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???
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.
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.
You might consider having a rewind shop relead your present motor for 240 or 240/480. Much cheaper than a rewind.
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.
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.
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.
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!