Wednesday, June 17, 2015

Three Phase Power, a work around

Every once in a while when a builder decides that they want to add a machine or two to offer fabrication options in their shop, I get an email about how to power these large machines. You see, most mills, lathes, etc that you find available are surplus or outdated industrial equipment equipped with 3 phase motors, whereas most home shops/garages are single phase power only.

So, how do we power this new toy?

What most folks first consider is "simply" replacing the motor with a single phase unit.  While possible, this is seldom a good option due to the necessity of fabricating custom motor shafts, pulley adapters, or mounting brackets; all timely and frustrating hurdles to get your machine up and running.

A popular option is a static phase converter, an in-line piece of equipment that is only activated when the machine is started.  Priced from 100 - 500 dollars dependent on motor size requirements, this will get your machine up and running, although at a reduced/loss of power around 2/3rd of it's rated horse power.  While effective, the disadvantage is that you must purchase a static phase converter for each piece of equipment you wish to power.

The option I want to share today is using a idler motor as a integrated piece of electrical equipment to provide the requisite power requirements for your new machine.

A single three phase motor can be wired into your system as a rotary phase converter.  This is accomplished because a three phase motor can be run off two poles, allowing the third pole generated from the idler motor to be fed back into the machine circuit.  This will provide an unbalanced three phase power that will allow your machine's motor to run at full capacity.  When wired into your machine circuit, this single converter can be used to power all your machines simultaneously.  The have to provide some type of mechanical force to start the idler motor turning (pull start) and your energy consumption will be higher as you will be essentially running two motors during machine operation.

I like to have an idler motor that is 20- 30% larger than that of the highest rated HP motor in your machines if you want to run multiple pieces of equipment. For example, if you have a machine with a 5 hp motor, look for at least a 7 hp idler.

Use a good quality motor.  I like Baldor motors for their smooth bearings and quality build.  The motor will have an information plate which tells not only it's specifications, but also the appropriate wiring configuration...

I typically turn down a piece of aluminum round stock to fit over the motor spindle, machine in a keyway, and then glue a piece of automotive rubber hose over the whole shebang.  This allows me to wrap a flat piece of webbing tightly around the spindle to give it a smooth pull and get the motor running...

In this case, we are using low voltage connections.  There are a total of three wires leaving our panel , going to the idler motor (red, black, green).  Our two power leads (red and black) will power the motor once it is spinning.  So using this chart, our Red lead will attach to wires 7/1, our black lead will attach to wires 2/8, wires 4/5/6 are bundled together, and our green ground to the motor ground.  The White wire, left out from our initial run, will then leave from the motor after attaching to wires 3/9 and go out to the breaker in the panel for our machines.  Coupled with the other two power leads,  the idler motor generates the third pole that our machines will use.

To use, I simply wrap and pull the motor spindle in the correct direction of travel, turn on the breaker or disconnect switch to keep it running, and then the machines already wired in the shop circuit have the capacity to work all day on generated three phase power.

Note, there are comprehensive guides available online to help you set up an electrical system to meet your 3 phase needs.  This is intended only as an awareness piece, not a "how to" guide.  If in doubt, contact a licensed electrician to help discern your shop needs.

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