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Converting G to 12 volts

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JohnCO View Drop Down
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Joined: 11 Sep 2009
Location: Niwot Colo
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    Posted: 15 Feb 2018 at 12:12am
I've got a couple questions regarding the change to a one wire alternator.  Do I need a resister on the wire from the alternator to the battery (amp meter)? and which side of the 12 volt coil will the ignition wire go to, considering it will now be a 12 volt, negative ground? 
"If at first you don't succeed, get a bigger hammer"
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DaveKamp View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DaveKamp Quote  Post ReplyReply Direct Link To This Post Posted: 15 Feb 2018 at 2:34am
Hi John!

So, I don't know the G's original wiring configuration, but with all alternator conversions on a battery-coil ignition system, the same general rules apply:

The one-wire alternator needs nothing to connect directly to the battery.  IF you choose to utilize an Ammeter, the alternator's single wire connects to one pole of the ammeter, along with the accessory/ignition feeder.  The other side connects to battery, so that when the engine is running, alternator charge current swings the needle towards battery CHARGE, and with the engine off, current from battery to the accessory/ignition feeder swings the ammeter needle towards DISCHARGE.  If you find the needle swings oppostie, reverse connections on the ammeter.

If your system was originally 6v, and you're converting to 12, either switch to 12v lamps, or take the opportunity to install LED replacements.  ;-)  Filament lamps don't care about polarity, but the LEDs often will.  Most are set up for negative ground convention, so if you're going negative ground, it'll be fine.

Reversing the wiring on the small terminals of the ignition coil isn't mandatory- it will work in either direction, but some purists insist that it makes a big difference.  I usually reverse the connections on coil primary, but I've seen many run for decades backwards with no noticable issues.

A 6v starter runs great on 12v.  Every so often you'll find a starter bendix that doesn't respond well to the extra snap... the Conti in your G will probably actually like it.  For what it's worth, the DC starting motor has some current self-limiting tendancies as a result of the physics involved in armature rotation, so as long as you don't stall the starter armature, it generally won't burn itself up.  Frequently, a parts lookup will reveal that the difference between a 6v and 12v starter is... absolutely nothing.


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DiyDave View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DiyDave Quote  Post ReplyReply Direct Link To This Post Posted: 15 Feb 2018 at 4:46am
John, just connect the one wire terminal to one of the big wires, in the original wiring harness.  Trace it back, so you know its the one that goes back to the oem amp meter.

If ya wanna get fancy, then swap the 2 wires on the amp meter, and then the amp meter will read charge, when charging.

To be technically correct, you should also swap the wires, on the coil, so that - goes to the dist.  If you have original solid points, this will extend the life of the points.  I have gone to replacing points, with pertronix electronic ignition, cause its the same labor, and once done, never has to be done again EVER...
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jaybmiller Quote  Post ReplyReply Direct Link To This Post Posted: 15 Feb 2018 at 7:07am
If you buy a 'Denso' or similar alternator you will NOT have to cut the tin to make it fit. A GM CS-130 series 'might' be OK but NOT one of them big old beasties. Since you're going to all the trouble( pleasure) of updating the G, it'd be nice to use the physically smaller alternator for looks !
Maybe Steve@B&B has an 'upgrade' G kit ? If not, perhaps it's something he'll consider !!
Jay
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Kubota BX23S lil' TOOT( The Other Orange Tractor)

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K-Mo View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote K-Mo Quote  Post ReplyReply Direct Link To This Post Posted: 15 Feb 2018 at 8:01am
Ignition Coil connection. If Positive GND, wire from distributor goes to "+" on the coil. If Negative GND, distributor wire goes to "-" on the coil.
Assuming you have an original 6 volt coil, add an ignition resistor between the ignition switch and the coil. Not all ignition resistors are the same. The resistance values vary greatly. I usually use a resistor with about 1.4 ohms. The proper resistor should give you about half the battery voltage at the coil with the distributor wire grounded.
I prefer a 3-wire alternator which insures alternator "turn on".
A 1-wire should work as well, but you may need to rev up the engine to get the alternator  to turn on.
In an automotive application, the alternator operates at a much higher RPM which gives a quick alternator turn on. In an Allis G, the alternator RPM will be much lower.
Not all alternators are the same. Some alternators are equipped for a lower turn on threshold.
I prefer the 3-wire because the ignition switch provides the turn on for the alternator. In tractor installations, it is usually really a 2-wire installation. One wire on the alternator determines the point of regulation in the circuit. This is often just jumpered to the alternator output terminal. The other wire to turn on the alternator is excited by the ignition switch through a diode, idiot light or resistor. If wired directly, the alternator will back feed after the ignition switch is turned off and the engine will keep running.
If using an idiot light or resistor, the amount of resistance will affect the alternator turn on. The more added resistance, the higher RPM to excite the alternator. IH tractors used a 25 ohm resistor. If using a light, select a bulb which is used as an alternator idiot bulb. A diode will provide the most optimum alternator turn on.

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JohnCO View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JohnCO Quote  Post ReplyReply Direct Link To This Post Posted: 16 Feb 2018 at 12:19am
Thanks for the info guys.  This is a working tractor so running well is more important then looks, although it may someday get a paint job.  Paint is pretty good right now considering it sat outside for who knows how long.
"If at first you don't succeed, get a bigger hammer"
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