MEP-016B 3 Phase Generator and Loading

[ETN550]

Trying to understand the 3ph generator and what acceptable loads are.

The unit is 3KW rated but shows about 95% load when a 4kw resistive load is applied at 240VAC 1ph.

With the redistribution switch in the 240 VAC 1ph position the load switch will register the same load for L1 and L2.

The generator appears to accept loads indicating less than 100% in excess of 3kw load in all of the redistribution switch positions. This is with adjustment of voltages to the nameplate spec of the driven equipment.

Question #1: Is it ok then to live by the load meter regardless that the apparent load is greater than the rating as long as it is under 100%? Or Reading the fine print on the meter (Load at 1.0pf) do I need to stay under 80% for constant duty?

Queston #2: Is is correct to assume that running single phase output in this 6 lead 3 phase machine will not cause undue stress on the rotor and windings due to unbalance non-3 ph power being extracted from the machine? I was told it was not a good idea to have unbalanced loads in the windings.

I am very impressed with the robustness and overdesign of these generators. I am looking forward to running the in a variety of applications.

Doug

 

[Ken_86gt]

My opinion is that you can overload the generator for a short time with no issues. Many commercial grade gens will run at 120% nameplate for an hour if it is rated as prime power, not if rated as standby. You should limit the load for normal operation to it's nameplate rating and take into account de-rating factors.


The generator has no problems with imbalance running in a single phase configuration. The only imbalance issue that people talk about is running a machine that is in a 3-phase configuration with a single phase load. I don't believe that this is as big a deal as some people think it is as long as you operate the unit within it's designed specs. If you overload a particular winding there should be protection to trip the unit.

 

[Keith_J]

When running in 3 phase, you have 208 volts between phases and 120 volts to ground from each phase.

When running in single phase, two wire 120 volts, the windings are paralleled in a high leg delta, the load is balanced over L1 and L3.

In single phase, 240 volts, L1 and L3 are again the load with L0 being neutral and ground at the generator. Always ground... Anyhow, the windings are a double paralleled single delta. Again, the load is balanced.

Now for 3 phase 208 volts, the windings are in a paralleled wye. Voltage from L1-L2, L2 and L3 , L3 and L1 are all 208 volts. But L1, L2 L3 to ground are 120 volts. So you COULD run three circuits of 120 volts with 3 phase BUT if one circuit were to have more load, this would imbalance the engine and cause issues with the governor or engine.

Yes, when running pure resistive loads, the power factor of unity (1) means your generator can tolerate greater overload. But running a motor/transformer load, you should stick by the power meter. Starting large motors will spike it, as long as frequency stabilizes, all is fine.

These generators are built far better than any consumer grade you can buy. They are on par with commercial standby units as far as load and durability.

 

[ETN550]

When running in 3 phase, you have 208 volts between phases and 120 volts to ground from each phase.

When running in single phase, two wire 120 volts, the windings are paralleled in a high leg delta, the load is balanced over L1 and L3.

In single phase, 240 volts, L1 and L3 are again the load with L0 being neutral and ground at the generator. Always ground... Anyhow, the windings are a double paralleled single delta. Again, the load is balanced.

Now for 3 phase 208 volts, the windings are in a paralleled wye. Voltage from L1-L2, L2 and L3 , L3 and L1 are all 208 volts. But L1, L2 L3 to ground are 120 volts. So you COULD run three circuits of 120 volts with 3 phase BUT if one circuit were to have more load, this would imbalance the engine and cause issues with the governor or engine.

Yes, when running pure resistive loads, the power factor of unity (1) means your generator can tolerate greater overload. But running a motor/transformer load, you should stick by the power meter. Starting large motors will spike it, as long as frequency stabilizes, all is fine.

These generators are built far better than any consumer grade you can buy. They are on par with commercial standby units as far as load and durability.

Okay, I think I got what you are saying. However, on this generator L1 and L2 are the single phase outputs for both 120 and 240. If I understand it this might be a difference between the 016B/E series and the 016A/C/D series.

Realistically I have no three phase devices to run and I do not have three evenly balance single phase devices to take advantage of the three phase configuration. Nice to know it is there if needed though.

I will live by the load meter and go up to 100% resistive and 80% =/- for the inductive loads. The biggest inductive load i have is the camper A/C and it is about 40% load running. I believe this generator could run two camper roof air units given its ability to handle a starting surge.

The manual does have some errors labeling the legs on their winding connection diagrams so I am hesitant to say this unit can produce 120 and 240 single phase at the same time. The data plate does not list a 120/240 mode for single phase. Specifically, it wants one leg of the 240 output grounded yet it will produce 120 (with no ground) at the service outlet while in 240 mode. Why can't I get 120 even if it is +/- 60 to ground if I don't bond the neutral to ground there should be no issue??

I plan on using 120 single phase mode on my 30A 120 VAC camper connection which will be perfect for this generator. However, I cannot see how I can backfeed a 240 breaker to my house to make 120 and 240 which I was hoping to do. Having to ground one leg of the 240 means it cannot be tied to the residential 240. Anyone got around this? I could run just 240 appliances and turn off all the 120 breakers to avoid puting 240 on a 120 line in the house but that gets too complicated. Can L0 be grounded to make 120 from L1/L0 and L2/L0 while having 240 at L1/L2?

 

[Keith_J]

Always check voltage to ground before using. Yes, when you ground the middle leg of 240-3 wire, you still have 240 volts over the other two legs and 120 volts to ground.

That is how 240 works, it should be the same with your generator set. This is a safety issue, there is never any more than 120 volts to ground, yet you have 240 volts for larger loads.

 

[derf]

That gen should run 4kW loads all day long. In the eyes of the military that gen will put out AT LEAST 3kW, even at extreme temps and altitudes. In normal situation it will do 4.5kW and probably surge even higher for short periods.
Disposable crap generators are over rated. Military generators are under rated. The truth lies in the middle. That gen in the civilian market would probably be rated 4.5kW and cost $2500 new.

 

[ETN550]

Always check voltage to ground before using. Yes, when you ground the middle leg of 240-3 wire, you still have 240 volts over the other two legs and 120 volts to ground.

That is how 240 works, it should be the same with your generator set. This is a safety issue, there is never any more than 120 volts to ground, yet you have 240 volts for larger loads.

Yes I agree and I am going to explore that configuration when I run it again. What through me for a loop is the manual says in 240 mode to ground 1 of the 240 legs! However, in the 240 mode the service recepticles on the front do produce 120!

 

[ken]

Im with derf. Every piece of military equipment i have is underated. The civi version of my MEP003 is rated a 15KW. And the civi version doesent come with the oil cooler. I too have ran 4K off of mine with window unit AC's. The load meter showed 80%.

 

[derf]

Yes I agree and I am going to explore that configuration when I run it again. What through me for a loop is the manual says in 240 mode to ground 1 of the 240 legs! However, in the 240 mode the service recepticles on the front do produce 120!

When you change the switch, you change the wiring to the terminals. The convenience outlet on the front panel is for lights or whatever and is not affected by the output switch located inside the box.

 

[ETN550]

That gen should run 4kW loads all day long. In the eyes of the military that gen will put out AT LEAST 3kW, even at extreme temps and altitudes. In normal situation it will do 4.5kW and probably surge even higher for short periods.
Disposable crap generators are over rated. Military generators are under rated. The truth lies in the middle. That gen in the civilian market would probably be rated 4.5kW and cost $2500 new.

I ran a 4Kw heater and load meter was at about 95% on the meter.

Probably cost a lot more than $2,500 if made today to the same standards. The military's acquision cost sticker on mine is listed at $3,460.00 in 1988. The quality of the connectors, fuel system, controls, switches, meters, aluminum frame, real industrial fuel filter water separator, all reinforced hoses with screw on AN fittings, aux fuel pump, 3phase generator, 603cc american made Onan diesel (biggest yanmar single used is 418cc) speaks volumes for it.

I worked on commercial engines that used those same screw on Cannon connectors on the wiring harness and they cost $20 to $50 each and more. That big one behind the control box to the engne harness is probably a $200+ connector new from Cannon. Plus each individual pin, plug, socket, connector cap, and body is separately available from Cannon for repair. This means we can add wires through the existing connectors, eliminate wires, repair individual pins and sockets, etc. Really, Really top shelf!

 

[Keith_J]

When you run over the rated load, the load meter will reflect this. Just watch the frequency meter to make sure you are in the 59-61 Hz range. I wouldn't run over rated load at the extreme temperatures, the magnetics (iron) will handle it, the copper is the problem as its resistance increases with temperature and you could have insulation failure in the windings.

In cooler weather, you can run them up to the circuit breakers. I remember powering the MKT and their industrial toaster with the rest of the TOC using a single MEP 002a (5kW diesel). Total load peak was in the 6.5 kW per data plates on all consumers.

 

[derf]

IMO, Yanmar > Onan when it comes to MEP-016s. I like the pull rope a lot. The MEP-016D uses a Yanmar L70. I would trade one of my 701As for a very nice 016D. The Onan single cylinder Diesel is a stout, good motor, IMO, too, but I just like the Italian/Japanese Yanmars.

 

[steelypip]

Probably worth mentioning that the load meter on these mil spec generators assumes a .8 power factor. So if you're using a resistance heater as your test load (power factor =1) then rated power is at an indicated 80%.

That said, they're very stout. I had my MEP-002A at 100% indicated load on resistance heaters on Sunday and while it was definitely working for a living, it was nowhere near bogging or black smoke in the exhaust. I suspect your Yanmar will behave similarly.