Re: [CAD_CAM_EDM_DRO] relay help req.

Hello Terry;
Horspower ratings for consumer appliances are grossly inflated. This is an
accepted (albeit dishonest) practice.

One horsepower is equal to 746 watts. The efficiency of various motors runs
from say 50% to about 85%. For purposes of simplifying things, you can
assume it takes 1000 watts to get one horsepower from an average motor.

7 amps times 120 volts gives you 840 watts, or a little less than one HP.

I've digressed completely off the subject. Couldn't help it.

Manufacturers also will underrate current requirements occasionally. Your
vacuum may draw more than 7 amps, though not likely. Bear in mind that a
centrifugal blower (vacuum) draws maximum power when the intake is least
restricted. Put your hand over the nozzle and the motor current goes down
while speed increases. Thus, a vacuum could not generate its rated peak
power the way a table saw does for that millisecond before the motor stalls
or the circuit trips.

Your 16 amp SSR should be adequate.

Doug

PS: Sears started this shameless advertising technique about 25 years ago.
15 years ago they had a 3HP, 4HP and 5HP compressor, all of which were
identical except for the size of the motor pulley. The motor manufacturer
apparently agreed to leave the HP rating off its silkscreened data plate.
Sears just stamped them in with a stencil later. Go look at any Home Depot
compressor and you will notice something similar.

----- Original Message -----
From: Terry Ackland <hexagon@...>

> Hi,
> I have just managed to get my computer to switch a relay on/off which
> I wish to use on a ShopVac which the label says is 7amps with a 3hp
> peak. My s/s relay has a 16 amp rating and would like to know if it
> is safe to use on the vacuum?
> Thanks and a happy new year, Terry