Magneto to charge battery

[rainer]

Hello.

My '16 Touring has no generator, bit war upgraded to have an electric starter by the former owner (I guess). Also headlights are electric (6V) with two-filament bulbs.

I do not want to install a dynamo under the hood, this is a too brutal change, so the Magneto is my first choice.

Now I know that the magnets of magneto are easily discharged by drawing too much current from it. At the moment I have a very well working magneto, I don't want to damage it.

How much current can I safely draw from magneto without having to fear that this will harm the magnets? Is 0.5-1.0A ok?

Based of a very simple Diode + Bulb schematic I found somewhere in the Internet, I added charging control to my self built direction light flasher. (I had to build it by myself because my LED direction lights draw so low current that no standard LED flasher works.) My charging control turns on such previously described Diode+Bulb combination when battery voltage drops below 6.7V and turns charging off above this 6,7V. So the battery will a.) not be overcharged and b.) the magneto is not permanently under load.

To find the right bulb, I need to know the "safe for magnets" current.

If somebody can help?

Thank you!

[MKossor]

I don't believe the magneto will be damaged by excessive current draw. My 1927 Touring developed a short to ground that didn't adversely effect the magneto field strength after fixing the short.

Magneto magnets can, however, be discharged by inadvertently connecting battery power to the magneto so do be very careful not to do that.

Regarding the Magneto diode and light bulb battery charger (AKA "Hot Shot" battery charger), an 1156 bulb is the standard bulb typically specified. It is inexpensive, does work but inefficient. The 1156 bulb can get pretty bright and hot so be sure to factor in those considerations when mounting it in your car.

[speedytinc]

I can confirm by experience.
My 14 charges a 12v battery continuous @ up to 3 amps. I run a 1157 bulb, both filaments.
Mag puts out 35+V. Burns bulbs out on single filament 12V bulb or dual filament 6v bulbs. Your bulb needs will vary based on mag output.

[Cap]

I'm using this on the 6 Volt '13

https://www.snydersantiqueauto.com/prod ... 82457&cat=

here is it installed in the Car..

The Car already had been converted with 6 Volt Turn Sig, but no Charging or fuses.. So I was able to add a few things I thought were necessary..

Tail lights..

https://www.ledlight.com/g18-s25-6-12v- ... arity.aspx

and somewhere in there is the Model T/A Led Headlights.. 6V..

Found them..

https://www.ledlight.com/1142-miniature ... 0-smd.aspx

Cap

[TXGOAT2]

Would it be practical to build a device that would rectify mag output and regulate it so as to be suitable for battery charging and operating 6 or 12 volt lights, etc? I have a wind turbine outfit that produces 3 phase AC current. The voltage, amperage, and frequency vary with the turbine speed from very low up to around 4300 watts at 340 volts. The raw output is first rectified to DC and then processed to single phase AC at a regulated 240 volts at 60 cycles. Only the current then varies with wind speed, from very low up to about 4200 watts. Voltage and frequency are held to spec. Each phase of the wind turbine has about the same general electrical characteristics as the Model T magneto, and the drive speed varies widely, just like the model T engine speed. The turbine alternator has a permanent magnet rotor, like a T magneto, and multiple poles/windings which I believe are in series.

[speedytinc]

I'm using this on the 6 Volt '13

https://www.snydersantiqueauto.com/prod ... 82457&cat=

here is it installed in the Car..

13 fuse block.JPG

The Car already had been converted with 6 Volt Turn Sig, but no Charging or fuses.. So I was able to add a few things I thought were necessary..

Tail lights..

https://www.ledlight.com/g18-s25-6-12v- ... arity.aspx

and somewhere in there is the Model T/A Led Headlights.. 6V..

Found them..

https://www.ledlight.com/1142-miniature ... 0-smd.aspx

Cap

Part # T-5165-6 | Model Year 09-27
"Finally a way for you guys with early non-starter T's to be able to charge your hot-shot or accessory battery. Charges battery with current supplied from the magneto post. Not recommended for use with original style ignitions/coils. Limited supply of these 6-volt units available. U.S.A."

Interesting disclaimer. The perfect product not recommended with a stock ignition/coils.

[Cap]

Interesting..I've missed that disclaimer..

I am running an E Timer on this car, so it's always on battery.. I reconfigured the wiring in the battery box to be battery on both sides of the switch..

I'd like to see the waveform out of the mag with the 'device' and without to see what might be the issue..

I understand the "hot Shot" charger does not have this limitation..

Cap

[rainer]

Thanks for showing me this item at Snyders, but this price is really high.

I think I will start with a 24V/21W bulb. This bulb draws 21W/24V = ~1 Amp at nominal operation. As it is good for 24V, it will match well the average Magneto voltage of 29V during normal drive ( I found that value somewhere in the Internet), 29V - 6V of battery gives approx 24V on the bulb.

This way I should theoretically get charging current of 1A, sufficient to almost recharge what the starter has drawn.

If it charges too slowly, I can use a bulb of higher wattage or two bulbs in parallel.

[speedytinc]

Its gotta be a funny typo.

[rainer]

@TXGOAT2:

Would it be practical to build a device that would rectify mag output and regulate it so as to be suitable for battery charging and operating 6 or 12 volt lights, etc?

Well, this is exactly what I do (PCB board is finished, but I didn't test yet.

Because the magneto is connected to chassis ground on one side, it produces ±29 Volts AC (plus and minus, alternating). So I can only use a strong diode to cut off the negative half wave. Result is a half-sine, only the positive half of the entire AC cycle. Frequency does not matter, the diode is for sure faster. Then I use the bulb in series to limit the current.

What I do in addition is:
I already use a very small microcontroller to generate the on/off for direction lights. In total I use 4pcs of 3W LED, this is so low current that the LED-Blinking relay I tried did not work properly. So this was the primary use. But I had lots of resources free, so I added measuring the battery voltage and switching a MOSFET transistor (good for 65V/25A) on/off. This way I can stop charging the battery when it is full, otherwise it would only draw current and produce hydrogen gas.

[TXGOAT2]

With a regulated device to manage magneto voltage and the battery charge, I'd do away with the generator.

[Steve Jelf]

Being an electronic dummy, I was unaware of a danger inherent in the magneto battery charger using a bulb. Don't let any of the charger wiring get within a half inch of high voltage (spark plug) wires and terminals. An electric expert tells me that high voltage can jump into the charger wiring, overpower the diode, and go to ground through the mag coil. This is probably why my car will no longer start on MAG.

[speedytinc]

With a regulated device to manage magneto voltage and the battery charge, I'd do away with the generator.

After I had & continue the success of the system mentioned above, I did the same for a customer's 25. His original block was deemed unusable. He accidently replaced it with a 15 block & didnt realize the mistake till I got it for final long block building. Adding an outside alternator didnt work out. Did the same setup. mag runs the ign. & charges an 8V battery for electric start. Hot ignition & electric start all day & night needs.

[dykker5502]

Now I can't find the picture, but I once saw a solution John Regan had made where a ½ inch wide circuit board was cut out and drilled to fit between the magneto and battery terminals on the coil box. I then holds the diode and socket for the #1156 bulb and necessary wireing between it all.
Neat solution, but of course not discreet when you opened the hood.
I suspect it was a prospect Fun Products product that only made it to prototype.

[rainer]

Hello.
I bet all this very compact solutions are more or less based on a diode (for rectifying the magneto AC output and preventing DC flowing from battery to magneto) and a bulb for limiting the amps drawn (otherwise the battery would brutally pull down the magneto to 6 Volts on one half of its AC output).

This asymmetric load to magneto is what makes me a bit nervous when drawing higher current, because this generates some kind of indirect DC. In one half of the sine wave, magneto has to drive buzzer coils + battery loading, in other half of the sine it has to supply the buzzer coils only. I am not sure if this will not have effect on magnets.

So I will limit the battery charging current strongly (at most 1 Ampere), so it is close to a buzzer coil. Charging will need long, of course, but this is better than re-magnetizing the magneto. And after 1-2 hours the battery will have got back what the starter possibly has drawn.


Thanks for your very helpful comments.

[speedytinc]

Hello.
I bet all this very compact solutions are more or less based on a diode (for rectifying the magneto AC output and preventing DC flowing from battery to magneto) and a bulb for limiting the amps drawn (otherwise the battery would brutally pull down the magneto to 6 Volts on one half of its AC output).

This asymmetric load to magneto is what makes me a bit nervous when drawing higher current, because this generates some kind of indirect DC. In one half of the sine wave, magneto has to drive buzzer coils + battery loading, in other half of the sine it has to supply the buzzer coils only. I am not sure if this will not have effect on magnets.

So I will limit the battery charging current strongly (at most 1 Ampere), so it is close to a buzzer coil. Charging will need long, of course, but this is better than re-magnetizing the magneto. And after 1-2 hours the battery will have got back what the starter possibly has drawn.


Thanks for your very helpful comments.

I can tell you from experience. My 14's mag charging specs. Fresh set up 5 years ago. Rebuilt field coil & off flywheel magnet charges. Mag output 35V. With it charging 12V full size car battery reads 33V. No change in 5 years. Charges 3 amps @ moderate speed. Regulated with 1157 tail bulb, both filaments Otherwise they burn out first burst of speed. (low gear wind up).
I did the same setup on a 15 motor in a 24, charging an 8V battery. Same numbers. This one has only a few miles so far.

[TWrenn]

Seems to me it would be a lot simpler to hook up connection wires to the battery with mating connectors from a remote charger. If you have a GOOD battery and not running headlamps much, if at all (why do we need to drive in the dark anyway?) you should manage on only one overnight charge a month. I did that all last summer with my Fordor and a new good quality battery while fighting with a non functioning generator. Finally put on an alternator anyway. Just my two cents.

[speedytinc]

Seems to me it would be a lot simpler to hook up connection wires to the battery with mating connectors from a remote charger. If you have a GOOD battery and not running headlamps much, if at all (why do we need to drive in the dark anyway?) you should manage on only one overnight charge a month. I did that all last summer with my Fordor and a new good quality battery while fighting with a non functioning generator. Finally put on an alternator anyway. Just my two cents.

Being a 14, no place for a generator. Not going to ugly it up with a remote & drive issues.
The battery stays charged & T always @ the ready. I have a modified 12 starter. I can run on mag or battery with the infinite advance curve. My lights are 12 halogen, pull a lot of power. LED's were not bright enough for the little night driving I do do. The device was simple to build. A successful experiment.
AND because I can.

[rainer]

I can tell you from experience. My 14's mag charging specs. Fresh set up 5 years ago. Rebuilt field coil & off flywheel magnet charges. Mag output 35V. With it charging 12V full size car battery reads 33V. No change in 5 years. Charges 3 amps @ moderate speed. Regulated with 1157 tail bulb, both filaments Otherwise they burn out first burst of speed. (low gear wind up).
I did the same setup on a 15 motor in a 24, charging an 8V battery. Same numbers. This one has only a few miles so far.

This sounds better than I thought. My biggest fear was this magnets because they are lots weaker than today's ones. But what you tell me here sounds good.

I am a bit confused with this bulb numbers, so I googled for 1157 bulb. What I could find out is: This number only tells the bulb socket. 1156 bulb is one filament (one contact at bottom of bulb), 1157 is two filaments (two contacts at bottom of bulb). But it does not say anything about bulb wattage and voltage. This should be stamped into the metal socket right below the glass bulb.

Anyway, what I also googled was the approximate voltage generated by Magneto. What I found matches well what you measured. Somewhere between 29-35V at higher engine rpm.

So let's do a little math:
Magneto supplies 35V (worst case), the battery has 6V. Because the voltage of battery is almost stable (5.6V ... 6.7V). the voltage difference (mag - battery) is approx. 29V max. to be consumed by the bulb.

Using a two filament 12V bulb:
Of course, using a 12V bulb with only one filament will not work, it will immediately burn out. This also explains to my why bulbs with two filaments are used. If you connect only to the contacts at bottom side of bulb, you actually have both filaments connected in series to each other. This is no lucky choice because filaments are for different power 21W and 8W, therefore dividing the voltage in ratio 3:1 in this case. So the weaker filament will get a much higher voltage of approx. 20V, while the stronger one will get only 8V. So the 8W filament will be extremely overloaded (be shining extremely bright). I guess it only survives because nobody will run the engine very long at high rpm (so the voltage is less than 29V).

What I (will) do is:
Instead of using a normal 1157 car bulb for 12V with 21+8 Watts, I (will) use a 1156 bulb for trucks. This bulb is for 24V and has only one filament with 21W. At 24V it will draw approx. 0.9A, so it will be about 1A on 29V. So the result is better, I do not overload one filament (of two) so much. The bulb should live much longer.

I will keep you updated in how this 24V bulb will work.