Magneto voltage: Am I reading it correctly?

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Model T Ford Forum: Forum 2015: Magneto voltage: Am I reading it correctly?
Top of pagePrevious messageNext messageBottom of page Link to this message  By Steve Jelf, Parkerfield KS on Thursday, July 23, 2015 - 12:05 pm:


I can start easily on BAT, but it annoys me that I haven't been able to start on MAG lately, so today I'm investigating that. The way I read this meter, I'm getting 17 volts at idle. Am I reading it right? The most I was able to get cranking by hand was a little over 1 volt, maybe 1.5.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dan Treace, North FL on Thursday, July 23, 2015 - 12:24 pm:

Yep.

On the 50v setting the red scale at the middle mark (5) would be 25vac, so what I see is about 15vac or smidge more.


My healthy mag reads 12v at idle. :-)

Maybe hand starting is more carb or timer setting?
Or coil setting (HCCT ?) or points or plugs?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Charlie B actually in Toms River N.J. on Thursday, July 23, 2015 - 12:28 pm:

14 volts. Others will chime in but it appears a re-charge might be a possible cure for a weak mag. Check the post too.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kevin Holland, Utah on Thursday, July 23, 2015 - 12:35 pm:

Steve, Mine at idle reads around 15 Volts AC and at speed my magneto meter is buried at 30. I always start on battery and switch to mag. But the old 1917 we had at the ranch would start on mag. It was a motor that had never been rebuilt. It ran down the road wonderfully on magneto.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Steve Jelf, Parkerfield KS on Thursday, July 23, 2015 - 01:21 pm:

Well, I did the most obvious thing.






I don't understand how non-conductive fuzz on the mag post can affect output, but after cleaning it I was able to start on MAG again, although I still didn't see much needle movement when pulling.

Anyway, it's nice to have the MAG start available again, though I had to set the gas above idle and choke a couple of times. I doubt that I have even 500 miles on the recharge and the Patterson coils, so I'm thinking my MAG start, as long as the post is clean, has mostly to do with carb setting, and maybe timer setting. Although I don't detect much of a meter reading when I pull the crank, there's enough juice to get started, and idling at 14 or 15 volts and getting over thirty when running faster suggests to me that the magneto is pretty good.


Top of pagePrevious messageNext messageBottom of page Link to this message  By george house . . .caldwell county, TX on Thursday, July 23, 2015 - 01:35 pm:

Good for you Steve!! Congrats! No tell me you DO have some kind of outside oil line to number 1 rod and main bearing


Top of pagePrevious messageNext messageBottom of page Link to this message  By Steve Jelf, Parkerfield KS on Thursday, July 23, 2015 - 01:43 pm:

That's on my list, George. I have it, but I haven't installed it yet. :-)


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dan Treace, North FL on Thursday, July 23, 2015 - 02:16 pm:

Steve

That fuzz you had on the mag post IS CONDUCTIVE!

That is why you always check and clean. If you have an oil screen it will catch a lot of that too.

But....when the fuzz gets on the contact, it holds the conductive metal debris from engine wear, bearings against steel crank, steel trans gears, piston and ring wear.....all that conductive stuff gets in the oil and can stick somewhere there is a clog of material to hold it.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mike Kossor - Kenilworth, NJ on Thursday, July 23, 2015 - 10:05 pm:

Those analog meter scales sure can be confusing to read indeed; I think Charlie has it correct at 14VAC. Unfortunately, the voltage really does not provide much information on magneto strength unless you know the engine speed which the voltage was measured. A further complication is the type of meter used to measure the magneto voltage, many inexpensive meters use a D’Arsonval meter movement which really measures a DC voltage from the rectified AC waveform on a scale calibrated to read AC Volts RMS assuming the waveform is sinusoidal (like from an AC outlet); A Model T Magneto is not sinusoidal and will introduce error in the displayed RMS value on that type of meter.

Here is a solution for reliable magneto testing that I've been working on:

ECCT Magneto Tester GUI

The magneto field strength factor is calculated and displayed numerically and graphically to provide a concise indication of the magneto's ability to properly operate a Model T coil.

Calculating the magneto field strength factor requires knowledge of the true RMS output voltage of the magneto (under load) and the engine RPM at which it was measured. These values can be displayed if desired, but not necessary. An added bonus is a real time tachometer display that comes in handy for engine performance testing.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Steve Jelf, Parkerfield KS on Thursday, July 23, 2015 - 10:39 pm:

What do yellow and red at the higher RPM's indicate? How costly is the tester?


Top of pagePrevious messageNext messageBottom of page Link to this message  By John P. Steele, Montana on Thursday, July 23, 2015 - 10:57 pm:

Steve it means your about to throw a rod. :-)


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mike Kossor - Kenilworth, NJ on Thursday, July 23, 2015 - 11:24 pm:

Good synopsis John.

Unfortunately, the tester is not a standalone instrument. Its an option that can be added to the ECCT platform which was needed to make it a true replacement of the venerable HCCT which also provided a magneto test feature. More information about the tester can be found at www.modeltecct.com You can also download the instruction manual which explains operation and contains some useful information on coil point adjusting:

http://www.modeltecct.com/uploads/ECCT_Instructions_V8.pdf


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jim Thode Chehalis Washington on Friday, July 24, 2015 - 01:21 am:

From John Regan, "When seeking an absolute determination of the magneto health the actual voltage reading of a magneto is meaningless unless you can establish the exact RPM and exact load current that is connected to the magneto at the instant that the voltage is measured."

From:
http://www.mtfca.com/discus/messages/506218/536818.html?1430095748

Here is the poor mans test:
"John Regan’s simple magneto output test.
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.
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 7–8 volts AC across this load at a brisk idle.
If your magneto output passes this test it has sufficient output to power coils. "

Jim


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mike Kossor - Kenilworth, NJ on Friday, July 24, 2015 - 08:04 am:

The simple voltage test using an 1156 bulb as a load will provide an indication of magneto output for sure. The problem is; there is no standard for indicating the magneto's ability to properly operate a Model T coil (poor, weak or good) from the data.

For example, what exactly is low, moderate and high speed? 400, 600, 1000 RPM or 600, 1000, 1500 RPM? or 500, 1000, 2000 RPM? or perhaps 500, 1200 and 2500 RPM? The true RMS output voltage of a properly functioning magneto is nearly directly proportional to engine RPM so each of these scenarios will result in radically different sets of data.

John is exactly correct; determining magneto health from the magneto voltage alone is meaningless unless you know the exact RPM and load current the instant the voltage was measured. That's how the ECCT Magneto Tester works to provide an absolute determination of magneto health.


Top of pagePrevious messageNext messageBottom of page Link to this message  By George John Drobnock on Friday, July 24, 2015 - 09:23 am:

So what is the proper voltage (AC) from a Model T Magneto? The 1926 edition of the Model T Ford Car, by Victor Page states that with the engine throttled down to idle, voltage of 8 VAC is sufficient to generate current for the ignition. The text states that output varies from 6 to 20 volts per rpm range.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mike Kossor - Kenilworth, NJ on Friday, July 24, 2015 - 09:53 am:

Exactly! Is that 8VAC peak or RMS?; the difference is nearly double for the Model T magneto. Throttled down to "Idle" is 400RPM to some, 650RPM for others. The difference in voltage of a properly functioning magneto is again more than double between those operating conditions.

The "proper" voltage from a Model T magneto DEPENDS upon the exact engine RPM and load current at the instant that voltage was measured.


Top of pagePrevious messageNext messageBottom of page Link to this message  By George John Drobnock on Friday, July 24, 2015 - 10:24 am:

I have to ask. The large iron enclosed case AC Volt meters that are shown in period drawings and photographs of Model T Ford magneto under test, are these illustrated volt meter and the accompanied text showing and describing a meter with a VAC scale or an RMS scale? And if one is more important than the other, should not the 1926 text state RMS or VAC?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bob Cascisa - Poulsbo, Washington on Friday, July 24, 2015 - 12:20 pm:

Those are iron vane type voltmeters. By design they display true RMS values.

Be_Zero_Be


Top of pagePrevious messageNext messageBottom of page Link to this message  By Royce in Georgetown TX on Friday, July 24, 2015 - 12:32 pm:

I've found that the Regan - Patterson memorial test instructions yield excellent results using my easy to understand Radio Shack analog meter. The 1157 bulb costs $2. The meter cost me $19 with tax. Anything you spend over that amount to measure magneto output is a waste of money.

7 - 8 volts at idle is sufficient, in fact I find that a coil set properly on a hand cranked coil tester will function great down as low as 4 volts AC.

I would not "fix" a magneto that measured 18 - 20 volts using the same test at cruising engine speed. It is not broken.

Remember, it's a Model T Ford. Modern electronics are not needed.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kevin Holland, Utah on Sunday, July 26, 2015 - 02:58 pm:

Oh NO! Magneto Coil pickup fuss. Yuk!


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