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Converting Table saw to 240volts

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ElTel

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Does anyone have experience of converting a Startrite 275 Tilt Arbor Table saw to 240v. Are the motor mountings on a foot plate similar to the Wadkin AGS10 which appear to make changing the motor quite straight forward?
Any answers/diagrams/photos would be greatly appreciated.
 

dickm

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Don't know that saw in detail (come back Scrit for an authoritative reply!) but I would be surprised if it didn't just have a standard foot mounting motor. My Startrite 352 bandsaw has a flat plate for the motor, and I converted it from 3-phase to single phase with no problems. But don't forget you will need a new starter unit as well as the motor.
And if the motor is 3-phase that can be delta connected, save it in case you ever want to make a variable speed unit by adding an inverter :)
 

BillP

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You could always consider building your own 3 phase converter. It is not really difficult. There are some really good guides available on the web. I have built two. It only takes a little bit of electrical knowledge and some simple wiring skills. If you are interested in trying I would be happy to share my practical experience.
BillP.
 

9fingers

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BillP,

Where do you get the 240/415v transformers from? Despite all sorts of attempts to get cheap ones - they have all fallen through leaving the only choice to pay fancy money. Transwave will sell ones as used their converters.
Maybe you are making converters for delta connection only? Much easier to source the bits. Still not found cheap voltage sensitve relays for auto start switching though. Have you?

Bob
 

BillP

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Many motors are dual voltage. They will run with either 380/415 or 240V 3 phase. Star or delta. I have built 240V 3 phase converters based on a 3 phase motor. The line voltages are balanced by carefully selecting the capacitors. I now run a Startrite Tilt arbour saw and a Medding pillar drill using this supply. As long as I start the phase converter without any load I never have any problems. Both tools have Brook Crompton motors. Whilst neither is new they were both built as dual voltage motors. I understand the problems with voltage changes from 240 to 380 but the dual voltage motors overcome this problem. Does this help?
 

9fingers

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Thanks Bill,

Yes I understand the basics of converters with a motor to balance the phases as well as dual voltage motors. Although I've not built a converter with its own motor. 240 v delta connections make life much easier.
Do you switch in extra capacitors to start your converter motor or will it get going without?
Most of my 240v 3 phase kit I run using inverters as I need variable speed.
One day I will get round to a 415 volt converter as I have a 50 year old pillar drill with a 4 speed 3 phase motor and cannot be connected in delta. I have read that multi-speed motors on converters are best with motor based ones.
The motor is heavily integrated with the mechanics and the gearbox so not practical to put a modern motor onto it.

Bob
 

BillP

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Dear Bob,

I have found that the motor run capacitors are critical for the running of the phase converter. As long as the capacitor between the live 240V in-coming and the pseudo third phase is a higher value than the capacitor between the neutral 240V in-coming and the third phase the motors always start and turn in the same direction. I don't know if this is universally true but it is my experience that this is the case. I don't use additional capacitors to start the motor. It does mean that there is a high current as the motor starts but the power supply to my workshop copes with this brief load.
I have thought about using a two-button starting system in which I have an additional start capacitor which is switched by pressing a second button for a few seconds but since my system starts without this I have not bothered to build it in.
I did speak to someone recently who had bought a transformer from one of the phase converter manufacturers but I don't know how much he paid for it. He was keen to have a 415V system rather than changing all of the coils in his motor start conntacters. I will get in touch with him and ask him how much it cost. Cheers, Bill.
 

9fingers

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Hi Bill,

Happy New Year and thanks for your latest post. I've not seen a design with run capacitors between both live and neutral and the pseudo phase.
I've only put capcitors between live and the pseudo phase before. I generally reckon on 40 mFd per horsepower for run and between 80 and 300 mFd per hp for starting on load.
What sort of capacitor values do you use in live-pseudo phase and neutral to pseudo phase?

With your extra motor there seems no need for starting capacitors but direct on the machine motor they are necessary and you can either do a two button start on a one button with the start capacitors only switched in whilst you have you finger on the button. The third way is the voltage sensing relay which looks at the voltage between the phases and switches in extra capacitors until the 3 phases become reasonably well balanced.

Best regards

Bob
 

BillP

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Hi Bob,
When I built a converter using a 1.5 H.P. motor I used 80 micro farad between the live and 3rd phase and 50 micro farad between the neutral and the 3rd phase.

When I tried it first I only used a capacitor between the live and 3rd phase. The motor would start and run but it was very rough. The voltages between the phases were not well balanced. It still worked with the Startrite saw but was very noisy. When I had some time, and extra capacitors to play with, I spent an afternoon changing the configuration and checking the voltages under a nominal load. I found that the 80/50 combination gave very good voltage values and the converter motor was smooth and quiet.

The extra capacitors in the neutral to 3rd phase certainly helped in this case.

Cheers, Bill.
 

9fingers

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Thanks Bill,

I'll file this away mentally until I get round to making an 415 converter.

Thanks for your help

Bob
 
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