Selling Machine Tools - Single Phase vs. Three Phase Price Differential.

I'm looking at selling my Harrison Milling Machine in the near future, and am trying to decide if I will see a return on my investment by converting to single phase before I do.

Ultimately I need to realise as much value as possible to refill the hole in my bank account left by the mill that will be replacing it, but it still has a few electrical kinks that need to be worked out before I could sell it on in good faith (given it was rescued from a scrapheap).

If I'm doing that, it's probably not much bother to install a VFD or switch the motor for a single phase one, the question is if it adds enough to the value to justify the cost of doing it (ignoring my time, because this is my hobby after all).

My experience has always been that single phase machines command a price premium, but it's hard to quantify how much.

There's also a question of if having features like the DRO and vertical head (albeit not the Harrison one) would already put the machine's value up towards the top end of the market, and if offering delivery would push the value up further.

Any advice willingly received.

Edited By Jelly on 01/04/2023 21:54:47

A VFD is cheaper than another motor, but if you figure out the electrical issues, it should sell for more than a single phase machine as it effectively is then a single phase machine. But sometimes it is alot of work for the return. If you have the time that would be the way togo. Out here in NZ, 3phase machines go alot cheaper than single phase, mainly due to the costs now to put a single phase motor and then the wiring that will need to be done.

Not many homes have 3phase power. I was lucky in building my house to actually have 3phase power. Some are now putting in a 3rd phase for charging electric cars, but not sure if the 3 can be used in a workshop for example like I have. The councils out here consider if you are putting 3phase power for a workshop that the purpose is for commercial machines and then working from home.

Adding a DRO will increase the number of watchers, but won't return the costs of installing it all. Leave that for the next owner. Unless you can get a really good deal on a reliable DRO then instal as with a DRO makes the machinetool more desireable.

Make sure that it is really clean. Clean machines are more desireable as well, no matter how old it is.

First question is: 220 or 440 volts?

+1 for fitting a VFD. The import VFD boxes are so cheap that it's a no-brainer decision. If it's a permanent star connection the 380 V breed will do fine. Basically one less problem. Buy, move, wire and go is attractive. Extra value might not quite cover the extra cost but will certainly lead to an easier sale. One less lever for "How about ......." ££ less than the asking price.

Fitting a DRO is generally a pain due to the accurate mechanical work involved in getting the scales lined up. I suspect that value wise a DRO is either zero sum at best where the extra value equals the cost of the DRO or loose a bit. I'm inclined to think that a high end DRO set up only adds the price of commodity E-Bay / box shifter set up.

Clive

I would go with a VFD and give your M/C a good clean before trying to sell it, makes it so much more attractive, some jokers don't even bother to clean the swarf off their for sale machines, sort of tells me how they have been looked after.

Tony

Can't say without locating the data plate on the motor by shoving a smartphone and a torch into the machine base; I've always run it off 415v 3 phase, but that's not to say it isn't a ∆ 240v - Y 415v motor in there.

Is this implying that:

• if I can convert it to run ∆240v off a 240 single phase to 240 three phase Inverter it will probably make financial sense,
• but if it needs a 240 single phase to 415 three phase Inverter the cost wouldn't be recouped.

The DRO is already fitted as it's something I found useful, I will certainly chuck the cost of the DRO onto the asking price but perhaps more.

Second question, how many kilowatts?

My take:

Comparing 3-phase to 1-phase motors, 3-phase wins hands down. They run smoother, are far more reliable, have more torque, don't get so hot, and have a better power to weight ratio. With electronics they are easy to speed control. In contrast, a single-phase motor is almost the worst choice for a machine tool. They vibrate, don't like stop/start operation, torque is the low side, and they have delicate features that go wrong: thin start windings, centrifugal switches, and capacitors. No speed control.

In the good old days, single-phase motors had one overwhelming advantage - they run off ordinary single-phase mains, with acceptable performance. The problem with owning 3-phase equipment in days of yore was finding a way to power it.

In the last century getting 3-phase into a workshop was often tricky and expensive, maybe requiring a large noisy and moderately unreliable box. No speed control. So most customers preferred single-phase machines because they were convenient. Plug and play.

All change today. The availability of affordable VFDs changes the game entirely. Now you can buy a small magic box that plugs into ordinary single-phase mains and converts it to 3-phase. And more! Speed control, soft-start and braking etc. There are limitations, but VFDs are mostly straightforward, especially if the simpler consumer type are bought. Or a package from one of the specialists.

Whether there's a premium on a particular motor type probably depends entirely which buyers turn up on the day. Anyone comfortable with VFDs will likely want to buy a single-phase machine cheap so they can replace the motor. Another buyer might desperately want single-phase to fit into his workshop.

I guess the market for single-phase is in sharp decline. It's for people who need a machine but don't trust electronics or want to learn new tricks, or just want to plug in and get on with cutting metal. I feel anyone who is comfy with electronics and wants to get the best out of the machine will want 3-phase. Newcomers are likely to be happier with electronics than my generation. (Despite 60 years progress I still believe Valves are more reliable than transistors, because the early transistors of my youth were so delicate.)

What the balance is at the moment I don't know, but I suggest the reason single-phase machines commanded premium prices in the past is severely undermined.

Today's electronics affordably speed-control brushed DC, 3-phase and brushless motors. And these types all out-perform single-phase motors.

Dave

For me conversion of a 3-phase machine to single phase means I'd pass. I suspect that the availability of cheap VFDs means that any single phase premium is a lot smaller than it was. Even for hobby applcations my time is valuable and is taken into account when deciding what to do, and how to do it.

Andrew

I think you've summed up the situation nicely there, even 3-4 years ago I wouldn't have been asking the question, because it would have been obvious that single phase would command a higher price for a machine small enough for a home workshop.

Looking at recent sales on eBay and elsewhere however it's not nearly as clear cut anymore.

.

Oh and 2kW, which is firmly in the "chocolate box VFD for under a hundred quid" range.

I am in agreement on that, even if I wanted VFD converted equipment, it's something I would want to do myself so I understood the modifications which had been made (not so bad on something as simple as the Harrison, but on the mill I've just bought, it would be nightmarish trying to trace undocumented modifications).

Whilst I initially disregarded time, you do have a point:

For me to do a VFD conversion I was happy selling I would probably need to invest a substantial amount of time on wiring the controls, finding a sympathetic way to add speed control potentiometers to the control panel, programming the VFD, packaging it all into an enclosure, and updating the wiring diagrams.

That would only get worse if I was to program it to run the table feed and coolant pump motors (via momentary buttons triggering stepped increases in the power output and latching control signals from the VFD's auxiliary outputs to contactors), although ideally that would need an additional VFD for the auxiliary loads).

The more I think about it, I am not comfortable selling it with a "eh, good enough" VFD retrofit, and doing a good VFD conversion would not be cost effective, so sorting the electrics out for three phase operation and leaving it at that would be best.

Edited By Jelly on 02/04/2023 12:05:09