[Farmall] Farmall not starting---still!

[dan-0001 at comcast.net]

If you have no current flow the voltage will match the source assuming a  high impedance meter. The only way the resistor exactly divides the voltage is when the resistor and coil have the same resistance. The resistor will limit the current when the points close and the voltage will be   Vbatt*coil resistance/ (Coil resistance + Resistor resistance) .Ohms law.  I suspect the resistor value was selected more to limit current than exactly make 6V. I believe the difference in 6V & 12 volt coils is wire size. Smaller wire means you can get more turns on the primary in the same amount of space so you get the same secondary voltage with 1/2 the current. But also more heat due to wire resistance. 



You should check to see you have voltage on the open set of points (12 v)  and  0 volts on the coil (-) when the points are closed.  

I think you should be able to make a spark by touching a wire from the coil negative to ground this would permit checking with out cranking the engine.I have not tried this but it should work. 



 I would not assume because the starter is grounded that rest of the system has a good ground. On the H the ground goes to a bolt on the starter. The ground for the block goes through the bolt. It's possible the 2 can be different. I'm not sure how yours is connected but a good cleaning is quick and can't hurt. 



Just my thoughts 

Danny 




----- Original Message ----- 
From: szabelsk at gdls.com 
To: "Farmall/IHC mailing list" <farmall at lists.antique-tractor.com> 
Sent: Monday, August 3, 2009 11:11:10 AM GMT -06:00 US/Canada Central 
Subject: Re: [Farmall] Farmall not starting---still! 

Assuming that you are supposed to have 6v at the points and not 12v (???), 
the only way you would have 12v is if the resistor is shorted out. Are you 
sure it's in the circuit properly? Are the resistor leads touching 
together or are both touching some thing else? Normally I put a small 
piece of insulation sleeving on each lead (assuming you have a resistor 
with leads) to ensure they don't short out. If the resistor is open 
circuited, you should get nothing at the points. 

Have you checked to make sure the points are not shorted? You could be 
getting voltage to the points going right to ground instead of through the 
points. 

The condenser is actually a capacitor rated at a higher value than what it 
is intended to be used for, however they can short out internally without 
any visual sign. The condenser's main job is to build up a charge and 
release that charge at the right time to provide the higher power you need 
for the ignition system. The release is triggered by the opening/closing 
of the points. Think of it as another power source for your ignition 
system. 

As far as the coil(s) it should not be damaged.  You can check them by 
doing resistance measurements. 

Carl Szabelski 





ebony51 at frontiernet.net 
Sent by: farmall-bounces at lists.antique-tractor.com 
08/03/2009 11:29 AM 
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Kirk Rinne <krinne at windstream.net> 
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Re: [Farmall] Farmall not starting---still! 






Okay, I tried something else.  I put my voltmeter on and I am getting 12+ 
volts running from the coil to the points.  Now, I would have thought the 
resister was supposed to take that down to 6 volts.  So, do I have a bad 
resister?  And would that have friend my coils (both of them)?  And would 
it have damaged the condenser? 

Larry 



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