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ChuckDynasty
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# Posted: 13 May 2018 07:44pm - Edited by: ChuckDynasty
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I have a question regarding a craftsman 3hp 20 gallon compressor.
It's wired for 120 but have not reliably been able to run it off 120. For 120 I need to use an extension cord. It'll either not start, just barely start and runs or trips a breaker. The breaker is a shared 20a breaker and pretty sure nothing else is running on that at the same time but not positive.
So, I usually run it from a 6250 generator which is good and bad. Good because it gives a seldom used genny some work bad because it's a pain to get the genny out of the shed and to the driveway, especially in the winter. And also this compressor is too much for a Honda 3500w genny.
The compressor has a short cord...and only a 6ft hose. Short hose and high flow fittings for more power. I switched to short hose and new fittings to remove a cam bolt on honda van when replacing timing belt. So I like the added power but it needs to be close to the vehicle.
I need a minimum 35 ft, 40 would be better of extension cord.
What gauge cord would you think would be needed for that run? I was thinking 10 gauge but was hoping 12 would do. The cords used previously were lighter duty (not sure what gauge) 50 ft.
What ever cord I try I was thinking of wiring direct to generator if I can sucessfully run it from 120.
Any suggestions? Thanks
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neckless
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# Posted: 13 May 2018 08:48pm
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compressors are bad for gennys...it take three times the rated amps to start...probly start with no air in tank.. but will not restart..... get a booster pack with a air built in
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Fanman
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# Posted: 13 May 2018 09:01pm
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A 3HP motor running on 115V will draw 34A. On 230, 17A. That's 3910W, which is why your 3500W generator won'd do it. Those are full load current. If the breaker doesn't blow right away, it's probably because the motor isn't working as hard until the pressure in the tank builds up.
A 10GA cord is rated for only 20A. You'd need a 6 or 8GA for 34A. That's why people use 220, to cut the current (and therefore the required wire size) down.
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ChuckDynasty
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# Posted: 14 May 2018 01:35am - Edited by: ChuckDynasty
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Thanks for the replies, I appreciate it.
According to a manual for 3hp 20 gallon craftsman air compressor it says can be operated on a 15 amp circuit if...see attached
And also says...Minimum extension cord wire gauge 12ga
air_compressor.png
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Extension_cords.png
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Fanman
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# Posted: 14 May 2018 06:47am
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If it can be run on 15A it's not 3HP... but manufacturers notoriously exaggerate HP claims, there was even a class action lawsuit over this.
Given that the manual says 15A and a 12GA cord you should be fine, unless there's something wrong with the motor that's making it draw more current.
If it's having trouble starting, look at the pressure switch. Most air compressor switches have a check valve between the compressor and tank and unloader valve in the pressure switch that releases in the line so the motor can start easier. You should hear a momentary hiss of air escaping when the switch shuts off the motor.
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ChuckDynasty
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# Posted: 14 May 2018 07:56am
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Yes, I just read on another forum about the HP on the side of a compressor probably not the actual motor HP. Nothing on a plate anywhere that has any info.
I hear the hiss when the motor shuts off. I replaced a leaking check valve when I picked this up 8 or 10 years ago. Looks like this compressor is c. 1990
I have a new 50ft 12/3 I just came across and will try that today. Thank you.
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Steve_S
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# Posted: 14 May 2018 08:16am
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I have a 3hp, 20 gal unit which will run off my Big Genny 7200/9000W but not my 3000W Inverter one. To run that off a 15A plug it will BUT you need a min 12ga or better 10ga extension cord. Most cords are 14ga and just can't do it. The longer the cord the higher the gauge should be. 50' of 12ga maybe, that's pretty long.
Good Luck.
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ChuckDynasty
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# Posted: 14 May 2018 09:02am
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Yeah, I was thinking about making a 35-40ft one. I don't know how much that shorter length would help though.
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