farmall cub alternator

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36farmallf20
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farmall cub alternator

Postby 36farmallf20 » Fri Jan 03, 2020 10:55 pm

I would like to install a 3 wire alternator on my cub( I know a 1 wire would be easier but i am not fond of them). My issue is that I have magneto ignition therefor my ignition switch is only a ground and cannot be used to supply power to the exciter wire. I am also lazy and forgetful so I do not want to a secondary switch/push button for the exciter circuit, not to mention it would look out of place on the dash. I was wondering if it would be possible to tap into the cranking side of the starter button to supply the exciter wire with power, or if the manner the switch makes contact to the starter would render that impossible.

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Re: farmall cub alternator

Postby Frozenstate » Fri Jan 03, 2020 11:35 pm

Relay?

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Re: farmall cub alternator

Postby tst » Fri Jan 03, 2020 11:49 pm

3 wire does not excite because of the low rpm of a cub, the one wire is a better choice, the napa RAY 2134011SW is made to excite at low speeds, the power to it should be switched off when the engine is turned off, hooked to the starter that would not happen

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Re: farmall cub alternator

Postby Jim Becker » Sat Jan 04, 2020 12:43 am

You can use a switch triggered by oil pressure. You can tee in at the pressure gauge. You could also tap in to any gallery plug but I'm not sure any of them is easily reached.

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Re: farmall cub alternator

Postby radioguy41 » Sat Jan 04, 2020 9:17 am

Jim Becker wrote:You can use a switch triggered by oil pressure. You can tee in at the pressure gauge. You could also tap in to any gallery plug but I'm not sure any of them is easily reached.

Yep, here's how I did mine. This setup hides perfectly under the hood (see 3rd photo).

Click on an image for a larger view.
wiring-diagram-for-denso-alternator-magneto.jpg

1948 Farmall Cub-353.jpg

You can barely see the threaded rod.
1948 Farmall Cub-374.jpg

MCC 50V 6A Current Blocking Rectifier Diode
Denso Mini 12180 CW alternator (shop around, prices vary greatly)
132244R91 Switch, Hour Meter Pressure (also sold as an oil pressure switch)

I used the stock generator mount drilled out to accept 3/8" threaded rod. The slotted adjustment bracket just required a bit of massaging with a 3lb hand sledge to straighten it out a bit (but not completely flat) and it lined right up. I did grind just a bit of metal off the bottom edge of the bracket where it touched the alternator. I probably could have skipped that but why take a chance.

I tightened the nuts in the following order.

Thread on the rear nut until it's flush with the end of the threaded rod.
Tighten the front nut to tighten the alternator.
Tighten the one directly under the alternator.
Tighten the 4th nut last.

I also used 2 flat washers between the alternator and the bracket to space it out to fine tune lining up the belt. Not real pretty but functional.
Last edited by radioguy41 on Sat Jan 04, 2020 2:04 pm, edited 1 time in total.
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Re: farmall cub alternator

Postby Jim Becker » Sat Jan 04, 2020 11:27 am

An equivalent pressure switch is probably also listed some places as a brake light switch.

In the wiring diagram, the wire from alternator #3 should go to the other side of the ammeter. As is, the ammeter will never show charging from the alternator.

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Re: farmall cub alternator

Postby Eugene » Sat Jan 04, 2020 12:21 pm

1948 Cub, what are you going to do with the light switch? You could use one of the positions on the light switch to excite the alternator.

2nd question. What is the objection to single wire alternators? I've been using them for years, no problems.
I have an excuse. CRS.

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Re: farmall cub alternator

Postby radioguy41 » Sat Jan 04, 2020 2:06 pm

Jim Becker wrote:An equivalent pressure switch is probably also listed some places as a brake light switch.

In the wiring diagram, the wire from alternator #3 should go to the other side of the ammeter. As is, the ammeter will never show charging from the alternator.

My bad. Too much of a rush. Corrected now. Thanks for pointing it out Jim.
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Re: farmall cub alternator

Postby BigBill » Tue Jan 07, 2020 2:50 pm

One wire is so much easier. Pick up a 10si alternator and a one wire 105 amp kit from ebay. There’s a non exciter kit. I’m running this kit on my fcub before it died. I took off a mile of extra wire the PO tried to wire a 3 wire alternator. It didn’t work, I stripped it and rewired it.

My PO cut the hood for the alt wires wouldn’t rub against it instead of rotating the rear alt body I was lucky to find a good hood.
I'm technically misunderstood at times i guess its been this way my whole life so why should it change now.

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Re: farmall cub alternator

Postby radioguy41 » Tue Jan 07, 2020 4:06 pm

I tried a one wire and it was a real hit or miss. Sometimes it self-excited and sometimes it didn't. The problem is the low RPMs of the Cub engine. I would also point out the smaller size of the alternator I used. It hides perfectly under the hood, nothing rubs or interferes. If you shop around for that alt you can find it quite inexpensively, I paid $42.75 including shipping. In addition no installation kit is needed save for a length of threaded rod and some nuts & washers. All told I shelled out $60 including a new belt. The pressure switch was already in place for an hour meter but that would only add another $10 or so. I could be wrong but I haven't seen a complete one wire kit for anywhere near that cost.
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Re: farmall cub alternator

Postby Cub-Bud » Tue Jan 07, 2020 6:10 pm

I have a one wire alternator on a '49 FCUB with distributor ignition and 12V conversion. What is the best way to excite in this set-up :?:
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Re: farmall cub alternator

Postby radioguy41 » Tue Jan 07, 2020 6:34 pm

Click on image for a larger view.
wiring-diagram-for-denso-alternator 2.jpg
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Re: farmall cub alternator

Postby tmays » Tue Jan 07, 2020 9:16 pm

Thomas

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Re: farmall cub alternator

Postby 36farmallf20 » Wed Jan 08, 2020 8:38 pm

for now its on the light switch until I can get an oil pressure switch, thanks for the help/ideas

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Re: farmall cub alternator

Postby tst » Wed Jan 08, 2020 10:05 pm

not all gm/delco one wire alternators are the same, they need to be set up to excite at a low rpm such as the napa RAY 2134011SW, excite speed is around 750-1000 rpm, many do not work till around 1500-2000 rpm


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