Magneto output questions

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Model T Ford Forum: Forum 2016: Magneto output questions
Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Lynn on Sunday, October 30, 2016 - 05:06 pm:

Ok my friend and I just finished "charging" the magnets or field. Not to tough. So my questions are now the following.

At idle what should the mag put out?

At full or almost full throttle what should the mag put out?

I have about 6.5 at idle and almost full throttle I have 25+/-.

This then leads to another question.

Using magneto headlamps (24v) each when set up in parallel they should require 48v to be bright correct? If so there is not enough power to do it unless I run hot leads to each lamp and grounds which Ford did not do.


Top of pagePrevious messageNext messageBottom of page Link to this message  By David Hagerty on Sunday, October 30, 2016 - 05:51 pm:

Not sure I understand the various choices for electric headlamps. Aside from what volt bulbs are used, there being what voltage is supplied, relative to wiring methods and or any means of inline resistance to prevent burnout from mag voltage at higher rpm. I can say, parallel wiring is, as the name implies, the same from the source down the line to each lamp in the 'row' of the two wires. Series wiring will in a sense 'divide' power to each lamp in the 'loop' If you have 24v and 2 lamps in series, each will receive 12v. For example, 3 lamps in series would receive 6v and so on. So... if you did have 2 24v bulbs in series, only then would it require 48v for max brightness.
Dunno if this helps.


Top of pagePrevious messageNext messageBottom of page Link to this message  By David Hagerty on Sunday, October 30, 2016 - 05:56 pm:

Sorry, That should read 3 lamps in series would receive 8 volts NOT 6 volts!!! I knew that... my mind is just slow today!


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Lynn on Sunday, October 30, 2016 - 06:40 pm:

Dave, makes sense to me but that does not explain why the system is set up that way. at idle you would not have more than a glow if that. You would have to be cruising down the road at a pretty good clip to still only get dimly lit lamps. And in the case of my truck why the use of a dimmer if I cannot even get much above dim due to lack of power?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Royce in Dallas TX on Sunday, October 30, 2016 - 06:59 pm:

Sounds like your magneto is working great.

Magneto bulbs are 9 volts. Obviously they are brighter than normal if the car does not have any sort of resistor as Ford used on the 1919 and later cars. So if you have a 1917 - 18 with no resistor keep the revs down when running on MAG headlights. Bear in mind the ignition uses some of the magneto output, so the headlights and the ignition together should keep the voltage low enough that you would only blow the lamps if you revved the engine to the moon in neutral.

Here's my 1917, with its original headlight bulbs running on MAG:
https://www.youtube.com/watch?v=h51z8Ir3Yz0


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Lynn on Sunday, October 30, 2016 - 07:18 pm:

Nice video. That is what I wish mine did but do not. I have new everything in the fixtures, new wires, 24 volt bulbs and good ground. I get nothing at idle and not much more at high speeds.

Where I am confused is that if I am only getting 6.5 volts at idle how could that even light them up like yours?

Also if I have 25+ at high speed I should get something close to what yours are at low speed or higher but I do not. The volts are there but not working.


As I stated above it seems impossible to have them work if they are both 24 volt bulbs when I am only getting about 25+ at full speed.

I don't know much about electricity so I apologize in advance for all of the questions.

I had 2 electrical engineers over today who are puzzled by this issue also. I think we are missing something.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Royce in Dallas TX on Sunday, October 30, 2016 - 07:36 pm:

You have 24 volt bulbs. You need 9 volt bulbs.


Top of pagePrevious messageNext messageBottom of page Link to this message  By George Mills_Cherry Hill NJ on Sunday, October 30, 2016 - 07:38 pm:

Yes....the 24V lamps are the problem. As Royce points out...original lamps were 9 V, and 2 daisy chained together was 18V. Important point! If you have something on the dash that looks like a crude doorbell transformer, then you have something else! That version is the reactor block +6V +6V all daisy chained together.

Lamps 101...in a general sense, lamps will not even dimly glow until half nameplate voltage is reached. Conversely, once a lamp sees more than about 120% of its nameplate...it gets mighty bright, but lamp life goes in the toilet real quick! Now you understand why Ford had trouble with magneto illumination once roads provided better speeds.

Finding 9/10 V lamps is difficult. If you have the reactor block then change the lamps to 6V rating..but be careful of high revs, even in low. An alternative if you do not have the reactor is to just go 12V lamps daisy chained. They might not even glow at idle, but they will do well at the higher speeds.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Lynn on Sunday, October 30, 2016 - 07:59 pm:

That is very helpful George, thank you. I bought the lights from one of the suppliers since they were stated to be (magneto) type, now I have to try and find the 12 bulbs you had mentioned. Do you know a part number that would work,i.e., (1157) Next question is related to the above again.

What is the output supposed to be on a mag at idle (number) and at high speed? I am just curious. It seems like mine is ok but wanted numbers to compare to.

Again thanks to all of you guys, I don't know a lot about T's but I do enjoy them and I am doing my best to get this one on the road and performing well.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Lynn on Sunday, October 30, 2016 - 08:00 pm:

I forgot to mention that the bulbs say 24 volt on them. Should I send them back and ask for some kind of 12 in their place?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Royce in Dallas TX on Sunday, October 30, 2016 - 08:07 pm:

You can use three six volt bulbs in series to get a good working setup.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Lynn on Sunday, October 30, 2016 - 08:14 pm:

Starting to do a search and realized that I don't know what to search for when looking for a 12 volt headlamp bulb that is single filament but with 2 buttons on the bottom that can be used as a head light. I have found some that are dual filament but I know these will not work.


Top of pagePrevious messageNext messageBottom of page Link to this message  By George Mills_Cherry Hill NJ on Sunday, October 30, 2016 - 08:30 pm:

As Royce points out, you can also 'hide' a 6V lamp somewhere...3 x 6 =18V. Pickes up the low end RPM sooner...Will burn out much faster if higher speed is your goal...you will be unimpressed with the real light produced as it was more for being seen than actually seeing yourself!

Anyway...your magneto output sounds OK. Magnet strength is only one factor...distance the actual coil is from the magnets another...your's is reasonable...but do check it under load just because.

Here is a chart for 12V lamps on magneto...before someone jumps on the formula used...there is NO perfect formula...this was good enough to instrument lamps on the WW2 aircraft to the Apollo space missions!

Leslie Henry also made a chart of suggested average magneto output v. speed. I can't find mine, maybe someone else can post it.

There are several 12V single post lamps around...1143 is prob the most common...dunno if the vendor will exchange, but hey, worth a call! He would prob tell you the 24V is for Ford magneto...if...if...you ran everything in parallel! It would nameplate at 27MPH or so...but then probably not even glow under about 15MPH




Top of pagePrevious messageNext messageBottom of page Link to this message  By Royce in Dallas TX on Sunday, October 30, 2016 - 08:50 pm:

You can " hide" the third bulb in your tail lamp.


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