Running capacitors can be used to balance voltages between the three legs. You’ll note that my design does not include them. Many phase converters use running capacitors. It is important to use AC rated capacitors for 230 VAC. I have also added in the ground wires to the diagram which are very important and should not be ignored!ĭesign of the starting capacitor was inline with the common guideline to use 100 uF per hp on the idler motor. I have also tapped off the three-phase power (horizontal lines) below the fuse block for distribution thru the shop to the various machines. If you look closely you will see all the basic elements from the very simple static phase converter diagram shown earlier.Ĭontactor C1 has replaced the drum switch, and Contactor C2 has replaced the momentary pushbutton for connecting the starting capacitor between L2 and 元. Field WiringĪbove is the field or power wiring diagram.
After the time delay, in this case around 1.0 second, TR50 will reverse state and the normally closed contact in rung 3 will open, effectively dropping out the starting capacitor. Subsequently contactor C2 is energized which brings in the starting capacitor. On Rung 3, as soon as the coil of CR40 is energized, we already have continuity thru the normally closed contact of TR50. On Rung 2, when the run relay CR40 is energized, the two-pole contactor C1’s coil is energized (performing the single phase power switching to the motor) as well as TR50’s coil which is a time-delay relay. There are two other normally open contacts on CR40. The coil of CR40 will then be energized until the circuit is broken by depressing the Red Stop PB. When the normally open contact marked ’40’ closes, it then bypasses the Green Start PB (which will be released and go back to normally open). Pushing the Green Start PB energizes the coil of relay CR40.
If you’re new to “ladder” logic, consider that a “rung” (horizontal line) has continuity when the circuit is completed.įor example, on the first rung, the Red Stop PB has continuity being normally closed.
3 PHASE POWER CONVERTER MANUAL
Instead of the drum switch I used a two-pole 30amp contactor, and instead of the manual push button I used a timed relay to drop out the starting capacitor (thru a single-pole contactor).īelow is the relay logic diagram for the controls, all of which are 120VAC. In my converter, I elected to automate the drum switch and the manual push button for the starting capacitor. The points where we are measuring the three voltages is where three-phase power is now available! This is where to tie in the other machinery motors we want to run. Once running, if we measured all three voltages (L1-L2, L2-元, and L1-元) in the above diagram, after the motor is running, we’d find approx 230VAC for each measurement. Rotary conversion begins once a three-phase motor has been started and is running on single phase in static mode. In my case I automated this process using a timed relay to connect the starting capacitor to the circuit, then drop it out.
The second, and simpler method is to start the motor electrically with a capacitor. This is typically a belt-drive arrangement from a smaller single-phase “pony” motor, and requires lots of design and safety considerations. Most basically, we can start the three-phase motor mechanically by spinning its shaft with an outside source of power. There are two ways to start a motor that is going to be run with static phase conversion.
3 PHASE POWER CONVERTER HOW TO
The issue then becomes how to start said motor, because a three-phase motor will NOT START on single phase by itself. Otherwise said, with single-phase power we can run a three-phase motor. We say this has “2 legs”.Ī three-phase motor will RUN on only two of its three legs. In a typical household, 220 VAC exists on double-pole breakers. The idler motor in the rotary converter starts and runs in a static mode. To get to rotary conversion we must first understand static conversion. The frame spec and shaft condition of the idler is not important so a surplus motor can be used. My largest machine tool motor is 3hp and thus I bought a spare 3hp, three-phase motor to be my idler. The general rule of thumb is that you can start and run a motor equal to the hp of your idler.
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