15-kw 400 cycle diesel gen.set

[Speddmon]

Sir,

You probably need to flash the field to get it generating. Look in the manusl you, and they should have instrucions for flashing the field.

Later military generators, automaticaly flash the field when they start to prevent this problem.

As mentioned in earlier post, the 400 HZ machines are basically usless for the average person. They are used for Aviation, and can not be converted.

If you do not have the manuals you need, PM me, as I probably have them in my collection.

Good luck
Avn-Tech

Avn-Tech,
When you say "later" military generators automatically flash the field, what year approximately did they start doing it automatically? I was lucky enough to win two Mep-003a's that are supposed to be of early 90's production, just curious.

 

[Avn-Tech]

speddmon,

I do not know what year or model the military started flashing the fields automatically(through the start switch). When I went through AF Power Production school last year they said that the avg military generator would sit long enough to need to have the field flashed.

Even on some of the newer models, the field will need to be flashed a second time on start up. So we just hit the start swith again to flash the field.

I am including an excel file I have put togeather on generators. The file list all of my generator manuals and specs for the different mep series generators. Sorry I do not seem to have an operators manual for the MEP-003, but I do have the other manuals if you need them.

Maybe one day when the page is finished, it can pe permently posted on this web site. (Assuming I get all of my projects completed and have time to work on it)

Laterrrrr
Avn-Tech

 

[Avn-Tech]

Group,

Sorry, but the link does not come through, email me and I will send the file.

Laterrrr
Avn-Tech
fish@aviation-tech.com

 

[OPCOM]

Well, if you can use it a Variable Voltage/Variable Frequency Converter will get the HZ you want and the voltage too. However, new cost for them is about $2950. I believe FCC might have used them on ship before (depends on system he worked on). If it was the iron cannon then probably not

Do you have any manufacturer data on those kind of units? It would be simpler to put something together for 60Hz output only.

The simple trick would be to rectify the 120VAC to +/-DCV and make the 60Hz with a PWM stage, which is how most of those work. Some go another step and use power factor correction (better for the generator as it does not see your nasty loads) The problem is that there is very little publicly/freely available as far as plans, schematic diagrams, etc for the large size equipment.

 

[Wrench Wench]

Maybe we could start generating some? This is SteelSoldiers, if I'm not mistaken. They also serve who only stand and generate.

I was thinking about the problem of 400 Hz power when I saw a turbine powered genset on GL. I assumed they used 400 Hz more on aircraft because of the normally high RPM of turbine engines. If the genset is geared down from the turbine shaft power output, then 400 Hz isn't as far to gear down as 60 Hz.

But then I thought, is there a convenient gear ratio to go from 400 to 60? I knew there wasn't an integer ratio because 6 goes into 42, not 40, but integer-wise, how close could you get? Well, 400/7 = 57.14. Most 60 Hz equipment I've ever heard of wouldn't be able to tell 57.14 Hz power from 60 Hz power with a 4.76% variance.

So, just average the power output over 3 full cycles and a half cycle to produce a 60 Hz peak. Then, do it again, to produce the 60 Hz trough. The averaging would just be a simple rectifier charging a capacitor, a really big capacitor. Using simple digital control electronics to count the peaks and troughs and some really beefy solid state relays, while one capacitor (trough or peak) is charging, the other is discharging, either pushing its electrons out onto the hot lead, or recharging, filling its holes from the hot lead.

If the voltage of the 400 Hz generator is still 120, then the 57 Hz power thus created would be much higher voltage than 120 VAC, but then, that's what a transformer is for, transform the HVAC 57 Hz back down to 120 VAC 57Hz.

A pair of rectifiers, a pair of capacitors, a pair of SPDT solid state relays, and an oil-cooled transformer. Not sure, but I think the capacitor stage would even satisfy most PFC requirements. The only difficulty would be that the digital switching would introduce a lot of distortion, more than the transformer stage could reasonably compensate for. But, if the equipment can tolerate a 5% variance in the frequency, then a little distortion in the sinusoidal waveform isn't gonna freak it out much either.

This scheme is a little more involved then just rectifying to pulsed HVDC, filtering and smoothing, and then using a PWM, but it has the benefit of not needing nearly as complicated a set of digital control electronics, and distorted though it may be, I'd think the waveform generated would be much cleaner than a PWN generated waveform.

Does any of this make sense, or have I been out of a college physics classroom too long?

 

[StrykerPez]

Totally get what you're saying, but it just seems simpler to put a new (different) genhead on one.

 

[Wrench Wench]

And if one is available for less than the costs of the components of a frequency divider, then I agree with you, absolutely, but the physics and electronic principles behind such a device would be an invaluable source of information for SS members, as would the details behind any successful 60 Hz genhead swap projects.

Since the principles of the frequency divider aren't specific to any given frequency or voltage or current output, a completely generic design could be made. Provided it can handle up to 480 VAC and up to 225 A and up to 1000 Hz, it should be able to divide the frequency down to as low at 30 Hz.

The divider could be controlled by a simple digital input to the microcontroller from 1 (don't divide at all and just pass the power through) to 32 (which could take 1000 Hz down to 31.25 Hz).

As long as the capacitors could handle it, if the transformer was replaced by a rheostat, the output voltage could then be transformed down to whatever output voltage you wanted with the corresponding increase in current, modulo power losses to heat in the frequency divider.

Okay, so the full 480 VAC, 225 A input might be rather cumbersome to divide conveniently, but a smaller class of frequency dividers for up to, say, a 10 kW plant, another up to 30 kW and a third up to 100 kW could be manageable. It wouldn't be a generic-input-any-frequency-voltage-current-output-any-frequency-voltage-current-black-box, but it would be close, and putting such a device in your emergency vehicle could assure you that you could hook up to any source of power you came across and manage approx. 60 Hz 120 VAC power.

You'd only be able to get a lower frequency than that supplied. A frequency multiplier would be needed to get approx. 400 Hz from 60 Hz power. You'd also need a separate unit for each phase involved.

Stampy: You sure those are 300 Hz gensets and not 400 Hz? I have yet to see 300 Hz as a power frequency on any GL auctioned units.

 

[Wrench Wench]

Hey, swampy, didja manage to score those two Unicor Model 5485 10 kW 60 Hz genheads I clued you into on GL? They went for only about $270 for the two of `em. If so, my finder's fee is a sequence of highly detailed conversion project write ups on your two 300 Hz gennies, with plenty of photoes.

 

[stampy]

No I got beat out. I was leaving for a trip Thurs afternoon and got out bid. Thanks for the help though I will put a higher bid in next time! If you see any more let me know I will keep looking too.

 

[Wrench Wench]

Right now, there's just one 60 kW monster up for bid. Pretty sure your 10 kW portables would choke, gag, and die on that gen-head.

Although, there are three disembodied rotors of unknown spec. coming due in two weeks. Assuming someone could find the specs, would a rotor swap be sufficient to change the power frequency/voltage of a genset, keeping the same stator magnets in the same can? 99.999% sure the answer is no, but I don't know the specific engineering that went behind these MEP units.

Sorry to hear they got away Stamps. Better luck next time.