3 Phase to Single Phase Step Down Transformers

[3gunguy]

Hey All,

Does anyone have any experience with these? They are about $2500.00 but If I understand them correctly ( I am a total novice), you can plug your 3 phase gennie into it....and out the other side comes single phase for your house without having to lose 1/3 of the gennie's power.

My thought on this is that even though its pricey, when you add it to the cost of a mep-804a, mep-004 or 805, 005...et al.... it is still cheaper than a commercial generator and way more durable to get the power you need to run a whole house, turn key without load balancing considerations.

Thoughts? Suggestions? Education?

 

[rickf]

The way I understand it those transformers draw full current on two legs and zero current on the third leg. I am not a generator guy but to me that seems like a bad idea. I am curious to see what the experts say.

 

[Ray70]

I'm waiting for the experts to chime in as well, but I believe Rick is correct. If so, there's really no point.... it would be no different from running the set in the 208V mode and pulling off 2 legs. I think all the "transformer" does is drop the voltage if you're using high voltage input.
Also, the 004 and 005 CAN easily be reconfigured to single phase because they are 12 wire generators. Only the 804 / 805 etc. have the 10 wire generator head which can not be reconfigured.

 

[Evvy Fesler]

Placing a transformer between the generator and load can’t make single phase. It does, however, keep the generator in balance and distributes the heat from the generator to the transformer, a chunkier hunk of iron. This will help maximize the life of the generator.

 

[3gunguy]

I am curious too. I am not sure that is the case because they make a simple adaptor plug I found that does that for 150.00. I am however VERY curious about this 12 wire generator concept you speek of. Please, please that is an awesome opportunity it appears?

 

[glcaines]

Placing a transformer between the generator and load can’t make single phase. It does, however, keep the generator in balance and distributes the heat from the generator to the transformer, a chunkier hunk of iron. This will help maximize the life of the generator.

I'm not saying you are incorrect as I am absolutely not an expert. However, I don't understand why using the transformer would keep the generator in balance if only two of the three legs are pulled from, the third leg has no load, and both of the legs pulling a load are likely to have different loads. I'm assuming the heat generated in the transformer rather than the generator head is due to the higher amperage in the transformer output due to the lower voltage supplied by the transformer?

 

[Scoobyshep]

You can make single especially if you can tap to a low zigzag.

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[Evvy Fesler]

I'm not saying you are incorrect as I am absolutely not an expert. However, I don't understand why using the transformer would keep the generator in balance if only two of the three legs are pulled from, the third leg has no load, and both of the legs pulling a load are likely to have different loads. I'm assuming the heat generated in the transformer rather than the generator head is due to the higher amperage in the transformer output due to the lower voltage supplied by the transformer?

Three legs, i.e., the three phases will circulate through the primary, while the single phase is circulated through the secondary using L1/L3. That causes heat, which the transformer can handle, but doing that directly with the generator will likely cause it to overheat.

 

[kloppk]

A few people on here have successfully converted 804's to single phase 120/240.

 

[Poccur]

The way I understand it those transformers draw full current on two legs and zero current on the third leg. I am not a generator guy but to me that seems like a bad idea. I am curious to see what the experts say.

Try this webpage, it explains it a little better:

Three Phase To Single Phase - Carroll & Meynell

Three Phase to Single Phase Three Phase to Single PhaseTHREE PHASE TO SINGLE PHASE TRANSFORMER OPTIONSIt should be noted that it is impossible to create a perfect current balance on a 3 phase supply when feeding a single phase load. Consequently there are several different methods of producing a...

www.carroll-meynell.com

.

 

[3gunguy]

I read it and it seems to be above my technical knowledge. It is my plan to call them and see if they can splain it to me in British.

 

[87cr250r]

Here is a description of various connection diagrams for the generator.

https://www.marathongenerators.com/generators/docs/manuals/Connection%20Diagrams.pdf

 

[DieselAddict]

I need to ask the obvious question - why are you wanting to do this?

As an aside, the 004 and 005 generation machines can be wired single phase. It is a bit of work but possible.

 

[Scoobyshep]

Gonna come down to how much you wanna spend and how much power you want. The more power you want the more it will cost

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[3gunguy]

I need to ask the obvious question - why are you wanting to do this?

As an aside, the 004 and 005 generation machines can be wired single phase. It is a bit of work but possible.

The reason is that I want to run my whole house on a generator without having to load balance, especially because my line of work takes me away from home during hurricanes and such so I want to be able to tell my wife...just keep feeding it diesel and you are good. I just bought this MEP-803A that is in wicked great condition with only 118 original (not tier 2) hours on it. But with my electrician's help, we have determined I really need about 18KW to run this place soup to nuts with zero concerns.

I am learning this about the 004 and 005 models. They appear very hard to come by in good shape with low hours. There are several 804 and 805 models out there so If I could get something that would give me all the power of these without 2 legging it and also putting unbalanced strain on the unit, that would be something I am in to.

Unfortunately, I am totally not an electricity guy so this is all at a very high, consumer level that I am trying to figure this out.

Thank you, and everyone for all your help and input. I am up for suggestion, guidance and education.

By the way, I am a diesel addict too. I have a 7.3 F250 and VW Passat TDI. My wife drives an Audi Q7 TDI and I have 2 Mep 531a's and a 3Kw older diesel mil generator that I need to get running. I do nothing with gas.

 

[Scoobyshep]

00s are getting very hard to find. If it were me, I'd zig zag it trick is finding the right transformer

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[DieselAddict]

The reason is that I want to run my whole house on a generator without having to load balance, especially because my line of work takes me away from home during hurricanes and such so I want to be able to tell my wife...just keep feeding it diesel and you are good. I just bought this MEP-803A that is in wicked great condition with only 118 original (not tier 2) hours on it. But with my electrician's help, we have determined I really need about 18KW to run this place soup to nuts with zero concerns.

Right now there is a generator listed for sale on FB Marketplace that would work far better than trying to take one of MEP804/805 machines and forcing them into a scenario they were never designed for.

I love these machines but I also know they aren't for everyone nor are they for every job. I'd recommend avoiding any of the 80x series machines that aren't single phase compatible out of the box. Look for a MEP004 or MEP005 and do the single phase conversion if you really want some retired military gear. Outside of that I'd strongly recommend buying a civilian machine that fits what you need.

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[3gunguy]

Right now there is a generator listed for sale on FB Marketplace that would work far better than trying to take one of MEP804/805 machines and forcing them into a scenario they were never designed for.

I love these machines but I also know they aren't for everyone nor are they for every job. I'd recommend avoiding any of the 80x series machines that aren't single phase compatible out of the box. Look for a MEP004 or MEP005 and do the single phase conversion if you really want some retired military gear. Outside of that I'd strongly recommend buying a civilian machine that fits what you need.

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That is my long term plan, I will just run this one in single phase and run what it runs. Wiring my house to take the bigger load for the future and will eventually sell or shelf this one and get an 004 or 0005 and do the switch over.

 

[glcaines]

I don't understand why you would need 18 KW to run your house. I have a very large house, totally electric. I have an MEP003A, a 10 kw machine that feeds a 400 amp square D manual transfer switch. I don't have any load switching at all. We have frequent power outages because we live remotely on 40 acres in the mountains surrounded by national forest. Some outages have lasted a week or more, both summer and winter. When I start the MEP003A, it is business as usual. I don't pay any attention to what is turned on. The genset handles it all, albeit somewhat noisy. Just because there are a lot of things in the house that pull power, doesn't mean that they are all on at the same time. We run the HVAC, dryer, washer, dishwasher, etc. and have never had any problems. I like the MEP003A because it is very simple, easy to service and is air cooled, so no potential problems with liquid-based cooling systems. It puts out both single and three-phase power. It uses about 1 gallon of diesel per hour at full load and is very easy to start. Even my wife can start it without problems. I purchased it at auction in 2009 and it has run almost completely trouble-free since then. It was never rebuilt by the military and has 8085 total hours on it. It was freshly back from Iraq when I got it and is trailer-mounted, which makes it nice to be able to move it easily around our property when power is needed remotely. I previously also used it in three-phase to power a lot of three-phase power tools in my shop before a installed a rotary phase converter. Talk to other people that currently use 10 kw MEP gensets to power their houses for backup power.

 

[patracy]

Doesn't the MEP-803A have a switch for single vs 3ph?

And to add to the sizing discussion, 18kw is gonna be hard to load up with just a house. I've got a 23kw and I can't load it enough from my house. I actually let my neighbors stretch cords over to run their lights and low current stuff. (Not that it couldn't handle it, just that drop cords in hundreds of feet isn't a good idea)