Really Dumb question

[tim]

Is there a relationship between wattage and horsepower that is interchangeable? ie what is 1HP in watts or is it not that simple? Maybe the most obvious answer to engineery types but not me.

Thanks

Tim


'Mercifully free of the ravages of intelligence' :wink:

 

[Anonymous]

I'm fairly sure that 1hp approximates to 750 Watts. I'm very sure that someone will correct me if that's wrong.

Graham

 

[Nigel]

Tim
Graham is about right it is actually 746watts

Nigel

 

[Adam]

Is there a relationship between wattage and horsepower that is interchangeable?

Yes, if it wasn't for the fact that some people measure watts going into a device, wheras some people measure the watt coming out, e.g. a 750Watt electric drill made really cheap with poor bearings might only put out 250W at the chuck - maybe twice as much for a premium brand. Their is always losses due to heat, friction etc.

Also, different companies measure their products at different loads, e.g. the maximum load it can drive indefinately 100% loading, some people cheat and use the power at 40%, e.g. it can only operate at 100% power output, for 40% within any time period, e.g. 40 minutes out of every 100 minutes.

The most honest of the bunch seems to be Jet, who measure the output of their products, at 100%. E.g. as a professional, you could run their spindle moulder non-stop all day, and it wouldn't overheat, or get upset at being overworked. It's almost impossible therefore, to compare between brands.

Adam

 

[tim]

Great

Thanks guys. I knew there was something fishy about it re input and output like cfm but didn't know what. So basically its a marker in the sand based on trust in the manufacturer :shock:

Really helpful to at least know the relationship. Is it safe to assume a linear relationship ie w = 75%HP?

Cheers

Tim

 

[Losos]

Adam - I agree it's very difficult to compare brands because the actual method of measuring is never given. One would assume that when quoting HP the manufacturer is measuring the output since that's the power that any customer is mostly interested in. Wattage inwards might be of concern in some cases, perhaps when running of a portable generator.

 

[tim]

or when trying to make it look more powerful than it is. I spent 10 years in marketing doing exactly that kind of thing :twisted:

T

 

[ike]

A standard way of specifying electric motor performance now, is to quote 'P1' (Power input in kW), 'P2' (Power Output in kW) and 'T###' which is the duty cycle in %.

So for example a motor on a PT might be rated something like 'P1= 2.8, P2=2.0, T=60.

This gives a lot of information such as (P2/P1)x100 = efficiency. A well designed motor should be around 80-90% efficient at converting energy. The rest of course is heat (and a bit of noise). So for a less efficient motor (or one with poorly designed heatsinking), usually the duty cycle will be lower.

So if P1, P2 and T are given, you have all the info.

cheers

Ike