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Ballast resistor heats up

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Ozark kurt

08-17-2007 09:29:20




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I have 6.7 volts at the battery, 3.5 volts across the ballast resistor and around 1.5 volts at the coil. All connections are bright shinny and tight. This is on a 6V front mount 8N engine 9N everything else.
I am grounding my multimeter against the manifold so that may be why it is less than 3.5 volts. I noticed that the ballast resistor was heating up when the ignition was on for approximately 30 to 40 seconds;just long enough to measure the current. I know the resistors job is to drop the current for some reason (unknown to me, but why could not the engineers design this system to use the battery voltage of 6V. ?)I assume the energy loss at the resistor is transfered to heat. But should it be so noticeable as to cause an oder? Is the resistor bad?

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Phil (NJ,Az,Sask)

08-18-2007 08:34:13




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 Re: Ballast resistor heats up in reply to Ozark kurt, 08-17-2007 09:29:20  

Ozark kurt said: (quoted from post at 09:29:20 08/17/07) I have 6.7 volts at the battery, 3.5 volts across the ballast resistor and around 1.5 volts at the coil. All connections are bright shinny and tight.
This is on a 6V front mount 8N engine 9N everything else.

I am grounding my multimeter against the manifold so that may be why it is less than 3.5 volts.


Kurt,
The only load (Resistive devices) of the ignition circuit should only be the Ballast R & the coil. The SUM of your voltage measurements MUST be equal to the Battery voltage (6.7) but you only have 3.5 +1.5 = 5.0V (you are missing 1.7 volts)

The Voltage across the Ballast 3.5V is equivlent to ~2.6 amps , and that would mean that the OEM 1 ohm coil must have a voltage drop equal to 2.6 Volts (1.0 Ohm X 2.6A =2.6V)

I would re-do your measurements because the COIL voltage indicates 1.5 amps and that is Very LOW! The OEM Coil resistance is 1.0 ohms and that provides for a simple Conversion of a voltage reading directly to amps (they are the same)

Ohms law: V divided by Ohms = Amps ( 1.5 / 1.0 = 1.5)

The Ideal voltage reading across the coil is 2.8V (2.8A). To get acurate reading's remove the coil, leave top wire connected, and Jumper the Coil Pigtail connector to a good ground. Connect one meter probe to the Coil Pigtail (leave it there) and just move the other probe to each test point

IE. Top of coil (VD of Coil), Ballast R Terminal (= Coil VD + wire VD), other Ballast R Terminal (= VD of Ballast + VD of Coil + VD of wire)
When the Sum of Voltage drops are Equal to the battery you have found all resistive devices
Hope this Helps,

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duey

08-17-2007 13:14:59




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 Re: Ballast resistor heats up in reply to Ozark kurt, 08-17-2007 09:29:20  
A LIGHT BULB is a form of a resistor, too.... don't they get hot, too???

It can't 'resist' and not heat...

duey



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old

08-17-2007 10:33:56




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 Re: Ballast resistor heats up in reply to Ozark kurt, 08-17-2007 09:29:20  
Sounds like its working just fine. Yes they heat up and can heat up real hot DO NOT touch one or you will be looking for an ice cube to hold on your fingers. So yes what its doing is normal



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ED-IL

08-17-2007 10:25:41




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 Re: Ballast resistor heats up in reply to Ozark kurt, 08-17-2007 09:29:20  
The resistance increases wwith the heat. So, when you switch on the ignition, less heat sends more volts to the coil to aid in starting the tractor. As the resistor heats up, the voltage drops to normal operating range. If the voltage at the coil is too high, the coil will burn out. A common fix to poor ignition is to bypass the ballast resistor, which helps the tractor start quicker, until the coil is gone (as me how I know).

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LeeMo

08-17-2007 10:08:04




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 Re: Ballast resistor heats up in reply to Ozark kurt, 08-17-2007 09:29:20  
New resistors will often smoke and have an odor until they burn off any oils or contaminants from manufacture. Not anything unusual.



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