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Car engine generator - how to control RPMs?
By zmoz, Section Homebrewed Electricity Posted on Mon Jan 19, 2004 at 04:15:54 PM MST
I'm building a generator out of a car engine....

I haven't decided on a particular engine yet, but I'm going to be building a 25kw generator from a 4 cylinder fuel injected car engine. I know lots of you guys have done something similar...how do you control the RPMs? Like when there is a load on the generator, how do you keep it at a steady speed?

Car engine generator - how to control RPMs? | 15 comments (15 topical)

Re: Car engine generator - how to control RPMs? (none / 0) (#1)
by Electric Ed on Mon Jan 19, 2004 at 04:33:29 PM MST

I use a centrifugal governor on the engine that powers my sawmill. It advances the throttle when the RPM drops due to increased load.
The one I have is similar to the ones used on farm tractors and is driven by the fan/accessory belt.

Electric Ed

Re: Car engine generator - how to control RPMs? (none / 0) (#2)
by Parameter on Mon Jan 19, 2004 at 04:53:08 PM MST

I will probably to the same with a sentra carburetor engine this summer. This engine will never die... I too was also wondering about the control circuit.

It would be nice if it could start and stop depending on battery voltage and load.

Could an electric cruise control controler be used to throttle it?
With a small rpm or voltage drop monitoring circuit?

Will be a nice little job to rewire the injection computer and all. Remove the battery first as I have seen baloons go off when the car computer is being ungrounded.

Para

Re: Car engine generator - how to control RPMs? (none / 0) (#3)
by Homebrewed12vdc on Mon Jan 19, 2004 at 04:55:39 PM MST

a aftermarket cruise control well work for this, play with ti so you go tthe engine running where you want it and set the cruise there.

Re: Car engine generator - how to control RPMs? (none / 0) (#4)
by zmoz on Mon Jan 19, 2004 at 06:08:29 PM MST

But isn't cruise control based on the speed, not RPMs?

Re: Car engine generator - how to control RPMs? (none / 0) (#5)
by veewee77 on Mon Jan 19, 2004 at 07:32:05 PM MST

Yes a cruise is based on speed, but it is the speed of the wheels (RPM).

You'll need to know how the cruise gets it's reference signal and either gear the output of the engine down or use some kinf of frequency divider to simulate what the engine would be turning at 1800RPM (4pole gennie) or 3600RPM (2pole gennie).
One way to do this is to get in a car of the same type as the engine you are wanting to use and with a tach and set the tach at 1800 RPM and check the speed you are travelling. Then find out what type of speed sensor it has and figure the frequency of the sensor. It would be best to use 4th gear (direct drive on 5 speeds with OD) because the frequency would be the same as the output shaft since most cruise control sensors are detecting rotation of the drive shaft. The 1800 RPM should be 1800 at the output shaft with the trans in 4th gear.

Maybe this'll help. . .

Re: Car engine generator - how to control RPMs? (none / 0) (#6)
by Budgreen on Mon Jan 19, 2004 at 08:47:42 PM MST

check out mid 80's GM products, a lot of the cruise controll systems were held by the vacuum system, the manifold vacuum pulls a diaphram thingie that is also connected to the throttle/carb linkage, when you set it it tried to maintain that set manifold vacuum by holding rpm, might be a simple way of doing it for you, possibly less precise than faking a VSS signal :)

[ Parent ]

Re: Car engine generator - how to control RPMs? (none / 0) (#11)
by elvin1949 on Wed Jan 21, 2004 at 01:21:43 PM MST

don't use the vacum cruise control
when you unload the engine it will
RUN AWAY lots of rpm's
been there done that
later
elvin

[ Parent ]

Re: Car engine generator - how to control RPMs? (none / 0) (#7)
by rhud on Tue Jan 20, 2004 at 12:07:52 AM MST

Hello,
Wondered about the same thing. the old gm's used an input from the speedo cable which was measuring the rpm (mechanical/gear) of the output shaft of the transmission. they used vacuum to supply the muscle needed to control the throttle linkage. the aftermarket cruise controls (back then) also used vacuum (many valves and automatic controls used vacuum as muscle) to operate the linkage but used a small magnet which was tie-strapped to the output yoke of the transmission. a pickup was used to count the turns of the magnet and give the cruse control an input. i would be guessing, but i would think that newer cars use a variation of the transmission/ speedo cable. except now instead of a helical gear driving the speedo cable, its probably an electrical signal from a hall effect sensor with a slotted disk on the output of the transmission. (i'll talk to our automotive instructor next time i see him)

External/belt driven centrifugal governors are still available, try www.ytmag.com and do a search, i think its been mentioned there. if no luck, go to the "tractor talk" section and state your problem, you should get a solution or some ideas from those people.

seems someone with the know how could measure the rms voltage of the generator and use it modified as an input to an automotive curise control. the newer computer controlled engines have a slotted wheel and hall effect on the engine itself. the system is so accurate that it can tell within one rotation of the crankshaft which cylinder is misfiring or loosing power.(got that from the last time i talked to the automotive instructor) if you could tap into that kind of control system, maintaining rpm/voltage would be surperb. would like to hear what you decide on.

Re: Car engine generator - how to control RPMs? (none / 0) (#8)
by Gordy on Tue Jan 20, 2004 at 01:46:06 AM MST

Hi All,

I have installed several after market cruise controls. These used 4 magnets (evenly spaced) wire mounted to the drive shaft, with a pick up coil mounted close to the magnets. The coil is wired to it's control / computer, which is wired to the vacum actuator for the throtle.

This system should work, just mount the magnets to the harmonic balancer. There are generaly plenty of bolt holes near by to mount the pickup coil. I guess I'll have to go out to the old junker and pull the CC back off of it, before the junk man comes for it.

If your generating AC you'll want to get a frequency meter to set your RPM's by (50 or 60 hz).

If I did the math right 25k comes out to 33hp. You'll want to check into the hp rating of the engines your looking at, NOT at the peak rpm's but at the lower 1,800. Of coarse if you use the transmition you'll have a built in gear reduction.

If your thinking about fuel economy you might want to check out those 3 cyl Geo engines or a 4cyl deisel.

Good luck,
Gordy

Re: Car engine generator - how to control RPMs? (none / 0) (#9)
by Wolfles on Tue Jan 20, 2004 at 10:22:21 PM MST

I too, had thought of doing a car engine as power to a generator. I was told that you would need 1.5 HP per 1 KW, so if you needed 25 KW's X 1.5 = 38 HP
or there abouts. I'm going with a diesel engine as I had been advised a gasoline engine would not hold up under continued or prolong use.

Then again, for charging bat's who knows it's life span. Using what you got is the key here.

From my scrap pile, what I's hooks up, burns up,
Wolfles

[ Parent ]

Re: Car engine generator - how to control RPMs? (none / 0) (#10)
by brock on Wed Jan 21, 2004 at 09:10:28 AM MST

Weird, the cruise controls I have installed all used a tach wire from the engine. It didn't care what gar the car was in. Maybe that's because it was for manuals? If I set it for 1800rpm it stayed there no matter what gear it was in. I would think that would be the way to go.

Re: Car engine generator - how to control RPMs? (none / 0) (#12)
by elvin1949 on Wed Jan 21, 2004 at 01:25:56 PM MST

it is
later
elvin

[ Parent ]

Re: Car engine generator - how to control RPMs? (none / 0) (#13)
by pwmvsi on Wed Jan 21, 2004 at 09:22:34 PM MST

I think Electric Ed has the right idea with the belt driven govenor. The trick is mating the govenor to the engine. Woodward makes nice govenors that are simple of the mechanical and electro-mechanical (The dans probly have a couple kicking around the force field advanced reasearch facility). I think they are called UG-8's and are very manageable. They make an electronic one that is really slick called a 2301. Series 'c' are easy to find.

WEMPEC SLAVE

Re: Car engine generator - how to control RPMs? (none / 0) (#14)
by hotshotharry on Thu Jan 22, 2004 at 02:42:15 AM MST

Hey guys, you might have noticed I am a new face here. I have been through this website a couple times, lots of useful info here thought maybe i would share my thoughts.

obviously the easiest answer would be the cruise control that read engine rpm from the distributor, probably form a standard like someone said. But the one that reads the magnets on the drive shaft would work as well. I don't know how many magnets it usually has, probably just one, but thats something you would have to check. Simply mount this magnet on the flywheel of you engine, and the pickup accordingly, or the harmonic balancer, or another pulley. The drive shaft spins the same speed as the engine in last gear, as long as its not overdrive, so the unit should work on a wide range of speeds by adding or removing magnets accordingly :) All it really needs is a reference rpm, the actual number is irrelevant, kinda like x :)

another option would be to build yourself a mechanical governor, perhaps out of an old pulley driven from the belts, again rpm is irelevant. using flyweights which operate against adjustable spring tension which actuates a rod then the carb throttle plate lever through a series of simple arms and levers might be the option. Depending on how sensitive you want the rpm control to be..... will decide the dimensions and weights of your governor unit. ------ or perhaps using the gov assembly out of an old automatic tranny would lend itself to easy modification in some way. Or the flyweights out of the ditributor, i dont know that these would be sensitive enough though, if you were to run it at one rpm you wouldnt need the flyweights for their intended purpose any more.

Another way you could somehow use a small generator with the output through a coil of wire and a fixed resistive load, changes in rpm would reflect a change in voltage thus a change in pull from the coil on a shaft or apparatus fixed with an adjustable spring tension. With the carb spring removed the throttle plates are very easy to move, such a device with the proper design could work for you, though this device might be the least precise. But then again with a little fiddling, might work very well, it would be finicky though :-o

However one thing to remember is that whichever way you choose, be sure that if you have a governor failure, it will go to idle and not WOT. that could be disasterous on many levels. :-)

Harry
professionals built the titanic, amateurs built the ark.
[ Parent ]

Re: Car engine generator - how to control RPMs? (none / 0) (#15)
by pat on Wed Apr 07, 2004 at 06:05:53 PM MST

You might want to have a look at this:

http://www.oldengine.org/members/jdunmyer/genset/

These guy are using a military surplus governor from
http://www.saturnsurplus.com/

You might want to consider a DC system (large frame alternators+inverter) so that you don't have to control RPM.

PAT

Car engine generator - how to control RPMs? | 15 comments (15 topical)

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