How to test Magneto Output

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Model T Ford Forum: Forum 2005: How to test Magneto Output
Top of pagePrevious messageNext messageBottom of page Link to this message  By Chuck S. Lebeda on Monday, May 07, 2007 - 10:32 pm:

I do not get any spark from magneto when I short it out and hand crank engine. Car will start with tow on magneto but not start with hand crank. I removed magneto post and it looks good. Can the magneto posts go bad? Or would this most likely be magnets. I have never worked with the inside magnets or coils. Thanks, Chuck.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ron Patterson on Tuesday, May 08, 2007 - 04:58 pm:

Chuck
Try this simple to perform test and report back the results.
Go to your local auto parts store and buy a #1156 bulb. This is commonly used as a back up light bulb in modern cars. This bulb will come close to simulating the load of a typical Model T coil. You may want to pick up a socket for it too and put some wires on it to make a regular test light out of it.
Connect the bulb across the magneto output and ground while you running the car on the battery with the emergency brake pulled all the way back and set. Using an analog voltmeter check the AC voltage across this bulb as a load.
Provide the following test results back to me via email:
AC Voltage reading at engine idle:
Lamp Brightness at engine idle:
AC Voltage reading at engine moderate speed:
Lamp Brightness at engine moderate speed:
AC Voltage reading at engine high speed:
Lamp Brightness at engine high speed:
A good magneto will produce at least 78 volts AC across this load at a brisk idle.
If your magneto output passes this test it has sufficient output to power coils.
Ron the Coilman


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ron Patterson on Tuesday, May 08, 2007 - 05:09 pm:

Chuck
Sorry, I reread your post.
It is very hard to see much when hand cranking. You can run the test above to verify the magneto's health. If you can tow the car and it will start and run with the switch on magneto the magneto is probably OK. Hand starting on magneto per Ford recommendations is tricky and everything must be set exactly correct. It requires the initial timing be set correctly, the spark lever set properly and properly adjusted ignition coils.
If you want more info on this let us know.
Ron the Coilman


Top of pagePrevious messageNext messageBottom of page Link to this message  By Chuck S. Lebeda on Tuesday, May 08, 2007 - 07:29 pm:

Ron: Thanks for the info. I checked the output with my voltmeter when it was running on battery and I good not get a continous output of 7-8 volts. It jumped from a low of 2 to a high of 19. Maybe I did not have things hooked up? This car started easily with the crank last Fall and this year I can not start it. Shorting the magneto post out, I do not get any spark with the crank. Chuck


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ron Patterson on Tuesday, May 08, 2007 - 07:47 pm:

Chuck
Contact me off forum at modeltcoils@alltel.net.
I will walk you through the details, if you do as I ask we will find out what the problem is.
Ron the Coilman


Top of pagePrevious messageNext messageBottom of page Link to this message  By Warren Mortensen on Wednesday, May 09, 2007 - 06:06 am:

Best to use an analog meter when testing the mag unless you're using a high-end digital meter. Most of the digital meters I've seen are subject to RF interference from the ignition and the reading will be all over the place.


Top of pagePrevious messageNext messageBottom of page Link to this message  By John F. Regan on Wednesday, May 09, 2007 - 08:57 am:

Warren:

The problem you are talking about is NOT related to the cost of the meter per se. I have seen labratory grade meters do the same. It is just VERY IMPORTANT to use an ANALOG type meter when making measurements on a T when the engine is running. All readings using digital meters when engine is running is likely to produce jibborish.


Top of pagePrevious messageNext messageBottom of page Link to this message  By VRay on Wednesday, May 09, 2007 - 10:34 am:

John is right about the meters. I have both a Fluke and a $3 Harbor Freight digital. Both jump all over the place while my analog stays nice and steady. I think it is the meter response time, but I really do not know.

Starting a car on magneto can be frustrating. It took me a long time to learn how to do it. To keep the frustration and the tired arm to a minimum I usually switch to battery for hand cranking to start then switch to mag for running.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bob Cascisa in Poulsbo, WA on Wednesday, May 09, 2007 - 03:46 pm:

A great source for a GOOD analog meter is tBay. Many Simpson 260 and Triplett 630 analog multimeters go for $10 or less. These are great field use instruments.

Be_Zero_Be


Top of pagePrevious messageNext messageBottom of page Link to this message  By Chuck S. Lebeda on Wednesday, May 09, 2007 - 10:49 pm:

Fellows: I have a digital meter, that may be my problem in readings off the mag. QUESTION: This is a 1923 T and it does not have an Amp Meter next to the switch. Behind this blank is the dimmer resistane/dimmer circuit. In post 1178300562, Kenneth posted the wiring diagram; my T is not wired quite this way at this dimmer circuit. But the 'dimmer circuit' looks like a small coil of wires with three wires wired into it. It was covered with industrial goop. Does this circuit ever go bad? It appears to be a coil of wires (all rusty) about the size of a small spool of thread. Where can I get this type of 'dimmer resistance'? Ron, I am working on what you emailed, but may not get to it until weekend. Thanks, Chuck.


Top of pagePrevious messageNext messageBottom of page Link to this message  By John F. Regan on Wednesday, May 09, 2007 - 10:53 pm:

Vray:

The problem is NOT the response time. The problem is that all digital meters have this circuit called "sample and hold" which takes a sample of the voltage, resistance, current...whatever and then holds it in a charged up capacitor while the digital circuit does a "successive approximation" to determine the value. All of this takes place many times per second but if there is any spikes of noise or "transients" as they are called, this process gets screwed up and the output is jibberish. Shielding helps and it WOULD be possible to design a digital meter for exactly this application but it really wouldn't tell you any more than a decent analog meter since one really doesn't need 1% accuracy to see if the varioius voltages in the T are OK for normal use.

Bob's recommendation is RIGHT ON.

The Triplett 600 series was a most prized Christmas present from my mom when I was 15 or so. It just blew me away to have such a fine measurement device for my ham radio projects. Alas mine got broken but I have another and still like it a ton. The Simpson 260 has been the work horse of almost every major company in the U.S. at one time or another. I suspect you will still find them in some company labs. Those clearly would be a great meter(s) to own.

Showing my age.


Top of pagePrevious messageNext messageBottom of page Link to this message  By James A. Golden on Thursday, May 10, 2007 - 12:08 pm:

Those 1156 bulbs usually come in two packs. A good idea, as a bulb is only good for one test with a good Magneto.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mike Cullen on Thursday, May 10, 2007 - 03:22 pm:

Your Analog meter has a much lower sensitivity as well, sometimes as low as 2K ohm/volt where your digital meter may be as high as 10M ohm/volt. The analog meter actually loads the circuit and in higher frequency AC applications or light to no load DC circuits your readings can be altered. Since VOMs were the standard when the T was engineered and voltage readings were published, you will get much closer readings using a cheaper analog VOM than a DMM. A Digital Multimeter will read all kinds of RF noise, etc. In analog VOMs you can't get any better than a Simpson 260 or a Triplett. They are accurate to about 1-3% of full scale and are perfect for pre electronic ignition automotive work. Don't forget to zero the meter on the ohms scale before use to verify the battery.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Michael J McCrary on Thursday, May 10, 2007 - 09:28 pm:

another dumb question
I think my mag may be sufficient and it wont start with with spark fully retarded, will run ok, but not start. Do I need to advance to start on mag? I have never tried that. thanks
Mike


Top of pagePrevious messageNext messageBottom of page Link to this message  By John F. Regan on Thursday, May 10, 2007 - 11:11 pm:

If you don't advance about 3 or 4 clicks when starting on mag you won't have a timer connection when the mag pulse shows up that you HAVE to use when starting on mag. NEVER advance the spark lever beyond the full retard when starting on BATTERY but advancing it 3 or 4 clicks when starting on magneto will make it POSSIBLE to start on magneto - not necessarily easy. You might want to read Ron Pattersons excellent article on the T ignition system. It explains why this 3 or 4 click advance is necessary.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Michael J McCrary on Friday, May 11, 2007 - 09:37 am:

Thanks John, I'll give it a try and see what happens.


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