Motor Input and Output Power

[Ketan SwaliParticipant @ketanswali79440]

Over the past year, I have come across various inquirers questioning the motor power for the various machines which we sell.

For example, manufacturer/supplier 'X' is stating 500W, and ARC is stating 350W. What is the difference?

Normally, ARC responds by saying that perhaps the manufacturer/supplier X may be stating input power as part of their marketing exercise. ARC is stating output power. Perhaps the person asking the question should ask the same question to the supplier of the machine?

This issue also arises when customers are looking to buy replacement 'brushed' motors too.

Going forward, should ARC consider stating input and output power both for the mills and lathes ARC sell?

In my opinion, there seems to be confusion resulting from the marketing exercise figures suggested by certain suppliers and lack of clarity on this subject.

It would be interesting to understand the electronics bods opinion on this subject.

Ketan at ARC

[Ketan SwaliParticipant @ketanswali79440]

[Ian ParkinParticipant @ianparkin39383]

I would quote both to prospective buyers

[Michael GilliganParticipant @michaelgilligan61133]

Ketan,

Stating both Input Power and Output Power would be very helpful.

Both are relevant, for different reasons; and, of course, the percentage ratio between them gives us efficiency.

MichaelG.

Edited By Michael Gilligan on 13/10/2015 13:39:50

[AjohnwParticipant @ajohnw51620]

Both Ketan – as all "real" motors are marked. I feel output should always be specified as efficiency varies. It pretty clear than many areas now use input as part of the numbers in the spec game. Some areas even involve a time limit. I had noticed that you state output.

Input may have it's uses too. I have a Ryobi radial arm saw with a universal motor. Fine but a jam always possible with this sort of saw would blow the motor rapidly. To prevent that I fitted a 5amp fuse. Mains fuses blow above the rating so it cuts ok. Periodically when I start up the fuse blows as they wear out over time – much better option than having to buy a replacement.

John

–

[LambtonParticipant @lambton]

As I understand it the power rating that a manufacturer states ( e.g. 750 watts or 1 hp) relates to the maximum power the motor can produce in response to an applied load. Such a motor will draw only a small current when idling so will not be consuming anything like 750watts however at approaching stall conditions it will produce its maximum power and will draw its maximum current and will therefor be producing the full 750 watts output. The power consumed (input) under these conditions will be higher than 750 watts as motors cannot be 100% efficient. Many motors are no better than 80% efficient.

Some manufactures quote a maximum time at full power as all motors heat up when delivering power and it is important to limit then temperature rise to the designed maximum.

John W1. I am glade that you are providing some protection to your radial arm saw by using a 5 amp fuse. However you should be using a proper motor starter with a correctly set overload. Fuses are intended to protect wiring rather than motors. Starters with overloads are designed to protect motors rather than wiring. A starter will also give the benefit of no volt release.

[Ketan SwaliParticipant @ketanswali79440]

OK,

So I discussed this at some length with certain people with the knowledge in the SIEG factory, as well as with certain people in competitor factories.

It was explained to me that there is a growing trend of 'mine is better than yours', especially after the introduction of brushless motors and torque issues effecting sales of brushed motor machines.

As a marketing tool, well known badged brands as well us unknowns piggybacking, are choosing to quote input power – as it is obviously higher, but when challanged, still say it is output power. Apparently this is acceptable too, because it has something to do with temperature and peak over time !?!. This went a little above my head, as I am a commercail person, but again, how can this be correct ?.

In other words, how can someone say that they have a 1,100W brushed motor, when what they really mean is that it is about 700W motor output, and still be correct in saying it is a 1,100W motor. How cn this be right?

The issue of efficiency and temperature was also discussed, and I hope to address this shortly, once I can get my head around it.

Ketan at ARC.

[Clive FosterParticipant @clivefoster55965]

Hard to beat the old style industrial machine data plate with input voltage and current, or currents in the case of single phase motor with start winding, and continuous output power. These are what the user needs to know to select correct motor, or estimate appropriate workload for one fitted to a machine, and set the starter overloads.

Never liked input power specifications at the best of times and really got a down on them after Northern Tools sold me a 5HP cap start / cap run motor whose data sheet revealed the actual output power to be a claimed 2 1/2 HP. Said claims proved more than dodgy as the actual useful continuous output when driving a compressor was around 1 1/2 HP whilst drawing down nearly 6 Hp worth of electricity! Wonderful heater but pants as a motor. Almost worst part was when I complained and was blandly told "Yup. Sounds about right." Eventually got a refund by waving trades description act and trading standards at them and next issue of catalogue said 5 Hp input power 2 1/2 HP output power. Don't think they sold many after that.

Legal advice at the time was that quoting input power only was prima facia misleading as a motor by definition is bought for its output power which must always be less than the input so quoting input only is deliberately intended to deceive. It was also said that specified output power should be continuous unless operating time caveats are included. Said caveats should also be reasonable. For example electric hand drills are rarely used continuously so 50% duty cycle with say 10 minute maximum continuous operating period is probably acceptable. Sub one minute ones aren't. Which I have encountered when a friends uber cheap drill burnt out on the third hole. He got his £5 (or thereabouts) back.

Clive

[Ketan SwaliParticipant @ketanswali79440]

I get your point Clive, but I am guessing that there must be a legal loophole, especially if the big boys can get away with it!…as I said earlier, I guess they can prove things based on some kind of woodoo figures relating to peak wattage over temperature and time.

An example is a 250W output brushed motor being marketed as a 300W motor, to promote a particular mini-lathe. I could give plenty of such examples for other Mills and lathes.

Truth be told, I feel a bit miffed at loosing sales resulting from others wide spread industry practice of marketing input power figures to promote their machines.

Ketan at ARC.

[AjohnwParticipant @ajohnw51620]

Quoting the input power is pure and utter rubbish Ketan especially as efficiency can vary. This has no bearing on temperature at all. The only way it could be justified is on brushed motors. These will tend to produce what ever power is needed right up to them burning out so a short term rating based on input might work out. Short term is likely to be very short. Perhaps one aspect that is missing from just stating output power is the word continuous. Some motors can be run continuously at their maximum rating for ever. They will get hotter so a "real" motor specification will also mention a maximum ambient temperature and the expected temperature rise when run at full power. Some makers motors are more conservative than others.

There is another way of spec'ing motors. Common on a number of things and not always mentioned. It often is on cheap bench grinders which of late do seem to spec input power. So many mins on and so many off – usually a lot longer as things cool very slowly. The input power does directly relate to the heating effects as does efficiency. This is often one of the factors that set the price differences between professional as against amateur / hobby power tools. When the figures aren't given the manufacturers are making assumptions about how the tool will be used. Some just make the amateur version less powerful and perhaps a bit more flimsy but this will still cost more than the well it's only going to be used for a few min brigade. As an example in a rush I bought a cheap 4in angle grinder from a DIY store as I needed to chop up a stair lift in a hurry – it failed on the last cut. Maybe 20min of continuous use. My Bosch one wouldn't even notice this but I didn't have it with me. My unusual industrial Makita would do this sort of thing all day long. Another example. B&Q were selling Ryobi drills at one point – with a different make of motor from the USA fitted. Burn out the Ryobi one – very unlikely even if stalled for short periods but the American one was a lot more powerful and probably cheaper too. Ryobi now probably make and fit motors similar to the American ones in order to be competitive or maybe the motors are still changed.

Lathes/mills – I don't think an input power is of any use to users on this sort of forum. It is very likely to be used for extended periods that make the hobby use only a silly thing to say – they should buy something else but instead I suspect they get over heat sensors one way or the other. Maybe electronic current measurement as that is cheap to do indirectly these days, simple to use chips are available.

Some retailers will sell ac motor 3 phase inverters in the same way but the problem is different. Yes set any speed you like. Higher than stated speeds might burst the motor. Low speeds will overheat the motor if significant power is extracted for long enough. The current levels as far as the motor is concerned doesn't vary – the speed of the cooling fan does as will the torque that is available for cutting. TEC are about the only people who show graphs of what can actually be done – if that particular catalogue can be found.

My Ryobi radial arm saw has a key which I always remove when not in use. They don't make them any more. Pity really but they were intended tor on site use and a dust mask and ear defenders are much needed when using it. I'll stick to the fuse – copper wire fuses very very quickly if needed so providing the wire in the fuse is a suitable size all is ok.

John

–

[Ketan SwaliParticipant @ketanswali79440]

Posted by John W1 on 13/10/2015 16:43:27:

Lathes/mills – I don't think an input power is of any use to users on this sort of forum.

John

–

Agreed, but that is the basis on which a growing number of lathes and mills are being sold…in my opinion, and the masses are happy to accept it…unfortunately.

So how does one prove it ?, can anyone suggest a simple way?

For example:

An old C2 – brushed motor (not brushless), has body diameter of 83mm x 145mm long. We state that it has an output power of 250W, where as it is stated elsewehere as 300W upwards.

An old X2 – brushed motor (not brushless), has body diameter of 83mm x 180mm long. We state that it has an output power of 350W, where as it is stated elsewhere as 470W upwards.

The figures we have given are output power as given by SIEG. I would therefore presume that one cannot just flick a switch and say that the same motor has just had a shot of steroids and gained power out of thin air.

The comparison doesn't stop here. Other machines manufactured by other factories with broadly similar sized brushed motor bodies have suddenly gained exponential power wattage. Botox?

Example: on one site, a brushed motor fitted to a popular mill has a wattage statement of 1100W, which is simply amazing, if the said motor is similar in size (not exactly) with windings and magnets to an old X3 brushed motor which has output of 600W according to SIEG. Admittedly it is not a machine made by SIEG, but considering it is a brushed motor of similar dimensions etc., would I be right or wrong with some or many of my presumptions?

This marketing hipe of 'mine is better than yours' is getting out of hand, and it is simply wrong. Why make these statements?

Ketan at ARC.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Ketan Swali on 13/10/2015 17:27:18:

So how does one prove it ?, can anyone suggest a simple way?.

.

Ketan,

This type of Magtrol Dynamometer is ideal for quantitative testing of motor output.

MichaelG.

Edited By Michael Gilligan on 13/10/2015 17:51:23

[AjohnwParticipant @ajohnw51620]

The jury is out as far as I am concerned on brushless Ketan because of the hype on other types. I do believe that permanent magnet motors can be smaller for the same power output and would assume that applies to brushless. I can also see that better low speed control could be achieved but have doubts about more torque other than it being a more powerful motor.

The other factor that can have an effect is motor speed. Motors have what is called a windage loss due to the parts shifting air about but it's not a dramatic one so higher speed can result in smaller motors for the same power output. Power is a function of both speed and torque so say some motor produces it's max power at 10,000 rpm and that is then belted down to 2,500 torque will be roughly 4 times higher than the motor gives at 10,000 rpm. This is how electric hand drills etc get their power and size usually needing cooling. They run at very high speeds.

What I suppose some one could "fairly" do is say we fit a 10,000 rpm 1hp motor and use a belt drive to bring it down to 2,500 rpm so it's 2hp. Ie the same torque as a 2,500 rpm motor would give if it was 2hp. This is sort of reasonable compared with "real" lathes. My boxford for instance should I think be fitted with a 1/2hp 1400 rpm motor. The max speed is 1300 rpm so I will get close to 1/2 hp at that speed. The biggest difference though is that at 650 rpm I still have 1/2 hp as torque has been increased where as the fictional 2hp variable speed set up would also give around 1/2 hp at 650 rpm, more usual actual power levels a lot less. Joe public seems to be completely unaware of this factor unless some one spells it out to them. It's the same situation with inverter drives.

I've fitted a 1hp to it as I also fitted an inverter. More heating up capaciiy and the same torque at 1/2 speed that I had and can there for use for short periods.

Doh got some number sums wrong but some should see what I mean.

John

–

Edited By John W1 on 13/10/2015 18:36:35

[jason udallParticipant @jasonudall57142]

Ketan.
You have my sympathy.

This specmanship is everywhere.

You can “fight” this by having the higher input ratings (and making these available) to hand.
So when asked you can inform the prospect.

“Yes sir we do appear to say our motor is lower power but that is because we tell you the power available to work not the heating effect on you workshop”..
Why don’t we quote it like the others?..we have over the years found honesty and forthright advertising to be better recieved.
Now how many would you like?

[Steve PaveyParticipant @stevepavey65865]

 

If customers are comparing machines on your web site with those on other dealers web sites and coming to incorrect conclusions then you need to educate them. I would put a bit more information on your Machines and Accesories page on the website – Some basic info on input and output power, a bit of background on the sort of motors fitted and some words of wisdom on efficiency and running costs maybe, maybe even get some renowned expert to write an article on the subject you can link to on your machines web page – not only would this inform your potential customers it would give you the moral high ground in marketing terms.

Edited By Steve Pavey on 13/10/2015 18:49:59

[Michael GilliganParticipant @michaelgilligan61133]

Posted by John W1 on 13/10/2015 18:34:35:

What I suppose some one could "fairly" do is say we fit a 10,000 rpm 1hp motor and use a belt drive to bring it down to 2,500 rpm so it's 2hp. Ie the same torque as a 2,500 rpm motor would give if it was 2hp.

.

No, John … It is not 2hp and never can be.

Torque x Revs = Power

MichaelG.

[Ian PParticipant @ianp]

Posted by Michael Gilligan on 13/10/2015 18:51:14:

Posted by John W1 on 13/10/2015 18:34:35:

What I suppose some one could "fairly" do is say we fit a 10,000 rpm 1hp motor and use a belt drive to bring it down to 2,500 rpm so it's 2hp. Ie the same torque as a 2,500 rpm motor would give if it was 2hp.

.

No, John … It is not 2hp and never can be.

Torque x Revs = Power

MichaelG.

… and to add what Michael says, with the belt speed reduction the available power is reduced even more by the belt losses.

Ian P

[Ian PParticipant @ianp]

I think the best thing that Ketan can do is to quote verbatim whatever accurate figures the motor/machine manufacturer makes available to him, but then have a few sentences of text in the catalogue explaining what the figures mean and what buyers should be aware of when comparing or making their buying choice.

Ian P

[duncan webster 1Participant @duncanwebster1]

Kewtan asks 'So how does one prove it ?, can anyone suggest a simple way?.'

I'd use a rope brake, pulley on motor, rope over the pulley, weigth on one end , spring balance on the other. This measures torque output, you can get RPM with a non contact tacho, multiply them together in the right units and you have output power.

Note all the power is converted into heat in the pulley, so be quick about it and use a hemp rope so it burns rather than melts. if you want prolonged runs you arrange a chanel in the pulley and spray water into it for cooling, but it gets a bit messy at this point.

[Michael GilliganParticipant @michaelgilligan61133]

Nah, Duncan

The Magtrol is much simpler

… Just a little pricey.

MichaelG.

[Ian PParticipant @ianp]

From a machine sellers point of view its just not realistic to do your own testing. It would have to be done at a certified test house (at significant cost) if one wanted to use the results as part of a sales pitch.

Even then, the figures from one dealers machine would only be of use to the buyer if they could compare them with figures from other dealers/machines so it would only work if all the dealers tested all their machines, just not going to happen.

Its the manufacturer that should (already does?) state the specification of the machine. In theory they would have traceable results that they pass on to their agents. I think the problems nowadays is the presence of multiple variations of similar machines being made in different factories with, I suspect, not all factories being 100% truthful.

Ian P

[Clive FosterParticipant @clivefoster55965]

It will be interesting to see if the development of l'affaire VW has any effect on the acceptance of this sort of "mine is bigger than yours" specmanship. UK and European law has lots of pretty big teeth which are supposed to deal with this sort of thing but are routinely ignored because its too expensive / too much hassle to make a prosecution stick and even then the punishment isn't effective. At the time of my motor episode I had informal access to high powered legal folk, the right person owed me big time for a favour, and the big beast consulted positively salivated at the prospect of getting some interpretations into law via what he claimed to be a slam dunk case. Like I was going to drop a hundred grand or so to prove fraud over a £55 (I think) motor. My experience is that legal beagles have no sense of proportion.

Given there are UK, European and International standards for pretty much everything you can think of I would hope that l'affaire VW will lead to all power and similar performance claims being, by law, to be made in relationship to a recognised standard whose requirements are accessible to any member of the public on demand. (Its surprising how many standards joe public simply can't get at even via library services.) Inducement to purchase by unsupported or irrelevant claims could then be considered criminal fraud with automatic custodial sentences for upper management of the companies responsible. Impossible to deal with the Chinese suppliers directly but there ought to be ways of cutting repeat offenders off at the knees by creative use of the import control legislation. I understand there is a lot of powerful legal stuff that has never been repealed, just kicked into the long grass and much precedent that has been tacitly ignored to avoid embarrassing les politicos.

Other side of the coin is does Ketan actually want the sort of customer who doesn't make specification checks or even bother to search out the relevant information. Nice though extra sales are the wilfully ignorant can be even more demanding than the excessively perfectionists (like me!). Given that Ketan made his good reputation by going that bit further and that bit better than other purveyors of similar equipment maybe its prudent to accept that most of those swayed by overhyped specifications are initially at least lost customers. Odds are that those disappointed folk who want something better will find their way to fora such this or other knowledgable advice "Should have gone to Arc Euro mate. Ketan will see you right". Being prepared to make like Rikki-Tikki-Tava and run and find out seems to be indispensable to anyone intending to make fist of this hobby. Hardly matters how fictional the motor spec is on the bought on a whim and left in the shed machine. Regrettable though it may be the fact is that the capabilities of the machines in the cheap seats always came with significant airbrushing and hype. I started with a Portass S which barely made it onto the lathe performance scale, about half a rung above Adepts.

Clive.

[Ketan SwaliParticipant @ketanswali79440]

A lot of what you guys are saying came up in my discussions with the SIEG and the competitors factory.

So, the guys at SIEG told me that they came across the same problem during last year, and they addressed it via

http://www.siegind.com/new/&i=3&comContentId=3.html

link. It is a bit Chinglish, but it gets the message across.

The motor making arm of the factory does have specialist equipment for testing the motor output as MichaelG suggests. The results are the output power figures which the SIEG factory state, and in turn which ARC states.

The figures which the big brand manufacturers state, especially the Germans when they buy from the Chinese manufacturers are what they want the factory – their sub-contractor to state on the machines – which as I said before, they are not wrong in stating, even though the idea is a bit questionable. In turn, the 'smaller' piggyback 'brand' manufacturers prefer to carry on using and stating input power, for better marketing. In the majority of cases, it is not the manufacturer who is specifying what is to be written for marketing. There are a few 'so called' Chinese factories which have been mentioned on this forum who also use the same input power marketing language, but on the whole, the importers do play a significant part in this….more then they care to admit.

Perhaps the way forward can be through educating the potential buyer in the ways suggested here, and stating both input and output power. I will discuss this further with the factory and see how it may be possible to address this in time.

Ketan at ARC.

 

Edited By Ketan Swali on 13/10/2015 20:29:44

[Neil WyattModerator @neilwyatt]

Prony brake.

Neil

[Ketan SwaliParticipant @ketanswali79440]

Clive,

With the right presentation and marketing patter it is possible to project a picture which a potential buyer chooses to believe or accept. More than 50% of the buyers are begginers, and many fail to understand the difference between AC, DC, 3-Phase motors with/without inverters. I include myself in this when I first started. It is a lovely learning experience for anyone. So, if questioned, one could quite rightly say, 'I am not an engineer' as the VW U.K. Chairman said to the Parliamentary Committee yesterday

Joking aside, the probability of the buyer figuring out anything about anything are low, because at the end of the day, the motor is just one component in the assembly, and experience or lack of, are regularly discussed on various forums. ARC has a reputation, and we try to be open as far as possible. We are no saints – depending on the buyers experience with ARC, and SIEG is no saint when it comes to assembly. One also has to consider 'expectations for the price paid' (a new tool in the sale of goods law amendment) which adds to the loopholes available.

I guess it boils down to the word 'choice'. The manufacturer – biggest or smallest chooses what they feel is right for them to say. The buyer chooses to believe what they want to. This is the one thing which will remain a constant.

Ketan at ARC.

[Author]

Posts