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

[wcampbell47]

My air compressor has been wired for 220 for years simply because 220 is more powerful than 110 and draws half the amps. The air compressor is old and has leaks so it leaks down between usage. My generator will power it up the first time and run it until it reaches full pressure. After that forget it. Gasoline powered compressors have a relief system that opens and allows the gas motor to keep running when tank pressure is reached. I think switching to that type of relief system where the electric motor always runs might cure my issue. I have a very similar issue going on with my RV generator and roof top A/C. As long as I keep the temperature set at max the generator will pull the A/C. If the A/C cycles off and on again the generator stalls.

 

[Soundguy]

Bert,

I'm afraid you are missing he point. The "4 HP" number is bogus. It's not a 4 hp motor. That is an exaggerated advertising claim.

The specs say it is 115V and 16A.

The question here is how to get it to start, not whether the motor output is the same on 120 as it is on 240. We all know it is the same.

It seems clear that it is much more likely to start on 240 volts than 120 volts from the generator because of the generator design and the wire size.

No need to re-invent the wheel or delve into electrical theory here. Just give the thing more starting watts and that's it. The generator can do that if the compressor is hooked up to, and wired for 240 volts.

there is negative reading comprehension going on here.. BADLY going on here.

the few of us with an electrical background are trying to explain something.. those with no electrical background are missing the bus.

we know it's a bogus 4hp # the quick has I did shows it's closer to 2 than 4.. but apparrently chim can't read..

 

[Soundguy]

I appreciate the bone and your patience, but your approach is totally bogus. The 17.4A is certainly not "very close" at nearly 8% off the target. As soon as I see someone posting on a non-electrical forum and throwing out terms they picked up at an adult ed evening course instead of real numbers that work, the flags go up. I don't know your background, but it doesn't appear to be in power. Don't feel badly. I couldn't design a pair of earbuds without more schooling.

look.. aparrently you can't read.. or won't. i said it was a quick hash.. an estimate. im not doing any power factor math.

if you are trying to decide if a motor is 2.x hp or 4hp and you can bang out 3 # and be 92%.. that should tell ya something.

bert summs it up well in a post.

we know the 4hp # is not rms.

looking at the calcs.. the motor is likey int he 2.4-2.8hp range just looking at it's stated draw.

my quick has supports that.

and no.. it wasn't an adult ed classe.. it's a BS degree.

soundguy

 

[Soundguy]

No offense but you are adding to the confusion, this is a simple motor hookup to a pressure switch. There are no lights bells whistles or other diagnostic circuits to deal with.

there are for sure some people adding tot he confusion.

they refuse to read or pick up a calculator.

 

[Soundguy]

I'm enjoying all this too I think one poster is confusing BS peak hp ratings with peak sine wave voltage-not the same.
Just think, elec motor are so predictable that they ae allowed to publish power based on the fuel they consume...electricity. Imagine if it was done that way with combustion engines. Instead of cheating with locked rotor amps, they would be putting in oversized jets in the carbs to run richer, so they could advertise more HP, based on fuel consumption. I'm surprised nobody engaged me on the mention of rotor slip? Go buy a "cummins tool sale" motorized tool that runs slow and heats up in seconds, and you'll have yourself an introduction into slip and why it matters.

i'm not confusing anything.

a hp can be directly converted into wattage.

there are some power factor calcs i'm leaving out to do quick hash math.. but looking at the amperage draw for the hp of motors in question.. it's easy to see that the motor is in reality int he 2.x range.. not 4.

doing the match on the power side prves that.

no confusion.. just thinking outside the box with a little estimation...

 

[Soundguy]

Imagine if it was done that way with combustion engines. Instead of cheating with locked rotor amps, they would be putting in oversized jets in the carbs to run richer, so they could advertise more HP, based on fuel consumption. .

this kind of exageration with IC engines is done all the time...

no accessories.. no belts.. no coling system.. no charge system.. different fuel mix.. etc. all stuff the end user will never see.. but they can rat that engine like that to sell it.

same reason my my neighbors '25hp' rider lawnmower bogs down finish mowing a 46" patch of thick grass.. yet I can run an antique tractor with less 'hp' and cut more grass.. faster..

 

[Domush]

well.. that's pretty much exactly what I said..

peak draw.. possibly at stall / max torque, converted to hp figure.

and yes.. i'd call that the same type of logic used to rate small gas engine hp.

somewhere in some lab, using 0w1 oil, and straight ether for ful, with no belted equipment, no pumps.. no fans , etc.. carb running out of epa spec in a manner the end user could never see it operate, at an rpm band 200 nanoseconds before it detonates on the test stand. they clock that hp .. and then poof.. you have an engine the size of a basket ball making 25hp..

Haha! That is precisely what I imagine when I see HP ratings on small engines. Some steel plated room with a giant clamp to stop the engine, with a pile of "too late" engines on the floor. All in the name of rounding up to the next HP.

Sent from my SCH-I500 using TractorByNet

 

[Raspy]

I have a very similar issue going on with my RV generator and roof top A/C. As long as I keep the temperature set at max the generator will pull the A/C. If the A/C cycles off and on again the generator stalls.

I had the same issue with my RV A/C. Genny could not start it. I installed the starting aid capacitor (very easy to do) and it runs just fine. Try it.

 

[Soundguy]

Haha! That is precisely what I imagine when I see HP ratings on small engines. Some steel plated room with a giant clamp to stop the engine, with a pile of "too late" engines on the floor. All in the name of rounding up to the next HP.

Sent from my SCH-I500 using TractorByNet

yep.. or a bunch of 'also rans' where they kept incrementally upping something.. either rpm or fuel mix till they could get it running long enough for the dyno to spit out a test number on a slip so they could slap that on the engine with some sort of smug 'certification'

and in a few cases.. I don't doubt there was a sacrificed chicken somewhere..and a few 'look the other way' type tests done..


soundguy

 

[joshuabardwell]

Frankly, I wouldn't be surprised in the least if the motors were rated using some formula instead of an actual dyno run. At this point, it seems like small engine design is pretty standardized. I bet you an engineer could take the specs of a motor (number of windings, cylinder bore, whatever) and approximate the HP to a high degree of accuracy. Since nobody is really checking these things anyway, why would a manufacturer bother putting their motor on a dyno? But yeah, it's kind of a joke when a 120-volt motor claims something like 5 HP. Just. Not. Possible. At least not using typical household wiring.

 

[DarkBlack]

Frankly, I wouldn't be surprised in the least if the motors were rated using some formula instead of an actual dyno run. At this point, it seems like small engine design is pretty standardized. I bet you an engineer could take the specs of a motor (number of windings, cylinder bore, whatever) and approximate the HP to a high degree of accuracy. Since nobody is really checking these things anyway, why would a manufacturer bother putting their motor on a dyno? But yeah, it's kind of a joke when a 120-volt motor claims something like 5 HP. Just. Not. Possible. At least not using typical household wiring.

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.

 

[chim]

look.. aparrently you can't read.. or won't. i said it was a quick hash.. an estimate. im not doing any power factor math.

if you are trying to decide if a motor is 2.x hp or 4hp and you can bang out 3 # and be 92%.. that should tell ya something.

bert summs it up well in a post.

we know the 4hp # is not rms.

looking at the calcs.. the motor is likey int he 2.4-2.8hp range just looking at it's stated draw.

my quick has supports that.

and no.. it wasn't an adult ed classe.. it's a BS degree.

soundguy

I'm glad Bert was able to explain it so you could grasp it. You were starting to confuse me, but then I'm not accustomed to dealing with someone who has a degree in BS.

 

[DarkBlack]

i'm not confusing anything.

a hp can be directly converted into wattage.

there are some power factor calcs i'm leaving out to do quick hash math.. but looking at the amperage draw for the hp of motors in question.. it's easy to see that the motor is in reality int he 2.x range.. not 4.

doing the match on the power side prves that.

no confusion.. just thinking outside the box with a little estimation...

Actually you are. You know more than the average bear about electric,( I'm not your average bear), but you were using a convention to convert from sine wave voltage P-P, to RMS voltage, to explain advertised "peak" HP. It's not the same thing. Not trying to start a fight.

 

[Raspy]

Another good example of false advertising in motors is to look at shop vacs.

I've seen different shop vacs, from the same manufacturer, with the exact same motor. The only difference was the canister size.

They will have a rating of 3HP on the small one and 6HP on the big one.

Unfortunately, most folks can't see it's deceptive. If they did, why would they buy a product from a manufacturer that is trying to trick them?

To me it's a silly waste of time to even try to figure out how they came up with those numbers using any electrical theory. It's simply lying and false advertising. Or what I call, "Sears Horsepower". Bigger is better in many people's minds and a bigger number must be worth more. It has little if anything to do with electrical or motor theory.


This same trickery goes on with tires too. How many times have you heard about 10 ply tires? The truth is they are only two or sometimes three plys. Next time you doubt that go read the fine print on your own set of Load range E 10 PR tires on your pickup.

That's just the way the modern world works with advertising.

 

[DarkBlack]

Ha! I know what you mean. I think Sears has turned it around a little bit in the last 5 years. On their ICE's they have been very strict adhering to the no HP advertising, only CC and tourqe ratings. Of course.. torque without RPM's is meaningless... but that's another thread.

 

[Soundguy]

yep.. were you gonna get a 40a plug for it..

 

[Soundguy]

Another good example of false advertising in motors is to look at shop vacs.

.

look at home vacume cleaners.. same deal....

 

[Soundguy]

Actually you are. You know more than the average bear about electric,( I'm not your average bear), but you were using a convention to convert from sine wave voltage P-P, to RMS voltage, to explain advertised "peak" HP. It's not the same thing. Not trying to start a fight.

your right.. but .. now here's the stick in the mud.

I know peak hp is a different measuring convention than peak rms.

BUT

when you use quick and dirty match and convert over .. it works out pretty darn similar.

it's a good go/no go gauge if you can do a 10 second calc and get 92% 'close' it's better than horseshoes.

i'm not trying to start a fight either. I'm trying to show that you can make a 'GOOD' guestimate with that cal and come out with the SAME answer.

IE.. we KNOW that a 4hp claim with 16a stated current is NOT correct.

doing the regular rms calc on the hp gets you DARN close!

that's my only claim.

I did say it was quick and dirty math

 

[DarkBlack]

P-P and RMS is like feet in a mile. It's a no gray area proven science formula. Now.. advertised "peak HP" from vendors around the world, that is open to interpertation, depending on among other things, who's pockets you line.

 

[SPYDERLK]

i'm not confusing anything.

a hp can be directly converted into wattage.

there are some power factor calcs i'm leaving out to do quick hash math.. but looking at the amperage draw for the hp of motors in question.. it's easy to see that the motor is in reality int he 2.x range.. not 4.

doing the match on the power side prves that.

no confusion.. just thinking outside the box with a little estimation...

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