8N voltage question

   / 8N voltage question #1  


Apr 23, 2012
The kid up the street offered to clean the carb while I was doing other stuff.
A bit later I see him on tractor riding around. I asked how he knew it was pos ground since I didn’t have a battery in it.
He had put in a 12v car battery, grounded to negative and no clue what it meant.
Started and ran fine. Ammeter was confused and -6 to +6v. Lights worked and battery seemed to charge.
I got a new 6 for it and only difference is ammeter shows steady 10v charge.
No apparent damage after 2 days of 12v. Lights didn’t even blow.
What gives?
No idea how it started, charged, and ran wired backwards like that, not to mention wrong battery.
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   / 8N voltage question #2  
That’s interesting. I may need a new 6 volt battery myself. I took the good one out of my 1951 8n and put it in a Farmall Cub that I bought last fall. The Cub hadn’t been run in 17 years and the 6 volt battery on it was shot.

It came with another 17 year old 6 volt battery that had never been used. I filled that one with distilled water and charged it for about 20 hours at 7 Amps with a 6 volt charger. After that, the 17 year old battery cranked my 8n over for a little while, but not long enough to start it. I hadn’t ran the 8n since last fall.

At that point, I did my first ever 6 volt on 6 volt jump, which worked very well. After starting the 8n, I ran it over an hour plowing, and the dash gauge was showing that it was charging pretty good. It will be interesting to see if that old battery will start the 8n next time without a jump.

That may be a long ways off, because we are supposed to be getting 8 days of rain, starting Friday. There will be no more plowing or disking for me for quite some time.

I prefer leaving my old tractors 6 volt, but those batteries are not easy to find. When I only had one 6 volt tractor, I would use a 12 volt tractor or truck to jump it, with the engine off. That worked ok, but still cranked it over real fast. This 6 volt on 6 volt jump start was much smoother.
   / 8N voltage question #3  
You can jump a 6-volt tractor from a 12-volt battery, just don't connect the two batteries the way you would on a normal jump. If you are jumping your 6v 8N, first make sure it is NOT in gear because you will be standing right in front of the rear tire and you may run yourself over. Connect the positive cable from the 12v battery to the lug on the starter and touch the negative cable to ground on the tractor being jumped.
   / 8N voltage question #4  
The 8n really doesnt have any electronics and could really care less which way its wired. Calling one side of a battery positive and another side negative is just arbitrary. Current flows, it has a path from one post to the other.

When people convert the tractors to 12v....the go to the more common negative ground....no issues.

Some say that when running on POSITIVE ground with 6v on the 8n....that you loose about 25% of your ignition power (spark from coil). And while that is sorta true....it basically means you are running the coil backwards. If you look at the top of a coil......it has + and - terminals. By reversing the battery.....and NOT reversing the coil you technically have coil hooked up backwards and its less efficient. But you could simply swap the coil.

But my guess is that the 12v more than overcame the weak spark by having the coil polarity backwards.

Its also likely that it DIDNT charge the battery at all. But simply the reserve capacity of the battery was enough to to power the ignition....which is all that is needed because there is nothing electrical on the 8n other than the lights. Were those even being used? IF not would explain why they didnt blow. But most likely those lights can handle 12v....which is all they were being fed since there was no alternator bumping voltage to ~15v. Throw in a little voltage drop and maybe the lights were only getting 10-11v. But when the generator and tractor is working normally....your system is running around 8v. So its not as bad as it seams and probably the reason the lights are fine.

What I am surprised at though is that it is charging fine now without having to re-polarize the genny
   / 8N voltage question #5  
What I am surprised at though is that it is charging fine now without having to re-polarize the genny
Me, too. Were it me, I would polarize it - can't hurt.