| fordmerc | -- 01-06-2019 @ 1:04 PM |
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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
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| supereal | -- 01-06-2019 @ 1:22 PM |
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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.
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| ford38v8 | -- 01-06-2019 @ 1:40 PM |
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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
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| fordmerc | -- 01-06-2019 @ 1:54 PM |
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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.)
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| fordmerc | -- 01-08-2019 @ 7:17 AM |
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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?
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| ford38v8 | -- 01-08-2019 @ 8:50 AM |
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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
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| 40 Coupe | -- 01-08-2019 @ 3:01 PM |
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Charge your battery and take it to a auto parts store that can check it. Voltage should not drop that fast.
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| fordmerc | -- 01-09-2019 @ 5:52 AM |
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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.
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| TomO | -- 01-09-2019 @ 6:48 AM |
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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
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| LarryK | -- 01-10-2019 @ 9:06 AM |
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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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| fordmerc | -- 01-10-2019 @ 10:37 AM |
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I am troubleshooting a problem that the engine stops when it gets warm/hot. My previous efforts were guided by my initial post: https://www.earlyfordv8.org/forum/viewmessages.cfm?Forum=18&Topic=12442&keywords= Since then I note that the spark at a plug started to become irregular, and then disappeared at the time the engine stopped. Gas seemed to be coming into the carb at that time when I pumped the throttle. I am now trying to see if I can find an electrical problem to blame since the low voltage at the coil stands out as a big red flag. I can conceive that a resistor becomes so hot that it will drop the voltage to the coil after a while, and I have tried three resistors without benefit. The coil was rechecked by Skip Haney without a problem found. I have replaced the condenser once. The distributor was checked by Bubba and found to be OK. Each wire/link in the system has been checked an no resistance is found in the wires. I wanted to be sure that I understood that a “short” in the system would not cause a constant current flow leading to resistor overheating. I disconnected the spark plug wires on the theory that that was where the current flowed but I guess that theory fails also. I continue to appreciate the help from this forum, so I will explore any avenue within my competence (which isn’t very high). Thanks to all who have responded. This message was edited by fordmerc on 1-10-19 @ 10:40 AM
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| ford38v8 | -- 01-10-2019 @ 12:35 PM |
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As Skip has checked your coil already, and you have changed your condenser also, what remains as possible electrical causes are connections and size of wires and cables. Engine compartment heat and vibration can compromise connections that may test OK otherwise. Check your distributor and condenser for bare metal contact, no paint, and for tight bolts. Condensers may fail right of the box, so change it again now. Clean and grease battery posts, and ensure that those cables are correct for 6 volt, not 12 volt. Inspect condition of battery cables also. Even a good looking braided ground cable can be corroded inside at the terminal, making it useless. This alone can certainly be your problem, including a charging deficiency making you think you generator or battery is bad. Alan
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| supereal | -- 01-10-2019 @ 1:16 PM |
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Alan: I have been receiving a question about brake adjustment on the '38 cable brakes. It would be helpful to post your advice regarding this, as you are the cable brake "guru". I have given general advice re this often perplexing system. The questions started because the owner has a "grabbing" wheel. I suspect the cable from that wheel may be sticking or stuck in the sheath. Regards, Bob
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| ford38v8 | -- 01-10-2019 @ 9:02 PM |
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Bob, it was good talking with you tonight! It's been a long time! Tell your friend to give me a call, you have my number, or email me. Alternatively, he can post his question here and I'll pick it up, and maybe help some others as well. From what you said here, a "grabbing wheel" could describe a problem with brakes, or perhaps a wheel bearing, but doubtful it would be stuck in the sheath. I can, with more information, track it down, and it would be best to start right here on the V8 Forum. We have to get on the horn more often! Alan
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| TomO | -- 01-11-2019 @ 8:46 AM |
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Fordmerc, does you meter have a capacitor test position on it? If so your capacitor should show about 3uf. You can try this test, remove the condenser and connect an ohmmeter across it. It should show an immediate short and then quickly show an open. Reverse the meter leads and repeat the test, you should get the same results. If you don't get those results, go to NAPA and get another condenser. If you have a dwell meter, connect it to the distributor and let us know the reading. Tom
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| fordmerc | -- 01-11-2019 @ 9:16 AM |
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Dwell checked by an experienced friend with a professional analog meter- he said OK but I don’t know the number. I will check the condenser and I have a new one on order
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