Wadkin PK 3 phase to single phase

[markturner]

Hi, I am moving my workshop from my business premises to my new house, which does not have 3 phase supply. I know you can run a 3 phase machine on single phase using an inverter, but that is about the extent of my knowledge...

Anyone here who knows about this? My saw is an old PK, what rated supply would it need and any recommendations as to the kit to buy?

Many thanks

 

[Jelly]

The first thing to do would be to ring your local Power Distribution Network Operator (UK Power Networks for London and the south east) and get a budget estimate for getting 3-Phase, to compare other options to.

It's often exorbitant, but sometimes you'll just get lucky and it's cheaper than going down the VFD or Rotary Phase Convertor route.

If the PK is the only 3 phase machine you plan to move, a VFD is likely the way forward (and can add Soft Start and DC Braking).

If you do (or could) want to run multiple three phase machines a rotary phase convertor is likely to work out as the better option.

You could also just fit a new single phase motor and DOL starter, and keep the old one in a box in case of future need, which may be the cheapest option, but is not without its pitfalls.

 

[DBT85]

On your motor will be an info plate telling you power, phase, and a few other goodies. If you're in luck it'll have a little triangle or the word delta on it.

 

[shed9]

Be aware you will likely need an appropriate RCD if running an inverter. This might be useful.

https://inverterdrive.com/howto/How-to-Use-Inverter-Drives-with-RDC-Earth-Leakage/
I run a few motors with VFDs and had to replace some MCB's for specific type RCD's because of tripping. It was a real head scratcher at the time.

Try and avoid the cheap VFD's, not the best and a bit of a skeet shoot.

 

[Fitzroy]

The PK manual says it’s a 4HP motor, you’d need a 3kw VFD which would need a 16A connection.

If your motor is dual voltage (ie you can rewire it between star and delta to change the voltage to 220v) then you just need a single phase to three phase 240v VFD. If the motor is single voltage 440v then you are into a more expensive electrical box to go single to three phase and voltage increase or you’re intervening in the motor to find the star point and solder on some new wires.

Post a picture of the motor plate to answer that question.

The main downside of a VFD is that it directly feeds to motor so reusing the machines original run and stop switch is difficult. The main upsides are it adds a soft start and you can wire in a breaking resistor quite easily.

Lots of conversation one forums regards cheap eBay VFDs vs. more expensive branded makes from the likes of inverterdrives. I have cheap eBay ones on my planer and bandsaw and have had no problems (famous last words) but mine get light occasional diy use. In a professional, time is money, environment I’d be buying a branded unit.

No experience of rotary or static converters.

Fitz.

 

[Farmer Giles]

I intend to run my PK off of a digital converter, it gives 415v out so no need to worry about delta, star will be fine. It is very unlikely that you will get delta out of a PK motor without delving into the windings and breaking out the star point. I already have the converter, it is a digital equivalent of a rotary converter, its not a VFD.

Here the data label on it

Its in quite a large box, I use it to drive my Colchester Triumph lathe which has a 7.5hp motor. Because I'm in the sticks and my nearest transformer on the pole didn't have 3 phase, this was far more economical. I would have a 3 phase supply if I could but this has been great so far. From a workshop point of view, it feeds the whole workshop so feels like a standard 3 phase supply. I just have to be careful not to run two big motors simultaneously, however its just me in there so unlikely. I have a 50 amp type C MCB for it.

I've only just moved the PK into the workshop but hope to power it up soon. I have a bit of fettling to do before I do that.

Cheers
Andy

 

[Vann]

...You could also just fit a new single phase motor...

Unfortunately on a Wadkin PK that's not possible. The blade sits on the end of the rotor shaft.

Cheers, Vann.

 

[shed9]

Unfortunately on a Wadkin PK that's not possible. The blade sits on the end of the rotor shaft.

Cheers, Vann.

You could get a machine shop to make an adapter and probably still be financially better off, have a brand new motor and less effort all round.

 

[wallace]

You could get a machine shop to make an adapter and probably still be financially better off, have a brand new motor and less effort all round.

The pk motor is precision mounted and has dowel pins to locate it, it spins an 18" blade, your not going to get a single phase motor any where near that quality and then get a custom made adapter machined up for the price of VFD. The motor will have 6 leads coming out so changing voltage should be ok

 

[Farmer Giles]

I stand corrected, I assumed they would be fixed star/415v at that age. Having dual voltage means a VFD would be the way to go. I guess I underestimated Wadkin, again.

Page 13 of the PK users manual shows the 6 and 9 wire motor wiring https://www.daltonswadkin.com/wp-content/uploads/2015/10/Wadkin-PK-Panel-Saw-Manual.pdf

 

[Spectric]

Hi

You can buy a single phase motor for less than a decent VSD, don't buy cheap VSD's. The digital converter is the better way to go rather than the invertor.

 

[Ttrees]

I can't say I've any bother with my far Eastern VFD's on my 12" tablesaw and 24" bandsaw....
Yes I fried the first one I had by bogging down the bandsaw, which was entirely my own fault just being a numpty (these things like a motor that is spinning at a good RPM)
My motor even got a bit hot when that happened.
And that VFD did have issues tripping with a pot installed also.

That's about the only negetive things that I recall, my 3hp TS will rip iroko using a 3.2 kerf blade at full height for an hour or so the odd time without fault.
A hundred quid well spent IMO.

 

[shed9]

The pk motor is precision mounted and has dowel pins to locate it, it spins an 18" blade, your not going to get a single phase motor any where near that quality and then get a custom made adapter machined up for the price of VFD. The motor will have 6 leads coming out so changing voltage should be ok

Assuming that the VFD route is done properly, then a decent drive such as Invertek, Siemens, IMO, Parker, ABB, etc is not going to be cheap. That doesn't include electrical wiring, panel upgrade, Type B RCD, mounting fixings, etc. VFD sizing is based on full load amperage not HP, VFD's don't produce HP or torque, they supply the relevant amps at a specific frequency that moderates motor speed so you will likely need something over 3kW. Also VFD's don't output sinusoidal waveforms but are generally PWM, it's close to sinusoidal but its not really pure and this can put a strain on some older motors in the case of bearings and wiring. My point is you may end up replacing the motor anyhow.
Compare this to the cost of a new 4HP motor, suitable mountings and an adapter and I reiterate that this may be a more viable option, even more evident if the original motor needs replacing sooner than later. Let's be honest, engineering has moved on a tad these days, even with that a lot of machining shops probably run the same Bridgeports used to machine the original parts on this particular PK.
VFD's are great but they aren't always the best solution. Sure you can put a cheaper VFD in there but this seems to defeat the point when resurrecting an aircraft hanger sized and prized saw like a PK.
Not saying it's the way forward, just putting out options to be considered at an early stage is all.

 

[Spectric]

Hi This synario shows that the VFD did not have sufficient internal protection, a good VFD will detect overload and shutdown, it will also be monitoring the drive devices whether they are Igfets or Mosfets and again if the junction temperature rises it will shutdown to protect the devices rather than go into meltdown.

I have seen to many fires caused by poor quality electrical/electronic systems and don't take any chances, especially in high risk zones such as places with wood dust and the like.

Yes I fried the first one I had by bogging down the bandsaw, which was entirely my own fault just being a numpty (these things like a motor that is spinning at a good RPM)
My motor even got a bit hot when that happened.

 

[Ttrees]

I won't argue with that Spectric,
it sounds too good to be true though, so I must question this, if I may?

...Presuming everything is installed and checked over by a qualified person...
Are you saying that you cannot damage a motor by bogging down in a cut if you have a fancy VFD?

I always have a feel of the motor if I am using it for considerable amounts though,
and have my VFD's enclosed in a sturdy metal box, with proper cable glands and crimp on terminal connectors.
Good enough for me.

With something like a PK though, I suppose it depends if its more of a functional work of art or a workhorse.
Jack Forsberg is in both of those camps with his machine.
A cheapo VFD might suffice if its only the OP who would be running the saw,
if not then it may well be considered abuse to let some un-knowledgeable (in regards to special motor/cheap VFD combo) employee go to work, fooled by the fact that the machine looks invincible.

Cheers
Tom

 

[Spectric]

Hi there

A "fancy VFD" will provide several levels of protection and one of these is overload current but it is a parameter that needs to be set to the right value. Before modern electronics motors were driven using relays that would trip on overload but now the VFD will perform this task. With larger motors they will have a thermistor in the windings that allows the VFD or softstarter to cut faster as it detects winding temperature rise. Many low priced electrical / electronic goods reduce cost by reducing or not having these safety features, Lithium battery chargers is a good example, cell failure and charger keeps going until the device either just cuts out or goes bang, Lithium batterys can put on a spectactular show!

From an electrical installation perspective the protective device will protect the supply cabling, which has been sized to be capable of carrying the full load current in the event of a short circuit but with a motor overload the current is often not sufficient to operate the protective device and is why motors are fitted with other protective devices so that the wiring is not damaged, in your case the VFD became a protective device. In industry motors are operated from dedicated motor control centres which provide everything needed to operate one or more motors, and frequently from remote locations using networks.