SEE RELATED ARTICLE
GENERATOR SET, DIESEL ENGINE DRIVEN, TACTICAL
SKID MTD., 60 KW, 3 PHASE, 4 WIRE, 120/208 AND 240/416 VOLTS
| DOD MODELS |
CLASS |
HERTZ |
N S N |
| MEP006A |
UTILITY |
5 0 / 6 0 |
6115-00-118-1243 |
| MEP105A |
PRECISE |
5 0 / 6 0 |
6115-00-118-1252 |
ENGINE
ALLIS-CHALMERS 3500a
426 cu in turbo charged
HP roughly 135-150 at the flywheel
1985 is the last year of Allis Chalmers engine production
There were only a couple of industrial applications that the 426 went in.
Most parts marked with a CAGE code:
https://www.bpn.gov/bincs/begin_search.asp
GENERATOR/ALTERNATOR
Company Name: LIMA ELECTRIC CO INC THE
CAGE Code: 36156
ZIP Code: 45801
State: OH
Phone: 419-227-7327
Address: 200 E CHAPMAN RD
City: LIMA
ZIP: 45801 - 2012
State: OH
County: ALLEN
Generator ID plate looks like this:
|
DEPARTMENT OF
DEFENSE |
|
NOM. |
GENERATOR, ALTERNATING CURRENT |
|
SYNCHRONOUS
BRUSHLESS |
|
MAKE |
MILITARY DESIGN |
| MOD. |
70-1900 |
| SER. |
|
NO.
OF WIRES |
12 |
| VOLTS |
120/208-240/416 |
AMPS |
208-104 |
| KW |
50/60 |
KVA |
62.5/75 |
PF% |
80 |
| CYCLES |
50/60 |
RPM |
1500/1800 |
| MFG. |
36156 |
PH |
3 |
|
30554-70-1925 |
FRAME AND SUBSYSTEMS
http://www.engineeredsupport.com/fermont.htm
Company Name: ENGINEERED ELECTRIC COMPANY DBA FERMONT
CAGE Code: 93742
ZIP Code: 06606
State: CT
Phone: 203-366-5211
Address: 141 NORTH AVE
City: BRIDGEPORT
ZIP: 06606 - 5195
State: CT
County: FAIRFIELD
EXCITER CIRCUITRY
Company Name: ELECTRIC MACHINERY DRESSER INDUSTRIES INC
CAGE Code: 19899
ZIP Code: 55413
State: MN
Phone: 612-378-8000
Address: 800 CENTRAL AVE
City: MINNEAPOLIS
ZIP: 55413 - 2403
State: MN
County: HENNEPIN
This is a graphic of the component location for
the 12 wire board.
Studying the wiring diagram for similar 12-wire
generators, I have determined that the generator is wired in a 12-wire WYE or
STAR configuration.
See related story UNDERSTANDING HOW GENERATORS WORK
The wiring board has built in capability for
HIGH 240/416 or LOW 120/208 wiring.
The blue squares are interconnects. Lugs are labeled
similar to the winding wires, ie: T1, T2, ect...
Windings are shown in red, they were inferred by the changes
that take place when the interconnect board is moved.
Subsequent testing with a meter proved the diagram to be
correct.
The CURRENT CURRENT EXCITER are the items from the first
illustration that the generator leads loop through on their way to the interconnect board. The longer loop-through is labeled
"Exciter" and diagrams state that the other loops are for load
measuring.
Working from this configuration, it seems possible this unit
can be re-wired for single phase 120/240 in a ZIG ZAG.
In this a ZIG-ZAG configuration you would have 120v from L1 to N and
from L3 to N, 240v from L1 to L3.
This is the final output with the ZIG ZAG configuration.
The phase sum can be visually calculated by visiting:
http://www.udel.edu/idsardi/sinewave/sinewave.html
and entering 60 cycle 100 amplitude for each wave, 120 phase
for first and 240 phase for second.
Some people seem to think that the final result is "out
of phase" and therefore not 240v.
I hope this graphic puts their fears to rest.
SEE RELATED ARTICLE
The genset is obviously now DE-RATED.
What does this mean? Well, I used to have a three phase
generator with 60kw total rating - 20kw per phase. I no longer have three
phases, so I obviously don't have 20 x 3 = 60kw anymore. What do I have?
Some people think I only have 20kw, since I only have one
phase now. This is a misconception, a misunderstanding of residential
power. Residential power is often referred to as single-phase.
That's because the power company generates and transmits power as three phase,
and taps a single phase with a transformer to drop to a residence. What's
missing from the equation is the nature of the transformer: it has a
center-tap. Residential power has 240v from leg to leg, and 120v from
either leg to the center tap, or "neutral".
It would be more accurate to refer to residential power as SPLIT-PHASE.
This is what we are generating with the zig-zag configuration:
split-phase power. Two hot legs, or phases, that are anti-phase to each
other and share a common or "neutral" connection. We are
emulating the output of a center-tap transformer.
To DE-RATE the generator, we could simply say we have two 20kw
phases, or 40kw. This is oversimplistic, but it works: when re-wiring a three-phase generator for split-phase residential power, de-rate the generator
to 2/3 the original power.
A more complex analysis tells us there are three major factors
involved when rating a generator.
The first is the power factor of the prime mover - in this case the horsepower
of our engine. This is usually the limiting factor in a generator
set. In this case, we know we have sufficient power to generate 60kw, so
it is not a limiting factor.
Ditto for the second factor: magnetic field strength.
The third factor, which is the capacity of our windings and leads to carry current, can be quite complicated. (calculations of the effect of field and flux on the windings are tremendously difficult) We know there must be an upper limit, and we know what each phase can carry safely, but we don't have enough information to calculate the true upper limit. If we load the generator to
it's original rated capacity, we could burn out our windings - or our output leads. Without further information we have to de-rate the genset by 33%
for safety.
My genset has LMUs (Load Measuring Units) that will automatically shut down the exciter if the load on any phase exceeds 110% of the rated load. So in my case I can rate the generator at 22k x 2 = 44kw, or about 25% of original rating. 25% is usually a good de-rate measure, but don't take that as blanket permission to overload YOUR genset! If you are not sure your set has overload protection, connect it to your load with a line breaker rated at 75% maximum of your original load rating - or 66% for ultimate safety.
Here is how I converted my genset.
First I cut the buss bar from T12 on the back of the reconnect
board. I left it laying there so you could see what I cut off.
Then I added a battery cable to choose which position I would
connect T12.
If I connect T12 to the N lug, I have WYE in LOW or HIGH.
If I connect T12 to T2, I have ZIG ZAG in LOW or HIGH.
(Yes, it's connected to T8 and the moment, but since I have no
use for 240/480 I won't be moving the selector plate up anyway!)
I have perfect output and run my entire house with no problems. This particular genset de-rates to 44kw (183amps) wired zig-zag, but since my main breaker is 150a (36kw) I can't even use that much!
