VFD to power 415v 3 phase engine from 240v single phase

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Re: VFD to power 415v 3 phase engine from 240v single phase

Postby antus » Sun Mar 12, 2017 11:06 am

Thats a good thead you linked there, and likely would have been a good solution if I was able to get the coupling off no damage and had the time to undertake it.

I did score a win with the local engine shop. It turned out the engine was a standard ML90L-2 frame engine with a B3 foot mount, so I purchased a single phase engine. The B3 foot mount had holes 45 degrees rotated from the original engine, but the hydrolic reservoir had 8 holes so included support for both footprints. Once received and opened up it was interesting to find that it still had the same 3 phase coils and a start and run capacitor similar to the mods on the internet for converting a 3 phase engine to a single phase engine. The new one also still had the bridge network for 415 or 240v but also rotation direction. I got the engine shop to swap the coupling over saving me the risk of breaking it not knowing what im doing and the new one bolted straight on. The bridge network needed to be swapped for clockwise direction and a quick test showed all is well.

The other thing learnt is that the coil in the magnetic starter was a 415v coil and not strong enough to actuate the contacts at 240v. That also needs replacing.

The final piece of this puzzle which I havnt quite figured out is the relationship between 240v and 415v. Is this correct - 240v delivered to my house refers to the voltage difference between each of the 3 phases in the street and the neutral which is a center tap back to the transformer in the street from the next voltage level up in the supply network. 415v refers the voltage difference between any of the 3 phases and describes the potential difference of one phase at its peak to another phase which due to being out of phase will be swinging in the other direction?

If this is true and I had chosen the VFD option it'd have 1 phase at 240v input and advertises 'equivalent' output - 240v per phase. And if so wouldn't the measurement between phases once they are created by the VFD still provide 415v difference? And therefore maybe I would not have needed to convert the original engine configuration at all and could have just used it in start configuration as is? Im happy to have converted things - its been an interesting experience and its nice to end up with the most simple solution, but maybe the VFD would have been the cheapest option.
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Re: VFD to power 415v 3 phase engine from 240v single phase

Postby antus » Sun Mar 12, 2017 11:34 am

Im also going to store this manual here for the Molnar MF4923-75 and MF4923-RT for others. The original scans, from Molnar, came in 2 pdfs where the second file images were the wrong size, rotation and difficult to print not looking like postage stamps. I extracted the images, cut and rotated exactly 90 degrees to prevent quality loss and loose the overkill white space and put them back together for a single file that should work much better.
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Re: VFD to power 415v 3 phase engine from 240v single phase

Postby antus » Mon Nov 20, 2017 5:23 pm

Just to dig this back up, eventually I did confirm that you can get 415v between any 2 phases in a 3 phase system. So, probably, my original engine would have worked just fine with the street 3 phase supply. To illustrate the options for voltages though I just found this image from http://www.itacanet.org/basic-electrica ... -phase-ac/ which shows it quite nicely.

lines-600x334.jpg
lines-600x334.jpg (31.8 KiB) Viewed 1682 times

A 3-phase 4-wire supply carrying 240V in each wire.
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Re: VFD to power 415v 3 phase engine from 240v single phase

Postby Antwon » Sun Nov 26, 2017 10:19 am

I'm not sure about using the vfd on a hoist but I have one powering my mill and my lathe and have not had any issues yet. my first hoist before I got a workshop was 3ph and I converted it to 1ph but was a pita had to swap out motor and the relay setup motor was the relay setup wasn't best of luck with it I have the same hoist I can send pics of the relay I needed but doubt you need it

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Re: VFD to power 415v 3 phase engine from 240v single phase

Postby antus » Sun Nov 26, 2017 11:58 am

Thanks for the offer. Yeah I got it going, I purchased a 240v coil for the mag start switch, which almost fit. After a bit of cutting it fit in there and with the original switch is working so the 240v conversion was completed. The gotcha for me was the voltages. I missed the fact that single phase 240v is between neutral and ground, and 415v is the same circuits, but between two phases. The higher voltage is from the difference in phases. My mistake was that I thought residential 3 phase was 240v and industrial 3 phase was 415v. Ooops! The whole conversion would not have been required if got the 3 phase feed from the house run to the shed and cost would have been similar to the conversion in the end. Oh well a working solution is better than none.
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Re: VFD to power 415v 3 phase engine from 240v single phase

Postby Antwon » Mon Nov 27, 2017 8:54 pm

Lol atleast it’s working now

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