Mag Voltage vs RPM - 1911 t
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Topic author - Posts: 111
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Mag Voltage vs RPM - 1911 t
My refreshed 11 t (rebuilt mag and rechaged magnets) hasn't run as well as I think it should. So I've been running on a 12V battery and performance is excellent. This morning I took the car out and had my wife jot down mag voltage at different speeds running on 12V.
Here's the result:
MPH Output RPM
10 10 407
15 14.5 610
20 18 813
25 20.9 1016
30 24.4 1220
35 26.5 1423
Output is AC volts and rpm is calculated from tire diameter (30") and gear ratio. I have the smaller field coil magneto bought it from Langs earlier this year. Magnets I recharged myself using a model t piston as a gage. Magnet to mag clearance set to Ford spec.
Voltage seems low to me, this values are all no load.
Thanks
Here's the result:
MPH Output RPM
10 10 407
15 14.5 610
20 18 813
25 20.9 1016
30 24.4 1220
35 26.5 1423
Output is AC volts and rpm is calculated from tire diameter (30") and gear ratio. I have the smaller field coil magneto bought it from Langs earlier this year. Magnets I recharged myself using a model t piston as a gage. Magnet to mag clearance set to Ford spec.
Voltage seems low to me, this values are all no load.
Thanks
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Re: Mag Voltage vs RPM - 1911 t
Are your coils set properly??
Andre
Belgium
Andre
Belgium
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Re: Mag Voltage vs RPM - 1911 t
Didn't see you test without a load.
Connect a 12V 21W lamp between the magneto post an the frame. connect your Volt meter over the lamp and test again.
Andre
Belgium
Connect a 12V 21W lamp between the magneto post an the frame. connect your Volt meter over the lamp and test again.
Andre
Belgium
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Re: Mag Voltage vs RPM - 1911 t
Test was without a load, yes coils set per ECCT.
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Re: Mag Voltage vs RPM - 1911 t
What is the magnet to field coil air gap?
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Re: Mag Voltage vs RPM - 1911 t
Philip,
It would be interesting to know what the current draw of your four coils are if now tried on a HCCT ?
Coils set up on an ECCT are powered by a DC supply and are good on battery powered Model T and are good on a strong magneto powered Model T. That being said and you said that your magneto is a small bobbin coil setup you may have to reset them on a HCCT.
Regards.....N.
It would be interesting to know what the current draw of your four coils are if now tried on a HCCT ?
Coils set up on an ECCT are powered by a DC supply and are good on battery powered Model T and are good on a strong magneto powered Model T. That being said and you said that your magneto is a small bobbin coil setup you may have to reset them on a HCCT.
Regards.....N.
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Re: Mag Voltage vs RPM - 1911 t
Try setting the coils to draw 1.5 amps when they spark. If it is higher, it might take too long for the current to build up to spark before the voltage begins to drop in the mag. With a battery, you have full voltage and build up a charge when the when the timer rotor contacts the segment and it is 12 volts until it comes to the end of the segment, however, on mag, the voltage builds up to a peak and then drops and reverses direction for the next segment. If the coils are set correctly, they will work fine on 6 volt battery and also on magneto.
Norm
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Re: Mag Voltage vs RPM - 1911 t
I am missing something in your report you say "while running on 12 volts", if you are running on 12 volts the magneto is not in the circuit the switch on your control would be on battery. Also in 1915 they double stacked the coils to increase the AC output to accommodate the electric head lights that were 9 volts each in series therefore consuming about 18 + volts. With normal operations this voltage was sufficient. At very low RPM the lights were somewhat dimmer than at higher speeds and in some extreme cases at very high RPM the lights could burn out. This problem became more of an issue if the 9 volt lights were replaced with 6 volt lamps. I understand that magneto voltages were somewhat lower than the 1915 voltages as there only duty was engine ignition. I don't know what the magneto voltages were prior to 1915 but 12 - 16 volts would appear to have been sufficient. With a properly set up magneto and timer and the spark control properly set the first electrical pulse from the magneto would be just past top dead center and even at cranking speed the current is sufficient. If the system is off somewhat it may never start or with great difficulty hence the 12 volt battery. A good deliberate pull over center should be all that is needed for a quality start. It is understood that not all of us have the strength and adjility to start a Model T and the 12 volt battery is a welcome friend. Starting procedures are somewhat different with and without a battery. With a battery it can kick back where as starting on mag it will not.
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Re: Mag Voltage vs RPM - 1911 t
What timer do you use??
I have seen the "Flapper" timer with 18° difference between two contact point, resulting in a bad running engine.
I should set the coils correctly by a HCCT. This machine give you AC voltage and current. The coils should take 1.3A to 1.5 A and properly set the coils will start to spark at 2.0Vac.
The HCCT give you the same electricity as your magneto will do.
Good luck
Andre
Belgium
I have seen the "Flapper" timer with 18° difference between two contact point, resulting in a bad running engine.
I should set the coils correctly by a HCCT. This machine give you AC voltage and current. The coils should take 1.3A to 1.5 A and properly set the coils will start to spark at 2.0Vac.
The HCCT give you the same electricity as your magneto will do.
Good luck
Andre
Belgium
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Re: Mag Voltage vs RPM - 1911 t
Philip, a few comments and suggestions for your magneto performance investigation:
Coil Adjustment Comments
When were the coils last checked on the ECCT?
What was the multi-spark firing consistency test result?
Coil point adjustment does drift with time/usage and is vulnerable to mis-adjustment if not handled with care while installing the coils, even a gentle bump! Coils adjusted for >85% coil firing consistency at 0 deg timing error provide excellent results.
Magneto Operation Comments
No load magneto voltage measurements are of limited value if there is high internal contact resistance to the magneto coil
Test Magneto function using the ECCT while operating on battery. The ECCT Magneto tests the magneto output under no load and loaded conditions to measure the contact resistance and provides a measure of the Magneto Field Strength which remains essentially constant during normal engine operation. The magneto field strength is a reliable indication of magneto performance.
For completeness, I thought it may be helpful to review normal magneto operation. The magneto outputs pulses of electricity that are synchronized with piston position. There are typically 4 magneto pulses that can be selected using the spark lever to operate the coils, each of which have differing ignition timing. You need to select the proper magneto pulse with the spark lever for optimal engine performance:
Mag Pulse 1 (fully retarded spark lever) is too retarded for starting or hand cranking
Mag Pulse 2 is selected by advancing the spark lever a few clicks down, the engine should pick up RPM and run better but still too retarded for optimal engine performance
Mag Pulse 3 is selected by further advancing the spark lever a few more clicks down, the engine RPM should increase again and smooth out; this is typically the optimal spark lever position for Magneto operation.
Mag Pulse 4 is selected by further advancing the spark lever to near full advance; the engine RPM may increase further and may begin to knock. This magneto pulse is usually too far advanced for optimal operation.
Engine performance operating on magneto on the 1st or 2nd magneto pulse will typically be worse than operating on battery.
Side note regarding Magneto polarity; Magneto output is AC as others have stated but operation is commonly misunderstood. Each of the 4 selectable magneto voltage pulses are of differing polarity (+ and -) and change polarity from one selected pulse to the next. HOWEVER, the polarity of THE selected magneto voltage pulse selected by spark lever position remains CONSTANT (all + or all -) depending how your magneto is wired. This common misunderstanding about Magneto operation that Coils are subjected to AC voltage (+ and -) as they are charged to fire spark is totally false. The statements regarding use of AC versus DC to adjust coils when operating on magneto are without merit for this reason. The fact is; the ECCT uses a fast pulse of electricity (polarity is irreverent) that emulates magneto output at normal engine speeds and normal ignition operation allowing the coil to rest in between firings. The HCCT subjects coils under test to a continuous stream of AC pulses (+ and -) never allowing the coil to rest in between firings with abnormally low magneto output (2-3V) resulting from abnormally slow cranking (~120 RPM) in which the car will never operate. The metric used to adjust points is not the precise dwell time to fire THE spark that determines combustion like the ECCT but rather the average coil current of hundreds of sparks as an indirect approximation of average dwell time to fire spark. It is amazing the HCCT works as well as it does but no comparison to coils adjusted and measured to have equal and consistent firing TIME!
Hope this helps, please let us know how you make out.
Coil Adjustment Comments
When were the coils last checked on the ECCT?
What was the multi-spark firing consistency test result?
Coil point adjustment does drift with time/usage and is vulnerable to mis-adjustment if not handled with care while installing the coils, even a gentle bump! Coils adjusted for >85% coil firing consistency at 0 deg timing error provide excellent results.
Magneto Operation Comments
No load magneto voltage measurements are of limited value if there is high internal contact resistance to the magneto coil
Test Magneto function using the ECCT while operating on battery. The ECCT Magneto tests the magneto output under no load and loaded conditions to measure the contact resistance and provides a measure of the Magneto Field Strength which remains essentially constant during normal engine operation. The magneto field strength is a reliable indication of magneto performance.
For completeness, I thought it may be helpful to review normal magneto operation. The magneto outputs pulses of electricity that are synchronized with piston position. There are typically 4 magneto pulses that can be selected using the spark lever to operate the coils, each of which have differing ignition timing. You need to select the proper magneto pulse with the spark lever for optimal engine performance:
Mag Pulse 1 (fully retarded spark lever) is too retarded for starting or hand cranking
Mag Pulse 2 is selected by advancing the spark lever a few clicks down, the engine should pick up RPM and run better but still too retarded for optimal engine performance
Mag Pulse 3 is selected by further advancing the spark lever a few more clicks down, the engine RPM should increase again and smooth out; this is typically the optimal spark lever position for Magneto operation.
Mag Pulse 4 is selected by further advancing the spark lever to near full advance; the engine RPM may increase further and may begin to knock. This magneto pulse is usually too far advanced for optimal operation.
Engine performance operating on magneto on the 1st or 2nd magneto pulse will typically be worse than operating on battery.
Side note regarding Magneto polarity; Magneto output is AC as others have stated but operation is commonly misunderstood. Each of the 4 selectable magneto voltage pulses are of differing polarity (+ and -) and change polarity from one selected pulse to the next. HOWEVER, the polarity of THE selected magneto voltage pulse selected by spark lever position remains CONSTANT (all + or all -) depending how your magneto is wired. This common misunderstanding about Magneto operation that Coils are subjected to AC voltage (+ and -) as they are charged to fire spark is totally false. The statements regarding use of AC versus DC to adjust coils when operating on magneto are without merit for this reason. The fact is; the ECCT uses a fast pulse of electricity (polarity is irreverent) that emulates magneto output at normal engine speeds and normal ignition operation allowing the coil to rest in between firings. The HCCT subjects coils under test to a continuous stream of AC pulses (+ and -) never allowing the coil to rest in between firings with abnormally low magneto output (2-3V) resulting from abnormally slow cranking (~120 RPM) in which the car will never operate. The metric used to adjust points is not the precise dwell time to fire THE spark that determines combustion like the ECCT but rather the average coil current of hundreds of sparks as an indirect approximation of average dwell time to fire spark. It is amazing the HCCT works as well as it does but no comparison to coils adjusted and measured to have equal and consistent firing TIME!
Hope this helps, please let us know how you make out.
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Topic author - Posts: 111
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Re: Mag Voltage vs RPM - 1911 t
Answers to you inquires:
1. Timer - Anderson, new at the time.
2. air gap if I remember correctly between .025/.030"
3. Car was running off 12v while I performed the test, my magneto voltage results are no load at speed indicated.
4. Coil adjustment done on EECT, all coils are the same manufacture (KW), g'pa bought new in 1954, new capacitors from Langs and points. No double spark and fire consistencies are excellent. Car will start quarter turn on bat and occasionally on magneto (engine is fresh).
5. All voltages taken with analog ac voltmeter 0-30V resolution.
6. Three voltage readings taken for each speed and then averaged.
1. Timer - Anderson, new at the time.
2. air gap if I remember correctly between .025/.030"
3. Car was running off 12v while I performed the test, my magneto voltage results are no load at speed indicated.
4. Coil adjustment done on EECT, all coils are the same manufacture (KW), g'pa bought new in 1954, new capacitors from Langs and points. No double spark and fire consistencies are excellent. Car will start quarter turn on bat and occasionally on magneto (engine is fresh).
5. All voltages taken with analog ac voltmeter 0-30V resolution.
6. Three voltage readings taken for each speed and then averaged.
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Topic author - Posts: 111
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Re: Mag Voltage vs RPM - 1911 t
Did a real quick unloaded voltage drop measurement, with the car running on magneto I get a 5vac drop in voltage at a brisk idle (15v vs 20v). I don't have a AC ammeter to check current.
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Re: Mag Voltage vs RPM - 1911 t
The effect of voltage vs amperage are often confused. The analogy often used is to compare electron flow to water where voltage is pressure and amperage is volume of electrons. As you are aware the lights get dimmer when more load (objects needing amperage) are applied. The only variable between running good vs bad is the mag vs the battery. That would imply nothing wrong with coils or timer. So if the coils take 1.5A each your mag needs to put more than 6 amps to get the same performance as what your battery provides (its amperage output is constant for the most part). Suggest you check the amperage the mag is putting out for various speeds with just the load of the coils.AndreFordT wrote: ↑Sun Aug 23, 2020 2:49 am.... The coils should take 1.3A to 1.5 A and properly set the coils will start to spark at 2.0Vac.
... Good luck Andre Belgium
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Re: Mag Voltage vs RPM - 1911 t
Phillip Berg and others
Please ignore the Model T Ford magneto ignition system explanation provided by Mike Kossar in this thread.
Either Mike simply doesn't fully understand how the Model T ignition system works or he is not incapable of writing a technically correct description of how it does work........or perhaps it is just specious technical spin to justify you buying his product?
Which of these, I know not, but I know that it is not an accurate description of how the Model T Ford ignition system operates
Ron Patterson
Please ignore the Model T Ford magneto ignition system explanation provided by Mike Kossar in this thread.
Either Mike simply doesn't fully understand how the Model T ignition system works or he is not incapable of writing a technically correct description of how it does work........or perhaps it is just specious technical spin to justify you buying his product?
Which of these, I know not, but I know that it is not an accurate description of how the Model T Ford ignition system operates
Ron Patterson
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Re: Mag Voltage vs RPM - 1911 t
Ron and other Model T enthusiasts.
Ron, Thanks for the Big ones for your expertise and electrical knowledge of the Model T. I have asked for verification of different explanations of his Ecct Model T electrical/coil testing principals but never get an answer.
I have always wondered why the other professional Coil / Magneto rebuilders have never commentated or query the system. The system is OK for Montana 500 and speed cars running 12volt batteries and or late model magnetos but for the earlier antique Model T's the ttf current draw exceeds the magneto output.
As previously mentioned in this thread and not answered was, "It would be interesting to know the current draw of the said coils if were put on a HCCT' ? Plus or minus around 1.3A as the HCCT specs would be my goal with a ttf retarded some 2/3 degrees .
It would also be interesting if the professional Coil/Magneto builders would explain the ins and outs of setting up and adjusting coils to run as HENRY intended with a HCCT......Regards....N.
Ron, Thanks for the Big ones for your expertise and electrical knowledge of the Model T. I have asked for verification of different explanations of his Ecct Model T electrical/coil testing principals but never get an answer.
I have always wondered why the other professional Coil / Magneto rebuilders have never commentated or query the system. The system is OK for Montana 500 and speed cars running 12volt batteries and or late model magnetos but for the earlier antique Model T's the ttf current draw exceeds the magneto output.
As previously mentioned in this thread and not answered was, "It would be interesting to know the current draw of the said coils if were put on a HCCT' ? Plus or minus around 1.3A as the HCCT specs would be my goal with a ttf retarded some 2/3 degrees .
It would also be interesting if the professional Coil/Magneto builders would explain the ins and outs of setting up and adjusting coils to run as HENRY intended with a HCCT......Regards....N.
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Re: Mag Voltage vs RPM - 1911 t
Hi Ron, Good to see you active on the Forum again! I re-read my post and believe it to be accurate but acknowledge we all make mistakes. I certainly would not have intentionally posted false or misleading information. Please let us know what I stated that you feel was incorrect. Thanks!
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Re: Mag Voltage vs RPM - 1911 t
Neil,
Apologies if I missed your inquiries about the Time To Fire (TTF) method of coil point adjustment. The TTF method of coil point adjustment is done by applying a fast pulse of electricity to a coil at rest and measuring the Time it takes to produce a spark. For example, the coil current rises nearly linearly from 0A to about 6A at which point the coil fires spark. The entire process typically takes only 0.002 seconds to occur. TTF Coil current of 6A is an eye opener for folks familiar with the HCCT where the magic number of coil current is 1.3A indicating proper adjustment. You have to realize the 1.3A is NOT the current flowing in the coil at the moment the spark fires. The 1.3A is the AVERAGE coil current measured over tens or hundreds of sparks over time (including time when little or no coil current is flowing). The PEAK coil current at the moment the coils fires spark is MUCH higher; easily 6A during normal magneto operation in the car and again happens for a very short time.
Here is a link that explains more about the differences between the HCCT and TTF methods of coil point adjustment that you may find useful:
https://modeltecct.com/ecct-vs-hcct-difference
By the way, ALL well known professional coil re-builders use the ECCT as their default test instrument here in the US after experiencing the consistent results it achieves for their customers with one (1) exception that I am aware of. That decision not to use it is not based on lack of technical merit or consensus on performance (plenty of support for both) but rather bruised ego and personal animus from my understanding which is really unfortunate in my view for a professional.
Apologies if I missed your inquiries about the Time To Fire (TTF) method of coil point adjustment. The TTF method of coil point adjustment is done by applying a fast pulse of electricity to a coil at rest and measuring the Time it takes to produce a spark. For example, the coil current rises nearly linearly from 0A to about 6A at which point the coil fires spark. The entire process typically takes only 0.002 seconds to occur. TTF Coil current of 6A is an eye opener for folks familiar with the HCCT where the magic number of coil current is 1.3A indicating proper adjustment. You have to realize the 1.3A is NOT the current flowing in the coil at the moment the spark fires. The 1.3A is the AVERAGE coil current measured over tens or hundreds of sparks over time (including time when little or no coil current is flowing). The PEAK coil current at the moment the coils fires spark is MUCH higher; easily 6A during normal magneto operation in the car and again happens for a very short time.
Here is a link that explains more about the differences between the HCCT and TTF methods of coil point adjustment that you may find useful:
https://modeltecct.com/ecct-vs-hcct-difference
By the way, ALL well known professional coil re-builders use the ECCT as their default test instrument here in the US after experiencing the consistent results it achieves for their customers with one (1) exception that I am aware of. That decision not to use it is not based on lack of technical merit or consensus on performance (plenty of support for both) but rather bruised ego and personal animus from my understanding which is really unfortunate in my view for a professional.
Last edited by MKossor on Thu Aug 27, 2020 8:55 am, edited 1 time in total.
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NOTHING TO SELL
With all due respect to the authors Even I as a novice model T guy found a few apparent inaccuracies. statement. each one of the coils draws 1.5 amps You need 6 amps from the mag.1.5 X 4 =6. This would be true if all four coils were activated by the timer at the same time but this is not the case and engine would not run if it were since all four spark plugs would be firing at the same time. next I have never heard of four selectable magneto pulses. the model t engine is four cycle. The model T magneto has 16 coils and sixteen magnets which create 16 pluses of a/c +- voltage per revolution. The timer selects the piston position voltage is applied to the coils either from the battery or the mag. optimum point varies with engine speed and slight difference between mag and Battery in some cars others you can't tell the difference. To say the magneto is synchronized to the piston position is correct. the spokes on the rear wheels are also synchronized to piston position when the car is in gear. Does it matter! The magneto puts out 8 pluses of voltage on each of the four cycles of a four cycle engine or 16 per crank shaft revolution and there are multiple sparks during the window the timer has the power going to the coils which tend to give a more complete combustion and adjustment is not as critical as a one pulse distributor system. some modern electronic ignition system also put out multiple sparks. I agree with Rons post. I have nothing to sell and no products to promote.
Last edited by Novice on Thu Aug 27, 2020 1:49 pm, edited 1 time in total.
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Re: Mag Voltage vs RPM - 1911 t
Jim, your perceived inaccuracies are indeed just that. Here is a link to a great article that explains the Ford Model T ignition system and spark timing while operating on magneto that I believe you will find very insightful: http://www.funprojects.com/pdf/Model%20 ... iticle.pdf
Regarding coil current, the confusion appears to be caused by the misunderstanding between HCCT Average coil current and the Time To Fire (TTF) method that measures Peak coil current. The HCCT current is measured over tens of seconds as the coil under test is actuated by many magneto pulses (Each revolution of the HCCT crank produces 16 pulses of electricity; 8 positive pulses and 8 negative pulses per revolution; NOT 32). During this time, the coil current is continually varying (AC positive and negative pulses) including time when the coil current is 0A. The Average current reading is 1.3A for a properly adjusted coil averaged over tens of seconds due to this dead time in between firings. The Peak coil current at the moment spark is fired each HCCT magneto pulse is much higher (eg. 6A) at the moment spark fires. The TTF method of coil point adjustment measures the coil current for a single spark; the first coil spark starting from rest; the coil current starts at 0A then ramps up to about 6A. The single event only takes approximately 0.002 seconds to occur (NOT 6A averaged over tens of seconds over many sparks like the HCCT method). The PEAK coil current of about 6A occurs only at the very moment the coil produces the spark at which point the coil current ceases (0A) and the coil returns to rest. This will make more sense after reading the article on spark timing.
Regarding coil current, the confusion appears to be caused by the misunderstanding between HCCT Average coil current and the Time To Fire (TTF) method that measures Peak coil current. The HCCT current is measured over tens of seconds as the coil under test is actuated by many magneto pulses (Each revolution of the HCCT crank produces 16 pulses of electricity; 8 positive pulses and 8 negative pulses per revolution; NOT 32). During this time, the coil current is continually varying (AC positive and negative pulses) including time when the coil current is 0A. The Average current reading is 1.3A for a properly adjusted coil averaged over tens of seconds due to this dead time in between firings. The Peak coil current at the moment spark is fired each HCCT magneto pulse is much higher (eg. 6A) at the moment spark fires. The TTF method of coil point adjustment measures the coil current for a single spark; the first coil spark starting from rest; the coil current starts at 0A then ramps up to about 6A. The single event only takes approximately 0.002 seconds to occur (NOT 6A averaged over tens of seconds over many sparks like the HCCT method). The PEAK coil current of about 6A occurs only at the very moment the coil produces the spark at which point the coil current ceases (0A) and the coil returns to rest. This will make more sense after reading the article on spark timing.
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Re: Mag Voltage vs RPM - 1911 t
Mike,
Seeing that Philip hasn't reported back re the coil current drag when tested on a HCCT and I haven't got an ECCT, could you please redo a set of coils set up with a ttf of .002 seconds and report back with the current reading tested on a HCCT machine.
Also could explain to me where you get your .002 seconds ttf and your firing zero point from which could determine your high current draw. Is it a mathematical figure or an estimation.
The cost of an ECCT in Australia is so prohibitive for me to purchase so I will have to rely on your answer.
Neil.
Seeing that Philip hasn't reported back re the coil current drag when tested on a HCCT and I haven't got an ECCT, could you please redo a set of coils set up with a ttf of .002 seconds and report back with the current reading tested on a HCCT machine.
Also could explain to me where you get your .002 seconds ttf and your firing zero point from which could determine your high current draw. Is it a mathematical figure or an estimation.
The cost of an ECCT in Australia is so prohibitive for me to purchase so I will have to rely on your answer.
Neil.
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Re: Mag Voltage vs RPM - 1911 t
Neil, Unfortunately, HCCT vs ECCT test comparisons are a waste of time as they are based on entirely different principles for adjusting Model T coils.
The HCCT method is well documented and should be used as the guide. Best results are achieved when all 4 coils have identical physical and electrical properties, unfortunately, it is not easy to identify how well the 4 coils are matched without more test equipment.
Regarding the TTF method; A graphic may assist with understanding where the 0.002 seconds of dwell time to fire spark came from. Here is a oscilloscope capture of a TTF test: The yellow trace is the coil timer terminal; a fast rising 12V pulse is applied to the coil under test when the timer terminal is grounded (yellow trace goes to 0A at time 0 as indicated on the white scale on the bottom). The coil current (blue trace) begins flowing nearly linearly (straight line steady rising current). Note that the coil current rises to 6A after 0.00195 seconds. At that point, the magnetic field produced by the coil current is sufficiently strong to pull open the vibrator spring contact; breaking the primary coil circuit and interrupting the flow of coil current. The coil current abruptly ceases flowing (goes to 0A) which causes the magnetic field to abruptly collapse and in turn induces a voltage in the coil's secondary (high voltage) winding wound around the primary coil winding. The voltage induced in the secondary coil winding is much higher than the primary winding because the secondary winding has approximately 80 times more turns of wire than the primary winding thus stepping up the voltage by the same factor through transformer action. The next logical question is; 12V primary voltage stepped up by 80 times is only 960V which is not high enough to produce a spark at the spark plug at ambient pressure (14.7psi) let alone cylinder pressure so how does spark get generated? The answer is not obvious because the coil voltage is not shown. The coil is an inductor which opposes abrupt changes in coil current (when the points open). A mechanical analog from fluid flow is water flowing rapidly (coil current) and the faucet is closed abruptly (coil points open). The water flow stops abruptly and the pressure within the pipe builds rapidly (possibly causing pipe banging) many times higher than the normal water pressure. In the case of the Model T coil, the coil voltage builds rapidly when the current flow stops flowing abruptly and can reach 200V to 300V for a very brief time (microseconds) even though the initial voltage applied to the coil was 12V. It is this brief voltage peak of say 250V that gets multiplied by the coil turns ratio (80) to produce the secondary voltage applied to the spark plug: 250V x 80 = 20,000V which is more than sufficient to jump a 0.025" spark plug gap when the ambient pressure within the cylinder is 50psi or greater.
The ringing you see after the coil current ceases flowing at time 0.00195 seconds is energy being transferred back and forth between the secondary winding and primary winding as the spark plug is arcing (current flowing to ground across the spark plug electrodes). At this point, the coil points are still open and the capacitor across the coil points is still in circuit and functioning to produce this back and forth energy exchange between capacitor and secondary winding. The capacitor value (0.47uF) was strategically chosen to suppress point arc when the points initially open but also to optimize the spark plug arc "burn time" to ensure complete combustion.The spark plug spark (arc) lasts for approximately 0.0011 seconds. You can see the arc extinguishes shortly after time 3ms (0.003s) by the last perturbation in primary coil current. The coil returns to rest, ready for this next firing. Hope this helps to understand the TTF method better.
There are many ECCT users in Australia, check with your nearest club to see if they have one you can borrow or member who would be willing to assist you.
The HCCT method is well documented and should be used as the guide. Best results are achieved when all 4 coils have identical physical and electrical properties, unfortunately, it is not easy to identify how well the 4 coils are matched without more test equipment.
Regarding the TTF method; A graphic may assist with understanding where the 0.002 seconds of dwell time to fire spark came from. Here is a oscilloscope capture of a TTF test: The yellow trace is the coil timer terminal; a fast rising 12V pulse is applied to the coil under test when the timer terminal is grounded (yellow trace goes to 0A at time 0 as indicated on the white scale on the bottom). The coil current (blue trace) begins flowing nearly linearly (straight line steady rising current). Note that the coil current rises to 6A after 0.00195 seconds. At that point, the magnetic field produced by the coil current is sufficiently strong to pull open the vibrator spring contact; breaking the primary coil circuit and interrupting the flow of coil current. The coil current abruptly ceases flowing (goes to 0A) which causes the magnetic field to abruptly collapse and in turn induces a voltage in the coil's secondary (high voltage) winding wound around the primary coil winding. The voltage induced in the secondary coil winding is much higher than the primary winding because the secondary winding has approximately 80 times more turns of wire than the primary winding thus stepping up the voltage by the same factor through transformer action. The next logical question is; 12V primary voltage stepped up by 80 times is only 960V which is not high enough to produce a spark at the spark plug at ambient pressure (14.7psi) let alone cylinder pressure so how does spark get generated? The answer is not obvious because the coil voltage is not shown. The coil is an inductor which opposes abrupt changes in coil current (when the points open). A mechanical analog from fluid flow is water flowing rapidly (coil current) and the faucet is closed abruptly (coil points open). The water flow stops abruptly and the pressure within the pipe builds rapidly (possibly causing pipe banging) many times higher than the normal water pressure. In the case of the Model T coil, the coil voltage builds rapidly when the current flow stops flowing abruptly and can reach 200V to 300V for a very brief time (microseconds) even though the initial voltage applied to the coil was 12V. It is this brief voltage peak of say 250V that gets multiplied by the coil turns ratio (80) to produce the secondary voltage applied to the spark plug: 250V x 80 = 20,000V which is more than sufficient to jump a 0.025" spark plug gap when the ambient pressure within the cylinder is 50psi or greater.
The ringing you see after the coil current ceases flowing at time 0.00195 seconds is energy being transferred back and forth between the secondary winding and primary winding as the spark plug is arcing (current flowing to ground across the spark plug electrodes). At this point, the coil points are still open and the capacitor across the coil points is still in circuit and functioning to produce this back and forth energy exchange between capacitor and secondary winding. The capacitor value (0.47uF) was strategically chosen to suppress point arc when the points initially open but also to optimize the spark plug arc "burn time" to ensure complete combustion.The spark plug spark (arc) lasts for approximately 0.0011 seconds. You can see the arc extinguishes shortly after time 3ms (0.003s) by the last perturbation in primary coil current. The coil returns to rest, ready for this next firing. Hope this helps to understand the TTF method better.
There are many ECCT users in Australia, check with your nearest club to see if they have one you can borrow or member who would be willing to assist you.
I-Timer + ECCT Adjusted Coils = Best Model T Engine Performance Possible!
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Re: Mag Voltage vs RPM - 1911 t
The discussion seems to be drifting away from the primary issue - It runs better on battery than it does on magneto. Since the same coils are used running on battery or magneto, I would think that the coils are not the issue and focus needs to be on the magneto and what may need to be checked since the magneto was rebuilt and magnets recharged.
The past is a great place and I don't want to erase it or to regret it, but I don't want to be its prisoner either.
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Re: Mag Voltage vs RPM - 1911 t
fbergksi, I'm kind of surprised no one else has mentioned it, but those voltages don't look that bad imho if they are that good once you apply a load (like an 1156 bulb). I don't think I saw any loaded voltage results above, but I could have missed it. If you get similar voltages once you test with a load, the car should run better on mag than bat at higher rpms. As stated above, the timing can change when switching from bat to mag. Also, if the timer has inter-cylinder inconsistencies, they can be exacerbated when switching from bat to mag if you're just missing the rise on one pulse for one cylinder and just getting it on another. I would play around with the timing while driving on mag and see if it picks up, possibly swap to a different timer and see if there's a difference, and check that the timing cover is centered to the cam.
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Re: Mag Voltage vs RPM - 1911 t
Philip reported his no-load magneto voltage measurements dropped about 5V when he operated his car on magneto. That is a lot to drop, however, the magneto output is extremely noisy when operating on magneto so the voltage measurements may be skewed significantly. I agree a repeat of his original measurements with 1156 bulb as load would be more insightful in the absence of ECCT mag test or St. Louis Magneto tester which would be most definitive. The presence of loose/intermittent wire/terminal/connection is always a possibility too that might not be easily detected via voltage measurements.
Apologies for the thread drift, good questions asked and thought relevant to the discussion. Still waiting for Ron enlighten us on the errors in my post that warrant his directive for everyone to ignore the information I posted.
Apologies for the thread drift, good questions asked and thought relevant to the discussion. Still waiting for Ron enlighten us on the errors in my post that warrant his directive for everyone to ignore the information I posted.
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Re: Mag Voltage vs RPM - 1911 t
For sure. It's not going to run well on mag if there's a problem in the mag-to-coil box wiring or switch. Sometimes it's the simple thing that will cause a problem.The presence of loose/intermittent wire/terminal/connection is always a possibility too that might not be easily detected via voltage measurements.
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Re: Mag Voltage vs RPM - 1911 t
I have directly offered my assistance to Phil Berg.
He hasn't call me yet as I asked. The first thing I will do is have him measure the output of his magneto to get a baseline for future investigation.
I am highly skeptical of Phil's initial readings and want to use the gold standard St Louis magneto tester to understanding its health.
We move forward from there.
All this "forum fog" posting by Kossar is to make you believe he knows what he is talking about. In fact, it is nothing but than an endless Forum infomercial about the product he wants all you guys to buy.
Caveat emptor
Ron Patterson
He hasn't call me yet as I asked. The first thing I will do is have him measure the output of his magneto to get a baseline for future investigation.
I am highly skeptical of Phil's initial readings and want to use the gold standard St Louis magneto tester to understanding its health.
We move forward from there.
All this "forum fog" posting by Kossar is to make you believe he knows what he is talking about. In fact, it is nothing but than an endless Forum infomercial about the product he wants all you guys to buy.
Caveat emptor
Ron Patterson
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Re: Mag Voltage vs RPM - 1911 t
Ron, very disappointed with your belligerent tone, unsubstantiated accusations and disparaging remarks of my technical knowledge.
Concerned I posted incorrect information, I asked a knowledgeable peer to review my post for accuracy; concise and accurate was the opinion with one exception. My statement on magneto polarity being governed by the magneto coil wiring was incorrect. The magneto coil wiring has only one correct configuration, however, the orientation of magnets (N,S,N,S versus S,N,S,N) installed on the flywheel governs the magneto voltage polarity with respect to piston position of a particular magneto output (+,-,+,-... versus -,+,-,+... for the same piston positions). This inaccuracy was deemed minor and certainly Not worthy of your directive to ignore the entire explanation of magneto system operation I posted.
The St. Louis Magneto tester is an excellent choice if one is available. Philip said his coils were adjusted using an ECCT so I suggested it be used to test the magneto if so equipped. It too indicates magneto health (i.e. magnetic field strength) independent of engine RPM just like the St. Louis Magneto tester.
Caveat emptor indeed Ron! Its what makes great products the new norm and naysayer reputations ebb.
Concerned I posted incorrect information, I asked a knowledgeable peer to review my post for accuracy; concise and accurate was the opinion with one exception. My statement on magneto polarity being governed by the magneto coil wiring was incorrect. The magneto coil wiring has only one correct configuration, however, the orientation of magnets (N,S,N,S versus S,N,S,N) installed on the flywheel governs the magneto voltage polarity with respect to piston position of a particular magneto output (+,-,+,-... versus -,+,-,+... for the same piston positions). This inaccuracy was deemed minor and certainly Not worthy of your directive to ignore the entire explanation of magneto system operation I posted.
The St. Louis Magneto tester is an excellent choice if one is available. Philip said his coils were adjusted using an ECCT so I suggested it be used to test the magneto if so equipped. It too indicates magneto health (i.e. magnetic field strength) independent of engine RPM just like the St. Louis Magneto tester.
Caveat emptor indeed Ron! Its what makes great products the new norm and naysayer reputations ebb.
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Re: Mag Voltage vs RPM - 1911 t
Ron, the Forum deserves justification for your accusations discrediting my technical explanations or you owe me an apology for your unsubstantiated outburst. I would welcome either.
Leaving the good folks here dazed and confused not knowing what to believe about the Model T ignition system operation is NOT an option.
Leaving the good folks here dazed and confused not knowing what to believe about the Model T ignition system operation is NOT an option.
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Re: Mag Voltage vs RPM - 1911 t
Good point! Where were the voltage measurements taken from - the mag post, terminal block, ignition switch or the at the coil box connection. Lots of connections that could cause a problem. Yes, best to investigate the simple things and rule them out before diving into technical issues.
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Re: Mag Voltage vs RPM - 1911 t
Agreed. I thought your explanation was very informative. I knew that the mag output was AC, but never considered that the pluse that fired the coil was either + - and not both.MKossor wrote: ↑Sat Aug 29, 2020 10:34 amRon, the Forum deserves justification for your accusations discrediting my technical explanations or you owe me an apology for your unsubstantiated outburst. I would welcome either.
Leaving the good folks here dazed and confused not knowing what to believe about the Model T ignition system operation is NOT an option.
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Re: Mag Voltage vs RPM - 1911 t
I don't have access to an HCCT, I do have a ECCT that i've with used with great success. Haven't had time yet to do a 1156 bulb test. Ron I sent you an email earlier this week, check your email that you sent me. Took the car out for quick trip and the car runs ok on mag but at speeds of 30mph or higher I can hear a miss in the exhaust, running on bat no miss is heard.
Thx
Thx
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Re: Mag Voltage vs RPM - 1911 t
Phillip.... Check the AC voltage at different engine speeds, a good magneto will generate 30 plus ac volts at engine speeds above 30 mph. Magneto may have to be recharged .
Bob J.
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Re: Mag Voltage vs RPM - 1911 t
I guess the rebuttal/explanation is not forthcoming, but that was to be expected.
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Re: Mag Voltage vs RPM - 1911 t
Fred..... Considering the holiday weekend, give preference to family activities. As far as responding, I'm sure Fred needs some time to report his progress/new problems to the Forum.
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Re: Mag Voltage vs RPM - 1911 t
Duh..... PHILLIP, not fred........need my coffee.
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Re: Mag Voltage vs RPM - 1911 t
Working on other issues at the moment, I'll just drive the car on battery for now. Thx.