Being electronically challenged, I need some help with a few basic Model T electrical data. I've been asked for the following timer details:
I have no idea what amperage is involved in timer operation.
Voltage on BAT is 6; on MAG I believe it varies from 6 to about 30. Is that right?
RPM is also variable, of course. What would it be at idle and at red line?
Amps will be what the coils draw. Ideally, 1.3A.
Volts should be ~6.4V on battery. A 6v battery reading 6v is discharged. The magneto produces an AC waveform and will vary from -36v to 0 to +36 volts. The Root Mean Square (RMS) voltage ranges from about 3 to 36 volts depending on RPM.
RPM; Idle is about 400rpm at which point the mag produces about 7 volts RMS. The engine "red line" is really a moving target but would likely be considered around 2200rpm although power falls steeply after about 1400rpm. Some Ford test engines are known to have been run at over 3000rpm.
Corrected rmp to rpm in last sentence.
(Message edited by ccwken on March 09, 2015)
Idle: 3-400 rpm?
Red line: about 2000 with splash oiled babbitt, I think? With cast iron pistons less is preferred. In high gear with a standard T you won't get much over 1800 rpm on a straight road (=45 mph)
Isn't the coils getting about 1.3 A on average when running?
I forgot to mention that if the vehicle is equipped with a generator, the generator produces about 7.2 volts on the cutout side. So once the engine is running, the "battery" circuit will be at 7.2 volts.
Model T coils can draw between 4.5A to 7A before the points open depending upon how the coil points are adjusted and the operating voltage (Yes, Coil VOLTAGE absolutely DOES matter). Operating on 6V battery, the peak coil firing current can range from 4.5A to 5.5A when the points open. (Note that this is the current flowing in the primary winding at the time the points get physically pulled open by the magnetic field. The 1.3A operating coil current frequently discussed is the average RMS current measured on an HCCT during abnormally slow magneto operating RPM. The 1.3A current value is much lower than the peak firing current because includes/averages times in between firings when the coil current is much lower and irrelevant to spark energy. Spark energy depends on the peak coil current flowing in the primary winding at the time the points open. The HCCT 1.3A value is important because it provides an indication that the coil dwell time to fire on all coils adjusted for the same average RMS current are roughly the same, that is of course, all 4 coils have nearly the identical same inductance values, if not, adjusting them all for the exact same 1.300A pretty much ensures you WILL have ignition timing variation coil to coil; cylinder to cylinder.
The voltage across the Timer contacts when the roller/brush/flapper moves off contact typically rises to the 250V to 350V range; causing arcing/pitting as the contacts separate; no capacitor/condenser across the timer contacts as they separate to help suppress arcing.
Regarding the magneto output, the voltage of a good magneto (one that registers 1914 mark on the St. Louis Magneto Tester) has an output in the range of 13V to 55V Peak depending upon engine RPM. (8V to 32V) as measured on a good AC voltmeter.
Hope this helps.
This is going to be like getting the weather forecast from 10 different stations.
(Message edited by ccwken on March 09, 2015)
Don't forget that the timer rotates at 1/2 of engine speed.
I thought you only got electronics in a spiffy distributor - that's what the purists liked about the timer: no electronics involved. =P
LOL... Yeah, simple isn't it.
Actually, you are referring to the timer itself. Unless you have the infamous e-timer, it takes no volts, no amps and no current to operate the timer. All the timer does is ground each of the primary windings of the coils in the proper order to cause a spark to the spark plugs. So, technically, as long as the engine is turning, the timer is working. Of course, if the engine is not running, it would take the starter, the crank or pushing the car to work the timer.
There is also no required voltage to operate the timer. It can operate from 6 volts AC or DC to 30 volts AC. The current will flow in accordance to the adjustment of the points on the timer.
The most important things about using a timer are that it be clean, and concentric with the camshaft. There is a tool available to center it. The larger tool which fits in the same groove as the timer is the more accurate way of centering the front plate in which the timer operates.
The coils also should be adjusted close to 1.3-1.5 amps. They will operate at a larger amperage, however, the engine might not run well at idle on mag, or on 6 volt battery if the current is set too high. All coils should operate at the same amperage because as the voltage increases on the magneto, if one coil operates at a lower amperage than another, the timing will be uneven between the cylinders which will make the engine run rough.
I made the assumption that the function of the timer was understood (an electrical switch used to connect primary ignition coil windings to engine ground) and not in question. Therefore, my comments reflect the voltages and currents the timer contacts will typically be exposed to.
I disagree with the statement "The current will flow in accordance to the adjustment of the points on the timer" The current flow through the timer contacts is governed by the coil and coil points settings associated with the respective timer contacts.
I would be very interested in any data that substantiates the inference that adjusting all coils for the same 1.3-1.5A (on an HCCT at an abnormally slow RPM and voltage) will prevent timing from being uneven between cylinders at higher RPM as the magneto voltage increases.
I adjust mine for equal firing time rather than equal current as I have no magneto, and rely entirely on timer accuracy for the firing point.
I set for a firing time 3.5mS with a regulated 6VDC supply. (Firing time reduces slightly when in the car on 7V). Peak current is 4A or a little over.
Simply setting for a specific current can give quite a variation in firing times within any given set of coils.
There is a difference in how a timer operates on battery than on magneto.
On battery, the current flows as soon as the rotor makes contact with the segment.
On magneto, the voltage builds up as the sine wave peaks. Depending on where the timer is set, the peak could come somewhere after the rotor first makes contact. So you need the points to open at nearly the same current.
That is also why you can have the engine running on battery and then switch to magneto and the engine will usually speed up, or slow down. It is also why the timing will not change for a few notches advance of the spark lever and then it will suddenly advance as the lever is pulled farther down. It is even possible to set the spark lever in such a position that one spark plug will fire more advanced than the others. So you need to find the "sweet spot" where the engine smooths out. The sweet spot is where the sine wave builds up enough to fire the coil in the middle of the timer segment.
John, That is precisely the same conclusion Montana 500 participants and I came to. That is the basis of operation of the ECCT since most folks don't have an oscilloscope, current probe, pulse generator, electronic switch and knowledge how to set up, test and adjust their coils using that method. The ECCT does all that and displays the firing time using a simple LED display so each coil can be set up for a nominal firing time.
By the way, the Magneto output is NOT sinusoidal, it is a triangular waveform.
Has anyone performed the following test: Set up the ignition coils for an equal firing time and then placed those same coils in a HCCT and without adjusting the coils, see what amperage is indicated of the HCCT meter. It would be interesting to see how much variation there was between four different ignition coils.
Arnie, Yes, I did that test and was surprised to see the current was all over the place! Rather than speculate what that meant, I designed and built the Model T Data Acquisition System (TDAS) so I could accurately conduct coil A/B performance comparisons in my 1927 Touring on the road. The results were published in the VF. The conclusion was coils set up for identical firing times performed as good as professionally adjusted coils in MY 1927 Touring. The task this Summer is to determine if my car has other ignition timing variables which are limiting factors for performance. Several other folks who set up their coils using the same method of coil firing time report excellent results. I know at least two past Montana 500 winners used the method.
By "all over the place" do you mean the meter read 1.5, 1.4, or 1.6 amps rms, or was there a larger variation than that?
Arnie, I have measured the average current on coils set up for equal firing time (DC supply and moving coil meter, buzz box style)and found a variation of say 1.1 to 1.4A not unusual. No name coils seem to provide the greatest variation.
Adjusting by average or rms current alone will show up this limitation even more so when there's a mixture of coil brands in a car. As an example, a set I restored recently had a KW and three no name types. Had I set by current alone, the no name types would have fired a millisecond or so after the KW.
This is a mechanical guy talking electrical (so keep this in mind!!), and I ask the following:
Could one put a degree wheel on the fan belt pulley of the crank and run the engine without the fan, and using a timing light, determine just when each plug fires? This would mean connecting the timing light individually to each of the four spark plugs. Could this be a poor mans check of the firing? By adjusting the coils (trial and error) one gets to a point where the plugs all fire "x" degrees in relation to top dead center? Then if one moved the advance lever one could check to see if spark timing of all four individual plugs jumped the same amount of degrees.
Mike, would this work for you in trying to see what the best performance is (assuming best performance happens with each coil firing for each cylinder exactly "X" in relation to piston top dead center). Mike, should not this also compensate for any "built in " variables since you are setting each plug to fire at "X" degrees in relation to the piston position for that particular vehicle?
Arnie, I saw a wider variation in current than John did. In theory, I believe you could use of a timing light and degree wheel to adjust coils for the same ignition timing. In practice, I think it would be difficult to adjust coils using that method. The engine RPM does not remain constant enough to use the results observed to make corrective adjustments as the next time the coil fires the engine will very likely be at a different RPM and show under or over correction.
Good info but this is a lot of "Techno Babble" for the average Model T driver. Millisecond? Come on! You can get more than that by not having the timer centered to the thousandths of an inch. Most owners can't post pictures to the forum and you expect them to super tune their coils and engine?
I can adjust them by ear.
I find it easier to use my hands.
The more I read the less I know! Are you saying that the coil may fire at a different engine rpm and show "under or over" correction?
If that is the case, would not the same "over and under" correction happen no matter what method was used to adjust the coils"??
I read your article testing an improved touring and if I understand it correctly there was little difference in performance when operating on magneto between any of the coil adjustment methods tested. Am I correct in this evaluation?
Arnie, I think it would be difficult to adjust coils using a timing light on a running Model T.
The data I took on MY 1927 touring, comparing ECCT adjusted coils with professionally adjusted coils showed performance was comparable. There could be other ignition variables on MY 1927 touring that limits engine ignition performance more than the coils, for example, timer related cylinder to cylinder timing variation which I did not explore so the conclusion made was the ECCT using the coil dwell time method of coil adjustment is at least as good as HCCT coil adjustment by an experienced and skilled professional; not just any coil adjustment method!
I thought the Model T was a simple machine? Its gotten more complicated than it used to be.
I was thinking along the lines of adjusting the coils by taking them out of the vehicle and setting them such that the coil would fire later or earlier based on what the ignition timing indicated when it was installed in the car for a particular cylinder. It would be a hit or miss situation and would take time, but I was looking at it from a poor mans method to get better performance, if it was proven to be a worthwhile endeavor!
Arnie, There is but one sure way to answer your question; start experimenting! That is what I have been doing for the last 3 years with the development of the ECCT. Conducted many experiments and made many measurements in order to perfect a coil adjustment methodology that works well and is easy to replicate.
Steve J., did you ever find what you wanted to know, out of all this mish-mash of info ?