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11kw 240vac 60(ish) hz 1 cyl diesel Generator "problem"

So, I built this generator a few years ago. The thing is based on

1930's technology, its just plain simple and works (for the most part)

My old BackUPS 1400 finally got to the point I was tired of fixing it, so I erroneously replaced it with a SmartUPS 1400. Bad Idea, when I switched over to generator power in preparation for this years hurricane season the SmartUPS were too smart for their own good and wouldn't switch back over to "utility" power.

A few years ago when load testing the generator, I noticed that the stone age rotor power supply, while incredibly simple being built from only a rectifier, didn't put out very clean power. On my "ToDO" list was to build a more involved voltage regulator with an integrated engine management system (mostly because it sounds like a neat project, not because the system really needs it)

So anyway, I hoped that the noisy voltage output from the generator was source of the SmartUPS problems. With a little experimenting I found that 66vdc @ 5amps applied to the rotor winding made fairly nice looking 250vac sine wave output at 60hz no load. When a load was put against it, the voltage dropped down to 240vac and I thought for sure the SmartUPS would be happy (the o-scope showed rather clean sinusoidal waveforms). Not so much...

OK, SmartUPS must be un-happy with the frequency changing between power strokes, maybe having problems "syncing up" or something.. But fixing this is a problem.

#1 The ST generator head rotates at 1800 RPM to produce 60hz power. #2 The 1 cyl diesel is direct attached to the generator head. #3 While the diesel has a MASSIVE (24" diameter 2" thick) solid cast iron flywheel, I can still see the frequency change during each of the

4 cycles of the diesel engine.

Bottom line, for each revolution of the engine I produce two complete output AC waveforms from the generator. Every other revolution of the shaft has a power stroke from the single cylinder diesel. So I get one complete wave form during the power stroke, another during the exhaust stroke, another during the intake stroke, and another during the compression stroke. End result, the damn frequency of the generator is constantly changing (would you call that a "sub harmonic" or something?)

ANYWAY, the question to you scholarly folks is "What's the most direct approach to get the SmartUPS back on-line during an extended power outage"

Towards that end, here's my current thoughts, but I don't really like any of them.

#1 Replace 1cyl diesel with 4cyl engine (yuk on many levels, but probably the most "appropriate" solution. BTW, I now know why most large generators use 4cyl prime movers.....)

#2 Just Don't use the SmartUPS during a power outage (duh). I mean really, the cable company runs out of battery power in a few hours anyway, so what could I be running that needs battery back up? But, where's the fun in this solution :)

#3 Get a big battery charger and connect it to internal batteries on SmartUPS, add extra cooling and hope SmartUPS doesn't cook itself while running on batteries for extended periods. (YUK)

#4 Put "Something" between outlet and SmartUPS when on generator power. Such as:

A) AC -> DC -> AC converter (wow redundant) B) Transformer -> 60hz LC tank circuit -> Transformer C) magic pixie dust.

So any other thoughts?

--
Take Care,
James Lerch
http://lerch.no-ip.com/atm (My telescope construction,testing, and coating site)
http://lerch.no-ip.com/ChangFa_Gen (My 15KW generator project)

"Anything that can happen, will happen" -Stephen Pollock from:
"Particle Physics for Non-Physicists: A Tour of the Microcosmos"

" Press on: nothing in the world can take the place of perseverance.
Talent will not; nothing is more common than unsuccessful men with talent.
Genius will not; unrewarded genius is almost a proverb.
Education will not; the world is full of educated derelicts.
Persistence and determination alone are omnipotent. "
Reply to
James Lerch
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Someone beat me to it but the first thing that came to mind when I read your post was a ferroresonant voltage regulator. The only repairs I've had to make to such units was to replace the capacitor or capacitors if the regulator has more than one. If you build your own, I would suggest obtaining high quality caps or to have several spares on hand. I found a company that manufacturers some regulators but they only listed a max capacity of 2.5KW. A bit of searching the surplus market could turn up parts or a whole unit in your size because a new big one is quite expensive. Besides, it's more fun to roll your own.

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[8~{} Uncle Monster
Reply to
unclemon

I think your problem is related to the frequency variations. The SmartUPS tries to phase lock its internal AC to the line before it switches over from battery to line. Since your frequency is moving, it can't achieve phase lock.

You may be able to make some changes to the control circuits of the SmartUPS to make it less critical to the phase offset it wants to see before it switches over. I have had a hard time finding schematics for these and with a critical issue like this I'm sure you will need a schematic to make any progress.

Have fun. Mark

Reply to
Mark

OH it's probably worse than that, I probably would need the source code for the PIC that's actually doing the work.

Although if I could find where the PIC (or electronics) got it's reference voltage from, seperate that from the mains voltage, then build a PIC to LIE to the Smartups electronics (or at least a little fib) I might be able to get it to switch over. The problem would be, My pic would have to tell convincing lies, and keep the SmartUPS in phase (or close to it) with the actual power, lest the smartups does something stupid because I'm lieing to it :)

I've also recently found out a plain old induction motor can be used as a generator (if a few 100 uF of capacitance is added across the line output). Which makes a home brewed MG set kind of interesting....

OF course, if I wanted a real project, I wonder if I could pull the Rotor out of an induction motor and replace it with a home built slip ring based elctromagnetic rotor and build a more proper gen head. That could be an interesting project (that is if the idea would work...)

--
Take Care,
James Lerch
http://lerch.no-ip.com/atm (My telescope construction,testing, and coating site)
http://lerch.no-ip.com/ChangFa_Gen (My 15KW generator project)

"Anything that can happen, will happen" -Stephen Pollock from:
"Particle Physics for Non-Physicists: A Tour of the Microcosmos"

" Press on: nothing in the world can take the place of perseverance.
Talent will not; nothing is more common than unsuccessful men with talent.
Genius will not; unrewarded genius is almost a proverb.
Education will not; the world is full of educated derelicts.
Persistence and determination alone are omnipotent. "
Reply to
James Lerch

On Jul 20, 5:00 pm, James Lerch

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coating site)

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15KW generator project)

Another wild tangent idea. How about just connecting an induction motor ( even better with a flywheel or big pulley on it ) to the output of the generator. It should act as additional load when the frequency is increasing and an induction generator when the frequency is decreasing. Essentially a way to increase the flywheel on the diesel engine using an electrical connection instead of a mechanical connection.

Dan

Reply to
dcaster

Before doing anything, can you figure out by experiment exactly what the UPS is cranky about? E.g. can you temporarily hook up a motor and variable speed drive to your generator, disconnect the engine or take out the glow plug so it will turn over easier and then see: (a) Even with correct RPMs can you ever make the UPS happy? and (b) How close doe the RPMs and/or voltage have to be to get it working?

Chris

Reply to
Chris Jones

Another wild tangent idea would be to use a synchronous belt drive from the motor to the generator and make slightly oval pulleys. So the pulleys would compensate for the speed shift in the engine and the generator would run at a constant speed.

I don't think this is a practical solution as it would probably only work perfectly at one load condition. Still might be good enough for your purposes.

Dan

Reply to
dcaster

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