Mag running with a open circuit

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Model T Ford Forum: Forum 2016: Mag running with a open circuit
Top of pagePrevious messageNext messageBottom of page Link to this message  By Jerry Davis Houston TX on Friday, December 30, 2016 - 10:46 am:

Will shortly be changing my 14 to a distributor. Hopefully I will be able to use the 17v mag output as a battery charging source. My question is will there be any damage to the mag if it operates with a open circuit. Haven't quite figured out how I need to convert the mag AC 17v to a DC 13v yet but given some time and experimentation it will be done. Thanks for any help. May the force be with you...... Jerry.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Stephen, South Texas on Friday, December 30, 2016 - 11:02 am:

Running with the mag disconnected won't hurt a thing. It's done all the time on later year vehicles that have a switch that selects between BAT and MAG.

Fun Projects makes a battery charger kit but it's for 6v batteries. A similar device wouldn't be hard to make for 12v batteries. I thought I had a drawing that someone made but can't find it at the moment.

http://www.funprojects.com/products/hsbck1.aspx


Top of pagePrevious messageNext messageBottom of page Link to this message  By Les Schubert on Friday, December 30, 2016 - 12:21 pm:

Jerry
I've run my '13 for years using the mag to charge a 12 volt motor cycle battery using just a single simple diode. I went to this after I realized that the original Hienz coil design never was much good and went to a Trufire 13 years ago. It is suggested that hooking a 12 volt brake light bulb (1157 I believe) in series will provide some protection in case the diode shorts out internally. I plan to reinstall the Hienz coils with a E timer and redeploy the Trufire this year to a race car


Top of pagePrevious messageNext messageBottom of page Link to this message  By Harold Schwendeman - Sumner,WA on Friday, December 30, 2016 - 05:52 pm:

Les - Electricity is NOT my thing! I never did understand that #1157 light bulb/battery charging thing. You mentioned,.... brake light bulb in series will provide some protection,.... " How/why does the light provide "protection?"


Top of pagePrevious messageNext messageBottom of page Link to this message  By Val Soupios on Friday, December 30, 2016 - 06:38 pm:

The bulb will blow so it acts like a fuse.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Harold Schwendeman - Sumner,WA on Friday, December 30, 2016 - 06:53 pm:

Ahhh,....well,..... that's simple enough! Thanks,..... harold


Top of pagePrevious messageNext messageBottom of page Link to this message  By Hal Davis-SE Georgia on Friday, December 30, 2016 - 06:55 pm:

I gotta wonder if it should be an 1156. 1157 is a two filament bulb.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Royce in Dallas TX on Friday, December 30, 2016 - 07:09 pm:

The Fun Projects charger is OK for a 12 volt battery too, the only thing is it will charge at half the current of a 6 volt battery because the magneto output is still the same. Wattage is wattage.

A distributor and coils takes more power to run than a T magneto puts out, regardless of battery voltage. The magneto powered charger will make the battery run down less quickly.

This is one of the many reasons the Model T's ignition system was so superior to any of the other cars on the road at the time. It required no battery and was reliable as hell.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jerry Davis Houston TX on Friday, December 30, 2016 - 10:10 pm:

Les, Stephen, My mag will produce 17v. I thought of the diode. That would give me a half wave rectifier which would be a on/off DC. I believe the 1157 would act as a current limiter. No more than what we use these T's and starting out on these tours with a fully charged battery I think I should be in good shape battery wise. Do you-all agree?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tony Bowker, Ramona, CA on Saturday, December 31, 2016 - 12:29 pm:

Do not just use a diode without some form of current limiting. The purpose of the bulb is to limit the current to about 1 ampere. More than that will demagnetize the magneto as it only will be conducting on on positive and not on the negative because of the diode. The is the same as passing D.C. To the magneto post, which will cause magneto failure. It is best to use a 12 volt bulb, so as not to be damaged should the output ever be shorted.
Tunsten bulbs have an interesting characteristic in that used at the rated voltage they draw rated current, that current will hardly change when the voltage is reduced (or increased within limits). As the voltage is decreased, the filament gets cooler and the resistance drops, causing the current to remain almost unchanged. Thus a bulb can act as a constant (almost) current source. Going back to the T application, a 12v 12w bulb will draw 1 amp and this will remain similar when the voltage is dropped to 6 volts. Thus either the diode and bulb in series, the battery will get about 1 amp once the magneto voltage exceeds the battery voltage. Neet.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Les Schubert on Saturday, December 31, 2016 - 03:29 pm:

Tony
Fortunately for me, my T doesn't know any better. I've been driving it for many thousands of miles with my 12 volt battery being charged by just a simple diode. I realize I'm taking a risk magnet demagnetizations IF the diode fails. Probably this year I will get around to adding the light bulb


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jerry Davis Houston TX on Saturday, December 31, 2016 - 05:14 pm:

Tony, your comment concerning half wave rectification from the diode and it's effect on the mag is most interesting. Can you expand on that for me? And, if that is a concern, would using full wave diode rectification be a solution? Thanks in advance. May the force be with you. Jerry.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jerry Davis Houston TX on Saturday, December 31, 2016 - 05:26 pm:

Tony, your comment concerning half wave rectification from the diode and it's effect on the mag is most interesting. Can you expand on that for me? And, if that is a concern, would using full wave diode rectification be a solution? Thanks in advance. May the force be with you. Jerry.


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