Magneto battery charger
 

A buddy of mine has a 1914 T and wants to buy or build a battery charger that will take the magneto output and produce a regulated 12-14 volt output. Does anyone have any suggestions for something like this ? We’re specifically interested in having a regulated output so the charger doesn’t boil the water out of the battery, like the small chargers with a lightbulb in the circuit do.

Re: Magneto battery charger
 

Fun Projects (now Birdhaven) produced such a charger - might give Birdhaven a jingle.

Re: Magneto battery charger
 

Most magnetos generate an alternating current. Since they are residual magnets, they are somewhat limited in current output. AC power would require a rectifier set up to change the output to direct current. The pick up coils can limit the voltage output depending on how they are set up. I'm not sure what voltage a model T magneto puts out normally and the output can be pulsating direct current if there is a breaker set up but they usually use trembler coils to do that job.

Many of the old British motorcycles used a residual magnet alternator and they had a rectifier set that worked fairly well. the output was usually around 6 to 8 amps. These old Lucas units are a lot smaller than a model T set up. They had both 6 and 12-volt units. Japanese bikes were mostly 12-volt.

Will the car still be using the magneto for ignition?

Re: Magneto battery charger
 

All it is; a diode and 12 volt brake light bulb. Of course the Fun Project type might have a little more to it.

https://www.modeltford.com/item/HOT-SHOT-C.aspx

Re: Magneto battery charger
 

The diode in that kit will kill half of the AC wave for a half wave AC which is like a pulsating direct current. The bulb kills off some of the extra voltage since I think the Model T magneto can generate up to near 28 volts. It's not ideal but it will function. The battery might get overcharged to a certain degree. If it's a sealed one, it might not last as long as intended but it would charge it. A diode bridge with a Zener diode dump would likely do a better job if it is correct with the end result parameters.

Re: Magneto battery charger
 

Probably not- the car idles more smoothly running on a 12 volt battery.

Re: Magneto battery charger
 

We already have the Fun Project kit - the problem with it, as Rotorwrench points out is that the DC voltage the kit produces is not only very noisy (ie - not filtered to smooth out the AC pulses), it’s unregulated, and has boiled the battery cells dry on a long run - since it produces almost 30 volts at 2200 rpm.

Re: Magneto battery charger
 

I don't believe the Fun Project's charger was ever intended for charging a lead acid battery - more for a SLA or Hot Shot type.

Re: Magneto battery charger
 

The RPM's that was posted above are well above the average T operating in the 1400-1500 range and might be ok for the mag battery charger operating in the lower RPM range. A good mag should/could be making about 35 V-AC at around 1500 RPM. There are people that charge wet cell batteries using the mag. If you are going to be operating in the higher RPM range for extended time you might think about a left side mounted gen or alternator.

https://www.modeltford.com/item/5119ALTE.aspx
https://www.modeltford.com/item/5119ALTL.aspx
(Drivers side being US cars :) )

Re: Magneto battery charger
 

I built a full-wave rectifier circuit with an RC filter section consisting of 2 220uF capacitors with a 10 watt 10 ohm resister between the positive leads on the capacitors. At the output of the RC filter section, I have a 5-watt 14-volt zener diode to limit output to 14 volts to charge the 12 volt battery. We confirmed that the circuit works when connected to the Model T magneto - we measure 14 V DC.

However, when we connect the output of my converter circuit to the battery, output drops to 12 V - probably because the battery (motorcycle battery) has such a hugh reservoir of current. We probably need to connect an ammeter in series with the battery to see if any current is actually flowing to the battery to charge it.

Today, we ran another experiment - connected a Fun Projects 12 V regulator to the car and made the following observations.....with no charger connected, the car runs very smoothly on the battery. When it is switched to magneto, the engine rpm immediately drop and the engine does not run as smoothly. With the Fun Projects regulator connected, the engine continues to run smoothly when switched to magneto. However, we cannot tell if the battery is charging. An ammeter connected in series with the regulator and battery showed no current flow. I’m very puzzled....

Can anyone offer any insights ? From my point of view as someone who has worked with electronics for over 40 years, rectifying an AC signal into useable DC should be a very simple thing to do.

Re: Magneto battery charger
 

If the battery is fully charged, it may not put out much amperage. It still shares load with the battery while charging. The 3-brush generators with John's FP regulator only show a charge when current draw increases such as when the lights are turned on (on electrically lighted vehicles) but it will still taper off as soon as the battery catches up. I don't know about the magneto set up though. That's a whole different ball game.