Scroll saw motor 3 phase to single phase??

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Bluekingfisher

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meddings-scroll-saw-serial-jsb-07240-t111299.html

I hope I have added the appropriate link?

Basically I bought a Meddings Scroll saw (photos in the link) with a 3phase motor. The plate shows 220v and 380 - 440. Can the motor be reconfigured to run on 230v supply? And if so, will the original switch (as shown work).

I posted the query on the scroll saw board, although I suspect more likely to receive a response from the general woodworking board.

Thanks in advance.

David
 

Myfordman

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Good new bad news routine.
Yes the motor can be rewired to 230v but it is still a 3 phase motor needing three phase power.
David, If you can get a cheap inverter then that is easy.
For low power motors like this I often build a static converter but you need to know what you are doing for that. I'm reluctant to supply details publically for a diy build as people will have wildly differing electrical skills and safety is critical.
Motor change to single phase is not cheap as you have an imperial sized motor there and whilst they are still available, they sell at premium prices. Converting to a metric motor will require pulley to be bore or sleeved to fit which is an engineering job or the shaft to be machined which will compromise the motor warranty.

Hope this clarifies the position

Bob
 

Bluekingfisher

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Tom/Bob, thank you both for your response and information, very much appreciated.

I think consideration to an inverter at this time is secondary to perhaps replacing the motor?

Since my original post, Meddings have responded to an email I sent regarding a couple of other non essential replacement parts I was looking for. From the serial number I provided They informed me the saw was built in December 1977. In addition, they sent me a parts diagram and operators manual in PDF format. Unfortunately the one item I do actually require was shown on the parts diagram but no Part number, as the photocopied page had erased the last two part numbers for one of the parts I require. Just my luck. Although they do still carry some spares for this saw I was advised to contact them prior to ordering as not all parts are still available. I mention in case someone else has a similar saw and maybe looking for replacement parts.

However, Bob, you mention a replacement motor? I believe I have a compatible replacement, an old Brooks Compton motor of a similar amperage, albeit possibly a little older. I currently have a small polishing mop attached to it and was actually using it today and still runs wonderfully well with a quiet hum. It looks to be very similar in its dimensions, although I will now have to double check the shaft diameter and frame size tomorrow.

The other issue is the switch, I don't know from the photographs you are able to see the switch with the incoming wires? From the parts lists it is shown as a Three pole switch. Therefore would the existing switch be compatible with a new single phase motor?

Thanks again gents

David
 

Ttrees

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Similar amperage you say
But...Is it a two or four pole motor? (2 pole normally 2800 to 3000 RPM) four pole half that.
VFD's are cheapish for small motors

I wonder if variable speed would be any use on a scrollsaw

It would be a pointless load of faff, if variable speed is pointless and you have a suitable motor allready.
 

Bluekingfisher

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Good point Tom, I suspect 4 pole, although I will not be able to confirm until tomorrow.

TBH - I am not even sure what a VFD is? Where would I obtain one and information on how to install it. I have a basic understanding of electrical systems and operations albeit more practical hands on than theoretical. The language can often be confusing also, hence my preference to address the issue from a replacement perspective.

The scroll saw would indeed benefit from variable speed, currently speeds can be varied by physically changing a belt on a double pulley. Old technology, yet still effective, albeit it slow

Therefore ...... VFD, Where to buy?

David
 

Ttrees

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VFD's are the short name for Variable frequency drives or inverters... tomato/tomato
I think all the information is in that thread that I linked.
You sound like you are quite modest, and
I suspect you know much much more than myself on electrical matters.
If you can wire a plug, you wouldn't have much trouble.

I only got into these things because I needed a bigger bandsaw than easily available
to run a wide blade.

Happy to answer any more on the matter
Put it up on the forum if your not sure...
It won't be like a sharpening thread, as I think all are agreed on safe practice regarding electricity.
I haven't been disagreed with so far, and been ranting about them for a while


The only downside would be making a cabinet for dust protection, if you dont have a suitable auld box
to house it in.
Good luck
Tom
 

deema

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For a scroll saw adding an inverter will enable you to alter the speed and bumpy consequence its utility which is highly desirable. The switch will happily work with an inverter as it won’t be switching any load.
 

Myfordman

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On NO ACCOUNT should you fit a switch between the inverter and the motor. Only a direct connection with no fuses should be used. In practise, the wall socket can isolate power to the inverter and the controls on the inverter itself can be used to stop and start the motor when in use. The current switch is redundant but can be kept but non functional for cosmetic reasons.
 

Bluekingfisher

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Tom/Deema/Bob,

Thank you once again gents, very valuable information, gratefully received.

On reflection and having considered the option of VFD/inverter installation and conversion to single phase. I have have enough sense to realise it would be folly to disregard the information you have all kindly provided. Besides, the motor I have, although 4 pole is infact 1/4hp rather than the existing 1/3hp on the saw. In addition, the pulley shaft is smaller on the replacement, which would require pulley changes, at least at the motor side.

Is it fair to state a 3 phase motor with a comparable motor plate rating is by nature more powerful/resilient than it's single phase equivalent? Just thinking out loud really.

Anyways gents, I will go with your advice and add the inverter.

Can anyone recommend an outlet for the VFD. Is there a specific brand you can recommend. Is there a specific rating I need for the power output of my motor?

If the wiring process is as simple as bypassing the existing switch I could negotiate that I should think, anything more may have me questioning my abilities, particulary with the inherent risks of faulty electrics.

Thanks boys

David
 

Ttrees

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Read the thread I linked.
All the questions you ask are in the thread.
Its only a few months old, so still of much use
I tried to make it as clear as I could,
I was afraid the first time because I have no experience apart from wiring a plug.
Thats why I went to the trouble.
Good luck
Tom
 

Myfordman

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Single phase Vs 3 phase? think twin cylinder engine Vs a V6 more power strokes per revolution.

Convert the motor to delta 230v - if the info is not inside the terminal box, then look at my motor paper.
Just wire the inverter directly to the motor. No switches, NO DETACHABLE CONNECTORS, no fuses no nothing. Simples!
Your motor is 1/3hp that is 250 watts so get an inverter rated at 250 watts or more. If it is more powerful then programme it down to match your motor. The method will be in the manual. You don't need a very sophisticated inverter with lots of bells and whistles.
Once you have done it, you will wonder what the fuss was about. It really is that easy. After all Tom has done it :lol: :lol:
Bob
 

Bluekingfisher

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Hi Bob,

I suspected as much. I se the account up Originally with an email account that is no longer accessible. Since the changes it seems all PM are sent to private email address rather than the internal PM message system. I am reluctant to change until I can establish integrity of my existing account.

Anyway, I assume you can receive a pm sent from me? So, I will PM you now with my email address if that's OK.

If you haven't received my PM 5 minutes after posting this then please let me know, I will try it from a different approach.

Regards.

David
 
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