MEP-016B 3KW Generator Amp. question

[Doogdoog]

Aloha,
I have a MEP-016B 3kw military generator which I have posted before but after doing some caculations on the amp output, I have some questions. The data plate says:
240v 1ph 120/208 3ph
120v 1ph 120 3ph
10.4, 18, 15.6, 31.2 amps

Someone stated that the manual says:
120v=31.2a
240=15.6a
120 3ph=18a
120/208 3ph=31.2a

I was just going over the figures and something doesn't look right because I always thought that getting single phase out of a 3phase machine will be about 2/3 of the wattage. W=ExI so 120vx31.2a=3744w and that doesn't look right. Is this correct or am I doing something wrong?

Mahalo,
doogdoog

[armandh]

depends on the windings
if one uses 2 of 3 phases expect 2/3 the power
if windings can be connected to optimize single phase
expect optimal results.

[armandh]

don't forget the limit of engine HP may limit the rating
not to mention mill spec may be different from civ. esp continous duty

[Jim McIntyre]

Originally Posted by Doogdoog

...I always thought that getting single phase out of a 3phase machine will be about 2/3 of the wattage. ...

Good reason not to depend too much on 'rules of thumb'. In the case of these little air-cooled mil sets, they carry their full power rating even in single phase. So, the 31.2 Amps is the correct current rating at 120V. The math is thus:

31.2 A * 120V * .8PF = 3000 Watts.

The 0.8 is the power factor, and these sets are rated at .8 PF even in single phase.

If you don't fully understand power factor, don't fret. Just keep your load under 31.2 A, and will should be well. It is possible to put a slight overload on the engine by doing this, but in my experience, the engines are sufficiently oversized for this not to be an issue. In other words, yes, these little 3 kW sets really can put out 3750 Watts, even in single phase mode.


Jim

[Doogdoog]

Aloha,
Thanks for the replies and good information. Ok, with the 80% PF being considered, it does come out to 3kw. Thanks again and more good news, I just received my BatteryMINDer Mod. 12248 charger/maintainer/desulphator-
conditioner so I must test out this puppy to see if it helps out my battery.

Mahalo,
doogdoog

[Doogdoog]

Aloha,
Something still doesn't look right with the calculations. The data plate shows:
240v 1ph 120/208 3ph
120v 1ph 120 3ph
10.4, 18, 15.6, 31.2 A
The above is the order shown on the plate.
I would think that 240v 1ph X 10.4 X .8=1996.8 W
120v 1ph X 18 X .8=1728 W
208v 3ph X 15.6 X .8=2595.8 W
120v 3ph X 31.2 X .8=2995.2 W
This looks more realistic since the single phase readings looks about 2/3 of the 3kw wattage and the 3ph closer to 3kw. What do you think?? I will try to post the windings.

Mahalo,
doogdoog

[Jim McIntyre]

I think –

A) Your data plate is different from my TM,
B) I responded to this same question 2 years ago…
C) The TM’s for the MEP-016B do not mention the output rating ANYWHERE
And

D) you’ve not learned how to calculate 3-phase power properly.

The TM for the MEP-016A/C, which I believe contains the same generator, says this:

31.2A at 120V single phase
15.6A at 240V single phase
18A at 120V 3 phase
10.4A at 120/208 3 phase

All are shown at 0.8 PF

Calculating power:

31.2 A * 120 V * 0.8 PF = 3000 W
15.6 A * 240 V * 0.8 PF = 3000 W
18A * 120V * 0.8 PF * sqrt 3 = 3000W
10.4A * 208V * 0.8 PF * sqrt 3 = 3000W

Therefore, I conclude the MEP-016A/C is rated to provide 3 kW at any of its settings at 0.8 PF. What do you think?

I think the TMs for the –016B are very poor. There are already 2 apparent errors in the figure you posted – the voltage in the last diagram should be 240V, not 120V as shown, and it shows the terminal T-2 twice, and I’ve searched, but not found the output current rating anywhere in either the 12 or 34 manuals.

More questions?

[Doogdoog]

Aloha Jim,
Thanks for the reply and I looked everywhere for the current values for the different voltages and phases in the PDF manual but couldn't find anything. The thing that got me going was the data plate on the generator and the order in which the current was posted so I was trying to see what goes where. I posted this question quite a while ago and I believe it was you that gave me the voltage and amps but I never got around to figure out how they calculated the wattage from the data plate (until now). This is the exact way that it is shown on the data plate:
240v 1ph 120/208 3ph
120v 1ph 120 3ph
10.4, 18, 15.6, 31.2 amps

So I tried to do the math and it didn't come out but with the current reading that you supplied for the different voltages and phases it came out with the power factor added except for the 3 phase because I didn't know about the sqrt 3. Ok, now I see the light. Thanks again.

Mahalo,
doogdoog

[Jim McIntyre]

My pleasure. The -016B manual is really poor. No excuse for them leaving the current rating out of it. And the data plate is unclear, as you note. My belief is that whoever managed this program in the DoD didn't understand the current rating themselves, and never bothered to print the accurate rating.