Mep804a to single phase in SD

[davvy]

Hello. New here. I just bought a 2003 Mep804a with isuzu diesel for a backup for my home’s geothermal heating and other power needs. Then I realized from here it’s only three phase and inconvertible to single. I want to use its full capacity if needed. What would I look for in a transformer beside kva to hook it up? Props for any exmilitary units I can find that are emp proof which is why I bought this unit. I need 40 amps minimum 240v to power my geo if stuff gets wild at -20 temps in January. I see some on govplanet that are 460delta to 460wye/266 but not sure if that is what i need.

 

[87cr250r]

How many wire leads are in the generator enclosure? If it's a 12 lead generator set it can be wired as zig zag or double delta for a dedicated single phase output at full rating. Otherwise, you should be able to wire as open delta with some 55% of rated output.

 

[Coug]

How many wire leads are in the generator enclosure? If it's a 12 lead generator set it can be wired as zig zag or double delta for a dedicated single phase output at full rating. Otherwise, you should be able to wire as open delta with some 55% of rated output.

these are reported to be 10 lead heads so not really able to be converted unless you want to start tearing into the stator assembly itself to find where the other 2 leads should be (if I remember correctly, I could be wrong)

 

[Coug]

Hello. New here. I just bought a 2003 Mep804a with isuzu diesel for a backup for my home’s geothermal heating and other power needs. Then I realized from here it’s only three phase and inconvertible to single. I want to use its full capacity if needed. What would I look for in a transformer beside kva to hook it up? Props for any exmilitary units I can find that are emp proof which is why I bought this unit. I need 40 amps minimum 240v to power my geo if stuff gets wild at -20 temps in January. I see some on govplanet that are 460delta to 460wye/266 but not sure if that is what i need.

Converting from 3 phase to single phase is more complicated than just getting a transformer. You basically have to convert it to some other type of power (either DC voltage or mechanical power) and then convert it to single phase.

Unfortunately there isn't a good answer for this. By the time you get any type of converter, you're going to be suffering some losses from the conversions, possibly as much as 20-30% (probably less) for a rotary phase converter, which pretty well negates any potential benefits.
For a more efficient phase converter you're looking at a digital phase converter (2-4% loss) but for the output you need (40 amps) you're easily looking in the $3500 or more price tag (that was for single to 3 phase converters, I still can't find 3 phase to single phase converters so likely the price would be a lot higher for one of decent quality)

For everything to make it work you are likely looking at more money thrown at it than just selling it off and purchasing a 15-20kw non-military diesel generator.

It's possible you could run off 2 phases just for the geothermal, but that would require a lot of tricky wiring conversion in order to run anything else in your household wiring off the unused phase.


Just a note on the "EMP Proof" that you mentioned, there was a study done a couple decades ago about EMPs and cars. The main results of the study, at least regarding cars, is that only 1 car out of everything they tested wouldn't restart, 2 died but restarted, and the dozens of other cars were unaffected. For the EMP to be powerful enough to really kill the electronics, you'd basically need to be within the blast radius of the nuclear warhead.
It's fun to buy things for worst case scenarios, but having the grid taken down by an EMP, unless you have a couple thousand gallons of diesel stored and available, it doesn't really matter as the fuel stations will also be dead and you won't be getting any replacement fuel.


I don't know what all you are trying to plan/prepare for, but if it's simply to have power available when the grid is down, up to several weeks worth, you're probably going to come out ahead by just purchasing a propane standby generator like the Generac 20-24kw air cooled standby. At the temps you mentioned, I'd say get at least a 500 gallon tank, and bury it in the ground to protect it from the cold (I think they also sell a cold weather kit for it to keep the battery warm and stuff like that).

 

[Guyfang]

How many wire leads are in the generator enclosure? If it's a 12 lead generator set it can be wired as zig zag or double delta for a dedicated single phase output at full rating. Otherwise, you should be able to wire as open delta with some 55% of rated output.

No. It can not be converted.

 

[DieselAddict]

If you are determined to keep the MEP804 the simplest solution is to create a single phase critical loads panel with lights, fridge, microwave, etc on it for that "extra" phase on the generator. Run the other two phases to your main panel.

My setup here at home is kinda like that with my base loads running off an inverter in an off-grid type config. All my large 240v loads are still in the main panel powered by utility and backed up by a MEP803.

If you have room on the wall next to your main panel its a surprisingly easy job to move circuits over to a new sub-panel.

 

[Evvy Fesler]

these are reported to be 10 lead heads so not really able to be converted unless you want to start tearing into the stator assembly itself to find where the other 2 leads should be (if I remember correctly, I could be wrong)

It’s not possible to “pull out” the other two leads. I’ve taken the rotor out of the stator and have thoroughly photographed the inside of the stator. There aren’t any leads coiled up and connected together that could be pulled. The connection between the windings is simply not available for modification. Marathon Electric also confirmed that it can’t be done. If you are mechanically inclined you could purchase a single phase main generator. IM me if you’d like a reference to a series of Marathon generators whose shaft is in the same position. I didn’t research any further to confirm that the base mounting bores will line up.

 

[davvy]

Converting from 3 phase to single phase is more complicated than just getting a transformer. You basically have to convert it to some other type of power (either DC voltage or mechanical power) and then convert it to single phase.

Unfortunately there isn't a good answer for this. By the time you get any type of converter, you're going to be suffering some losses from the conversions, possibly as much as 20-30% (probably less) for a rotary phase converter, which pretty well negates any potential benefits.
For a more efficient phase converter you're looking at a digital phase converter (2-4% loss) but for the output you need (40 amps) you're easily looking in the $3500 or more price tag (that was for single to 3 phase converters, I still can't find 3 phase to single phase converters so likely the price would be a lot higher for one of decent quality)

For everything to make it work you are likely looking at more money thrown at it than just selling it off and purchasing a 15-20kw non-military diesel generator.

It's possible you could run off 2 phases just for the geothermal, but that would require a lot of tricky wiring conversion in order to run anything else in your household wiring off the unused phase.


Just a note on the "EMP Proof" that you mentioned, there was a study done a couple decades ago about EMPs and cars. The main results of the study, at least regarding cars, is that only 1 car out of everything they tested wouldn't restart, 2 died but restarted, and the dozens of other cars were unaffected. For the EMP to be powerful enough to really kill the electronics, you'd basically need to be within the blast radius of the nuclear warhead.
It's fun to buy things for worst case scenarios, but having the grid taken down by an EMP, unless you have a couple thousand gallons of diesel stored and available, it doesn't really matter as the fuel stations will also be dead and you won't be getting any replacement fuel.


I don't know what all you are trying to plan/prepare for, but if it's simply to have power available when the grid is down, up to several weeks worth, you're probably going to come out ahead by just purchasing a propane standby generator like the Generac 20-24kw air cooled standby. At the temps you mentioned, I'd say get at least a 500 gallon tank, and bury it in the ground to protect it from the cold (I think they also sell a cold weather kit for it to keep the battery warm and stuff like that).

Thanks for all that info! I’m not worried about the apocalypse, just a couple weeks of no power or a nat gas shortage that would do the same. Was just going to have a 200 gallon tank that I will refresh every year. I thought a transformer was much simpler than that.

 

[Mullaney]

No. It can not be converted.

.
So... What if...

For example, at work we are fed from the grid with a 40 kva 3-Phase transformer out back behind my building. Wires come into the building and into a 480v panel (MDP). Several machines here run on 480v power from the 4th panel (480 Distribution Panel). Then, MDP then feeds 3 other panels across the building using transformers to create ("make") our 240v and 110v. Lots of things here need 3-Phase power in assorted voltages (just fyi).

My WHAT IF question is: Why couldn't the MEP 804 drive a transformer in a similar manner?

.

 

[Guyfang]

I am but a simple generator mechanic. Maybe someone smarter then me can answer that. But I would think it can work that way.

 

[DieselAddict]

.
So... What if...

For example, at work we are fed from the grid with a 40 kva 3-Phase transformer out back behind my building. Wires come into the building and into a 480v panel (MDP). Several machines here run on 480v power from the 4th panel (480 Distribution Panel). Then, MDP then feeds 3 other panels across the building using transformers to create ("make") our 240v and 110v. Lots of things here need 3-Phase power in assorted voltages (just fyi).

My WHAT IF question is: Why couldn't the MEP 804 drive a transformer in a similar manner?

.

Give the transformers a look and see how they are wired. A photo of the data plate with wiring diagram would be helpufl.

Are they sending a single phase of 480v with a neutral (aka 277v) to create your 240/120? That would make the most sense and also be lower cost transformers since its a single phase primary to a center tapped single phase secondary.

 

[Evvy Fesler]

.
So... What if...

For example, at work we are fed from the grid with a 40 kva 3-Phase transformer out back behind my building. Wires come into the building and into a 480v panel (MDP). Several machines here run on 480v power from the 4th panel (480 Distribution Panel). Then, MDP then feeds 3 other panels across the building using transformers to create ("make") our 240v and 110v. Lots of things here need 3-Phase power in assorted voltages (just fyi).

My WHAT IF question is: Why couldn't the MEP 804 drive a transformer in a similar manner?

.

They aren't converting the three phase to single phase. They're converting from 480 volts to lower voltages and providing a neutral. What may be confusing you is that the panels take the three "legs" of the three phase and split them out along with the neutral to derive 240 (probably 208 ) and 110 circuits. The various transformers throughout the building are likely buck/boost transformers that convert the 208/110 to 230/120, or they may be isolation transformers for dedicated circuits.

You may notice on your generator that there are five lugs to which you attach the wires from the load. They are labeled GND, L0, L1, L2, L3. If you read through the operator's TM, you'll find a section regarding connections. They tell you that you can make a single phase circuit from any of 1, 2, OR 3 and 0 (neutral). You're actually in a good position to do this because you're not trying to retrofit a single phase home or shop to use a three phase source. You can buy a three phase load center from most of the big box home centers, connect the lines L1, L2, L3 to the main circuit breaker and L0 to neutral. From there you can use individual (GFCI) circuit breakers to create your 110v circuits to feed your loads. Or you can buy a single phase load center and connect L1 and L3 to the main circuit breaker and L0 to neutral. You won't get 15 kW that way, but you said your application only needs 10 kW (start surge 15kW) for the HVAC unit. The three phase panel is probably the easiest way to go because it will provide circuit protection for all of the circuits you need, or for at least the ones you have described.

TM 9-6115-643-10 is available in the TM forum. Download it. It will become your first best friend. The one that ends in 24 becomes your second best friend!

 

[peapvp]

.
So... What if...

For example, at work we are fed from the grid with a 40 kva 3-Phase transformer out back behind my building. Wires come into the building and into a 480v panel (MDP). Several machines here run on 480v power from the 4th panel (480 Distribution Panel). Then, MDP then feeds 3 other panels across the building using transformers to create ("make") our 240v and 110v. Lots of things here need 3-Phase power in assorted voltages (just fyi).

My WHAT IF question is: Why couldn't the MEP 804 drive a transformer in a similar manner?

.

Yes, thats exactly on how you do it, with a transformer delta / Wye and use only two legs and neutral on secondary of transformer.
That transfers your load imbalance from rotating genhead to iron - oversize transformer by 30% + from Genset rating (KVA)
Your genhead will be evenly loaded in delta

 

[87cr250r]

Typically, in an industrial setting, a 480 to 208Y/120 transformer is used. For single phase power one tap is used and neutral. Some consideration must be made to balance the load between the 3 phases if the single phase loads are large. In my shop, I have 3 single phase panels, each one is connected to a phase. It's mostly lighting loads so they balance out well I'm this configuration. You can also get 3 phase panels and install single phase breakers in them. In this case you stagger where the single phase breakers land on the bus bars.

 

[98G]

Typically, in an industrial setting, a 480 to 208Y/120 transformer is used. For single phase power one tap is used and neutral. Some consideration must be made to balance the load between the 3 phases if the single phase loads are large. In my shop, I have 3 single phase panels, each one is connected to a phase. It's mostly lighting loads so they balance out well I'm this configuration. You can also get 3 phase panels and install single phase breakers in them. In this case you stagger where the single phase breakers land on the bus bars.

Please elaborate on the need to balance loads between the three legs. How evenly balanced? How much imbalance will it tolerate before damage or accelerated wear occurs?

 

[Coug]

Thanks for all that info! I’m not worried about the apocalypse, just a couple weeks of no power or a nat gas shortage that would do the same. Was just going to have a 200 gallon tank that I will refresh every year. I thought a transformer was much simpler than that.

For the load you are talking about, in extreme usage, you'll be burning more than 1 gallon per hour. If running other loads than the heat pump such as water heater and whatnot on the 3rd leg, you might burn as much as 1.5 gallons per hour.
A 200 gallon tank would last you approximately 1 week of heavy usage, possibly less if everything is running 100% of the time, maybe longer if your house is really well insulated.
For what you are talking about, a 600 gallon fuel tank would be more realistic.

If you went the propane route you would need a minimum 1000 gallon tank (or 2 500 gallon) and they would need to be buried to keep them warm enough for vaporization to take place at a high enough rate to feed the generator.

 

[87cr250r]

It's complicated, it depends.

It would be nice to see less than 10%. The first issue that arises is voltage regulation. Small generator sets may only sense voltage on one leg so if that leg is under substantially different load conditions then the output voltage of the other two legs would not be nominal. Even with 3 phase sensing this is still a problem as the regulator can only set an average output for all 3 phases.

Secondarily, if your loads aren't balanced you won't be able to utilize the maximum output of the generator.

 

[Coug]

Please elaborate on the need to balance loads between the three legs. How evenly balanced? How much imbalance will it tolerate before damage or accelerated wear occurs?

most generators will be able to deal with minor imbalances without issues.
Typically for a 3 phase setting, you can load the generator to 1/3 of it's rated capacity per led before causing issues.
On a single phase split voltage (120/240) you can do up to 1/2 capacity per 120V leg.

These MEP-8XX generators are overbuilt for the task they do, so you probably aren't going to damage them even if you exceed those levels by a little bit.

The closer you have the generator to being evenly balanced, the more efficiently it will operate and the less fuel it will use. Not a whole lot of difference in fuel usage when imbalanced, but over the long term it will cost you more in fuel.

So you really do want it as closely balanced as you can make it, but it's not the end of the world if it isn't.

EDIT: In the civilian world I commonly see decals on generators specifically stating not to run more than 50% imbalance. It's mostly to do with what the gen head can handle for the wiring size and output rather than what is efficient.

 

[DieselAddict]

For the purposes of backup power, don't beat yourself up over phase imbalance. If this was a PRIME application where the generator ran months and months then maybe I would worry.