Electrical question---starter-generator - PeachParts Mercedes-Benz Forum

MS Fowler · #1 06-18-2012, 10:27 AM

This is a "how come" question.
Lots of the larger one cylinder engines used in Lawn and Garden Tractors in the 1970s and 80s used a Starter-Generator. It works as starter, and once the engine is running, it produces current like a generator. Basically they are 12V DC generators. The weak point seems to be the mechanical voltage regulartors that were used.
My question is simple--how come no one has designed or modified a solid state regulator to replace the mechanical ones? I know there isn't enough volume for commercial interest, but surely someone can design a schematic using solid state components that can do the job and be more reliable.
Any other old tractor people here have any idea how this could be done?

Air&Road · #2 06-18-2012, 11:04 AM

Which engine in particular are you talking about? There may be later components available to effect this change.

MS Fowler · #3 06-18-2012, 11:30 AM

Quote:

Originally Posted by Air&Road

Which engine in particular are you talking about? There may be later components available to effect this change.

Kohler KT series engines as used on Cub Cadets from the original ( 1962) thru the end of International production. Starter Generator produced by Delco.

Stretch · #4 06-18-2012, 02:44 PM

I'd say that that idea hasn't taken off because of the whole alternator dynamo thing...

...dynamos are dependent on brushes and commutators which wear and stop doing their job - whereas alternators electrically speaking don't depend on mechanical contact.

However these days with modern electronics and some electric cars using multi-phase alternating currents from batteries (Tesla motors for example) =>

If you could reliably produce a 3 phase power supply from a car battery for long enough to start an engine and then have your induction motor behave as an alternator...

...I think you'd be onto something as typically you'd need a smaller multiphase alternating current motor / alternator for an equivalent power output from a single phase motor / alternator motor and a DC motor / dynamo set up.

MS Fowler · #5 06-19-2012, 08:55 AM

Quote:

Originally Posted by Army

I'd say that that idea hasn't taken off because of the whole alternator dynamo thing...

...dynamos are dependent on brushes and commutators which wear and stop doing their job - whereas alternators electrically speaking don't depend on mechanical contact.

However these days with modern electronics and some electric cars using multi-phase alternating currents from batteries (Tesla motors for example) =>

If you could reliably produce a 3 phase power supply from a car battery for long enough to start an engine and then have your induction motor behave as an alternator...

...I think you'd be onto something as typically you'd need a smaller multiphase alternating current motor / alternator for an equivalent power output from a single phase motor / alternator motor and a DC motor / dynamo set up.

Wow that is overthinking the problem---at least from my POV.
The Starter-Generator works well in the small engine application. One component operates as both the starter, and the generator--simple is better. Typically in Garden Tractor use, these engines start once and then run for hours before being shut off and re-started, so the relitively low charge rate is not an issue. Small engines are also generally run at their full governed speed so that a generator works at the speed it needs to generate.
The problem is the mechanical points that operate the voltage limiting circuitry. They basically open and close rapidly to limit the effective charging rate to around 13 volts. Unregulated, they'd put out 18V or more which is bad for the battery. So the points close-the voltage rises. When the voltage exceeds a value set by interaction of spring pressure and electromagnetism, the point open and the voltage falls. Then they close and the voltage rises. All this happens many times a second. Its a balancing act between the spring pressure and the electromagnetism---its all mechanical.

Seems like someone should know of a solid state switching device that could produce the same result without the mechanical points.
Maybe not.

Air&Road · #6 06-19-2012, 09:01 AM

That would not be a difficult solid state circuit to design, but would it be cost effective? There is a commonly used 5V regulator in a TO-5 case that is used for on board voltage regulation. There might be a 13.5 volt version if someone were to research it. Or one of the semiconductor desing manuals might show a way to use passive components to fine tune the voltage point of a regulator chip near that voltage level.

MS Fowler · #7 06-19-2012, 09:07 AM

Quote:

Originally Posted by Air&Road

That would not be a difficult solid state circuit to design, but would it be cost effective? There is a commonly used 5V regulator in a TO-5 case that is used for on board voltage regulation. There might be a 13.5 volt version if someone were to research it. Or one of the semiconductor desing manuals might show a way to use passive components to fine tune the voltage point of a regulator chip near that voltage level.

EXACTLY!!!!

What I heard you say was the same as Charlie Brown's teacher speaking on the Peanuts cartoons, " Wahhh, wah wahh Blah blah blahhhh."

t walgamuth · #8 06-19-2012, 09:18 AM

They work fine in the Honda Insight and the Prius.

The insight starts so quickly you cannot believe it. All you need to do is touch the ignition starter switch and it is running.

Also if it is running and you accidentally hit the starter switch no grinding.

Dubyagee · #9 06-19-2012, 10:42 AM

Onan gensets use the same idea. Not a very efficient design in DC. I saw a Lister single cylinder using a golf cart set up to crank without using the compression release. It would then charge the battery at about 30 amps while the Lister ran a 5k genset.

Stretch · #10 06-19-2012, 02:21 PM

Sorry off topic question @ Dubyagee - what are forum seeders?

Stretch · #11 06-19-2012, 02:22 PM

Quote:

Originally Posted by MS Fowler

Wow that is overthinking the problem---at least from my POV.
...

Ha what's new! Wood? Trees? Wood? Oh I don't know!

Angel · #12 06-19-2012, 09:24 PM

To your original question - why did they start going with a seperate starter as opposed to continuing to use a starter-generator like in days of 'yore ?

I'm gonna guess cost - to wind and buy a small DC motor is pretty cheap, and since it is geared down the motor torque doesnt need to be very high to get you started.
If you were doing thing right on the crankshaft, you'd need to develop a full hp or so at a few hundred rpm - In one big disk. Not only would the electrics take up more space (and they are costlier per unit volume than pieces of metal) but you'd have to effictively wind your own large-diameter DC motor - lots of factories in the far east churn out millions(?) of DC motors in any size you want - no R&D required.
and given the expected life of a lawn tractor these days (less than a car? the cost for a motor-generator is definitley prohibitive.

Starter story - a few years ago my brother brought me a 17hp 1cyl craftsman something that wouldnt start (electric start) the starter motor just didnt have the arse to turn the motor over. We tried larger batterieis and everything - finally asked my FLMPS and they said "adjust the valves, if the clearance is worn too small, the 'compression release' feature doesnt release and the starter motor isnt sized large enough to turn the engine over at full compression (!! - they cheaped out on it that hard..)
...sure enough, I showed my little brother what feeler gauges were (same guy who built/paid for a 300hp Mk2 Volkswagen...), and 5 minutes later it fired right up. The starter was that cheap/weak. blah.