rewiring MEP004 for single phase

[FREDS]

I have been lurking around looking for someone who has rewired an mep004 genset for single phase. I know that I can effectively use it as a single phase generator by pulling power from two of the three legs.

What I am exploring is trying to avoid un-balancing the load on the third leg and maybe getting 240 out instead of 208. And I have been told that the brushes have been known to carbon up on some gennys if run unloaded or with a light load. So if all that needs to be done is switch a few wires around, I think it might be worth giving it a try.

There have been posts on SS where people discussed doing this, and someone said that a commercial outfit buys these gensets and does it before reselling them. Does anyone know someone who has one or has done it themselves?

If these gensets can be reconfigured to single phase, with real 240V, I think that would improve the genset, even if it degrades the output from 15 kw since I will be using it Single phase anyway and so it will be degraded in my application.

And whatever can be done can be undone.

Anyone using an MEP 004?? Please chime in.

Fred

mvpa 26292

 

[Speddmon]

Welcome aboard Fred. I replied to your PM this morning.

Although I explained it in the PM, I'll repeat it here for others who might have the same thoughts.

First these generators are a "brushless" design. Meaning that use an induced voltage to excite the rotating field rather than brushes and slip rings. This also serves to give you a much "cleaner" output power. Suitable to run electronics and such with it, less "noise" in the sine wave.

The bigger issue here is with wet-stacking the engine on such a large generator. 15 KW might not seem too large, but in reality it is. Just looking at the output amperage, you may think, hey, I've got a 200 amp service, and this thing only puts out xxx amps. In reality, just because you have the 200 amp service, does not mean you are actually drawing anywhere near 200 amps. In actuality, at any given time you may only be drawing as little as 2 or 3 amps per "leg" or phase, and as much as 30 to 50 amps, or more...but that's only for a limited time usually.

I'm not saying this to try to discourage you, I would just hate to see you have major engine troubles down the road. I wish you the best of luck in your endeavor, and if you have any questions or need any assistance, feel free to post up or PM me, or one of the other members here on the board.

 

[FREDS]

I appreciate your reply regarding wet stacking.

I believe that it exists. And is a problem I will have to deal with. You are right, Unless I am cooking, waching and drying clothes, running a dishwasher, or filtering the pool, my amp draw is minimal. Guess I will just have to live it up when off the grid. Party at Fred's house.



I am still inerested in the rewiring issue because of the 240V vs 208 V differeence.

Has anyone done it.

AM I nuts and should just hook the thing up on 2 legs, it is only a backup generator, will run a couple of times a year for a couple of hours, or maybe a couple of days. Unless the "big one" hits.

-Fred

 

[brianrbull]

Rewiring

Fred Welcome The MEP-004 is a strictly 3 ph genset.....BUT it has a 12 wire alternator, the military has the unit set up so it can be set bewtween 110.208-220-380 volts. the change over is accomplished by moving a "Board" up or down. this changes the way the fields are "Stacked" Inorder to get single phaze you would need to discard teh militarys "Board" and connect the fields your self. this is simple in "Civy" Gensets but the military in its infinite wisdome made these things "GI" proof. I will explore this idea a bit for you. I will try to have an answer in a couple days.
The wetstacking issue is a valid concern. depending on you rload you might want to consider a MEP-003a That unit is set up for either single or 3 phaze operation. and 10kw is a lot of power for backup needs.

 

[rmgill]

Are these things Wye or Delta wound? If Wye, can you not center tap them for neutral and run them at 110 and get your three phase with neutral setup that's needed? Ie run two of the phases plus a neutral and your ground.

 

[Speddmon]

they are Wye connected...from what I've seen the military like to use the Wye configuration a LOT. 120/208 and 240/416 are both wye voltages as is 480/277. 120/240 and 240/480 are standard delta voltages.

If you set the generator for the lower voltage of 120/208, you would indeed get single phase 120 volts from any one phase to the neutral center tap connection. But from phase to phase you get the 208 single phase...unless you rewire everything in your house, the 208 would cause problems with your 240 appliances.

On the other hand, if you set the generator for the higher 240/416 voltage, you would get 240 volts single phase between any phase and the neutral center tap. and 416 phase to phase...obviously 416 volts is too high for your average home. and the 240 is not like what you need for your home. When we talk about 240 single phase for a home use, what you are actually dealing with is 240 volt 2 phase...you are using 2 hot legs of a delta configuration, with the center being tapped for the neutral.

Now, that being said, if you rewired the output of the generator for a delta configuration, you must be careful which phases you use, because any of the pairs of phases would give you 240 volts, but only 2 of the phases will give you 120 volts to the neutral, the other phase will give you roughly 208 volts to the neutral.

Plus you have the regulation and metering issues to work out...you need to make sure your regulator is adjusted to work with the new sensing voltages you are going to create by rewiring the output

 

[brianrbull]

Cound You "ReStrap" the 004a with the same coil combinations as the 003 in 110/240 single phaze? I understand that it would take some work and would not be a 2 min process. (IE no more military connection board) or is there something "Different" about the 003 ? Other than the obvious convient switch that changes the configuration.

 

[Isaac-1]

Ok, let me jump in a couple of issues,

In the case of the MEP-004 and MEP-005 the generator end is a 12 lead reconnectable generator, however the connection board system that comes with it is limited to the few quick change options Speddmon has already mentioned. The majority of civilian 12 lead generators have no easy switching system, instead the 12 leads are combined together (often with a simple nut and bolt through the lug and some electrical tape) to pick the voltage range either wye or delta connected 3 phase or single phase. In the civilian world their are standard T# on the leads to know how to connect them, there are also tricks to measure out resistance and connect if the numbers are too faded to read, etc. As a rule of thumb connecting ANY 12 lead generator to provide single phase service will limit its output to about 2/3 of the full rated power, the exception being designed with oversized components to allow full load in single phase mode. So the "Modificaiton" that the original poster was asking about is basicly ripping out the military quick change board and manually connecting the leads.

As to the MEP-002/003, I don't know if these are also internally 12 leads or not, I do know that my little MEP-016B is a relativley uncommon 6 lead generator and can therefore only support wye 3 phase connections or sinlge phase (low wye or single phase only for the technical people following this) selected through a switch.

As to what is easiest, before going to all the trouble I would check to see if anything in your house (assuming it is for home use) needs 240V, or will it run on 208V, many is not most "240V" home appliances will in fact run just fine on 208V, this allows the manufactuers to sell the same appliance in light industrail settings that only have 120/208 avialable. Check the dataplates to see if they say 208-230, I know at my house all my "240V" aplliances are really 208-230. One thing to watch here might be if you have an electric stove or water heater, these may be labeled 230V only, but in all likelyhood will work fine on 208V, but will not get as hot (lower watt draw on 208V). The big thing to be concerned with is anything with a 230V only motor as these can burn up is ran on 208V, in my limited expereince the mix on 208-230V vs 230V only small motors is about 50/50.

Ike

p.s. there may also be a small control transformer that may need to be replaced, or change taps on depending on how the voltage regulator on the MEP-004 works.

 

[southdave]

holy Crap I never get my genny working.

 

[Speddmon]

Ike,

Good points, but with the appliances, especially furnaces and probably some stoves, and even dryers, the control transformer inside the appliance will need to be rewired or replaced, or you will not have the voltage necessary for the controls of your appliance. This in itself can be a PITA, and should not be attempted by the average homeowner, because sooner or later damage could result from something being overlooked or forgetting to switch something over.

I'm not sure if this is the transformer you are talking about in your P.S. or not.

And Yes the MEP-002 and 003's are 12 lead heads. The reconnection switch switches much more than just the generator leads, it also switches the necessary control wiring to allow the metering to work properly. And since these sets are only selectable for the lower voltage wye and not the low/high voltage like the 004a the voltage regulation in the 002 and 003 is not an issue. It may very well be an issue in the 004 and larger sets.

 

[m16ty]

I've got a question about "wet stacking". I know generator people like to throw that term around but I have run diesel tractors for days on end with little load without any problems. The tractors are mostly running water pumps and augers which require very little power but may have a 100hp tractor hooked to them because that's just what's available at the time.

Is wet stacking that much of a concern on a generator that may only run a few hours a year? I admit I may be way off base on this but I haven't noticed any problems with running diesels with light loads.

 

[Speddmon]

good point m16, but I'm also willing to bet that you don't use your tractors like that every single time you get them out too. The problem crops up a lot more because of prolonged usage like that...if you have a 60 KW generator that is running your 1200 sq/ft home, it's NEVER going to see enough load at any time to ever burn off the build-up that is present from the previous lightly loaded run. Whereas your tractors will get a good work-out, whether it be plowing or mowing or whatever, probably the next time you fire them up, if not the next time, very shortly after you had run them that lightly loaded.

 

[FREDS]

Brian

It looks like I will not get more than 10K out of this big genset after I rewire it. At least as far as Ike's post is concerned.

I understand the military board would have to go.

Attached ( if I did this right) is the wiring diagram and schematic for what I think would be the applicable part of the genset.

 

[rat4spd]

It depends on how under-rated the set is. The 003's run 100% in single phase because they are under-rated in three phase to begin with, purposely for a number of reasons.

 

[Isaac-1]

Ike,

Good points, but with the appliances, especially furnaces and probably some stoves, and even dryers, the control transformer inside the appliance will need to be rewired or replaced, or you will not have the voltage necessary for the controls of your appliance. This in itself can be a PITA, and should not be attempted by the average homeowner, because sooner or later damage could result from something being overlooked or forgetting to switch something over.

I agree, however many particularly newer appliances have switch mode power supplies, and therefore no need to reconfigure. For the air conditioning/heating systems I would certainly suggest talking with your local installer/professional.

Ike

 

[m16ty]

good point m16, but I'm also willing to bet that you don't use your tractors like that every single time you get them out too. The problem crops up a lot more because of prolonged usage like that...if you have a 60 KW generator that is running your 1200 sq/ft home, it's NEVER going to see enough load at any time to ever burn off the build-up that is present from the previous lightly loaded run. Whereas your tractors will get a good work-out, whether it be plowing or mowing or whatever, probably the next time you fire them up, if not the next time, very shortly after you had run them that lightly loaded.

You make some good points that I haven't thought about. I agree that the tractors do get a workout after their jobs of light duty.

 

[glcaines]

I have an MEP-003A GenSet and although I have let it run for extended times with minimal load, I have not had it wet stack yet. However, my Deuce will definitely wet stack if left idling for extended times and my John Deere 5520 (89 HP) tractor will wet stack very easily if left running at minimal PTO loads for several hours. I suspect my MEP-003A GenSet will do the same if low load run times are extended.

 

[rat4spd]

Your Deuce and the MEP have one distinct disimilarity, and that is one is air cooled while the other is water cooled.

 

[Speddmon]

Gary,

rat4spd is absolutely correct...wet stacking can occur with an air cooled engine, but it will not happen as easily. It's just the nature of the beast, an air cooled engine will naturally run a little hotter than a liquid cooled one.

 

[FREDS]

We'll see

I really don't think that if you have a decent size property you can operate the Genny right, you should be able to load it up enough to blow the crap out the stack. Run your Stove, electric water heaters, AC, clothes dryer, Well pump, and 110 stuff like the Dish washer. I checked, Most of the 220 V stuff I have are rated 208/220

I really appreciate all the comments here as I have learned quite a bit. Although I had heard and read about wet stacking, all the comments here have reinforced that I can't hook the genny up and let her loaf along for hours.

Certinly sounds like an 003 is a better genny for home use than what I own. But the 004 definitely has the cool looking factor to it.

I am also becoming less interested in rewiring the generator. It soulds like it is not easy, and no one has done it that I can find.

Might be different if I had one with bad controls / electronics/ Pannel, IE if I had to replace the regulator and stuff, then possibly it might make sense to look into commercial parts that would work with a rewiring of the fields, instead or replacing or repairing what I have. But since everything works, maybe the answer is, if it aint broke, don't fix it.

Still looking for more comments and advice on the rewire, but that is where I am leaning from what I have read.