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Harry Ferguson Tractors Discussion Forum
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Ceramic resistor??

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Steve Moyer

03-06-2008 13:03:10




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My 1950 TO-20 has a white ceramic resistor?? in line from the switch to the positive terminal on the coil. What does this do I seem some tractors with it and some without?




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Steve Moyer

03-08-2008 14:23:22




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 Re: Ceramic resistor?? in reply to Steve Moyer, 03-06-2008 13:03:10  
I am sure my TO-20 is a 6volt system. The generator has been rebuilt since I have owned it , the battery is a 8volt, and the coil is 6volt. Also I have replaced the voltage regulator with a 6volt unit. The ground is positive, so do I need the resistor or not???



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Jerry/MT

03-08-2008 14:37:34




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 Re: Ceramic resistor?? in reply to Steve Moyer, 03-08-2008 14:23:22  
How are you going to regulate an 8V system with a 6 V regulator? Are you going to adjust the out put of the regulator? If you do, you will have a 8v system and the primary circuit will have to have 2 ohms of resistance to maintain a 4 amp max primary current. Since your 6V coil has about 1.5-1.6 ohms resistance(nominally) you"ll need a 0.5 ohm resisitor in series in the primary circuit.



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George in Spokane

03-07-2008 21:15:27




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 Re: Ceramic resistor?? in reply to Steve Moyer, 03-06-2008 13:03:10  
I thought it was to avoid burning the points.



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Bob

03-07-2008 18:47:09




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 Re: Ceramic resistor?? in reply to Steve Moyer, 03-06-2008 13:03:10  
Bottom line is, with either a 6-Volt system, or a 12-Volt system, you want primary ignition current (ignition switch "ON", engine "OFF", points closed) to be in the 3-to-4 Amp range.

LESS current = weak spark

MORE current = short point life/burned points, hot coil/failed coil.

You can "fine-tune" a specific coil to a specific application by adding resistance, as needed, to get the primary current into that range.

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Richard L

03-07-2008 16:47:51




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 Re: Ceramic resistor?? in reply to Steve Moyer, 03-06-2008 13:03:10  
Mark I have no real answer for you. I would think if it cut the voltage from a 12 v. battery in half it should do the same from a 6v then there shouldn't be enough spark to start the tractor.



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Richard L

03-06-2008 13:10:08




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 Re: Ceramic resistor?? in reply to Steve Moyer, 03-06-2008 13:03:10  
If that is what I think it is your tractor has been converted to 12 Volt and you have a 6 volt coil so to protect the 6 v coil the resistor is there if you had a true 12 v coil you would not use the resistor.



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Mark from the fort

03-07-2008 10:46:50




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 Re: Ceramic resistor?? in reply to Richard L, 03-06-2008 13:10:08  
Richard, let me ask you this..
what effect would this resistor have on a 6 volt system?
I have a parts TO 30 that I bought many years back that came with a 6 volt battery and pos. ground, YET, has an "old" coil with a ceramic resistor built on the top of the coil.
I never attempted to start, 'cause I robbed the head and genny off of her, but I often wondered it it was actually a 12 set up or if a 6 volt would still work with the resistor.
Always wondered about this.
Thanks, Mark

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Gerald J.

03-07-2008 13:51:19




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 Re: Ceramic resistor?? in reply to Mark from the fort, 03-07-2008 10:46:50  
Some Chrysler cars used a 3 volt coil with a resistor for better high speed performance. And may have jumped the resistor while cranking for better starting.

Gerald J.



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