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

[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