GENERATOR QUESTIONS FOR YOU EXPERT ELECTRICIANS

[CobyRupert]

I saw something on wiring a zig-zag configuration on a MEPS 12 terminal type genset. It was not well explained. I am interested and will try and find something to make me understand it. Always interested in understanding how things work as opposed to just believing what I am told.

Zig-zag!!

I only heard of that configuration used as a grounding transformer.

I can get you through resistive grounding schemes, but if you're using zig-zag transformers for grounding, (or zig-zag gensets ??), that's beyond me!!

 

[Industrial Toys]

I only had heard of it for Rolling Papers! Maybe a scheme hatched after smoking some wacky tobakee.

Reconfiguring an MEP generator set for single phase 12/24 - YouTube

How to do it but not how it works.

 

[CobyRupert]

:laughing: :laughing: :laughing:

 

[nyone]

That video shows how to modify a 3ph only generator into single phase. The mep802 that i own has single and 3ph capability just by turning a switch. Its due to extra windings in the head.

 

[CobyRupert]

I got a crazy generator.
It is a 4 cylinder gas/propane generator, liquid cooled, but only produces 3000 watts. However, this is the crazy part, it produces that power at either 1 or 3 phase depending on what you want. I know there are many 3 phase generators, but I have never seen one so small in Kw's that can have either.

That video shows how to modify a 3ph only generator into single phase. The mep802 that i own has single and 3ph capability just by turning a switch. Its due to extra windings in the head.

...but the 3 phase kW/kVA rating is different than the 1ph kW/kVA rating....right?

 

[aczlan]

I saw something on wiring a zig-zag configuration on a MEPS 12 terminal type genset. It was not well explained. I am interested and will try and find something to make me understand it. Always interested in understanding how things work as opposed to just believing what I am told.

So do MEPPS sets typically have more windings than a run of the mill 3 phase alternator? Not that I yet understand the phase implications.

On the smaller MEP gensets (like nyone has), they ran all the leads out to a reconnection box so it can run either single or 3 phase.
The one in the video, IIRC had the leads brought out, but the genset was only setup for 3 phase, so you could only load it to 60% capacity.

That video shows how to modify a 3ph only generator into single phase. The mep802 that i own has single and 3ph capability just by turning a switch. Its due to extra windings in the head.

Yep, on your genset they ran all the leads out to the reconnection box so it can run either single or 3 phase. Most "civilian" gensets don't need that capability, so they save money by keeping those leads shorter and connecting them inside the generator head.

There was a thread on Steel Soldiers that went along with that video, I will see if I can find it.

Aaron Z

 

[nyone]

Of corse its rating is different not 1/3rd though.

 

[aczlan]

...but the 3 phase kW/kVA rating is different than the 1ph kW/kVA rating....right?

Not if you reconnect the wires to the generator head, if you do that, you will have the same watts available for single phase as it had for 3 phase. That was the point of doing that, more capacity at 120/240 single phase.

Aaron Z

 

[Industrial Toys]

I'm still going to try and understand this. But wording is important. Because a generator CAN be switched from 3ph to single, does not necessarily mean it will work to full capacity. It might, but it also might not.

I am just thinking out loud, but maybe the extra windings are to supply different voltage. Because you usually only get 208 when running single phase, which they say is generally not a problem, but I would disagree. I want 120/240. That extra series winding on each phase would make perfect sense if that were the case, but would not address the derating factor.

 

[grsthegreat]

208 is used all the time on 220/240 systems and is of no issue. A lot of apartments I worked on were supplied 3/0 to panels knowing everyone would have 208 volts. In the 100痴 of times I致e done this in over 35 years as an electrician I have had no issues. On average the only appliances using 208/240 in a residential panel are a/c, water heater, general heating and dryers. These are not effected by 208.

even if you rewire a 6 or 12 wire 3/0 to operate as single phase, you do get a loss in overall amperage available. Then again, I may be wrong Generator Phase Conversions: Electrical Conversion, Single Phase, Three Phase Power

It does get confusing.

 

[Industrial Toys]

I HAVE seen pumps not want to work on 208. And a transformer had to be used. For a resistive load, no big deal, just not a much heat. So they just go with a bigger heater to compensate, but you can't do that with a motor.

 

[Industrial Toys]

FERMONT MEP-84A 15KW Military Diesel Generator - Operating and Maintaining - YouTube

This is one hellova generator. The thing looks brand new! Why are these always available?

Video somewhat long winded and some editing errors.

Guy says 15 KW set will actually do 20 KW continuous single phase.

 

[HickoryFarms]

I'm still going to try and understand this. But wording is important. Because a generator CAN be switched from 3ph to single, does not necessarily mean it will work to full capacity. It might, but it also might not.

I am just thinking out loud, but maybe the extra windings are to supply different voltage. Because you usually only get 208 when running single phase, which they say is generally not a problem, but I would disagree. I want 120/240. That extra series winding on each phase would make perfect sense if that were the case, but would not address the derating factor.

Our Baldor generators at work can run single phase (120/240), 3 phase power and light (120/240/208 high leg), 3 phase power (120/208), and 3 phase power (277/480). Its changed via a switch and hooking up the leads at the transformer properly for the voltage required.

 

[aczlan]

FERMONT MEP-84A 15KW Military Diesel Generator - Operating and Maintaining - YouTube

This is one hellova generator. The thing looks brand new! Why are these always available?

Video somewhat long winded and some editing errors.

Guy says 15 KW set will actually do 20 KW continuous single phase.

They are available because they go through them and replace them so that they always work when they need them. Also, in the government budgeting system, if you don't spend all of your budget this year, you will be reduced by that much for next year.

It's probably rated for 15 KW at 5000 feet and 95 degrees ambient temperature. As such at a lower level and lower ambient temperatures, it can handle 20kw continuous.

Aaron Z

 

[Industrial Toys]

It frustrates me to work on projects and have to figure out every little detail and it's all done for you for cheap on these Mepps sets. What I don't get is, if these things are a no expense spared generator,why not pre lube or slow start and go to 1800 rpm when warmed up.

 

[aczlan]

It frustrates me to work on projects and have to figure out every little detail and it's all done for you for cheap on these Mepps sets. What I don't get is, if these things are a no expense spared generator,why not pre lube or slow start and go to 1800 rpm when warmed up.

No pre-lube and slow start are probably because it is supposed to be a simple "idiot proof" portable genset that will ALWAYS work as soon at it starts (hence the "battle mode" switch that bypasses all the auto shutdowns for if you MUST have power even if it means killing the motor in the generator)

Aaron Z

 

[nyone]

They are very idiot proof. Even down to the fueling. Hook up a remote fuel source and put the switch in aux mode. It will keep the onboard tank betwen 1/4-3/4 by its self.

At the price of these things MEP generstors now i would be buying a new one from a major diesel engine manufacturer, kubota or cummins. I bought mine and a few others directly from the military base. I had one mep803 with 2hrs that you could eat off of. I fully expect this generstor to last a few more decades with my minimal 25hrs a year use.

 

[Industrial Toys]

Not many people could look at the panel and understand it. Hardly Idiot Proof, if you ask me.

 

[RoyKing]

The 804a is a 3 phase only generator so you can only get 10k out of it for home use and you will only 208v check your AC. Plus running them un balanced at full 10k is not recommended, yes you can get 15k out because they will run overloaded.. So not what those in the know buy, that's why they are cheaper and plentiful. If you want 10k buy an 803a. Read up on Generators

 

[aczlan]

The 804a is a 3 phase only generator so you can only get 10k out of it for home use and you will only 208v check your AC. Plus running them un balanced at full 10k is not recommended, yes you can get 15k out because they will run overloaded.. So not what those in the know buy, that's why they are cheaper and plentiful. If you want 10k buy an 803a. Read up on Generators

The 804 is a 12 lead genset with 10 leads brought out, to convert it you would need to dig into the Gen head and break the connection for those two and bring them out.
It is possible to rewire the older MEP-004 generators for full output on single phase, see Sewerzuk's thread with the why's and the wherefores: re-wiring my MEP-004a for different voltages, including single phase

Aaron Z