85 quid is about 300 hours running, so that’s a month of 12 hour days. You don’t need a smaller motor you need w holiday

Agree with above, 3 ph every time.

Brian

Um, look for a fault or some other cause unless you've been been working the lathe really hard. At 20p per kwh £85 would buy you 212 hours continuous operation under full load. That's about 3 working weeks of 10 hour days cutting metal flat out. Depends on what you're doing of course but few hobby lathes are used like that.

Also motors shouldn't consume full power unless actually doing strenuous work. Unlikely on a lathe, partly because most cuts aren't that deep in tough metal with blunt tools and partly because full power is only consumed while actually cutting, which is intermittent. My lathe has an 1500W output motor but I rarely consume more than 600W during a typical cut. I'm not particularly delicate, and have hit 1400W cutting with power traverse and carbide going 1.5mm into mild steel. From memory, idling consumes about 150W, and driving the lead-screw & gearbox costs another 150W. Even so the lighting in my workshop uses more electricity than the tools.

If you're really using that much power to cut metal, switching to a smaller motor is a bad idea. It won't save money and cutting the same amount of metal will take proportionally longer.

As we're heading into winter have you been using an electric fire, perhaps leaving it on overnight to defeat condensation? Or is the lathe unusually stiff, you might have some bad bearings or a lube failure?

Dave

I agree with Simon Williams, that seems like a lot of power useage. assuming 17p per kW hr thats 10.6 hours per day running and loaded! Are you really working those hours, or have you got some other electrical problem, like for instance, a faulty immersion heater which is not RCD protected? To answer your question always go for three phase, they are more efficient and deliver smoother torque than single, and with the vfd you can do soft start and speed control too. Do you have a smart meter ? there has been talk about the smart meters ability to apply higher usage to inductive loads like motors which have poor power factor, but don't know if this is really happening (yet) or not. With a VFD in circuit, this may not be recognised by the meter as actually being an inductive load. Are you on the end of a long supply line in a remote area? If so, volts drop is a possibility too. Try the 3 phase/vfd motor for a month, and see if there is a marked drop in your consumption, if not, look for another problem!

Phil

Ha! You are probably the person who needs a smart meter – I knew there was one!

Wouldn't hurt to get a smart plug and test various appliances to see how much they really use.

Neil

Plenty of smart plugs on Amazon, and probably E-Bay too, for around £12 to £20. I shall get one if and when I have an issue that simple maths and specification data won't resolve.

Before buying tho' do verify how much space and where is needed. Most of them look as if they will at least partially obscure the switch. CPC (Farnell) sell a nice looking one with the display and control buttons below the plug part so the cable hangs down over it. D'oH. Supposed to be professional outfit yet sell summit with such an obvious design blooper. A mistake that obvious makes you wonder how good the innards are.

Clive

All joking about tumble driers aside, the OP has raised an interesting question regarding the relative efficiency of single and three phase motors.

Given that a single phase motor is a fairly nasty electrical load, but a three phase motor on a single phase supply suffers the conversion inefficiency of the VFD, there's likely not much to choose between them in terms of converting cost of electricity into work done.

Does anyone have any in situ estimates of the actual efficiency of power out over power in for the sort of size motor (1 – 3 HP say) we are likely to encounter in a home workshop?

Best rgds Simon

or look at this?http://ijcee.org/papers/010.pdf

As a machine tool motor in a home workshop is most likely to spend much of its time only lightly loaded then its efficiency is going to be poor. Rather like the optimistic fuel consumption figures for a motor car are only realised under ideal conditions an electric motor will only reach its maximum efficiency under optimum conditions. I think cutting the plug off the tumble dryer would have the the most impact on your electricity bill (and mine).

Mike

mark rand, that is exactly what it says in my post! their poor showing in the efficiency stakes, and the extremely high retail cost (£825.00 for the Siemens) shows how efficient they actually are! heat pumps may work, but add to complexity,. A ducted TD takes already warmed air from your house, heats it some more, it absorbs the moisture in the clothes, and then gets thrown out the duct, a condenser one has to cool the air down to its dew point every time it is cycled, then reheat it the actual efficiency gain is very marginal at best, as is witnessed by the poor results in the league table. I wonder if it would last long enough for you to save the difference in retail price, I very much doubt it!!

Sean, an important question that no one has asked yet:- What lathe is it?

1/2hp is suitable for a Myford sized lathe, but 3/4 is better for even an ML7 (I speak from experience). A lathe that's sized for a 2hp motor is not going to be happy with larger work or more aggressive cuts if hobbled by a 1/2hp motor.

In terms of power consumption, the losses of a 2hp single phase motor will be greater than those of a 1/2hp single phase motor or 3ph motor + VFD, but the difference is likely to be no more than 25-50W. I.e.. 3/5 of 5/8 of F-all, as one of my colleagues used to say.

The suggestions of getting a plug in power meter are your best bet. They are cheap these days (especially when Aldi or Lidl have got them on sale, but also from a number of online sellers), and can give you a good idea of just what in the house is eating the power.

Before you do anything else though, have you got an immersion heater that someone's turned on?

First question might be : what power motor was on the lathe, before the last month?

Second is where the power has been used. Our leccy bills always go up in autumn/winter. But not by £85 each month.

Regarding condenser or vented tumble dryers – at least the heat rejected by the condenser type heats the property – not just rejected to the .

Jumping to unsubstantiated conclusions is often proved wrong on proper analysis of the situation.