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Small engine Alternator experiment

4826 Views 9 Replies 6 Participants Last post by  larrybl
Based on two different alternator designs, We are trying to see if it is possible to Charge the battery and run the electric PTO from a two wire alternator. The orginal engine had a 15 Amp alternator with three terminal Regulator (Orginal set up). The Doner engine has the 2 wire alternator. The Alternator specification shows Red wire 12VDC @ 3 Amp, and Black lead 14.2 VAC.

Research shows the PTO requires a minium of 4 Amps, and an additional Amp to charge the Battery.

The Theory is to add an additional Diode to the Black wire, and combine the outputs of the Red (which already has a Diode) and the black to double the amperage to 6 Amps.

Picture 1, the theory, 14.2 VAC Center taped, fed to two seperate diodes, then combined.
Picuture 2, the modification.
Picture 3, the setup. I tried using a regular PTO, but my transformer is only rated at 2 Amps AC, So I use a 12V 1157 Lamp for the Load to prove the Theory.

Picture 4, One side of the Center taped Xformer through a diode oriented for a Positive output. 5.8 VDC @ .4 Amps.

Picture 5, the other side of the center taped transformer added through a Positive orientated Diode, 11.2 VDC at .8 Amps.

Picture 6, the 2 wire alternator, and Pic 7 the Center tap.

Picture 8, The diode orientation. (Note, Both need to be Positive orientated or sparks will happen).

By combining the Charge current, with rectifed Light circuit I show that the Amperage has doubled. The Voltage increase is due to the meter reading 1/2 wave vs Full Wave.


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why not just use the original regulator/rectifier? the only reason it would not work in place of the 2 diodes would be if the supply voltage is not high enough.
why not just use the original regulator/rectifier? the only reason it would not work in place of the 2 diodes would be if the supply voltage is not high enough.
I am trying to help another member, I think the Orginal alternator is a "single" wire, and the new engine has the "dual wire" These two alternators are wired different. The Dual is Center taped, alowing for two 14V outputs, One of which is rectifed. The Single wire outputs 24V which is fed into a Regulater (bridge) to output 12VDC at higher amperage.

I don't know if the alternators can be swaped.
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The original engine is a Kohler Magnum Twin 18.5hp, Doner is a Briggs & Stratton 20.5 Twin. I also have a alt for a 16HP Briggs & Stratton Twin II that had part of the wire missing, Both the Briggs 20.5 and kohler 18.5 have a two wire alt.
If I didn't have my work bench covered with a 50" deck, I would try setting up the spare 18Hp and the remote control, and swapping in this dual alt and try the added diode to see if this would work for real instead of theory.

If I get the deck done, I may just do it any how (unless someone else does) just to comferm or disprove the theory.


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Hi folks,

new here and been reading a lot.
there is a trove of great info on this board.
imagine if it were put into a book.......

anyway, I just stumbled across this thread...
I know it's dated, but how did it turn out?

does it work in practice like the theroy suggests?
did you have to do anything to regulate the charge to the battery?

I'm wanting to replace the ac light circut to power a pair of Speaker model 701 leds which requires DC. should draw a total of 2.4 amps vs 5.8 amps for the 4406 lights ( assuming they are 35 watts each and assuming I have my electrical theroy right...)

I'd like to , convert the AC leg to dc, combine the outputs and run it all as DC. and hook lights to the battery with a proper light switch and fuse.

is 6 amps dc over kill for charging the battery?
sorry for all the questions...
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also noting the date but my comment is that Ariens actually produced riders with the electric pto clutch and the charging system was only the the dual briggs system. I know because I provided a donor engine with the dual charger and verified that the original engine and the manual showed original was just the dual.
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Those two windings may not be identical. One winding is just plain old AC for running the lights. The other winding is for charging the battery, assuming some average load on it.

If you could isolate the DC winding from the other winding, and from ground, you could connect it to a full wave rectifier instead of the half wave. That would double the power output, but it would also double the current in the coil. I would worry about overheating it.
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The Left stator is a "dual mode" which means there is an inline Diode on one lead. If you notice the coil(s) are terminated next to the bottom righe mounting hole, effectively making two circuits.
1. Red wire with Diode to provide 13.5 VDC @ ~3A for Battery Charging.
2. Black wire provides 13.5 VAC @ ~3A for headlights

The Right Stator is a single wire, that uses a "tri circuit" (Dual reversed diode)
Notice the coil has a single termination on the bottom. The single wire output is 28 VAC, and once the dual diode is connected you have
1. (+) 13.5 VDC @ ~ 4A for Battery and PTO
2. (-) 13,5 VDC @ ~4A for Lights.

Now theroy says you might be able to add a Diode to the Black wire on the first "dual" stator and us it to power a PTO.

Another theory would be to un ground and insulate the connection on the dual stator at the point next to the right mounting hole. Ground the black wire, and add a dual diode to the red wire (after removing the inline diode) In theory this should make it a single wire 9A stator.

My 2c


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