jven avatar image
jven asked

MP II + 3 phase converter transformer VS 3xMP in 3phase wiring + phase converter transformer ?

Hi. I have a small farm in which I have various pumps, biggest one for now is 4.5Kw. I also have a house nearby and I'm considering getting a solar system given the provoked .....Erm, sorry I mean the current energy crisis... :) Anyway, all the pumps are 3 phase, the house is single phase. My initial thoughts were to get 3 Multipluses 3000 48 and set them in 3 phase, but then I remembered that I'd have to be very carefull because of a water heater and oven in the house, that together surely surpass the MP's 2400W rating. Now I found about 2 companies that sell transformers to the industry and they have 3phase to 1 phase converter tranformers and also vice versa!! For 5Kw those things weight more than 50Kgs !! But they cost about 2/3 of a single new MP.

The other option , which I'm pending to right now, is to get a single higher wattage MP (i.e. the 8000 48 version or even the 10000, although that is probably overkill and has too much losses for my taste, was thinking of minimizing the battery size for now) and put a single to 3 phase converter transformer in the circuit for the pumps.

Question is, which one would be preferable ? I know using transformers to make the conversion, one way or another, is going to incur in losses, does anyone have any experience with this ? The companies do provide a datasheet but they don't include the efficiency and why should I trust them for that anyway, the efficiencies for transformers are probably known in general.... Here is a link with an example:

Going with a single MP would be better in terms of future maintenance / repairs / replacement (although this shouldn't be a factor with Victron, given the higher quality, but eventually anything can die), given that if I have 3 MP wired for 3 phase and one of them goes wrong, I'd have to find a replacement with exactly the same model, whereas with a single bigger one I could borrow one / have a spare / more easily...

One advantage however if I go the path of 3MP wired in 3 phase is if one inverter malfunctions I would
still have the other two to feed the single phase circuits in the house, and could even wire it in parallel with the other one.

Decisions ....

But yeah, I'd like to know the potential transformer losses of the phase converter transformers and if anyone has any experience with this...

Also, another option would be 3 MPs wired for 3 phase and a separate MP for the house, no transformer losses then, although it's more expensive... In this case I could also go with smaller MPs for the 3 phase wiring...

What do you guys suggest ?

Thanks a lot!

3 phaseAutotransformermulti phase
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2 Answers
wkirby avatar image
wkirby answered ·

If the pump motors are the only three phase loads then setting up a 3 phase MultiPlus setup is probably not very advantageous.

Better option would be to have a single phase setup with one appropriately sized MultiPlus.

That Torytrans product that you linked seems to be more of a general purpose switching three phase power supply. I have not heard of that brand before, so I couldn't comment on reliability.
I think a better option would be to use a VFD (Variable Frequency Drive), one for each of your pump motors. These can be sized to match each of your pump motors. There are models which take a single phase input and create a three phase output specifically for driving an induction motor, for example. The frequency can be varied to adjust the speed of the motor if you need to. Probably not needed, but adjusting the pump speed might be able to reduce energy consumption.
These units are used extensively in industry, are very reliable and efficient.
Many reputable brands ABB, Siemens, Invertek are just a few that spring to mind.
I have a single phase supply and I use VFDs for the motors of my three phase machine tools.

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Alexandra avatar image Alexandra ♦ commented ·

I vote in favour of the VFD idea.

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jven avatar image
jven answered ·

Thanks. I have tried a VFD once a few years ago on one of the pumps and it started making this whining noise, I didn't like it. Then I started reading about the harmonics that it provokes, specially when long cables are used, which is the case of a borewell pump (mine is more than 100 meters...), and the effects it has on motor longevity... It was a decent one with included filter, a Schneider Altivar... I think this version was more for air conditioning in buildings but it had the filter so it could run other motors, in fact the manual had all the programing that could be made for different applications...

By the way, that transformer weights more than 50kg! I don't think it's a switching PSU.. I'll have to talk with the company directly.

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