ECN Forum Forums General Topics of the Trade General Discussion Area How does an Air Compressor draw...

IanR,

You are correct that their advertising was based more on "inrush HP" rather than delivered output.

But, I am concerned that too many people do not take into account the EFF and PF when they are trying to compare input amps with nameplate (output) horsepower.

I think this law suit established there was no way to come up with 6hp, no matter how much they cheated.
http://www.aircompressorsettlement.com/faq.php3

"But, I am concerned that too many people do not take into account the EFF and PF when they are trying to compare input amps with nameplate (output) horsepower."

A very valid point.
My apologies

Even a terrible engineer can't stretch the facts to imply that inrush current equates to HP, because the speed is essentially zero at that point, so the HP formula cannot work. HP does NOT relate directly to current, otherwise you could rate a transformer as having HP! Current relates to torque, and torque relates to HP, but the HP formula is Tq x RPM/5250, so if RPM is zero, everything else is zero. There is another explanation though.

In college in the '70s I worked for Sears selling bench power tools (table saws etc.) when they began using the marketing term "develops __HP". Being an inquisitive sort and an EE student at the time, I asked an Emerson rep one day what they meant by "develops" (Emerson was making all of the Sears brand tools at that time). He explained that they meant that when the load increased the slip to where it put the motor into Break Down Torque (BDT), the total HP could be "recalculated" at those values. Well on a Design B motor, BDT can be as high as 220% of FLT and even though speed would be lower in order to achieve that torque level, the total "recalculated" HP at that point came out to be higher than the "old" HP rating. For example, we had been selling a 1HP motor on the belt driven table saw one day, then the next shipment came in with the EXACT same motor and the literature said "develops 1-3/4HP". So at it's rated 1750RPM it was 1HP, which meant 3ft.lbs. of torque. That meant that BDT was 6.6ft.lbs. and occurred at about 80% speed (1400RPM) so at that point was theoretically 1.76HP! This of course was BS because in order to "develop" that extra HP it was no longer at rated speed and rated speed has everything to do with how a circular saw blade works, but apparently the marketing dept. had no qualms about it.

You could rate a saw like that, or for that matter any machine with a direct drive where a nincompoop operator 'controls' the torque by feeding into the work like a bloody maniac, ignoring the tortured screams of the mechanicals. How long before overheating or breaking a shaft or blade? How long before you fire his ass? A 4-pole @ 1400 rpm? The cooling fan runs too slow, it's less efficient electrically and there is more heat to dissipate.

But for a compressor to run at 220% rated, they'd have to deliberately change the drive ratio, making the machine useless for anything but brief operation and/or making it unstartable. I bet they didn't do that! - Badge Engineering by Marketing - much cheaper!
What we have here is a deliberate lie designed to mislead the consumer. An air compressor is sized by the user on how much air is needed for the job in hand, such as paint-spraying or portable air tooling. A 'below spec' machine usually gives lousy spraying results or an inability of airtools to work at the required speed or endurance.

In these circumstances the maker got off very lightly indeed by being able to fob off tricked buyers with some crappy low spec tools. The tools he actually bought the compressor for don't work properly!
A full refund plus damages, a few million dollars in fines plus the CEO locked up 2-10 would have been more appropriate. That's what you get for fraud isn't it?

Alan

What you get for fraud appears to be inversely proportional to what you can afford to pay for lawyers.