re-wiring my MEP-004a for different voltages, including single phase

[sewerzuk]

Sewerzuk !! Its great to have you back. As you can see you have been missed !!

Thanks! I really do try to keep up with my various online projects...but I have a lot of irons in the fire!
I have a couple hundred youtube videos up, am a technical editor for Zukiworld, husband and father, owner of 2 businesses, assistant fire chief on my local fire department, and more. Sometime I just have too many things going on at once, and I have to decide where to allocate my time. Since Ft. Lewis hasn't had any generators for the last couple of years I have been pursuing other interests. But, I'll still try to keep answering questions about the single phase mod...

 

[smurph]

I have run my MEP-005 into a 30Kw load bank for 8 hours and more on single phase. I do have the resistors on the CT though.

Sewerzuk, your conversion process and videos taught me a lot! And now I have a generators that are extremely flexible and reliable. (My residential grade Generac let me down with 48 hours of run time on it. They made good on it. But it was out of service when I needed it most.) 3 phase or single phase changeover that takes mere minutes, they are mobile, and they can handle a large loads. The Swiss army knife like abilities of a MEP-003 with a higher output! I'm loving it! I can power my M934, my house, or my machine shop with them. The ability to make parts when the power is out is awesome.

So thanks a million for your time!

 

[bimota]

While no one can diminish your SS contribution and resourcefulness I do want you to be slightly more forthright with our audience. Your quote "My conversion process does not reduce the generator's capacity at all" is 100% false - maybe you should the time to explain in more detail. Yes, I know you want to say a 15kw three phase converted to single phase will still make 15kw - that may be accurate but it is NOT the generators capacity - only a rating. As a community member please offer both the benefits and the costs so our community can make good decisions.

You may be selling video time and generators and want a large demographic the reality is that very few people will material benefit from these conversions and good machines will be diminished and made less efficient. So with all due respect - please deliver the full story rather than a marketing spin.

My conversion process does not reduce the generator's capacity at all. After the re-wire, these sets are capable of their full rated load in split phase.
I fundamentally disagree with your post; these sets make excellent backup generator sets for those of us with large power demands or extended runtimes. While a set like this may not be suitable for the average suburban home, they work quite well for a large demographic; a demographic that many of us here on the SS board fit into.[/QUOTE]

 

[sewerzuk]

While no one can diminish your SS contribution and resourcefulness I do want you to be slightly more forthright with our audience. Your quote "My conversion process does not reduce the generator's capacity at all" is 100% false - maybe you should the time to explain in more detail. Yes, I know you want to say a 15kw three phase converted to single phase will still make 15kw - that may be accurate but it is NOT the generators capacity - only a rating. As a community member please offer both the benefits and the costs so our community can make good decisions.

You may be selling video time and generators and want a large demographic the reality is that very few people will material benefit from these conversions and good machines will be diminished and made less efficient. So with all due respect - please deliver the full story rather than a marketing spin.

I don't know why you feel the need to, in a roundabout way, call me a liar but that is what you have done. I don't mind people pointing out my mistakes (I have made a few, and will likely continue to do so), questioning my process, or disagreeing with my opinions but when a person questions my integrity or intentions it pisses me off. You sir, have thoroughly pissed me off.

1. I am not in the business of selling generators. I am an ex-navy nuclear electronics technician, general contractor, firefighter, and inventor/tinkerer. I have bought, repaired, and and sold a few generators but do not advertise or offer single phase conversions, and I have not purchased a generator in about 2 years. I have done one conversion for a local guy who met me on youtube. I have converted two -006's and a few -004's (including one that I used for my own backup power). I generally enjoy interacting with people on forums, sharing knowledge and experience. I think that this kind of collaboration brings us all to a higher level of community. My local efforts have the ability to benefit more than just my local area. THAT is my motivation.

2. When I put together the conversion video 3 years ago I was NOT a youtube partner, did not have an adsense account, and therefore was not selling marketing space. I made absolutely nothing on the video. About 6 months ago I did become a youtube partner and there are now ads on my videos. I make a few dollars each month on the conversion video. This means that I made about $0.10 /hr for the time I spent researching, experimenting, and shooting/editing the video. The hours that I spent on this project were purely for the benefit of the community.

3. Contrary to your assertion that I am making "100% false" claims, the conversion DOES NOT reduce the generator's power capacity. After the re-wire of the generator head to the split phase zigzag configuration and with the addition of the resistors across the CT, it is limited by the same protection trip setpoints as when it is in its factory configuration. If you exceed these, the next limit is the power that the engine is capable of producing. After the conversion process, the generator is capable of delivering up to 130% of its rated output for an unlimited time (limited by the overload trips). It is capable of overload right up to however much horsepower the engine can deliver. These limits are the same limits that the set has when in its stock configuration. So, I meant to say EXACTLY what I said. If an MEP-004a was capable of 20kw (limited by engine horsepower) in 3 phase before the conversion, it is capable of 20kw in single phase after the conversion. The capacity is not diminished.

4. After conversion to single phase, the generator can easily be converted back to stock. No permanent changes are made (unless you cut the stock buss bar, but that can also easily be replaced with a jumper or a few $$ worth of copper). So, how does adding the ability of split phase power somehow diminish the value of the generator? You have an MEP-004a capable of 120/208 or 240/417 in stock configuration...after modification it is now capable of 120/208, 240/417, and 120/240. You state that you have diminished its value by adding this extra output voltage. Please explain why you feel this way, because I flat out disagree.

5. It is true that single phase motors (and some other loads) are less efficient that their 3 phase counterparts. But, if all you have to power are single phase loads, it makes more sense to re-configure the generator to supply split phase. A person that has a small shop and house that have a high power demand (electric clothes dryer, electric heat, electric hot water, A/C system, large air compressor, welders, etc.) can benefit from a converted MEP generator. A modified -004a is a much better generator than a 15kw aircooled generac generator is; it gets better fuel economy, has a longer life, handles overloads better, and usually has a much lower buy-in cost. A unit with the ASK is also quieter. If you have mostly 3 phase loads to power, then it makes more sense to leave the generator unmodified. But, the efficiency of of 3 phase or single phase systems has no bearing on the efficiency of the generator. It will use the same fuel producing 15kw of split phase as it does producing 15kw of 3 phase. You may not get as much work out of your single phase motors as you do from equivalent 3 phase ones, but this has nothing to do with the generator OR the conversion process. It isn't like people can simply choose to change over their entire shop or house from single phase to 3 phase...you have to supply power to match your loads.


I'm not sure why you feel the need to do this, but I would suggest that you re-evaluate your statements. You are wrong about my intentions. You are wrong about the generator's diminished capacity. And, you have accused me of intentionally misleading the SS community in an effort to line my own pockets. You owe me an apology.

 

[1800 Diesel]

While no one can diminish your SS contribution and resourcefulness I do want you to be slightly more forthright with our audience. Your quote "My conversion process does not reduce the generator's capacity at all" is 100% false - maybe you should the time to explain in more detail. Yes, I know you want to say a 15kw three phase converted to single phase will still make 15kw - that may be accurate but it is NOT the generators capacity - only a rating. As a community member please offer both the benefits and the costs so our community can make good decisions.

You may be selling video time and generators and want a large demographic the reality is that very few people will material benefit from these conversions and good machines will be diminished and made less efficient. So with all due respect - please deliver the full story rather than a marketing spin.

My conversion process does not reduce the generator's capacity at all. After the re-wire, these sets are capable of their full rated load in split phase.
I fundamentally disagree with your post; these sets make excellent backup generator sets for those of us with large power demands or extended runtimes. While a set like this may not be suitable for the average suburban home, they work quite well for a large demographic; a demographic that many of us here on the SS board fit into.

[/QUOTE]

I noticed an earlier post where you stated your negative opinions about converting these sets to single phase which I chose to ignore. In viewing this one however, you didn't just address the process but went much further to libel a fellow SS member with some downright derogatory remarks. I don't understand why you have chosen to get on this soapbox in the manner you did. I have been a follower of Sewerzuk's postings as they always provide helpful and generally accurate information. Anyone who can claim that everything they have posted on this site is 100% accurate with absolutely no mistakes is simply delusional. I have posted statements that I later corrected by editing and I'm certain that one could find existing threads of mine that still contain errors. That's the price of being a human--we all make mistakes from time to time.

Regarding the single phase conversion process, to date I have completed four MEP-004A conversions. All have consistently delivered a minimum of 18 KW based on load testing that went beyond one hour. Sewerzuk has continued to answer SS member's questions as they arise--this he has done at no charge and with no strings attached.

In conclusion I don't understand how you can bash someone who has worked so hard in developing a means for people to modify their generators to suit their own backup or shop power needs. From working on these units (3KW up to 30KW models) myself, I can relate to the time consumed in just trying to troubleshoot a problem, let alone trying to develop & test a significant change in configuration, not to mention the risks involved in using one's own equipment for testing purposes. You should really take a look at what you're trying to accomplish here; from what I can see, the fruit of your efforts will not be positive for anyone.

I join others in supporting Sewerzuk for all the time & expense he has spent (and continues to spend) in proving out the single phase conversion and helping others when asked. I for one greatly appreciate his continued participation in the SS forum.

Kevin

 

[captain]

Sewerzuk,

Thank you for all the time and effort you have spent on not only figuring out how to convert the 15KW+ gens but your continued support in helping us convert ours. My little MEP-004a is perfect for my home. It does everything I need at a fraction of the cost of a perkins or cummins onan. I like its simple design and ease of maintenance. Its a generator I can fix and have back up on the bus in short order if it ever breaks down during an outage. You have gone above and beyond in your detailed explanations of the generator configuration including its process, causes, effects and how to reverse the single phase conversion.

Thank you.

 

[bimota]

Ok, I get that my writing style falls far short of producing the desired effect and since I've managed to piss off a few good people I guess I better man up and deliver rather than ramp up the rhetoric. So I'll take that challenge if for no reason to prove myself wrong (based on the arguments to date that is highly possible). But, I choose to perform actual testing rather than debate this on line, with limited space, limited data and personal experiences which may or may not add clarification.

So I've got two MEP-004, one converted to single phase and one stock three phase - I'll put them on the load tester, video tape that and present the results. I'd also like to add in fuel consumption and even emissions results though I'd need some simple and low cost ways to measure those. This will take some time too setup in a structured way and I don't own a decent video camera so I've got to work that hurdle.

If I'm wrong them I'm buying you all beer and eating my hat, fair enough? If I'm right - what do I get?

 

[sewerzuk]

Ok, I get that my writing style falls far short of producing the desired effect and since I've managed to piss off a few good people I guess I better man up and deliver rather than ramp up the rhetoric. So I'll take that challenge if for no reason to prove myself wrong (based on the arguments to date that is highly possible). But, I choose to perform actual testing rather than debate this on line, with limited space, limited data and personal experiences which may or may not add clarification.

So I've got two MEP-004, one converted to single phase and one stock three phase - I'll put them on the load tester, video tape that and present the results. I'd also like to add in fuel consumption and even emissions results though I'd need some simple and low cost ways to measure those. This will take some time too setup in a structured way and I don't own a decent video camera so I've got to work that hurdle.

If I'm wrong them I'm buying you all beer and eating my hat, fair enough? If I'm right - what do I get?

It wasn't so much your writing style as it was the content of your message, but I appreciate your willingness to conduct the test.
Allow me to explain why I took exception to your comments. Had this interaction occurred on youtube, Pirate4x4, or any number of other forums I would have taken your comments in stride and appreciated the fact that you didn't simply call me an asshat numnut (or some other nonsense). Here on Steel Soldiers I have become accustomed to a more respectful level of interaction. When you claimed that my conversion reduced the capacity by 1/3, that I was making 100% false statements, and that I was withholding information and presenting a marketing spin in an effort to sell generators and marketing space, I became more than a little irritated.
The fact is that I have made maybe $6 on my youtube video. I've never offered the conversion to anybody (although I have reconfigured a handful of generators that I have sold at the request of the buyers, free of charge). I'm not withholding any information from anybody. If you take the time to read through this thread, you'll find that I've stated on several occasions that there are advantages to leaving these sets configured for 3 phase. I even put together a video that focused on using a 3 phase generator to power both single phase and 3 phase loads, and discussed how this differs from the conversion to split phase. I updated this thread during my testing, and even included some rather blatant mistakes when I was making modifications to the CT to adjust meter readings and trip setpoints. I have credited others who have PM'ed me during the process with their input, and welcomed suggestions from other SS members. I have also made it clear that since I cannot test every version of the MEP-004a that exists (I have seen a wide variety of components inside of the MEP's) there is no way that I can guarantee that the conversion will be successful for everybody. One person attributed a transformer failure to the conversion (though no testing was done to confirm this; the thread is somewhere in here). To date that is the only failure related to the conversion that I am aware of.

Though nobody can contest that a 3 phase system is more efficient than a single phase system, power is power (for the most part). Though you can pull power from 2 legs of a 3 phase generator to run single phase equipment, this DOES reduce the generators capacity by a little over 1/3 (limited by the maximum per-phase current, which reduces power output of an -004a to about 9kw). My goal for this conversion was to remove this limitation; to convert to 120/240 split phase and to be able to pull the same power out of the machine as it was capable of in 3 phase, and to adjust the meter readings and trip setpoints accordingly. As evidenced by my own load testing and the testing of others, the project was successful. As I have done extensive (though not exhaustive) load testing of my own including waveform analysis with my oscilloscope, and know of about 20 successful conversions by other people who have done their own load testing (I believe that many more than this have completed their own conversions), I have little doubt that you'll find that your comment that the capacity is reduced by 1/3 to be in error. I have only done resistive load tests at 240v, though I have run my own shop loads (which include some larger motors with high starting currents) at more than 15kw for many hours. You may find that the generator's output changes by a few percent, but for all intents and purposes the power capacity post-mod is the same as stock and is limited by the same trip setpoints and equipment limitations as stock. This removes the 1/3 power "loss" that exists when using 2 phases of a 3 phase generator.

I welcome your test. Depending on the kind of load bank that you have, you may uncover limitations that I have not. You will find that, if you do the conversion and complete the CT mod as I have outlined in this thread, the power generation capacity of your converted -004a is within a few percent of its pre-conversion power capacity. With regards to emissions and fuel consumption...I have done no testing on these. Although, I suspect that you'll find that a machine uses the same amount of fuel producing 15kw of split phase as it does producing 15kw of 120/208, 240/417, or any other voltage (15kw of real power...not reactive load).

No beer is necessary...but an apology would be appreciated.
As for what you get: If for some reason you can prove that I have deliberately been withholding information in an effort to make some money, and that the generator's capacity has indeed been reduced by 1/3, then I will offer you my apology. If you find that I made a mistake in my conversion process, then I will offer you my thanks for the information. If you find a problem with the conversion process and come up with a solution, then you'll earn the respect that comes with providing a valuable contribution to the SS community.

edit: in re-reading your last post, it appears that you already have an MEP-004a converted to single phase. How did you do the conversion? And did you complete the CT mod?

 

[smurph]

If I'm wrong them I'm buying you all beer and eating my hat, fair enough? If I'm right - what do I get?

I have no idea what you would get! How about nice single phase conversion whether you are wrong or right? Because that is what I got. Color me completely happy!

As explained before, I have a machine shop that has mostly three phase equipment. But no three phase power at the location! So I actually use a rotary phase converter to get the needed three phase. The MEP-005 would run the equipment fine on 3 phase but the wiring would have been more complicated having to have different boxes etc, depending on if the single phase line or the 3 phase generator was feeding the shop. So I wanted a high output single phase generator that could do the job to simplify the backup duties. The rotary converter is 20 HP converter and requires about 75 Amps to start the thing at 240v. The MEP-005 in single phase doesn't even blink. Peeeeeeeeerfect!

Now, being a believer in "trust, but verify", I have done some tests. As well as used these units in a real life practical application.

Fuel consumption (simple and low cost):
On a full 30 Kw resistive/inductive load, single phase, right at 2.5 GPH at 900 ft. above sea level. So about 8 hours run time on the internal tank. This is inline with the manual spec of 2.85 GPH fuel burn on 3 phase. (Efficiency isn't built into these units to begin with!) Two MEP-005s single phase conversions performed nearly identically. One unit having 17 hrs on it since rebuild and the other having 1159 hrs on it having never been rebuilt. With a 10 Kw pure resistive load, I get 1.7 GPH. All fuel consumptions tests based on a dry tank with 5 gallons added with a run time of 1 hour. The fuel was drained with the lift pumps and measured to calculate the consumption. There is a neat little fuel flow meter on an auction sight that will work on 24v that will be added soon!

Load Bank:
Resistive heat pump "emergency" strip heaters in a duct with a squirrel cage fan to cool them down. A "Poor man's load bank". 5 Kw, and two 10Kw strips that are switchable for any load combination up to 25 Kw in increments of 5 Kw. The load bank was built to clear wet stacking, if needed. I load the units to full 30 Kw buy turning on items in the shop for a 5 Kw draw and then throw the load back in on top. I had 35 Kw loads on them at times.

Emissions (lowest cost of them all!!!):
Not a concern in an emergency situation. But my built in sniffer says that diesel fuel is being burned.

Wet Stacking:
The MEP-005s appear to not exhibit any wet staking symptoms if they have at least a 10 Kw load during the summer. Not tested during the winter. The test was running at 10 Kw for 2 hrs and then adding 15 Kw after that time to see if any additional "clearing" smoke was evident.

It isn't all about efficiency, or a comparison with a commercial vs. military unit for a lot of us. For me, it was being able to get the job done in an emergency situation. A job that my commercial unit would not do. And to get one that would do that job would have cost me thousand more than the MEPs (if we are making comparisons).

I got MEP-005s instead of MEP-004s because I wanted a bit of head room as far as capacity goes. But now that they are converted and I see them running full 30 Kw single phase loads on my load bank, I'm now completely convinced that a MEP-004 would do the job. Through the conversion process along with the guidance of sewerzuk (who obviously knew way more about what he was doing than I did), I began to understand a bit about what was going on inside these things. I also began to understand that these units are built like tanks. I get the feeling that the generator heads can probably handle sustained loads far greater than their name plates say. And I believe that the prime mover is the bottle neck as to the total sustained output.

So the bottom line, for me, is that a MEP-005 "rated" at 30Kw does indeed do 30Kw in single phase configuration. Not just in theory, but in empirical testing, and most importantly, practical application.

It would be interesting to see what your MEP-004s do. But I wish you had some MEP-005s as well to compare with my results. The fuel burn rate is always going to be a bit subjective because of altitude/temperature/humidity variances.

Also, a note on what sewerzuk said on the failures and the differences between various MEPs. Out of the 3 MEP-005s I have converted, I found some wiring mistakes in one of the rebuilt ones (17 Hr unit) that effectively eliminated some of the fault protections!!! New means new. New does not mean good. Rebuilt means rebuilt. Rebuilt does not mean good. This very same unit also had a voltage regulator failure after the conversion. But the conversion was NOT the cause. Corrosion was! The VR just simply gave up at a coincidental time. I documented this and showed how to repair the VR on this site. Had I not already converted another one successfully, I would have surely suspected a problem with the conversion (either the process or a mistake by me). And I would have assumed wrongly! So just be careful of making assumptions if something doesn't go as planned.

 

[bimota]

Ok, let me start by apologizing to sewerzuk for being an ass. Coming across as an ass happens more often than I'd like because of my writing style and never in person. But that is just an excuse for never learning to write English in an way that gets the message across without irritating people. You should see how the local politicians react

So my thinking came from two realities that converged recently, and likely greatly influenced my prior posts. Probably fantasy but could be early mental illness....

One of our friends takes videos of her playing slot machines in Vegas and posts them on YouTube, she gets a $400 a month check from Youtube. The idea that people watch other people play slot machines and that taking cell phone videos and posting them can make you $400 a month starting twisting in my mind. So I made the assumption that sewerzuk was cranking in some cash from YouTube. Had I taken a moment and thought about it I'd realize there are about 1000 people in the country actually interested in this topic and probably only 20 that will actually do this conversion that would have stayed my hand.

Also, the fact that I have two beautiful, low hour, painted, load tested and ready to work MEP-004s that I cannot sell for dirt probably pushed me far into fantasy. Sewerzuk moving wheel barrows of cash to the local banker while I was chained to 5000lbs boxes of rocks kept floating thru my head. BTW - I sold eight Generac 14kw diesels in the last three months from $2000-$5000 per unit, could not keep up with the demand - three of the units were over 7000hrs. I pitched the MEP-004 with the single phase conversion to every buyer, no thanks was all I got. No amount of this is a way better machine, will last longer, only has 1750 hrs on it made a bean worth of difference. Both inexperienced and experienced buyers all made the same comment; harder to use, harder to fix, heavier, no thanks.

So maybe this clarifies that slowly and surely how I'm starting to hate these 5000lb boat anchors. Ok, ok, stop me from careening off into frustration land and saying something that will piss off more good people. The reality is that very few people want a 5000lbs single phase 15kw generator even if it produces 18kw but you could argue that even fewer people want a 5000lbs three phase 15kw generator that produces 18kw or more.

I still plan to do the test - why not, I can watch these units rust or I can play with them, learn more about generators and power generation. Maybe re-brand them as 20kw units and see if that helps, probably not. Maybe even make $6 from the videos like sewerzuk. Just so you know my business is a not profit and we create local jobs by recycling generators and building off grid power plants. So I'm not actually trying to make money just trying to keep the doors open.

 

[m-35tom]

Yep; my plan is to get 100% of the generator's rated output from L1 and L3 at 120/240v; same as common residential service. This also allows you to get 240v, instead of 208.



Wow...missed that one during my searches! The author of that web page did EXACTLY what I was planning to do, with reference to the low zigzag wiring. At least I can fire mine up now without worrying about wearing my firefighting gear

He accomplished the proper output voltage, but still had to live with the reduced output because of the overload trip setpoint, and the funny meter readings. I intend to solve and/or explain those issues with my conversion.

I'll get right to doing a "how to" video for the -004 and -005. I'll post it up here as soon as I'm done...

while you can get 120/240 output easily, you can NEVER get full potential power output of the gen head. you will get 66% of rated because any way you rewire a 3 phase gen you are only having 2 coils in parallel not 3. the current is limited by the wire size in the gen.
you might just as well leave it in 3 phase low voltage mode and get 120/208. that way you can get about 70% of available output because the 3rd set of windings is not producing heat.
the exception to this would be a generator, like a military unit, that is way under rated to start with. if you are going to do testing, start by knowing the wire size used in the coils and how many coil sets are parallel by design for each output coil.
also without reading all the posts let me suggest an easy way to deal with the load meter and overload circuit. simply reduce the number of turns going through the load sensing coils. that with some careful measuring will result in a dedicated single phase unit.

 

[sewerzuk]

Your comment falls into the "mostly technically correct but doest fully apply to this situation" category. The generator ACTUAL real power capacity os not diminished after the conversion to single phase. I will sit down at the computer later tonight to write a detailed explanation about the limits of the generators and how they differ before and after the conversion.

 

[m-35tom]

yes i realize that, but it is because the unit is grossly under rated to start with

 

[sewerzuk]

while you can get 120/240 output easily, you can NEVER get full rated power output. you will get 66% of rated because any way you rewire a 3 phase gen you are only having 2 coils in parallel not 3. the current is limited by the wire size in the gen.
you might just as well leave it in 3 phase low voltage mode and get 120/208. that way you can get about 70% of rated output because the 3rd set of windings is not producing heat.

Now that I'm home and at my computer, I can write a detailed response

I'm sorry, but I have to disagree with you. I can, and HAVE obtained the FULL RATED POWER OUTPUT of the MEP-004a and MEP-006a generators after conversion to split phase. This is 60kw for the -006a and 15kw for the -004a. I have done extensive testing at power levels above the rated output, right up until the engine can no longer maintain 60hz (over 70kw for the -006 and close to 20kw for the -004). This testing included operation of the installed protection setpoints, measurement of individual phase currents, and temperature readings with my infrared thermometer. If you need factory-installed evidence, the -002a and -003a sets have this capability built right into them. Operation of the selector switch re-wires the 12 lead head into the low zigzag configuration and re-configures instrumentation and control to account for the different voltages and currents. A -003a isn't de-rated from 10kw to 6 KW when you select single phase, and neither is the -004 if you complete the conversion I have outlined.

Perhaps you are arguing that a 12 lead generator HEAD will reach its design limits while producing split phase before it reaches those limits while producing 3 phase...and if that is what you are trying to say, then I completely agree.
BUT, the current carrying capacity of individual bits and pieces inside of the generator head and conductors inside of the generator are not the limiting factor in an MEP's power generation capacity. When determining how much power a generator set can produce, there are hundreds of possible limits; generator head design (including rotor torque capacity, heat removal capacity, current carrying capacity, slip rings and brush capacity where applicable, etc.), the current carrying capacity of the power distribution wiring (conductor size, connection points, main contactor capacity, etc.), field current power supply capacity, and much more. In the case of the MEP sets, that design limit is the horsepower of the prime mover. From my experience, the engine is capable of delivering anywhere from about 130-160% of the generator's rated output. Beyond that, frequency starts to drop off as horsepower demands are exceeded. After conversion to split phase, engine horsepower is still the most limiting factor. It will produce as much split phase power as the engine is capable of producing. So, if a particular -004a was capable of 19kw in 120/208 wye, it will be capable of 19kw in 120/240 split phase. The real power generation capacity is not diminished following re-wire to split phase.

I am not privvy to the design margins engineered into the MEP generator sets, but I have worked on literally hundreds of military and civvy generators ranging in size from 1kw all the way up to 300kw. I have a pretty good feel for how large a normal 12 lead 15kw generator head should be. The MEP's generator heads are SIGNIFICANTLY oversized. It wouldn't surprise me if they could handle 300-400% overload with 100% duty cycle. Even if we complete a modification with one of these sets that increases current flow in a few places, I firmly believe that we are still well inside of any normal design margins. Yes, we are operating closer to these limits. But operating closer to design limits is not the same thing as diminished capacity.

The best analogy I can come up with goes something like this:
I buy a used Toyota. It makes about 60 horsepower and can reach 90 MPH. It has performance tires that are rated for 150 MPH. I realize that I will be driving in the snow and ice, so I replace the tires with some new mud and snows. They are only rated for 124 MPH. I have NOT diminished the top speed capacity of the car. It was always 90 MPH, limited by horsepower and body design. Yes, I'm operating a little closer to the tire's limits, but the point is mostly moot since I can't reach the limit of either tire design anyway.
In the same way, we have not diminished the capacity of the generator. Its power generation capacity is limited by horsepower both before and after the conversion.

With respect to your suggestion that we are better off leaving the set in 120/208 for powering single phase loads, to that I also disagree.
If you intend to power loads that are rated for 240v with a generator, then the generator should be configured for 240V! While 95% of all 240v single phase loads will work OK on 208, your hot water heater will heat water more slowly, your dryer will dry clothes more slowly, your oven will produce less heat, your electric motors will draw more current and operate hotter, etc. If you leave the set configured for 120/208, the only way to get split phase is to pull from 2 legs. In this case, 100% of the load current will be passing through 4 generator windings and 2 windings will be completely unused. Because of this, you are limited to about 8700 watts out of an MEP-004a (limited by the 100% phase current, about 41.6 amps). So, if left in 3 phase, you can only get about 60% of the generator's rated output (not even 2/3). Of course, you can push this up to the trip setpoints, which, if you can ride that fine line of 130%, gets you about 11kw (realistically, only about 10kw if you don't want the set tripping off every 10 minutes). You are nowhere near the engine's horsepower limit in either case.
If you do the zigzag conversion and install the shunt resistors on the CT as I have outlined in this thread, the new output voltage is 120/240, the new meter readings and trip setpoints are designed to operate properly with the new voltage, and the new limit is engine horsepower. It is then possible to pull up to about 18kw indefinitely, and more for short periods (limited by horsepower and the inverse time contactor trip setpoint). The power limit is not reduced. The efficiency of power generation is reduced by a miniscule amount (a person can argue that increased current flow inside of the generator in single phase results in heating and increased power loss...and that person would be correct. But we are talking about maybe 1/10 of 1%). Yes, there are some higher currents flowing inside of the generator, and because of this we are operating closer to design limits. But we are able to obtain the full rated capacity of the generator in split phase.

 

[m-35tom]

yes i agree with this, but with this observation. the mil generators must be rated at the 120/240 configuration to begin with, and very under rated at that.
i have to wonder about the 10 wire units like mep-805 and 806 that have 10, 11, 12 wire tied together internally. i will have to load test a 805 at 30 kw from
just 2 legs and see how hot it gets since by design it was not intended to be rewired.

 

[R Racing]

yes i agree with this, but with this observation. the mil generators must be rated at the 120/240 configuration to begin with, and very under rated at that.
i have to wonder about the 10 wire units like mep-805 and 806 that have 10, 11, 12 wire tied together internally. i will have to load test a 805 at 30 kw from
just 2 legs and see how hot it gets since by design it was not intended to be rewired.

Please do and let us know. I have a mep-806a I plan to run single phase to 3 separate panels so first panel would be A to C 2nd B to C and 3rd A to B . The panels are pretty well balanced but the loads do very so I would be interested in your results.

 

[sewerzuk]

yes i agree with this, but with this observation. the mil generators must be rated at the 120/240 configuration to begin with, and very under rated at that.
i have to wonder about the 10 wire units like mep-805 and 806 that have 10, 11, 12 wire tied together internally. i will have to load test a 805 at 30 kw from
just 2 legs and see how hot it gets since by design it was not intended to be rewired.

I would be interested to have this information as well; but keep in mind that pulling 30kw from 2 legs of a wye generator at 208v produces significantly more phase current than pulling 30kw from a zigzag split phase generator; you'll be pushing your generator head even further beyond what it was designed for.
While your test results will be valuable, it isn't the same thing as the split phase conversion...

 

[R Racing]

I would be interested to have this information as well; but keep in mind that pulling 30kw from 2 legs of a wye generator at 208v produces significantly more phase current than pulling 30kw from a zigzag split phase generator; you'll be pushing your generator head even further beyond what it was designed for.
While your test results will be valuable, it isn't the same thing as the split phase conversion...

I agree with you !! oddly enough page 2-19 of TM 9-6115-645-10 says on the MPE-806A can run single phase from either neutral to any 3 legs or leg to leg if I read it correctly.

 

[smurph]

I agree with you !! oddly enough page 2-19 of TM 9-6115-645-10 says on the MPE-806A can run single phase from either neutral to any 3 legs or leg to leg if I read it correctly.

And that would be correct! One leg of 208 wye is 120v single phase. Leg to leg is 208v single phase. Run into a 3 phase breaker panel and that how one would use it. However, you would have to pay close attention to how the loads are distributed across all three legs with a generator. Not something you have to worry too much about with mains power. Since you would only be using two legs on a 208v single phase load, the expected output would be 2/3s rated output (20Kw on the MEP-806). That is where the 66% number comes from. But you would have 10Kw available on the spare leg to neutral for a 120v single phase load.

With careful load planning and electrical box configuration, one might not need to convert any of these things to split phase operation. But if your load is single phase to begin with (standard 240v single phase with neutral style electrical panels), then converting these things make a lot more sense.

Sounds like the MEP-804/5/6 may not be convertible unless you could get to the internally tied 10, 11, and 12 wires and break them out somehow. Bummer... Because I really would like a MEP-804!

 

[sewerzuk]

I have had at least 30 emails, PM's, and youtube messages from people asking how to convert the 804/5/6 to split phase. I've never had the chance to work on one!
Kinda makes me want to track one down to at least look at its "guts."

I actually used my -004a in 3 phase for backup power to my house and shop for quite some time. Since I had both 3 phase and split phase panels in my shop and a separate split phase panel in my house, I was able to keep the loads roughly balanced without exceeding current limits. But I have all electric appliances (no natural gas out here in the sticks where I live) and everything worked noticeably slower. The worst offender was our clothes dryer...seems like it took more than twice as long to dry a load of clothes running on 208.

I put together a video a while back on powering single phase loads with a 3 phase generator. It really does make sense for some applications...but for residential backup I feel like the split phase mod is the way to go most of the time.