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I just recently bought a John Deere Model 40-S and I am doing some work to it to get it running correctly. I want to switch it over from 6v to 12 volts. Does anyone have a write up on how to do this or can anyone help. Thanks
 

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Hi,

I've done this conversion on a few John Deere and Massey Ferguson tractors.

1. You'll need a 12v coil
2. If you want to have working lights, you'll need to change them to 12v
3. You will need a 12v alternator (common type is Delco Remy SI-10 type). I'd suggest a "single wire", "self-exciting" configuration. You can buy these at Summit Racing or Jegs, brand new, for a relatively reasonable price.
4. You will need a pulley for the wider section fan belt (check out the alternator pulley conversion for a Ford 8n tractor)
5. You will need to fabricate a bracket for the alternator to replace the 6v generator
6. You will "swap" the battery leads to convert it to 12v negative ground.
7. You will need to swap the ammeter and change the wiring to reflect the new ground (positive to negative)

You will *not* need to:

1. Change the starter
2. Change the switches
3. Change the wiring harness
4. Modify the distributor or change condenser

Also, you will not need the old style, mechanical voltage regulator. You can run the charging lead from the alternator, straight to the battery using a heavy (e.g. 8 ga or 10 ga)

A few comments.... The 12v alternator needs a lot more RPMs to generate power than does a 6v generator. So, you'll likely have a situation where you'll need to run the engine at higher RPMs for longer periods of time to get a good charge to the battery.

I suggest you might consider keeping the 6v system in place.

If you overhaul the 6v unit and ensure you have a good quality voltage regulator (NAPA Echlin or OEM Delco Remy) and heavy duty "0 gauge" cable for the ground and the battery. Preferably a flat braided ground cable.

Polarize the generator (see attachment or PM me ). Next, make sure the ground is attached to the frame and there is no rust or corrosion where the grounding terminal is bolted to the frame (use a grinding wheel to make the metal "shiny."

A 6v system has significantly more amperage than a 12v system and is good for the torque needed to turn over an engine. It is also set to "charge" at the engine's normal RPM range.


Good luck!
-Matt
 

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Never done it and probably never will, but I'm curious about the following:

Hi,
You will *not* need to:

1. Change the starter
I know they aren't rated for continuous duty, but is the shortened life of a 6v starter run on 12v significant enough to worry about?

A few comments.... The 12v alternator needs a lot more RPMs to generate power than does a 6v generator. So, you'll likely have a situation where you'll need to run the engine at higher RPMs for longer periods of time to get a good charge to the battery.
Can't this be rectified by going to a smaller diameter alternator pulley?

A 6v system has significantly more amperage than a 12v system and is good for the torque needed to turn over an engine.
More technically, a 6v system requires twice the current vs 12v to perform the same amount of work. 12v systems are just as capable and the advantage of the higher voltage is that the voltage drop in cables and joints is half what it is with a 6v system. For a given resistance, voltage drop is proportional to current, so halving current==half the voltage loss. More important, power varies with the square of current, so halving the current needed yields one quarter of the power loss vs the lower voltage system.


I'm with you. If the goal is to use a 70 year old tractor for real work, then convert it to 12v for practical reasons. If it is a restoration, keep all the 6v stuff original!

Al
 

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Never done it and probably never will, but I'm curious about the following:



I know they aren't rated for continuous duty, but is the shortened life of a 6v starter run on 12v significant enough to worry about?



Can't this be rectified by going to a smaller diameter alternator pulley?



More technically, a 6v system requires twice the current vs 12v to perform the same amount of work. 12v systems are just as capable and the advantage of the higher voltage is that the voltage drop in cables and joints is half what it is with a 6v system. For a given resistance, voltage drop is proportional to current, so halving current==half the voltage loss. More important, power varies with the square of current, so halving the current needed yields one quarter of the power loss vs the lower voltage system.


I'm with you. If the goal is to use a 70 year old tractor for real work, then convert it to 12v for practical reasons. If it is a restoration, keep all the 6v stuff original!

Al
Regarding the starter question from 6v to 12v:

No, it won't hurt the winding provided that the person starting the engine does not operate the starter for extended periods (for example, more than 30 seconds at a time). Operating the starter for extended periods with a 12v conversion can overheat it.
 
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