12v generator low rpm

Hello, I am looking for a generator that will charge a 12v battery at a low rpm idle speed. Working on a project and I remember my Dad's John Deere B seemingly running on a lower rpm. Thanks.

Any will work with a larger driving pulley or a smaller driven pulley.
Then again why lug the guts out of the engine pounding it at idle speed under full load.
The later 20amp generators used on the 20/30 series JD two cylinders were pretty good.

The original equipment gennys on those old tractors wouldnt set the world on fire (or charge the battery much either) at slow idle, especially if any lights were on, but at work RPM even if lugged at say 500 RPM, they ought to hold their own. The old tractros had Low High charge settings via a Low High Light Switch control while the later used a VoltaGE REGULATOR to automatically regulate charge rates. If the genny is in decent shape AND A GOOD BELT IS TIGHT, the original equipment will get him by just fine unless he were to set it at extreme low idle (say 250 to 300) and turn the lights on and leave it for hours but whose gonna do that??? Its true the two cylinder Deere ran at lower RPM then say a 4 or 6 cylinder IHC or Ollie etc, buttttttttt Deere wasnt stupid and their gennys did the job fine. Overcharging a battery n cooking it and boiling over can be as hard or harder on it then an occassional undercharge.........

Not to worry mate, if it aint broke dont fix it

John T

You are wasting your time with a generator if you want high output at 12 volts at low engine speeds.

A generator, in general, wastes more then half the power it makes - as compared to modern generator that uses recifiers - i.e. an "alternator."

An old (non-rectified) generator wastes a huge amount of output powering its own fields, and also only selects part of the power from the armature, in order to make DC current.

An alternator (rectified generator) uses very little field current and uses all the power from the armature (rotor) by running it through recifiers.

A John Deere B using the OEM Delco 6 volt 1101371 generator is rated:

6.5 to 8.5 amps output at 7 volts and 1800 RPM at the generator. It wastes 4.5 amps just to run the field while it makes the charge current. I think the B ran the generator at twice engine speed. So, it could put out 8 amps at 7 volts with the engine at approx. 900 RPM.

A typical Deere 1101859 "high output" 6 volt generator (like used on a 420) puts out:

20 amps output at 7 volts and 3000 RPM at the generator. It wastes 2 amps just to run the field while it makes the charge current.


Ratings are RPM that the generator is turning, not the engine. Since a Deere B runs full bore at around 1200 - 1300 RPM, the generator needs the smaller pulley than the drive pulley on the engine to reach max output of 8 amps.

Alternators on cars and trucks are usally run 2 to 3 faster than the engine turns. So an engine idling at 800 RPM has its alternator spinning at least 1800 RPM. A typical auto gas engine has an alternator running 2.3 times faster than the engine. Some diesels run a bit slower with the alternator running 2 times faster.

A cheap Delco 10SI alternator can put out 25 amps at 14.5 volts at 1600 RPM and 70 amps at 6000 RPM , i.e .the engine revving at 2600 RPM. It needs to spin at least 1100 RPM to make 8 amps.

A Delco 12SI alternator can put out 30 amps at 14.5 volts at 1600 RPM and 100 amps at 6000 RPM.
Again, with the engine revving at 2600 RPM.

A Delco 15SI alternator can put out 40 amps at 14.5 volts at 1600 RPM and 85-105 amps at 6000 RPM. So with the engine idling, this can put out over 40 amps.

Some CS130 Delcos can put out 100 amps at engine idle and 220 amps when the engine is revved to 3000 RPM.

No generator-equipped tractor I’ve ever run (includes Deere, MM, IHC, Farmall, A-C, etc) will charge at low idle. Even “modern” generator-equipped tractors like the Oliver 1600 and JD 3020/4020 tractors show a discharge at idle. It’s just the nature of generators – they simply do not generate current at low RPM’s

Low idle charging CAN be achieved by increasing the generator to crankshaft drive ratio (larger crank pulley and/or smaller gen pulley) to spin it faster. But you now cause increased wear on the generator (shortened life). You also risk overspeeding and “birdnesting” the generator innards at governed RPM.

Only an alternator can charge at low idle RPMs. Or if you insist on the original look - and have lotsa cash - get yourself a Genernator (http://www.gener-nator.com)

Hello idemaris,
GM Delco factory rep told me that the ratio in speed Between the crankshat and the a/c generator speed is 2 and 5/8. That was for class 8 truck application.
When you stated trucks i gather you ment
pick-up trucks.
Guido

To your point, I know how we all (most) love to see how slow we can get our old tractor engines to run. It is amazing how slow they will go when set up properly.
If you look at any of the operating manuals for these, they make it clear that the engines were designed to run primarily at "fast idle", or, top speed once they are warmed up. I realize there are times that we need to be at slow idle or not wide open, but not often.
I run generators on all of mine. I have no issues with charging.
Alternators win hands down for higher charge rates even at idle. But why ruin the tractor like that? I have never seen an alternator on an old tractor that did not look like a wart on someone's nose.
If you really want to go for higher output and more modern equipment, why not add LED lights and digital gauges? Then they would not just stare at the wart on the nose. LOL