Any suggestions about connecting an AC amp meter to the in car magneto? Service manual directions suggest connecting meter to output post and then to frame or engine. Similar to hooking a volt meter. Is the amp meter connected direct to ground for reading?
The AC ammeter should be connected from the magnet post to the load, such as the ignition coil.
By the way, make sure you really have an AC ammeter, they are not that common.
What paragraph in the service manual are you reading?
Paragraph 994 talks about connecting a voltmeter between the mag terminal and "a clean part of the cylinder or transmission cover"
Why are you interested in measuring the magneto current? If you are interested in testing the output of the magneto there is an excellent method described on the forum using a 1156 lamp bulb. Connect the lamp bulb from the mag terminal to ground and with the engine running, vary the engine, the lamp should vary from dim to very bright or even blown out. You could use a voltmeter on the terminal and you should get a few volts at idle to maybe 35 volts at a high RPM.
DO NOT connect the ammeter as a volt meter. Voltage is an across measure, whereas current is a through measure. A voltmeter is connected to ground and the point of interest, such as the magneto terminal, nothing is disconnected.
To measure magneto current, you must disconnect the magneto terminal wire. Connect on lead of the ammeter to the mag post and the other to the magneto wire that was just disconnected.
Mike
An ammeter hooked from the mag post to the frame will burn up. You are describing the connection for a voltmeter.
An ammeter must be placed in series with a load that is within the capacity range of the ammeter.
George, check Frank's T Parts.
www.frankstpartsltd.com
Well, that link says that Lang's has taken over all sales, but try this link which shows pictures of installation.
www.frankstpartsltd.com/default_files/Page923.htm
Ford Service Bulletin 15 Oct 1926. Two leads are attached to the tester; when checking the magneto one of these leads is clipped to either the engine or the frame of the car the other is clipped to the magneto terminal post ("A"). ... Testing a magneto. To test the magneto first test its strength at starting speed. To do this, turn the engine over with the starter leaving the ignition off. ..... proper reading is 3.5 amps.
Unless the magneto tester has a built in load, which is not indicated, the directions sound similar to connecting a volt meter.
Prior to 1926 for 15 September 1919, the Bulletin has values for magneto out put 2000 rpm 6.1 amps, 600 rpm 8.5 amps, and to 1200 rpm 9 amps.
The Bulletin is describing a specific tool, the KR Wilson Magneto Tester, for AC amps.
If just wanting to know the output of the Ford magneto in a linear way, using Frank Fenton Magneto Meter is just as easy. It reads in AC volts. Have one on my T and it works swell.
Fast idle
Slow idle
The Bulletin is describing a specific tool, the KR Wilson Magneto Tester, for AC amps.
What is in the Wilson Tester for a load? Resistance value?
Thanks
Not having the KR Wilson Magneto Tester, but an ampere meter with a range from 0 to 15 amps AC, would this work? To rest the amperage output of a magneto by using the starter, the resistance would be about 3.33 to 4 ohms? If volt output is 30 VAC, and max amp output 9 amps AC.
I don't believe the the KR tester uses a resistive load. It has a combination of resistance and inductance so as to better approximate the actual load the car (mostly ignition) places on the magneto.
Mike
Thanks. Then it may be possible to replicate the load with a meter in series with a (buzz) coil. Wire from magneto to amp meter, amp meter to coil, and coil to ground?
In my view if you want a serious tester to evaluate the Model T magneto get a St Louis Magneto Tester made by FunProjects. This is by far the most stringent and simple test.
The next best alternative is the 1156 bulb and AC voltmeter test, but the results can fool you adn should be subject to a review by a knowledgeable evaluator.
I have never taken a close look at the KRW tool so I cannot comment.
The Hoyt and "Magneto Meter" shown above are not all encompassing and definitive tests of the health of the Model T magneto.
Ron the Coilman
I have a period amp meter and need a winter project. I believe the following patent (circa 1916) shows the circuit design and the use of an ignition coil as the inductor/resistance may just work.
http://www.google.com/patents/US1270100
Thanks for the assistance.
Looking at fig. 274 shows that full scale is 10 AC amps.
Upon reading the service bulletin, one part says:
" Cars equipped with magneto ignition only must be tested in a different manner, as the test meter when attached to the contact post cuts out the magneto ignition."
This leads me to believe that the KRW device is just basically a 10 amp AC ammeter.
If you use any type of resistance or inductance for testing, the magneto output will be restricted by the impedance of the resistance/inductance.
George, what is full scale of your period amp meter?
The meter is listed as a Jewell Portable A.C. Ammeter (pattern 11). Manufacture date 1927. Rated at 15 amps AC.
I read the same description that the meter connected to the magneto would short out the magneto and power to the coils. However the suggestion that if a starter was available on the car it would be possible to secure a current output by using the starter to turn the engine. An other way to check output.