Its not that simple.
You have to change the motor voltage,usually by reconnecting in delta.
Take into account,starting torque and load torque.
Run capacitors are slow starting on their own.
Start capacitors need a means of disconnection.
Zanoter has the right idea,use a purpose designed inverter.
To answer the question (the way it is put): You can make the motor turn with just about any impedance that introduces a phase shift with regard to the inductive motor winding, you don't really need a capacitor. I once used an overhead projector just to make the point. So, making it run is not a problem.
The problem is to make it run efficiently with a load. And there, the 415 V motor will have a problem with 240 V. And you will never be able to get the rated power out of it. Not even if you reconnect for the existing voltage, which is not always possible.
Use a VFD. As has already been recommended. But you still need to adapt voltage. There are no VFDs that can produce three-phase 460 V out of single-phase 240 V.
If your motor can be reconnected as 240V 3 phase, then as Skogsgura said, it's only necessary to get the motor to START turning in the correct direction on a single phase supply, after that it will keep running. But it will no longer be capable of 5HP at the shaft, and you will have barely enough starting torque for the motor to accelerate its own mass, let alone a load connected to it. If you cannot change the motor in the machine to single phase, then either buy a 240V VFD that is at least 2x the motor HP (so a 10HP 230V drive in your case), or build yourself a Rotary Phase Converter (RPC), for which there are many many free design guides on the web.
If the motor cannot be reconfigured for 230V 3 phase, then regardless of which way you go, you must also then use a transformer to get your single phase voltage to 415V prior to trying to accomplish the phase conversion. All of this typically makes it simpler and easier to just go out and find a 5HP 230V single phase motor to be quite frank.
Crap, left this out, still no edit function in this forum...
The capacitor value to make it start, assuming all the other issues work for you, is 67mfd/kW. So if you dont know, to get kW from HP take the HP * .746 (there are 746 watts per HP).
I think what I'm looking for is the 67mfd. I think I have condensers so can do a trial run. Any further comments are welcome.
Thank you all for the responses. This is my first time on this forum and I love the response you have given.
For the record, I am an ex-electrical engineer in Australia and have managed 97 years without electrocuting myself so far.
My son-in-law has got me started on this forum and is typing this for me. My future messages may need allowances made for my keyboard skills, or lack thereof.
Thank you Gunnar
Apprenticed aged year 16
Winding armatures aged 14
Birthday 30/4/2017
To everyone else
Job 1. 3 hp vacuum pump 2800RPM star now delta
Capacitors fitted one 60 three 30s MFDs
Starts no problem. Runs enough revs. Motor gets fairly warm so using an external fan.
Job 2. Not started.
1500RPM compressor load will fit 2hp single phase to assist 5hp.
That's the spirit Henry! You beat me with my 26/5 1940 birthday. I thought I was one of the oldest guys around.
Did you reach that impressive age thanks to lots of safety measures (Hard Hat, Goggles, Rubber Gloves, Ear Protection, Steel Tipped Shoes, Breathing Mask, Arc Protection, Shrouded Banana Plugs, Fused Test Leads) and all such stuff?
If your budget will stand it, it sounds like a good application for a VFD. I was doing stage lighting when I was 13. The experience and contacts enabled me to find part time work wiring houses at aged 14. I'm almost as old as Gunnar, but I'm feeling young in this company.
An old electrician/engineer once told me;
"I never wanted to be the smartest electrician. I always wanted to be the oldest electrician!"
You have probably won that title, Henry.
Bill
--------------------
"Why not the best?"
Jimmy Carter
We had a slight technical hitch.......Henry accidentally started a new thread instead of replying on this one. So this is the son-in-law again, giving him a bit of a hand. He always excuses his errors by saying "I'm just a boy - still learning".
I've copied his reply from the new thread and it is below, with a few corrections (Henry makes no claims to being a keyboard whiz). I don't know if I can delete the additional thread but I'll try after finishing this....
This is Henry. I connected the 3hp star circuit to delta and put 200 mfds in one phase and started the motor. The motor ran up to full speed and I removed 150 mfds leaving 5o mfds. The motor stayed on full speed and did not get hot after running for 2 hours. I am so pleased for the help from the forum.
From 3 phase to single phase you most use an Steinmetz connection, the capacitor value could be calculated by the following:
C = 36*P* [(220/U) Squared] * 50/f where: C is microFarads, P is motor power output in kW, U is the single phase voltage and f is frequency in Hertz.
Taking account data provided your capacitor calculation is 112.6 micro Farads (I have use 230 V and 50 Hz) it´s a big capacitor, maybe you will need an arrangment of two 60 micro farads capacitors.
You can connect the motor in star or delta and it depends of your power source available, if you use 230 or 240 volts choose delta connection. ( if the original three phase motor connection is star for 415 Volts) and you will need an AC capacitor at least for 460 V.
For connection please take a look of attached pictures.
My experience sayd that this calculation is your starting point, so is possible that you need to deal with trial and error in order find the right capacitor (or arrangment), because you need watch the motor currents balance.
This connection has several drawbacks due to current umbalance and , 1/3 of power output loose.
For small motors the best alternative is use an inverter to perform this operation, there are several inverters availables in the trade.
Also could be good that you can take a look of this link
I have never tried the Steinmetz connection. I have used the capacitor method but the motor did run hot as it is very inefficient. Here are my notes.
Welcome to the forum. Lots to learn and nice people. I hope to emulate you. Well done. My dad was born in 1919. Survived WW2 and then was murdered in Bulawayo, Zimbabwe. It is always a joy to have young people introduce others to all the great stuff. Keep going.
![[ponder]](/data/assets/smilies/ponder.gif "[ponder] [ponder]")
