WARNING! - NOT FOR THE NON-TECHNICALLY MINDED. NOTE THAT HIGH VOLTAGES ARE PRESENT AND ALL SAFETY PRECAUTIONS SHOULD BE TAKEN WHEN HANDLING THIS EQUIPMENT.
Three phase motor conversion step by step.
STEP1, Obtain a 3 phase motor or dual voltage 240/440 volt motor. All 3 phase and dual voltage motors look more or less like this.
Here is the motor plate.
I prefer to use 3 phase motors as they are cheaper to buy than single phase and most motors that are for sale at rally stalls are usually 3 phase anyway.
STEP2, Check your motor is a 6 terminal motor, if 3 terminal don`t bother with it, (its a lot of work to do a 3 terminal one!). The bottom 3 terminals should be connected together, (star connection).
If motor connected like this.
(Delta connection), connect as star.
STEP3, Next test the motor using a multimeter switched to continuity test, Put one probe onto the three linked terminals then touch each of the 3 top terminals. you should get a continuity "beep" on each one.
If one does not "beep" then the motor is scrap as this shows a winding is dead.
STEP4, Ok, first off, connect an EARTH wire to one of the 3 linked terminals to the EARTH pin inside the terminal box.
This is essential and if not done you will get an electric shock off the motor body and all other metalwork associated with it when generating! (Believe me!!!).
STEP5 CAPACITORS,
most people say to use 25 to 50 uf capacitors on these motors, NO NO NO! this value is far too high unless your using a motor of, say 25hp (18kw)! for the standard stationary engine like a lister D or a petter A, a 1.5hp (1.1kw) or less is ample. Engines going up in hp can use bigger motors, say 4hp (3kw) for lister CS and so on. Even on a 4hp motor 3 x 7.2uf / 440volt capacitors will work fine, (I use 7.2uf for all my motors).
NOTE: Polarised capacitors MUST NOT BE USED!!!
If you use, say 40uf on a 3kw motor you will cook the windings in about 10 minutes! Lowest value capacitors will keep the windings cooler even at high loads. 7.2 uf power factor correction capacitors can be found in 8' twin flourescent lights or you can buy them at any electrical wholesalers for about 4 to 5 pounds each but they MUST be rated at 440volts. (the 240volt ones burn out instantly).
STEP6, CONNECTING TO THE MOTOR, With your EARTH wire in place you can now connect your capacitors to your motor. CAP1 goes to terminals 1 and 2, CAP2 goes to terminals 1and 3 and CAP3 goes to terminals 2 and 3 as in photo.
You can mount the capacitors remote using 6 core cable. (photo just for clarity), make sure the capacitors are EARTHED if metal can type.
STEP7, POWER LEAD, You can now put your power lead in for your 3 pin socket, (best use a RCD type socket).
Your LIVE, (phase) wire goes to any one of the 3 terminals with the capacitors on, this is your LIVE rail. Your NEUTRAL wire goes to any one of the 3 linked terminals, (the star point). This is also the EARTH point for the EARTH wire!, (sounds odd but thats the way its done).
The whole system when generating on a rally field should be EARTHED to a proper EARTH rod knocked into the ground. Unfortunately earth itself is a poor conductor unless it is very wet, and therefore you should bang about 2' of the rod into the field. My EARTH rod is 2 and a half foot in length.
STEP8, When all connected up run the motor on your engine, SLOW at first and just keep "blipping" the engine speed now and then. Have a multimeter connected so you know when the motor starts to generate. The motor will excite itself, there is no need to force excite it. Some motors take about 4 to 5 seconds to excite, some a few minutes.
DONT HAVE THE ENGINE SPEED TOO HIGH AS THE MOTOR IS CAPABLE OF GENERATING 500VOLTS IN AN INSTANT !!, and if you go above 440 volts you will burn the capacitors out.
IMPORTANT: the motor will not start to generate if under load, so keep the bulbs off it until you have 240 volts on the multimeter!
OUTPUT CYCLES: if 50 HZ is needed the generator should be kept within the nearest speed of the motor speed, ie...... 940 RPM=1000 RPM as generator, 1450 RPM=1500 RPM as gen and 2800 RPM=3000 RPM as gen. or you can add another capacitor to one of the other 3 doubling it from 7.2uf to 14.4uf, this brings the cycles up also.
For most lighting boards for displays however cycles are not important. You may choose to utilize all 3 phases, (as in 3 x 240 volts), but if you do bear in mind one thing.
Most safety officers will not take kindly to you running 3 phase from your "home made" generator on a rally field!!!..., Well thats it chaps, have fun but above all BE CAREFUL ! Regards
