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Three phase table saw

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artie

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Guys , if I wanted to run a 5.5 hp 3 phase saw off 240v, with the suitable adaptor. How many amps would I need?
 

Inspector

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The manual for my series shows a 5.5hp motor needing 50 amp input for 25 amp output. Others may be different and also remember you can program the VFD to soft start the motor limiting the current input so it doesn't momentarily pop the breaker like a single phase does.

Pete
 

artie

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Thanks Pete, Is a 13 amp socket no good then.
 

Inspector

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No not even close. If your breaker didn't pop the wires in the walls would get so hot they would burn down the shop. You'd be best to talk to a qualified electrician to see what is needed to make it work.

Pete
 

Fitzroy

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5.5hp is 4.1kw which at 230v is 17.8 amps. This is the current at full load.
 

artie

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Thanks again Pete, but no need for me to pursue it any further. I had the chance to pick up the saw for reasonably money, if it was just a matter of laying out for the vfd, it might be worth it, but not any more than that.
 

Inspector

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Fitzroy that is the current the motor needs with no losses. The input power to the VFD will be higher than what it can put out.

Pete
 

Ttrees

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Is it not possible for the Artie to de-rate the motor to say 3 hp with a suitable inverter.
Would this be OK if the saw gets light use, say a smaller blade fitted or adherence
to only doing very light cuts with the motor matched blade, and checking the lead is not getting warm whatsoever?
Thanks
Tom
 

Trevanion

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Out of curiosity, what do you boys reckon is the absolute maximum three-phase powered motor that could be run from a single-phase supply? I know a 4kw single-phase motor is just about the maximum you can run off a 32A circuit, with soft start and such would you be able to get quite a bit higher power?
 

Myfordman

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Out of curiosity, what do you boys reckon is the absolute maximum three-phase powered motor that could be run from a single-phase supply? I know a 4kw single-phase motor is just about the maximum you can run off a 32A circuit, with soft start and such would you be able to get quite a bit higher power?
See this table
rotary converter table.jpg
 

Fitzroy

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Fitzroy that is the current the motor needs with no losses. The input power to the VFD will be higher than what it can put out.

Pete
Yup yup, was just doing the basic maths of HP to kW to amps, as even this was way above a 13A plug :)
F.
 

Artiglio

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Trevanion, i’m running an 11kw rotary convertor from a 40 amp breaker, by rights it should be a 60 amp supply to get best out of it but my load ( only run 1 machine and extraction at same time) is well covered.
Previously i had a startrite saw ran fine from a 13 amp supply with a 10” bladebut would blow the fuse just about everytime with a 12” blade on start up.
 

Spectric

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Hi all

Dont forget that with Ac you need to account for reactive power (VAR) and not just active or real power in watts, often stated on motor plates as power factor.
 

Ttrees

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Interesting as it is, reading the fully loaded amps rating of various HP or kW rated induction motors, as which was implied in Artie's first post,
It seems from Artie's second post that the question is implying is it possible to run
a three phase tablesaw with presumably dual voltage motor from a VFD or other device from a 13amp plug.
I run a 12" blade on a tablesaw fine on 13 amp plug, 3hp motor and equal rated VFD
and the equivalent hp with the 24" bandsaw.
I've only ever checked the wheel on the meter with the bandsaw blade running without cutting, it was drawing about the same as an old laptop, certainly nowhere near the kettle.
I don't cut for hours or anything, maybe an hour max on the TS sometimes.
I have never noticed any warming of the extension lead, and its not a heavy gauge.

Are you guys saying that 3hp motors are the limit for me, for my limited use with my 13a sockets?
I thought de-rating motor hp with a VFD was a done thing, what have I got wrong here?
Thanks
Tom
 

Myfordman

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I did do some work for a chap who runs air raid sirens for WW2 re-enactment events. They have a 5hp 3phase motor and I ran this from a 13amp plug. It needed >20 sec ramp up but that sounded realistic in the application. The solution relied on the fact that a 13 amp fuse will pass much more current if you creep up on it slowly!

Derating power on a machine is not very clever as it will likely bog down in use and cause problems and maybe even ruin a job.
 

Ttrees

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Thanks Bob
Say if it was possible to make a riving knife on the saw to suit 12" blades...
This being the only thing that's the big factor here, that I can see...

It could possibly make sense in a temporary setting until one could afford
an electrician.
With the tablesaw, a 3 hp blade provides all the grunt for a 12" blade I'd ever want...
If one has no wish to be running a dado stack which would probably cost a good portion of the costs to upgrade to 16a receptacles, and keeps an eye out for any sign of leads warming whatsoever,

Would there be any difference in consumption or performance issues between a de-rated 5.5hp to 3hp motor running say a 12" blade,
compared to my Startrite 3hp /12" blade setup,
I have a good few seconds of ramp up time on my machines, and a coasting stop
as the cheapo VFD's have components omitted for a braking resistor.

I gather that an even slower start up would be required, as the machine might have a really chunky arbor, and possibly three belts compared to a pair on my machines, so that extra inertia would need to be considered.
Might be a good idea to get a VFD compatible with use for a braking resistor also, if one is very concerned in their own hobby workshop.

Am I missing something else?
Cheers
Tom
 

Sideways

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One catch might be the tool velocity. On lathes, higher speeds are used for small work and slower speeds for bigger work. All aimed at keeping the linear speed of the cutter through the work correct.
Most tablesaws are intended for a single size of blade so their pulleys are chosen to give a correct tooth velocity.
Fit an undersized blade and the teeth move through the wood too slowly.
A professional saw may be equipped with multiple groove pulleys so that you can spin small blades faster and large blades slower.
 

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