Magneto output voltage - revisitted.

Topics Last Day Last Week Tree View    Getting Started Formatting Troubleshooting Program Credits    New Messages Keyword Search Contact Moderators Edit Profile Administration
Model T Ford Forum: Forum 2012: Magneto output voltage - revisitted.
Top of pagePrevious messageNext messageBottom of page Link to this message  By David Dare - Victoria Australia on Thursday, May 24, 2012 - 12:44 pm:

Newly built meter and AC analogue guage all work, the light globe, poor thing must have nearly popped twice so far, but wow they certainly glow bright.
Wifes 26 Tudor - no recharge of the magnets.
-idle 9 volts
-mid range 19 volts
high revs - 26 volts
my 13 touring - fully recharged magnets.
-idle (low idle) - 13 volts
-mid range - 23 volts
-high revs - not that high - 29 volts.
13 runabout - no recharge on the 7 year ago rebuild
-idle - 11 volts
-mid range - 19 volts
-high revs - 27 volts

Thank you for the meter build idea, what a great piece to have to verify all is well inside.

David.

PS- l'm still waiting to see that light globe go POP.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bede Cordes, New Zealand on Friday, May 25, 2012 - 06:29 am:

Hi there,

I wonder how accurate this chart is for VOLTAGE output from the magneto for T's in general (give or take a load or no load), even though it relates to the early T. I can't remember where I scanned it from... can anyone comment ? It seems the highest output here is 150W, but Ron the Coilman says the T magneto can stretch to 200W (if I remember right)... presumably the earlier mags had a lower output as less electrical equipment was on the car. (Yes I'm sure this has been discussed before, but don't tell me off)

magchart

Regards,
Bede


Top of pagePrevious messageNext messageBottom of page Link to this message  By John F. Regan on Saturday, May 26, 2012 - 01:41 am:

Bede:

So far as I know there was only one set of readings ever published by Ford with regard to the magneto output. It was in the T service bulletins. It was then copied by Dyke's and others. You can tell that the data was hijacked from Ford because Dyke's and other sources have the exact same data and there is a MISTAKE in the data that is glaring. Can you find it in the data below.

RPM MPH Volts Amps Cycle
200 5 5 6.1 26.4
400 10 9.8 7.9 52.8
600 15 14.4 8.5 80.0
800 20 18.8 8.8 106.4
1000 25 22.8 8.9 146.4
1200 30 26.2 9. 160.0

The mistake is copied in all sources I have found so it has to have been Ford's original data. These data are not spec's but just some typical numbers that Ford said they measured and that is the only data I have ever found from Ford Motor Company so far. Sorry but I can't force the columns to line up but read the numbers left to right and note the column labels on the first line.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Craig Anderson, central Wisconsin on Saturday, May 26, 2012 - 02:12 am:

I think this is correct.......

John's Chart


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tom Carnegie on Saturday, May 26, 2012 - 02:21 am:

The formula for deriving frequency from RPM on a T is RPM/7.5 Therefore the correct frequencies are

200=26 2/3hz
400=53 1/3hz
600=80hz
800=106 2/3hz
1000=133 1/3hz
1200=160hz


Top of pagePrevious messageNext messageBottom of page Link to this message  By Craig Anderson, central Wisconsin on Saturday, May 26, 2012 - 03:14 am:

(I only straightened out John's chart)...... ;)


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bede Cordes, New Zealand on Saturday, May 26, 2012 - 03:59 am:

If you don't run your T at 1000rpm, the old results/chart will be fine then !

Regards,
Bede


Top of pagePrevious messageNext messageBottom of page Link to this message  By George_Cherry Hill NJ on Saturday, May 26, 2012 - 05:47 pm:

Maybe the rest of you see the glaring error, but I'm a little thick here....lol

Bede chart is for the older skinny wrapped coils, yes?

John list is for the later fat wrapped coils, yes?

Tom corrected the cycles as it's a fixed relationship, yes?

Or is there something else?

In the case of John list, can a later mag actually put out about 270w @ 30MPH?

So I imagine the amps start choking somewhere and the voltage keeps going - is that correct for any mag ? Or do they hit a watt limit and the amps actually drop? Have to admit, for us wrench rappers mags are a mystery :-)

Just trying to figure out what happens when a car gets up to 45 MPH. If there is a 9A flatline for example, does the voltage keep going or does it start to clip too? I know each mag is different, but just talking generally on say, Johns data mag example.

Thanks


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bede Cordes, New Zealand on Saturday, May 26, 2012 - 07:14 pm:

George,

the RPM and frequency (cycles) don't line up, yes it is a fixed relationship. It took me a minute to see it too. With an AC "alternator" which effectively is what a Model T Magneto is, the output frequency is always relative to the speed of rotation. Hence if you ran the rotating machinery in your power stations at half the speed you do now for example, your mains supply frequency would be 30Hz, instead of the 60Hz.

That's the bit I can answer ! My AC theory is a bit covered in cobwebs sorry, I'm sure one of the guys can give you an explanation further...

Regards,
Bede


Top of pagePrevious messageNext messageBottom of page Link to this message  By David Dare - Victoria Australia on Saturday, May 26, 2012 - 07:24 pm:

Well it ( the 12 volt globe ) finally POPPED at 29.5 volts, and the meter jumped from 29.5 V AC up to 34 volts AC.

Is that list above as released by ford, a hard and fast rule, or like cars built today that are sold and badged to be say 350HP from the factory can actually range from 350 HP up to say 390HP, or more???
An average ??

David


Top of pagePrevious messageNext messageBottom of page Link to this message  By John F. Regan on Saturday, May 26, 2012 - 09:14 pm:

The basic obvious problem one has is that any 2 RPM's that double should produce a doubling of the frequency. Assuming they actually had some tachometer device I could live with the inaccuracy but they should have caught it and at least realized one or the other was wrong when they doubled it. Thus 200 and 400 should be exactly double of each other as should 400 and 800. Notice that 600 and 1200 have the doubling of the frequency OK. Seeing these problems I did what Tom did and calculated the exact frequencies based upon 8 cycles of AC per engine revolution and then discovered that 1000 was further off than any of them as Tom posted. What I really wanted to point out though is that if you look in Dyke's you will find these EXACT same data with the exact same relationship as Ford "measured" them???? All data it would seem came from one questionable source namely Ford.

On another issue I am suspicious that Ford's method of measuring magneto AC current may have been to simply hook an ammeter from the mag post to ground thus shorting it out. If this is true then you really cannot take the Voltage output at any RPM and then take the posted Current at that RPM and multiply them to compute output power. That would not be valid. Voltage can be measured rather easily as open circuit voltage and is often published just that way but current output generally is at some understood load which could in fact be a dead short but in the absence of any data to exactly define it - I wonder how reliable the current readings are if taken from these same Ford data.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bede Cordes, New Zealand on Saturday, May 26, 2012 - 09:18 pm:

Gidday David,

have a look at John Regan's post in the thread titled "Magneto Power", about the 8th post down, I saw it after I posted earlier above. John sums it up, as usual. Your post lamp blowing voltage difference shows the difference between correct testing with a load and the misleading test without a load- 4.5 volts in this case. I would use the chart as a benchmark worth going by (with a load of course). You have to start somewhere. But then I'm no Model T expert...

Regards,
Bede


Top of pagePrevious messageNext messageBottom of page Link to this message  By George_Cherry Hill NJ on Saturday, May 26, 2012 - 10:48 pm:

Thanks guys....gets clearer....

All I know about frquency cycles is that in uni lab, we had to determine cycles' with a long string, some hooks, and an A/C solenoid spool. And then count waves as the string decided to sine wave as a standing wave.

We did everything right, right down to string length and everybody only counted 59. So called prof, he counts 59, says 'beats the heck out of me why' and gave the team guys a good grade. I haven't had a real firm grip on anything electrical since :-):-)

So one question remaining does a mag flatline on watts? I see the amps flatlining in the data but voltage is almost linear throughout the range. So does it just keep extending with more 'spin' or does it get into timing things too and start to flatline?

Thanks all...


Posting is currently disabled in this topic. Contact your discussion moderator for more information.
Topics Last Day Last Week Tree View    Getting Started Formatting Troubleshooting Program Credits    New Messages Keyword Search Contact Moderators Edit Profile Administration