View Full Version : transwave static conversion to rotary three phase conversion ?

Alistair Hosie
02-28-2015, 03:33 PM
Hi I have a transwave static convertor 5.5 kw or 7.5 hp I use this to power my big wadkin sliding table saw,which has a large motor also 7.5 hp and a much smaller scoring motor too.
I converted it sort of after talking to transwave many years ago by adding an inline motor,at the very start of the process.This motor is running without any load as I was advised to do.However the biggest three phase motor I could get at the time was approx 3 or 3,5 horse power.It works but I have often wondered if it is working properly.A few days ago I aquired a nice big 7.5 three phase motor compton parkinson type.I intend to take out the 3 or 3.5 as it might be and replacing it with the bigger one.Will this work better smoother and should it now be technically a rotary convertor?Alistair

J Tiers
02-28-2015, 03:45 PM
It sounds like it was always a rotary converter. Just a smaller one. And with a larger idler, assuming the rest of the "transwave" circuitry can handle the larger motor, it may be capable of driving more total load power connected to it.

Alistair Hosie
02-28-2015, 04:31 PM
Hi the transwave I am using is 5.5kw or 7.5 hp output this is the same as the new about to be fitted idler motor which is also 5.5kw or 7.5hp.
The last idler was fitted to my transwave and was only around 3hp or max 3.5 hp with a 7.5 hp static capacity.
I think or hope changing to the larger 7.5 idler from the old idler as said currently approx 3hp to match the transwave max output also 7.5hp will work better.Thanks for reply.So far Alistair

Alistair Hosie
03-01-2015, 08:01 AM
Anyone else with experience please chip in LOL Alistair

J Tiers
03-01-2015, 11:34 AM
OK, I went and looked at their literature on-line.... I looked specifically at their archived static converter info, since yours is presumably older.

If you have a static converter, AND it is rated for the motor size you have, it should just work. You shouldn't have to connect an auxiliary motor, unless your machine will be reversing its motor and you don't want to stop the motor and let it come to a halt before reversing.

They term this a "pilot motor". For that type service, they do suggest the motor should be at least equal in size to the machine motor. However, they also have limits on the multi-motor total load. For the 5.5kW /7.5 HP, they list the max load as 9.2 kW 12.5 HP. Technically, you would be connecting something over 15HP, including the smaller motor.

Most likely, if you have just the 7.5HP and smaller motor, the added load of the 7.5HP "idler" or "pilot", is not quite going to put you over, it doesn't put as much load on teh system as a fully loaded 7.5 HP motor. And you won't be using all 7.5 HP, most likely.

The result is probably only going to be a little better starting. Unless, of course, the machine has to reverse under load. A table saw should not have to do that, so really you likely do not need the extra idler/pilot, or at least do not need a full powered pilot motor.

Maybe the feed motor (if it has one) has to reverse.... But during that time, the saw motor should act as a pilot, since it won't be cutting when it is reversing.

When you connect an auxiliary or "pilot" motor, you essentially convert the static converter to a rotary converter, as I said above. The benefit of that is to make the 3 phase output a bit better, and probably increase the maximum power you can use from the machine motor.

However, I understand from the literature, and from seeing the Transwave innards also, that they use some electrical components to work with the load motor and improve the output relative to a plain static converter...

A plain converter starts as a "fake" 3 phase, and then runs as single phase. The transwave static converter seems to run as a partial 3 phase, a bit like the "Steelman" conversion system.

Bottom line is if you are not having problems now, the larger motor probably will not make any significant difference, AND it poses a question about the maximum connected total motor HP allowed on the Transwave unit.

03-01-2015, 01:04 PM
Here's my take on it (having had a very similar conversation with Transwave at Harrogate ME shinding last year) and as the user of a transwave static converter. The static converter as is gives you 2 of the 3 phases via capacitors which is enough to spin the motor up. Once running the motor generates the third phase, which feeds back to the converter, to allow the 'boost' relay (used in starting) to kick out. Bog the motor down, rpm falls, third phase drops, relay kicks back in.

Now add the idler motor. The third phase is now generated in the idler rather than the machine motor, so the machine motor 'sees true 3 phase'. However bog the machine down, now the load goes onto the idler motor as well. Which is being driven by the......you've got it, static converter. There ain't such a thing as a free lunch.

So my understanding was as follows. The idler should be the same (or larger) than the largest motor being driven, but the sum total of motors (including the idler) cannot be greater than the capacity of the converter. At least, that's how I understand it, YMMV, of course.


Alistair Hosie
03-02-2015, 07:20 AM
Thanks guys I tried without success to use an invertor, and also a transwave static convertor, on my Smart and Brown 10 24 variable speed drive.I eventually at the time was told I would need to buy a rotary convertor ,as the static and invertors would not work on this.Which I did a brand new one at 5 hp cost me almost a thousand pounds and I use it for most of the three phase machines in my metal shop.I was told then by transwave and others at the time, it would not run because of the variable speed drive only a rotary semmed to do it.I since then bought a very powerful sisxteen inch blade 7.5 hp wadkin sliding table saw now situated in another building my woodshop.I was told as said a while back it if fitted with a motor first in line without load it would also run much smoother and be better for saw and anything used in the woodshop as well.I also have three invertors one directly fitted to my milling machine in the machine workshop . as I was advised to do by the chap who sold it to me a nice gentleman.I do this to save changing gears in the gearbox all the time for speed control,which works out great.I use the other two invertors for speed control on my wood lathes of which I have three.a small delta for pen making a short bed viceroy for large bowls and another one which was originally a copy lathe with a six foot bed.I use this for most of my woodturning.As said to date I have used the three phaseinvertor with a three pahse motor of appox 3.5 hp well short of tjhe wadkins 7.5 hp motor .I will change it to the new smoothing motor which I got a few days ago it is 7.5 hp.Thanks guys Alistair

J Tiers
03-02-2015, 08:05 AM
Wait a second here....

Inverter? I thought you were talking about a transwave static converter.

The inverter needs (as you know) no added motor