Question about MEP-804A Generators wired 120/208.

[TheEquineFencer]

Does this generator have breaker protection? I figured I'd ask this before I dive back into the TM's for it. If not, what would be the correct way to wire breaker protection to protect the generator from an overload if you were to pull single phase 120/208 out of it? I realize this is only a 15KW until that can only do 52A on 3Ph. I'm thinking a 3Ph panel with a 50A main and seperate single or double pole breakers to feed single phase.

Please have mercy on me...it's been a hard week for me, I figured I'd try taking the easy way to start with...I've had to dig just over 3 yards of wet sand out to uncover some 500MCM feeder lines in a solar field...

 

[155mm]

Breaker protection like overloads?

 

[Coug]

The manual does say max of 52 amps for 120/208 operation.
So that gives you 2 legs of 52 amps 120V each, or a total of about 12,500 watts. You don't want to go over that as the generator head was not designed for an unbalanced load and you can cause major damage to it.

You'd want to use 50 amp breakers, so essentially you can run it as a 12KW max output of 120V power (only 10 KW of 208v)
Might get a few more watts of output if you increase the voltage, but I wouldn't go above 130V at most, and only that with dumb loads (only basic electronics/no electronics)


If you know exactly what you are doing and familiar with electricity, you can get away with a little more due to the .8pf the military builds into these things, but if you don't understand what I just said without having to look it up I strongly recommend against it.

 

[TheEquineFencer]

Breaker protection like overloads?

Yes, like overloads.

 

[Guyfang]

It has an overload, (K relay. It kicks out the K1 relay, (Output load)

 

[mciikurzroot]

If not tampered with, I'd way more trust the set's overload system than the typical inverse time possible ckt breaker you might use, you seem to understand your loads, thus im unsure why you dont take advantage of using all 3 of the phase's ... 120 is 120 no matter what phase you get it from and to go one more, seldom is the 240 load so critical that any or serious harm will come from operating the 240 load on 208.. You have a lot of capability with this set, take advantage of it.. mac/mc

 

[Coug]

If not tampered with, I'd way more trust the set's overload system than the typical inverse time possible ckt breaker you might use, you seem to understand your loads, thus im unsure why you dont take advantage of using all 3 of the phase's ... 120 is 120 no matter what phase you get it from and to go one more, seldom is the 240 load so critical that any or serious harm will come from operating the 240 load on 208.. You have a lot of capability with this set, take advantage of it.. mac/mc

If he's using it to power a panel originally wired to 120/240, then it would be a whole lot of work to separate out everything to operate on the 3 legs of 120/208.

 

[Coug]

It has an overload, (K relay. It kicks out the K1 relay, (Output load)

Will the relay kick out if it's just overloading one or two legs? I wasn't sure with the unbalanced load.

That and considering I put an almost 10kw load on my 802 once upon a time, and instead of tripping it bogged down the entire unit until it read 100% output (at something like 45hz) I'm not sure how much I trust it.

 

[TheEquineFencer]

The manual does say max of 52 amps for 120/208 operation.
So that gives you 2 legs of 52 amps 120V each, or a total of about 12,500 watts. You don't want to go over that as the generator head was not designed for an unbalanced load and you can cause major damage to it.

You'd want to use 50 amp breakers, so essentially you can run it as a 12KW max output of 120V power (only 10 KW of 208v)
Might get a few more watts of output if you increase the voltage, but I wouldn't go above 130V at most, and only that with dumb loads (only basic electronics/no electronics)


If you know exactly what you are doing and familiar with electricity, you can get away with a little more due to the .8pf the military builds into these things, but if you understand what I just said without having to look it up I strongly recommend against it.

Sorry, I just woke up from only 4 hours sleep and with a 192 blood sugar level. I guess 3 slices Pizza at 3-4 am from the local convenience store for a diabetic wasn't a good idea. I'll get my levels down a bit if I have to go chop wood , jog or something and get my my brain working right shortly. Coffee for now.

Resistive loads are at 1.0 PF, (perfect loads for testing output), capacitive loads and inductive loads are what the 0.8 PF ratings are for.

It came to me with a blown FU2 fuse that comes off G1,F1 going to A1,1. I figured it was from an overload.

I'm trying to figure a way so the guy can use it and have the generator protect itself in the future as the owner doesn't have a clue as to what he has. I'm looking a "cheap" safe way to do it. He's thinking of a fused 3Ph disconnect knife switch with 50A fuses in it. I'm thinking 3Ph panel, 50A main with single 20A breakers (120V 1Ph )and double 20A-30A (208V 1Ph) breakers out plugs for his loads. That way he could use it and if he overloads with an unbalnced load it would open breakers. He'd still need to try and balance his loads for it to "work right."

What he really needs is a 120/240 1Ph generator, but this is what he has to work with. It's a 10 lead stator, not a 12 lead, so that's not an option.

I was wondering also if it's possible to open the stator and find the leads where the connections are made internally and reconnect it as a 12 lead? I wonder if anyone has ever tried this? I ran into an old Electrical engineer a few years back that said he'd done that with I think an old Onan RDJC generator.

I'm open for suggestions.
EDIT: this failed to post when I wrote this yesterday, so I just went ahead and posted it.

 

[TheEquineFencer]

If he's using it to power a panel originally wired to 120/240, then it would be a whole lot of work to separate out everything to operate on the 3 legs of 120/208.

The actual owner will be pulling 1Ph power/loads from it for different loads. If I wire a 3Ph 50A breaker/panel and pull 1Ph loads from that panel box it'll have a bit more protection than it does now I think than him just wiring straight off the connection point on the generator.

 

[TheEquineFencer]

Will the relay kick out if it's just overloading one or two legs? I wasn't sure with the unbalanced load.

That and considering I put an almost 10kw load on my 802 once upon a time, and instead of tripping it bogged down the entire unit until it read 100% output (at something like 45hz) I'm not sure how much I trust it.

That's what I was wondering. My guess not, as it blew a fuse. I'm working on getting a "proper" load bank sized for this built.

I have one a I built a while back for a 3Ph 30Kw Onan I switched from 30Kw 3Ph to 20Kw 1Ph. I "picked" some heating elements from some old HVAC units until I got the correct amp load combination to put the generator at 100% at a 1.0 PF. Sunday afternoon I'm going back over to another "pickers" shop and scrounge through his stuff to get some elements I saw last night. I like building things BTW.

 

[Guyfang]

It came to me with a blown FU2 fuse that comes off G1,F1 going to A1,1. I figured it was from an overload.

This is the Quad circuit fuse. Read the attached document.

 

[TheEquineFencer]

It came to me with a blown FU2 fuse that comes off G1,F1 going to A1,1. I figured it was from an overload.

This is the Quad circuit fuse. Read the attached document.

Great info! Thanks.