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05-27-2008, 11:00 PM #1
Step up transformer for 5hp motor...
I'm looking for a transformer to use with my 5hp GreenLee 495S tablesaw. I have an RPC that produces 220v 3ph and the motor voltage on the TS is only 440v. I've been told by several people that I'll probably be OK with a 6kva or 7.5kva transformer.
Other than that I know nothing about transformers. Can someone tell me what sort I should be looking for? Anyone have an extra???
05-27-2008, 11:34 PM #2
It is fairly safe to have twice as many KVA on transformer rating as compared to motor HP, so figure 10KVA.
You need a General Purpose Three Phase Dry Type 480/240
Acme Transformer lists such things here:
(I see this does not show what I intended, so type in T-2A-53340-1S in the part number box and hit go. That is a 9KVA.)
They are quite pricey.
05-28-2008, 12:20 PM #3
You have three readily available solutions.
1. have the motor rewound for 230 volt / 460 volt operation
2. install a transformer as you are now thinking. You need about 7.5 KVA rating, 3 phase, 480/240 dry type general purpose as John has described. A table saw is not a huge starting load so you should be ok at 7.5 kva.
3. failing to find a three phase transformer, you could use three single phase transformers connected in closed delta. You could probably use 3 kva, 480/240 dry types for this hookup.
There is a 4th solution that I use. it is not necessarily the cheapest but it works. for my 2 hp lathe I have a 3 kva single phase transformer feeding a 5 hp, 460 volt, 3 phase VFD. This gives me 460 volt, 3 phase output for the lathe. My installed cost was about the same as for a three phase transformer considering I was shopping for all the items used. I do not think you need this for a tablesaw though.
You will need to make the decision based on cost and the amount of work you want to do.
05-28-2008, 06:12 PM #4
You might consider having a rewind shop relead your present motor for 240 or 240/480. Much cheaper than a rewind.
05-28-2008, 07:25 PM #5
adding the extra leads would definitely be the cheapest however a Greenlee tablesaw is quite old and it is very unlikely the windings can be seperated without damaging the insulation--if you try and it does not work then you will need a rewind.
05-28-2008, 09:00 PM #6
You really dont have to seperate the windings, as the jumper's and lead connection is tied down on top of the winding. By your HP rating, it is a 36 slot stator ( I would think a 4 pole ) which would have 12 groups of 3 coils. If you need the internal connect diagram, just send me a email and I could send you the diagram.
05-28-2008, 09:09 PM #7
Most of these machine tool motors are 36 slots.
Series ∆/Parallel Y, also called ∆/YY is usual, and these are constant torque.
Constant HP is a more expensive option, and one which I have mainly seen on specialized pattern-making wood lathes, where there are four speeds, and two windings which are constant horsepower.
05-29-2008, 04:11 PM #8
Thanks for your thoughts guys. I spoke with a gentleman at a local motor shop (he's rewinding a 575V motor for me to 220/440V) and he said he can probably get it to dual voltage without harming the windings. We'll see...keeping my fingers crossed!