicated as it is not. Just do the 240 volt thing as suggested by Raspy and it will work. I am an electrician and ran an electrical department in an industrial setting for 28 years. ( Not that it matters)
I bought a 2400 watt Yamaha inverter generator for an RV this year an it starts a 13,500 btu air conditioner fine.

Good luck

Harvey

 

[DarkBlack]

It might do it, it might not. Don't be so sure. My 5kw genny won't start my 4hp air comprssor @240v. As I posted earlier, my 1 hp well pump draws over 30 amps for a full seond at start up, at 240v.

 

[BertZegers]

They do. That's what I was 'referring" to in my previous post. Most small motors<(5hp) are wound in China and Mexico ( right now) and few other counties. Unlike recripricating engines elec motors are very predictable.Do you think the Kwang Doo company paid for a dyno run on a $20 motor for a Tractor Supply compressor? Nope. The motors make basicly no vibration or sound so all losses are heat. If they are a better company, they will measure the heat rise, and minus it off the power draw. There is where the real crappy winders make these motors with huge amounts of slip, but 99% of peple don't understand how they just got duped.

DarkBlack, sorry but you dont know anything about electric motors. The power is not measured on a dyno. The voltage and amps are measured and then you use the formula ( see my previus post) The rpms of the electrical motor are printed on the engine plate.( please compare North American with overseas motors) Slip has nothing to do with a good or bad motor. Besides heat loss there is also magnetic loss.
If heat loss would make a good or bad motor, then please put your hand on a HIGH EFFICIENCY motor from Baldur.

I do not post if I think I know, I have to be shure that what I post is right. But I am aware that there is always someone that knows more about the subject than I do.
I am not offended if I am corrected if I am wrong.

Bert

 

[DarkBlack]

Give me a break. You obviously didn't even comprehend what I wrote.

 

[Bladehauler]

Hmmmm, to the op , your compressor should have a check valve at the tank, you can check this by having air in the tank and cracking the discharge line at the compressor head, air may leak for a second or two but should NOT drain the tank. if the check valve is stuck open 2 4 or 24 hp is going to have a **** of a time starting it.240 volts will be easier on both the motor and the genset. another option would be a constant speed unloader such as use on gas powered air compressors.

C-Ya
Scott

 

[Boeing]

Thanks, Bladehauler, I'll make that check....then we'll know. And I plan on rewiring to 240V
Thanks everyone....:thumbsup:

 

[Boeing]

guys I'm in Virginia now and I rewired the compressor motor to 240 and changed the plug and the generator powered it right up.
I'm so happy, thanks a lot guys for all your input. I really appreciate it .

 

[Wheels2]

guys I'm in Virginia now and I rewired the compressor motor to 240 and changed the plug and the generator powered it right up.
I'm so happy, thanks a lot guys for all your input. I really appreciate it .

Glad you got it going.

Harvey

 

[Soundguy]

good to hear. 9 pages later and post #2 (spyder), 5 and many more after that had it..