Phase Convertors (making 3 phase power from single phase 220)

[desperado]

Now first off IF YOU DON'T FEEL COMFORTABLE ABOUT ATTEMPTING SOMETHING LIKE THIS, SEEK A PROFESSIONAL. YOU WILL BE DEALING WITH WIRING THAT CAN GET A BIT COMPLEX AND LETHAL VOLTAGES. YOU ARE ALSO DEALING WITH BOTH START AND RUN CAPACITORS. START CAPACITORS AND SOMETIMES RUN CAPACITORS WILL EXPLODE. YOU MUST ENCLOSE ALL CAPACITORS IN A METAL CABINET, FAILURE TO DO SO CAN INCREASE THE POSSIBILITY OF ELECTRICAL SHOCK AND FIRE.

I AM NOT RESONSIBLE FOR YOUR ACTIONS, ELECTRICAL PROJECTS, OR ANY ISSUE THAT MAY ARISE FROM ATTEMPTS TO BUILD THE DEVICES THAT ARE DISCUSSED HERE.

Sorry about the impromptu legal statement, but electricity can be dangerous if not treated with respect.

 

Phase converters 101

 

The ROTARY phase convertor, is a device that can create 3 phase power from a single phase source. The unit consists of a 3 phase motor and run capacitors that are wired to the motor.

 

The basic convertor will consist of a capacitor bank that will have an addes value of 10 uFD (microfarad) per horsepower of the rating on the 3 phase motor, there is a second bank of capacitors

with an added value of 5 UFD per horse power.

There are 3 wires to a 3 phase motor. known as L-1, L-2 and L-3

 

The single phase power feeds in on L-1 and L-2, and the capacitors connect from L-1 to L-3 and L-2 to L-3

the L-1 to L-3 will be the 10 uFD per horsepower and the L-2 to L-3 will be where the 5 uFD per horsepower will connect.

 

The 3 phase output is connected to the 2 lines of the motor.

 

Now, a three phase motor will not start on single phase power without help. There are several ways to do this. One way is the pony motor, where a pully is put on the 3 phase motor and a small single phase motor is set next to ht and spins the motor up. Once it is spinning power isapplied to the converor and the motor begins to run. Then the pony motor is disconnected from power and the belt is popped off.

This is a bit difficult and expensive if you don't hava the pony motor to use. The second way, which is really hillbilly is to wrap a piece of rope around the output shaft of the phase convertor and thn pull it as you would a lawn mower. then while the motor is spinning power is applied to the convertor and the motor will spin up the rest of the way. The third, and most complex is the start capacitor design. It will auto start the convertor with the touch of a button. It takes 75uFD per horsepower for the start capacitors to work, and the run caps can not be counted as part of that value. There are several circuit designs including using a time delay repay to control a contactor to connect the caps to start the motor and then disconnect it from the motor. It is not hard ot build if you have some electrical background, either a time delay relay or a standard pushbutton can be used to control the contactor for the start circuit. I am not trying to be vauge here but a full explanation for each design can be found by doing a google search for phase "convertor howto"

 

Sizing

Figuring the sizing to run motors is pretty simple you must have an idler motor (the one that IS the convertor) sized 15% to 20% larger than the largest motor you are running and it's best to stick with 20% for any motor that will be starting under load, like an air compressor. For welders and other non motorized devices, you need to find the max current draw of the device that that you will be wanting to run. All motors have a plate on them that will indicate what the max current draw for that size motor, you must have a motor that is between 75% and 110% of the max load that will be drawn. So an example would be a welder that at 230 volts will max draw 35 amps. The motor that you willl need to use as the idler motor will have amaximum current draw 75 to 110% of that 35 amp load that will be on it. If you are going to be running a device that will require 100% duty cycle at the max load then you will need 110% of the rating. For a better understanding, a welder will not run at 100% of it's rating all the time, unless it's a robot welder and its' running a continous bead. But a lathe, or a 3 phase furnace will draw it's max current for an extended period. This needs to be taken into account, and you should consider any additional devices that you may be adding later when you get your sizing for your motor.

 

Something else, a 20 HP convertor is about as big as you will ever want to build. If it's not big enough for what you are doing, build two and tie them together. Phase convertors larger than 20 HP are very difficult to start, and require alot of start current if they are capacitor started. This will typically exceed 100 amps of draw and blow most any service breaker to a garage in short order. If you have a larger motor and want to use it, start it with a pony motor, the starting current is greatly reduced by doing that. And the cost of the start capacitors will not break you.

[desperado]

This was something that I posted on another board after mentioning it in a thread and having several people PM me about it. I figured I would drop it in here as well in case some one knew where they could pick up some 3 phase equipment cheap but couldn't figure out how to power it once they got it.

 

Note to Admins and Mods.

If this is in the wrong area move it. If you don't want it on here, delete it.

[rl]

We use a 5hp 3 phase motor at the shop to run all of our 3 phase machinery (and a step-up transformer for the 440 stuff). Its rediculously simple, we use a capacitor to spin the 3 phase motor up - the single 5hp motor is fine with multiple peices of machinery running (we use it for a 440 lathe, drill press, band saw, drop band saw, mill and surfacer). We can run any two of them together at once without issue.