Quality Of Tools

The definition of one horse power to watts is 746.

Here's a good read for you:

Quite.

However, with the exception of cordless drills (where the "brand" manufacturers do quote the torque delivered, ie the useful measurement for the user) the power quoted is the input power, which as Cisco Kid says isn't particularly useful...

-- Richard Sampson

email me at richard at olifant d-ot co do-t uk

I completely agree. Input power is largely irrelevant, with motors ranging from good and decent in quality tools to diabolical at the bottom end.

It's relatively easy to measure input power and can also mean that seemingly impressive specs can be written. The Precision Performance Power Pro (or whatever they are called this week) routers from B&Q are the epitome of this, with a 2000W input power (allegedly) but with a performance equivalent to about half that at best.

There would need to be some standards for this, and probably to be useful, a measurement method for each type of tool under standard conditions - i.e. a cutter of a certain size on a router etc.

I don't see that happening any time soon, so in the meantime it's necessary to be guided by manufacturer, price, and ideally trying out the tool.

Yes indeed, but generally the same principle applies.

.andy

To email, substitute .nospam with .gl

Suppose output torque would be a useful measure. Don't see it happening ever, though... manufacturers will use whatever gives the highest number for the consumer to read. Suspect a 50% efficient 2000W tool would always sell better than an otherwise-identical 75% 1500W tool.

Amplifer power and music power springs to mind...

-- Richard Sampson

email me at richard at olifant d-ot co do-t uk

Unfortunately the quoted wattage is input power and bears little relation to the actual output. It's required by law to be on the tool.

Yes, let's never forget how PMPO has replaced RMS throughout the lower end of the audio ranges...

Exactly. The opportunities for the marketeers are there. That's why I think that for the measure to be meaningful, it would have to be related to the type of tool, or at the least there needs to be a standard method of measurement for the tool type. For example, it's easy to conceive how that could be done for a fairly simple rotating tool like a drill or router, but how would you do it for a belt sander?

Also, if torque becomes a measure of goodness, is that appropriate for the behaviour of all tool types?

Yes indeedy.

.andy

To email, substitute .nospam with .gl

An electrc motors efficiency varies dramatically as the load varies. Its not possible to give accurate output powers on them: Its not actually possible even to give accurate rated input powers, since again as voltage caries - and it does as batteries sag - the amount of input power that doesn't *quite* cause meltdown or demagnetisatin varies considerably (thats DC motors) On AC motors its still pretty indefinite.

Just learn your tools

Here's yet another good read:

It is a legal requirement to quote input power for electrical items and it may just be that the manufacturers don't want to confuse everybody too much.

Then again ....... :-)

Check out the Dewalt cat. lists in and output power on non battery tools interesting reading

Steve

Only in the same way that one pound of cheese is the distance between here and there, bypassing Tazmania.

no way. schoolboy physics:

work done = force x distance power = work done / time

therefore

power = force x distance / time

Your example does not mention any acceleration of the mass, ie implying a steady speed, therefore as it is a level surface without friction (ie gravity has no bearing here) then the force required to maintain this speed would be zero (force = mass x acceleration). Therefore the power would be zero.

-- Richard Sampson

email me at richard at olifant d-ot co do-t uk

I was just going to say "no it isn't". I prefer your version!

As has been said elesewhere, maintaining motion on a frictionless plane with no acceleration requires no energy or power.

One HP is 746W.

E.g., a 75 kW engine is equivalent to near enough 100 HP. A 50 HP engine, quite common, is the equiv of a combi boiler. Cars are now being rated in kWs.

I was more worried about a imperial unit being defined with metric units (other than the second) and the lack of friction.

Horse power is related to lifting a given weight in a given period of time, indeed 33,000 ft.lb per min or 550 ft.lb per second. Though the metric mob seem to have got hold of it and redefined it as 75kg/m/s... this should be indicated by PS rather than BHP though.

Brake Horse Power I think is heating a given amount of water a given number of degrees in a given amount of time. The heat coming from a brake on the output of a machine. But after a fair bit of digging and links all ending up in the same data source just presented differently I found:

BHP = (RPM * Torque)/5252 (Torque in ft.lbs)

Which makes far more sense than buckets of boiling water. B-)

You have to say "free". "Free watts with this drill". Then they flock in. Like the "free" mobile phone con. They cost in a phone replacement every year. So, if you don't get a replacement every year they make a killing. People think they get something for nothing when they ring up and ask for an upgrade of phone. Also the "free" minutes con too. If you don't use them then it becomes expensive.