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12v conversion
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negative amp reading

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Kevin

03-03-2003 12:39:00




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I installed a 12v conversion kit this weekend on my 1949 8N per the instructions that came with it. The tractor cranks up fine and runs great with the exception of one thing. When I increased the throttle to about half open, the amp meter showed a negative 20 amp discharge and slowly reduced to a 10 amp discharge. I shut the tractor down for a while, cranked it up again, went to half open on the throttle, and the amp meter jumped back down to negative 10 amps. Any ideas why it would do this? Thanks for the help!!

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Jim WI

03-04-2003 10:49:10




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 Re: 12v conversion - negative amp reading in reply to Kevin, 03-03-2003 12:39:00  
What you're seeing fits with having changed from positive ground to negative ground without rewiring the ammeter. Also check to see if the ammeter is wired so that all current to and from the battery is registered by the ammeter. One alternative wiring scheme only passes the alternator BAT lead through the ammeter so that you only see how much the alternator is putting out. While a reversed wiring version of the second scheme kind of fits with your "10 amp discharge", I can't be sure because you may not have kept the tractor running long enough to see it go all the way to zero (which would be correct for the first wiring scheme). Either one works as long as you know how to interpret the ammeter readings.

To fix the polarity issue on the ammeter:

If it's got two terminals, just swap the wires.

If it's the inductive loop style, pull the wire out and run it through the other direction.

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Kevin

03-05-2003 08:09:17




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 Re: Re: 12v conversion - negative amp reading in reply to Jim WI, 03-04-2003 10:49:10  
Thanks Jim - I have a two post ammeter that I ordered from Just 8N's for my 6v system. I'm assuming the polarity of the ammeter is setup for a positve ground. I will reverse the wires tonight and fix the problem. A message I received from "Jim-OR" suggested I turn the key on and see which way the needle deflects. I tried that but the needle does not move until the tractor is running. I'm assuming, like you mentioned, it is because of the way the schematic that came with the kit had me wire it. I appreciate your time and help in solving my problem. This site is a goldmine!!

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David - OR

03-03-2003 12:48:02




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 Re: 12v conversion - negative amp reading in reply to Kevin, 03-03-2003 12:39:00  
The most likely explanation is that the alternator is working fine but the ammeter is hooked up backwards.

If you turn on the key (without starting the tractor) and the ammeter deflects slightly positive (from the electrical load of the coil on the battery), then this is your problem.



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soundguy

03-03-2003 12:46:14




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 Re: 12v conversion - negative amp reading in reply to Kevin, 03-03-2003 12:39:00  
By chance do you have your polarities correct? Any wires emitting smoke? ( remember.. not good to let smoke out of the wires... when they run out of smoke you gotta replace them! )

Seriously though.. do you have your ammeter wiring backwards.. showing discharge instead of charge?

If it is starting ok, and running ok.. sounds just like it is wired backwards.. charging at 20 amps.. then tapering off as normal...

Soundguy

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