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Help needed - 3 phase converter advice

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Eldi76

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Good day all,

I have a new Sedgwick TA315 saw bench with a 3-phase motor, and currently it is running smoothly from a 3-phase supply. I will soon move the saw bench to a residential area, with no access to 3 phase supply.

So I would obviously need to buy a phase converter to run the saw bench from 240V supply, I have read a lot about this topic in the forum and elsewhere, and narrowed my choices to either a rotary phase converter or a digital phase converter.

However, it seems that the digital unit is extremely expensive. I contacted Drives Direct, and they explained that for choosing the right converter I would need to take the Sedgwick motor HP (it is 4HP), times this by 3 to get the starting load (=12 HP) and go for the next size up – 15 HP. The price for this digital phase converter is £4500 - £7400 (!!), depending on the specific model chosen.

My questions are: Does anyone have a Sedgwick TA315 or similar saw bench and encountered the same situation? Is there a good reason to prefer a digital phase converter over a rotary unit (except for the noise problem with the latter)? I must note that in the future I’m going to have an old Wadkin FM planer-thicknesser in my workshop and hopefully a Wadkin RS lathe, so the converter should be able to run all machines (not simultaneously, only one at a time).

Any help would be highly appreciated!

Eldi
 

Sideways

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Decide whether you have the knowledge to do electrical maintenance safely.
Look at the nameplate of the saw. See if it says 230V as well as 400V.
If it does, you are in luck and can buy a 3kW rated single to 3 phase variable frequency drive.
You should get a European one for under £300, a Chinese one for under £200
The VFD needs to be installed properly according to manufacturers instructions, and the motor rewired from Star to Delta inside the motor terminal box. You then have to program the VFD, but once done, a decent VFD can start your motor without ever exceeding the full load current. No big startup surges to worry about ever again.
If you are new to this, I would suggest a european branded device as you are more likely to get a proper set of instructions that you can a) read and b) understand. The job is more complicated than rewiring a plug....

For other / future machines, buy single phase or swap the 3 phase motors for single (cheapest approach), or rewire them with individual VFDs on a case by case basis.

If you go for a static or rotary phase converter, they are rated in terms of the maximum total load they can supply, and the largest single motor that they will start (and run). I would expect a unit rated maybe 6-7HP total to be able to start a 4HP motor. Remember the startup surge only lasts a few seconds. Most devices are designed to handle a certain level of overload for a few seconds (for example, the VFD's in my shop are designed for +50% current overload for 30 seconds).
 

Eldi76

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Decide whether you have the knowledge to do electrical maintenance safely.
Look at the nameplate of the saw. See if it says 230V as well as 400V.
If it does, you are in luck and can buy a 3kW rated single to 3 phase variable frequency drive.
You should get a European one for under £300, a Chinese one for under £200
The VFD needs to be installed properly according to manufacturers instructions, and the motor rewired from Star to Delta inside the motor terminal box. You then have to program the VFD, but once done, a decent VFD can start your motor without ever exceeding the full load current. No big startup surges to worry about ever again.
If you are new to this, I would suggest a european branded device as you are more likely to get a proper set of instructions that you can a) read and b) understand. The job is more complicated than rewiring a plug....

For other / future machines, buy single phase or swap the 3 phase motors for single (cheapest approach), or rewire them with individual VFDs on a case by case basis.

If you go for a static or rotary phase converter, they are rated in terms of the maximum total load they can supply, and the largest single motor that they will start (and run). I would expect a unit rated maybe 6-7HP total to be able to start a 4HP motor. Remember the startup surge only lasts a few seconds. Most devices are designed to handle a certain level of overload for a few seconds (for example, the VFD's in my shop are designed for +50% current overload for 30 seconds).
Thank you.

I think a VFD may be a possible solution for the Sedgwick saw bench, I need to check the motor nameplate.

However, as I will have a Wadkin FM made in the 1950s or 1960s and a Wadkin RS lathe, both have 3-phase motors which I have no idea whether they can be rewired from Star to Delta and run on 240V, I am looking for a more general solution to my problem.

I would say that I’m after a converter that is as close as possible to a 'plug and play' solution, something with a 3 phase output plug that I just need to connect my machine (whatever that would be) and be able to work. But the price of the digital phase converter offered by Drives Direct (£4500-£7400) is beyond a reasonable expense for me.
 

clogs

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Sideways
if the motor was NOT 240-440 capable, would it be cheaper to buy a new motor that is and then go for the VFD...
just interested...ta....
 

wallace

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I cant believe you would need a 15hp converter to run a 4hp machine. My old static is only 7.5kw and it runs spindle moulder which is 5hp with no problem at all. It struggles starting my 18" planer but once up and running it runs wide boards no problem.
 

Eldi76

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I cant believe you would need a 15hp converter to run a 4hp machine. My old static is only 7.5kw and it runs spindle moulder which is 5hp with no problem at all. It struggles starting my 18" planer but once up and running it runs wide boards no problem.
Thank you, this is what I was thinking. Hence I was very surprised to read the email from Drives Direct...I assume that they take into account the startup load/current that the saw bench withdraws.
With the prices of the digital phase converter, I am now thinking to get a rotary phase converter (despite the noise). Any recommendations? Has anyone used the rotary converters by Transwave? I believe that Transwave still makes the converters in the UK.
 

Fitzroy

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If you’re located luckily the installation of a three phase supply could be in a similar price range. That’s the ultimate turn key solution, an email to your supplier could get lucky.
Fitz.
 

Artiglio

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I have a rotary converter by “Converter king ltd”, off top of my head can’t remember exact specs but its around an 11hp constant and 15 hp ( peak/startup), well oversized for the kit i have , max i’ll ever has is extractor and either saw,spindle,planer at any one time (7 kw for two) though theoretically it’d drive more quite comfortably to my mind the extra cost was worth the future proofing.No hesitation on startup.
Aside from connection to your consumer unit ( ideally a 60amp supply, but i run mine on 40 amp) its all plug and play, mineplugs into a 3 way distribution board which has 3 plug in outlets.
 

Wisewood

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I did exactly this conversion on a TA315 many years ago. I first tried the Chinese VFD option and after a week of faffing trying to get it to work in sent the thing back as faulty. Only then did I notice that it's box was already sporting several other return codes!
By that time I was fed up though so I went for the new motor option. What I hadn't appreciated was the difference in size. A single phase motor is much bigger than a three phase of the same size. I did manage to make it fit but required trimming of the fan cover cage and the side panel is now permanently off the saw.
It also required new switch gear as the lower voltage will obviously mean more current for the same power. The same principle meant I even had to replace the power cable as the voltage drop became too much on startup, tripping a cutout.
If doing it again I might go for the VFD again but the solution is have ended up with has now performed solidly for about ten years.
 
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Wisewood

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I think I need to turn off my autocomplete! Post edited - might make more sense now...
 

Sideways

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Sideways
if the motor was NOT 240-440 capable, would it be cheaper to buy a new motor that is and then go for the VFD...
just interested...ta....
New motors - single or three phase doesn't make a lot of difference - typically run around £100 to £200 for a decent budget unit like a TEC made in Shanghai and easily bought online from a UK supplier.
It cost me about £180 for a new 3kW 3 phase model to put in my own tablesaw as the existing 4kW motor wasn't dual voltage.

If you go 3 phase, you then have the cost of the VFD. A Chinese one for the same price as a motor, or a European one IP66 fully sealed against dust and damp for two to three times the motor price.
I have an electrical background and simply prefer the combination of VFD + 3 phase motor because there is no startup surge to deal with, the option of speed control and all the other good stuff. Sometimes too, a 3ph motor is physically smaller than a single phase of the same power and is the only option for the space available.
I sometimes pick up new-old stock / surplus / or similar electronics at less than full price. This is not an option for a lot of folk because the capacitors in a VFD gradually deteriorate in storage and an old stock one may just go bang on you the first time you connect it up. You need knowledge and specialist kit to deal with this.
 
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Spectric

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Hi

A motor change is the easiest and possibly the cheaper option especially if it is belt driven.

Even if the motor cannot run 230 volt three phase, use a digital convertor and you will have 400 volt three phase but without the variable speed which you don't need on a sawbench. The rotary convertor is the ancestor to the newer digital convertors. Another bonus is that the convertor can run more than one load providing it has the power output wheras the invertor is a single machine. In my opinion the convertor is a better option than a VSD but you will miss your proper three phase supply.
 

Eldi76

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Thank you all for raising different possible solutions.
Changing the motor is out of the question as my saw bench is still under warranty and replacing the motor will void the manufacturer's warranty.
In addition, I know that I will have more three phase machinery soon (old wadkin planer-thicknesser, lathe, morticer) so I am looking for a more general solution to future-proof myself.
I believe the rotary phase converter is the the best option - in terms of cost and ease of installation - it is basically a plug and play converter, no need for rewiring star-delta and that sort of stuff.
Thank you!
Eldi
 
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