Author Topic: False product advertising (Read 515 times)

bloom25 · « **on:** October 27, 2002, 05:57:38 PM »

I spotted a great case of this today.

Take a look at the horsepower ratings of a Shop-Vac vacuum. I bought a small one today that has a 3 HP rating on it. Elsewhere on the box it notes the power consumption is 7 amps (it uses a standard 120V AC plug).

Here's some electrical fundamentals to get you guys up to speed:

Power (in watts)= Volts x Amps. 1 HP (horsepower) = 746 Watts.

If we multiply 120V * 7 Amps we get 840 Watts. Divide 840 by 746 and we have 1.12 Horsepower. That means the electrical power consumed by the motor is 1.12 Horsepower (maximum). No motor is perfectly efficient, so the mechanical power cannot possibly exceed 1.12 Horsepower. The BEST motors I've ever seen are around 90% efficient. Assuming that's true (and that's a BIG assumption) I get 1.01 Horsepower.

So here we have it, a 1 Horsepower motor (more likely 3/4 horsepower) somehow outputs 3 Horsepower.

I looked on Shop-Vacs site, and if you read really close you'll see that they claim 3 Peak Horsepower. I still don't buy that. If the motor was perfectly efficient it would have to consume:

746 x 3 = 2238 Watts

Meaning it would draw: 2238 / 120 Volts = 18.65 Amps of current.

Now we have a second problem. All 120 V AC outlets in the US are rated at no more than 15 Amps. Consider also that the cord on this vacuum is 20 feet long and uses 18 Gauge wire. There is NO POSSIBLE WAY anything close to 18.65 amps is getting through a 20 foot long cord off an outlet with a 15 Amp breaker. (Those of you who have ran power tools off a long extension cord know what I'm talking about here.)

Shop-Vac also advertises 6 HP + vacuums using 12' cords off 120V AC. If you think this example is bad, that would be even worse. It's completely impossible to run a 6 HP motor off a standard 120V electrical outlet!

I think what Shop-Vac is doing is taking the motor, connecting a very heavy weight to the output shaft and then bringing the motor to a sudden stop and measuring the impact force and using that to determine their "peak horsepower" rating. I can't see any other possible explaination. (This would most certainly damage the motor.)

I'll bet the motor used in their "3 HP" (it doesn't say peak on the package, only on the website) would actually rate somewhere around 1/2 to 3/4 horsepower. There's about a 300% to 600% difference between what's claimed and what's actually possible!

(I also have a 5 Horsepower motor on an air compressor. It's nameplate indicates a draw of 25 Amps at 220 Volts AC. That's 5500 Watts of power (or 7.37 HP). That motor would have to be(assuming the nameplate is correct) is 5/7.37=.678 or 67.8% efficient to output 5 HP (mechanical). This motor weighs close to 80 Pounds by the way. I was awefully easy on Shop-Vac on my example above by assuming their motor was 90% efficient!)

(I have a BS in Electrical Engineering, so I do know what I'm talking about here.)

What do you guys think about this?

SOB · « **Reply #1 on:** October 27, 2002, 06:18:44 PM »

I think you just spent waay too much time thinking about this. If the shop-vac does the job you need it to do and you feel it was worth the price you paid, use it and don't worry about the marketing BS behind it.

SOB

bloom25 · « **Reply #2 on:** October 27, 2002, 06:29:42 PM »

Maybe so SOB. I think I'm just angry about getting a jury duty letter in the mail Friday, considering I'm doing 3 seperate jobs right now. This must be because I haven't been able to play AH (or anything else) for weeks now.

I did actually figure out how they came up with the 3 HP rating though (and it's definately a scam):

I was actually right up above. Somehow vacuum cleaner motors (and ONLY vacuum cleaner motors) are rated in a totally BS manner by tying as much load as possible to them (without burning them up) in the form of a big weighted flywheel and then bringing them to a stop instantly. They get the "peak horsepower" rating from that by basing it on the assumption that a one horsepower motor can deliver 550 foot/pounds of torque for one second. (That formula is only valid if the motor can continue to provide that amount of torque.) Because of that, vacuum cleaner motors are rated in "peak instantaneous horsepower."

I found a funner explaination that claimed they get the measurement by:

"Dropping the motor off the Empire State building onto the head of the engineer that came up with the peak horsepower rating and measuring the impact force."

If you guys are ever shopping for vacuums, realize the HP ratings are total BS and vary from manufacturer to manufacturer.

AKDejaVu · « **Reply #3 on:** October 27, 2002, 11:29:21 PM »

OK Bloom.. whatever you say. Just don't get a shack and write a manifesto on us now.

Step away from the box. Turn on the shopvac and use it for what most college kids buy them for. You'll feel much more relaxed afterwards.

AKDejaVu

Furious · « **Reply #4 on:** October 27, 2002, 11:41:37 PM »

Just cause it can't draw the requesite amperage from a standard socket does not mean the motor can't produce 3HP under a different load.

F.

funkedup · « **Reply #5 on:** October 28, 2002, 01:01:58 AM »

Bloom if I am reading this right you are saying they figure out the stall torque and then multiply that by a time and they get horsepower? LOL!
Only in America.

bloom25 · « **Reply #6 on:** October 28, 2002, 01:30:01 AM »

LOL, maybe I overreacted a little bit.

Things like this just irritate me.

How do you figure that Furious? There is no way a 120V, 7 Amp, motor can possibly produce 3 HP continuously (as all other electric motors are rated). That would require it to be almost 300% efficient in converting electrical to mechanical power. If you can prove me wrong here I need to contract you to make me a perpetual motion machine.

As I posted above, vacuum cleaner motors are rated differently than all other electric motors. What they are rating is not the same as all other electric motors and isn't really horsepower at all.

BTW: The vacuum cleaner worked fine. It really sucks. DejaVu, do you know where I can get a good deal on a shack and publisher somewhere?

I'm actually not in college anymore. I was hired by a Eugene company back in July, but because of NDAs I can't talk about what I've been working on for them. I'd like to, because I know many of you would find it very interesting. (It's not related to vacuum cleaners in any way...)

bloom25 · « **Reply #7 on:** October 28, 2002, 02:00:28 AM »

It looks like I'm not insane yet. (Don't worry about the shack and publisher anymore DejaVu.

) http://www.ristenbatt.com/smpower.mv

It looks like that's exactly what they are doing Funked. It's pretty cheesy if you ask me.

I figured the rest of you would feel the same, but it looks like I was wrong.

AKDejaVu · « **Reply #8 on:** October 28, 2002, 08:26:49 AM »

Quote

Originally posted by bloom25
I'm actually not in college anymore. I was hired by a Eugene company back in July, but because of NDAs I can't talk about what I've been working on for them. I'd like to, because I know many of you would find it very interesting. (It's not related to vacuum cleaners in any way...)

What company?

I've dealt with a couple from Eugene.

AKDejaVu

P.S. You wouldn't believe what I'm working on now;)

popeye · « **Reply #9 on:** October 28, 2002, 11:58:03 AM »

"Peak" horsepower is probably a marketing term, but I'm not sure that continuous power would mean much for a vacuum cleaner, since it's operating load varies over a wide range.

Also, I don't think there would be any problem getting 20 (or 30) amps from a "15 amp" household circuit for a few seconds at least. Most fuses and circuit breakers will pass 200-300 percent of their rated value for a short time. (They do this so that motors and incandescent lamps can draw large surge currents when they turn on.) So, you could probably get 3 "peak" horsepower from a 15 amp circuit, as long as the duty cycle is very low.

http://www.faqs.org/faqs/woodworking/motors/

http://www.airpaxppp.com/pppsite/ialop.html#400

Furious · « **Reply #10 on:** October 28, 2002, 12:30:44 PM »

Bloom,

It was meant to be read as tongue-in-cheek.

I was pointing out that if you put enough juice through it, it might output 3hp right before it catches fire.

F.

Manedew · « **Reply #11 on:** October 28, 2002, 12:35:10 PM »

Bet they put a MEG in it WOW 300%

http://www.rexresearch.com/meg/meg.htm

MrLars · « **Reply #12 on:** October 28, 2002, 03:24:16 PM »

The lack of truth in advertising is rampant and disgusting....the fact that it's spilled over into politics us evidence of how well it actualy works.

I'm hoping that one day the Fed will levy huge fines for the worst cases and substantial fines for the lesser ones. Right now about the only protection we have is from consumer advocacy groups which have a hard time getting any legeslation passed because of the payola that goes on connected with lobbyists.

I wanna burger that looks like the one in the picture.

I wanna a car that has ALL the windows tinted.

Finaly...I want Red Bull Wings damnit!!! I'm tired of walkin'.

Tumor · « **Reply #13 on:** October 28, 2002, 04:01:34 PM »

Ever consider macramae or cross-stitch bloom?

DouglasA · « **Reply #14 on:** October 28, 2002, 04:57:38 PM »

My Vac sucks :-)