230V-50Hz tools running on 208V-60Hz 1

[ciao1982]

Hello,
my office is relocating me from Nairobi to Santo Domingo, and I am planning to put in the container all my garage tools (I am a hobbyist, doing on my free time mostly wood-steel furniture, but I have quite a few workshop machines). I have many single-phase electric tools 230V-50Hz, and a couple of three phase equipment 400V-50Hz.
In Santo Domingo I will have a house with 3 phases, so 120/208V-60Hz, and using the voltage between two phases, I am planning to equip my garage with an surface mounted electrical system having single phase at 208V-60Hz on the new garage sockets, so to be able to run my 230-50Hz tools. Regarding my machines which use 3 phases motors I am looking for suggestions, and please let me know also if you have any observations on the single-phase arrangement.
Thanks

 

[VEBill]

Larger tools (e.g. table saw) often have motors that could be very easily replaced.

 

[waross]

#1 Respecting the V/Hz ratio you will be about 75% of design voltage at 208 Volts, 60 Hz.
The V/Hz ratio at 230/50 is 4.6 Volts per Hertz.
4.6 Volts per Hertz at 60 Hz is 276 Volts.

400 Volts star = 230 Volts at 50 Hz, Again you need 276 Volts.

Lets see, a transformer rated for 240V/60V as an auto-transformer boost will give 300 Volts.
Connected to 208 Volts will develop 260 Volts.
That is about 6% below our target voltage.
At full current your motors will slide down the curve a little and develop a little more slip. (Run a few RPM slower.)

Solution: Two 4:1 lighting transformers connected in open delta will give you 260 Volts single phase and three phase.
Rating: Determine the maximum current expected. (Disregard starting currents.) That will be the current rating of the transformer secondaries.
So, a 5 KVA transformer will have a 60 Volt winding rated for 83 Amps. As an auto-transformer this transformer will support a 260 Volt load of 60 Amps x 260 Volts = 15.6 KVA.
WARNING: for three phase loads use the current. Do not attempt to add the KVA ratings. There is a reason.
Problem: A 240V/60V transformer may not be available.
Solution: Use a 480V/120V transformer. Again the size will be determined by the expected current on the 120 Volt winding.
You do know that your motors will run 120% faster, but with almost the same torque.
If your chosen transformers have taps you can get the voltage even closer.
Good luck.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[edison123]

For starters, all your motors are going to be spinning at 20% more speed. While the motors probably can handle the higher speed, can the tools and other equipments connected to the motors handle it?

Muthu

http://www.edison.co.in

 

[itsmoked]

faq237-1224

Keith Cress
kcress -

http://www.flaminsystems.com

 

[ScottyUK]

Motors are relatively easy to deal with. Some of the mechanical limits may not be. Woodworking machines often have high spindle speeds - be very cautious about increasing the speed of anything such as a planer-thicknesser or a spindle moulder. If possible look at changing pulley sheaves to restore the normal operating speed. A cutting head burst will be messy.