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Posted By Discussion Topic: electricity help -- page: 1 2     fordmerc 01-06-2019 @ 1:04 PM reply profile send p.m. New Member Posts: 180 Joined: Oct 2009 I need some basic electricity help with my '39 Observation 1: voltage at coil wire disconnected from coil is 6.1 V Observation 2: voltage at coil with wire connected is 3.2 V Problem: the longer the ignition switch is on, the voltage at coil drops about .01V every 10 sec ( Observation stopped at 2.7 V and falling) Question 1: how do I determine if points are open or closed? Question 2 should current be flowing whether points are open or closed? This message was edited by fordmerc on 1-11-19 @ 5:31 AM supereal 01-06-2019 @ 1:22 PM reply profile send p.m. Senior Posts: 6819 Joined: Oct 2009 With the points closed, the voltage at the coil input should be about the 3.2 volts due to the in circuit resistor between the switch and the coil. If the points are open, you will see battery voltage about 6.5. If the ignition switch is left on with the points closed (there are two in the distributor) the voltage at the distributor will fall due to the heating of the resistor. This is normal. No current should be flowing with either of the point sets open. this can be checked by placing a voltmeter between the coil input terminal and ground, As the engine is turned over by the starter, you should see the meter rise and fall. The two sets of points in the distributor operate by one set closing the circuit, and the other set opening, This is done to allow full saturation of the coil to increase the output to the spark plugs. ford38v8 01-06-2019 @ 1:40 PM reply profile send p.m. Senior Posts: 2795 Joined: Oct 2009 Fordmerc, My good friend Bob (Supereal) has provided you with an excellent answer and explanation of your ignition system, and I can think of just one detail you might find useful: A Digital Voltmeter's displayed values become unreadable while reading a spinning engine, which mandates the use of an Analog Voltmeter for this purpose. Alan This message was edited by ford38v8 on 1-6-19 @ 1:41 PM fordmerc 01-06-2019 @ 1:54 PM reply profile send p.m. New Member Posts: 180 Joined: Oct 2009 Thank you. Question answered. I will proceed with my troubleshooting. I appreciate the opportunity to ask basic questions to help me understand the car. (More may follow.) fordmerc 01-08-2019 @ 7:17 AM reply profile send p.m. New Member Posts: 180 Joined: Oct 2009 Another question: Voltage at coil is 6.0 with points open, all spark plug wires disconnected. Voltage drops to 3.1 with points closed, and then continued to fall to 1.8 over 10 min. when I stopped the experiment. This doesn't seem right (?) Where is the current going? (the resistor is hot - I have tried two other resistors with no difference) Am I missing something? ford38v8 01-08-2019 @ 8:50 AM reply profile send p.m. Senior Posts: 2795 Joined: Oct 2009 Same answer really, your system sounds very good. The resistor is variable, meaning that the more it is loaded, the less it puts out as it gets hotter and hotter, because heat creates more resistance. In your static trial, you've created an unusually high load because your points are continuously closed rather than open-close-open-close, which prevents overheating of the resistor. A further explanation of the great value of resistors, is to realize that while the load may fluctuate, the input also fluctuates due to the action of the generator, the condition of the battery, and other factors such as the draw of heater, radio, and headlights. The net result at the coil is a steady input, producing a consistent spark at the plugs. Bottom line, your question "Where is the current going?" Your current is producing heat at the resistor, as Henry Ford intended. Alan 40 Coupe 01-08-2019 @ 3:01 PM reply profile send p.m. Senior Posts: 1698 Joined: Oct 2009 Charge your battery and take it to a auto parts store that can check it. Voltage should not drop that fast. fordmerc 01-09-2019 @ 5:52 AM reply profile send p.m. New Member Posts: 180 Joined: Oct 2009 I have kept the battery on a charger and while it is two years old, I bought this one new because of the problem that I have. I want to blame the voltage drop on a current leak, but I can't find one and from other responses I seem to be barking up the wrong tree. TomO 01-09-2019 @ 6:48 AM reply profile send p.m. Senior Posts: 7274 Joined: Oct 2009 As Supereal explained, your readings sound normal. Are you troubleshooting a problem or just trying to find out what is normal? If you are trouble shooting a problem, describe the problem and maybe we can give you a good procedure to troubleshoot it. Tom LarryK 01-10-2019 @ 9:06 AM reply profile send p.m. New Member Posts: 105 Joined: Aug 2012 In your second post, you ask "Where is the current going?" With the points closed, current flows from the battery through the following components which are all connected in series: ignition switch, resistor, primary winding of the coil, to ground. This flow of current causes the resistor to heat up, which increases its resistance, and causes an increase in the voltage drop across it. There will be a corresponding decrease in voltage at the coil, as you have measured. With both sets of points open (they are connected in parallel), the circuit is opened and no current will flow. Thus your measured 6.1 volts at the coil. Larry

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