Magneto battery charger

[Mountainrider]

Does it matter if the diode is before or after the the 1156 bulb? I made mine magneto, bulb, diode, then battery. Searching old threads it’s say magneto, diode, bulb, then battery.

http://www.mtfca.com/discus/messages/411944/494541.jpg

Been running it a year that way. No I’ll effects that I can tell.

[Piewagon]

The bulb and the diode are in series so that part doesn't matter but you MUST make sure the diode is correctly installed since the cathode end (striped "banded" end) must point to the battery positive connection. The anode end of that diode must be pointed at the magneto connection. If you want to see a simpler version of this same device, I make them up with a printed circuit board and all parts mounted such that you only have to slip the thing onto the 2 ends of the coil box connections at the bottom. These are the Magneto (MAG) and Battery (BAT) connections that are the bottom 2 connections of the 10 connections on the engine side of the coil box. I will attempt to attach a picture of the device all built and ready to install. You can put it on or take it off in a few minutes with no wiring alterations other than removing the outer thumb nut on each side, then slide the Printed Wiring Board in place and reinstall the thumb nuts. If there is no picture posted here then send me an email or PM and I will send you a picture of the device.

[Loftfield]

Query: My brass T's do not have starter or generator (Armstrong starter only) but I keep a lead/acid battery for starting. Will these devices keep that battery charged? Will the battery be over-charged?

[Mountainrider]

I have a 12 volt motorcycle battery install for my head lights and for hand crank starting. I only have to put in on the battery tender if it’s a long night drive. I am using LED bulbs.

[Piewagon]

Tom:
Yes they are actually designed for just that purpose. Choice of bulb can increase or decrease charge rate depending on the Amp-hour rating and voltage of the battery you use. Contact me via email for more info.

[Fordwright]

For a considerable time, the charging rate was controlled by the operator, either by switching it on and off, or selecting between a high and low charge rate. Watching the brightness of the lights was about the only indication you had for the voltage of the battery. A simple regulator can be made using a resistor and a relay. While the ignition is switched on, a parallel switch can activate the regulator which has been adjusted to cut out charging once the battery voltage reaches full charge. Much simpler nowadays using off the shelf parts, but it's the owner's choice how authentic they want to keep their vehicle.

[Steve Jelf]

Here's how I charge the battery in my 1915 runabout. If my memory of the dim and distant past is right, I learned it from John Regan.

http://dauntlessgeezer.com/DG102.html

[Fordwright]

HSBC2.jpgThe bulb and the diode are in series so that part doesn't matter but you MUST make sure the diode is correctly installed since the cathode end (striped "banded" end) must point to the battery positive connection. The anode end of that diode must be pointed at the magneto connection. If you want to see a simpler version of this same device, I make them up with a printed circuit board and all parts mounted such that you only have to slip the thing onto the 2 ends of the coil box connections at the bottom. These are the Magneto (MAG) and Battery (BAT) connections that are the bottom 2 connections of the 10 connections on the engine side of the coil box. I will attempt to attach a picture of the device all built and ready to install. You can put it on or take it off in a few minutes with no wiring alterations other than removing the outer thumb nut on each side, then slide the Printed Wiring Board in place and reinstall the thumb nuts. If there is no picture posted here then send me an email or PM and I will send you a picture of the device.

An elegant and simple solution, but the charging current would double if you used a bridge rectifier.
https://canada.newark.com/solid-state/k ... -Discretes

[BE_ZERO_BE]

A Bridge Rectifier will not directly replace the single diode in this type of charger.
One leg of the bridge will be a short to ground.
In order to use a bridge rectifier, the magneto output must be isolated by a one to one isolation transformer.
Then a bridge rectifier will give you full wave output.
I have this arrangement in my '16 T.
It works great.

[SurfCityGene]

Bob, You want to show us how you hooked up that isolation transformer on that grounded leg? Sounds very interesting.

[BE_ZERO_BE]

Here is a sketch of my setup.
 

[Oldav8tor]

I bought the FP kit but never installed it. I run a 12 volt battery for starter and lights but also have a USB adapter that I use to power an old GPS that I use for a speedometer.

My question is, will this charger be safe to use with my USB adapter and GPS?

[Fordwright]

I bought the FP kit but never installed it. I run a 12 volt battery for starter and lights but also have a USB adapter that I use to power an old GPS that I use for a speedometer.

My question is, will this charger be safe to use with my USB adapter and GPS?

To be on the safe side, make sure the USB circuit is connected to the battery at all times, and install some line filtering to protect against voltage spikes.

[Oldav8tor]

Let's see if I have this right. John's charger is essentially a half-wave rectifier so it will output pulsing DC at whatever voltage the magneto is putting out at the time.

I have a USB adapter in my Model T that was originally designed to be installed in a boat. I assume it drops the input voltage (12 in my case) to 5 volts. I use it to run my old Garmin GPS/Speedometer and occasionally charge a cellphone.

My concern is whether the USB adapter can deal with the higher voltage pulses from the magneto without failing.... I also wonder if the pulses will put noise on the line that might interfere with the GPS. Currently the GPS is unaffected by the magneto a foot or so away. Does anyone have any experience with something similar?

[Fordwright]

The model T flywheel magneto was never intended as a charging system for the battery. It puts out AC current at voltages between about 5 and 30 volts, depending on RPM and load. It's not particularly spiky power, but I doubt the power regulator in your USB socket would be able to handle such a range of voltages. That's why I suggested connecting it to the battery instead, which acts as bit of a ballast, keeping the voltage near the 12-14V range.

The Model T trembler coil ignition was designed to operate on a wide range of voltages on either AC or DC power, but the same can not be said for modern electronic devices.

[Oldav8tor]

Greg,
The USB adapter is connected to a 12 volt battery as is the starter, LED lights and battery post on the coil box. I just assumed if we used the above charging circuit to charge said battery that the higher magneto voltages would be added to the mix, albeit as pulsing half-wave DC.

[Fordwright]

Greg,
The USB adapter is connected to a 12 volt battery as is the starter, LED lights and battery post on the coil box. I just assumed if we used the above charging circuit to charge said battery that the higher magneto voltages would be added to the mix, albeit as pulsing half-wave DC.

Well, that's good, because the raw DC rectified off the magneto would probably be too much for your USB adapter. Glad to hear you have a battery, but do yourself a favor and install a voltmeter and a charging switch. There's no regulator in that circuit, so you'll have to monitor it yourself and switch it off when the battery voltage gets too high (I'd guess at about 14.5V).

[Piewagon]

What a lot of folks don't seem to understand is that the light bulb acts as a current limiter to prevent the charging current from getting large enough to overcharge a small battery or large enough to pull the magneto down so the car won't run on magneto. This device was written up many years ago in the MTFCA elecrical manual and it is essentially a copy of the way the phone company used to limit the current to a given phone that was powered through the phone line. They put bulbs in series at the central office and those bulbs would light up bright if there was a short on the line but otherwise simply limited the amount of current that was available to the consumer's telephone. Telephones operated on very large 48 volt storage batteries and for many years they were essentially just a larger version of the batteries that were being used in our cars. Those batteries typically last for more than 20 years unless there was some major calamity that drained them completely.

The typical cell phone has a small voltage battery in it that is often about 3V or so. It is charged from a 5V source in the USB which is a regulated drop from the cars 12V supply. That makes it all battery derived.

The small charger I pictured above uses a lamp as a current limiter and a single diode to provide some charging current to the 6V or 12V battery that the car might have in it. If you rarely drive at night this charger will charge your battery with a small current that is there the whole time the motor is running. I have had them on my brass cars and never had a battery go bad using only this small charger to put back the current taken from the battery by a motor that is in very good tune and fires right up on the first spin. Full wave will increase the efficiency but it really doesn't make enough MORE power that you might need to keep up with headlights and tail lights. LED's will reduce the needed charge amount but the starter will need that larger reserve of a full size battery. This small charger does not need any switch or fuse because the bulb serves as a fuse and the diode is super heavy duty for the amount of current taken.

[Fordwright]

I was referring or course, to voltage, not current. The light bulb amounts to a resistor which provides a trickle current and varies widely, depending on the brightness of the bulb. For the first second or so, before the bulb heats up, resistance is very low, allowing higher current and not providing a voltage drop across the resistor (bulb). Since the magneto is capable of generating up to 30 volts, that's probably enough time to destroy the circuitry in the USB adapter.

If all you needed were a simple trickle-charger to keep up with the battery drain of a few lights while you're out on a few jaunts in your Model T, it might be fine. You may need to experiment with all sorts of bulbs to get the right amount of charging current, but a USB adapter needs a much more stable power source than such a system can provide.

I can't speak to the possible degradation effects that a half-wave rectifier might have on the flywheel magnets. It's possible that a constant DC drain could demagnetize the magnets.

For what it's worth, it's a much better idea to power devices such as a GPS from a rechargeable battery pack, than to expose sensitive electronics to the potentially erratic and dirty power that comes from such a setup.

[Steve Jelf]

Being a near-total electronic dummy, I can't explain why anything works or doesn't. All I can do in this department is relate my own experience. John's plan with the diode and 1156 bulb keeps the little battery strapped in my frame rail charged to buzz the coils if I need it for starting. I don't think it has discharged my magnets, and so far the phone I charge off the battery hasn't been ruined. If there's a chance that a surge at startup could damage the phone, maybe I should flip on the switch only after the car is running.

[Piewagon]

Since cell phones are so common and recharging methods vary so much, the "generic" cell phone's needs with regard to charging are pretty well known and it is in ALL manufacturer's best interest that they all can be recharged in what are nearly "standard" ways. It is almost like plugging things into an AC socket. Plugs are fairly standard for each phone and it is important to understand that a CAR Battery is not just a source of power but is also literally a GIGANTIC filter capacitor. If you connect your charging device to the correct voltage and have that size battery in your car the amount of power you need to start the car coils buzzing is way more than you need to charge your phone in a reasonable time. The light bulb absorbs current spikes and unless the battery is defective it is highly unlikely that any noise will emit from the battery toward your phone while it is charging. The magneto provides enough excess power to be able to run this small charger and it just turns out that there is enough power to pretty much get by without any other charger so long as you don't have a huge high powered load on the battery at the same time like head light bulbs or 2 or more brake light bulbs. The brake light load really varies depending on where you drive. The good news is that brake light LED's are plentiful and you can pretty much hang those in triplicate and still not have much drain. Headlights really don' t have the right kind of reflectors for use with available LED's. Yes they can be bright but that is not the issue that is difficult. Whether your battery is 6V or 12V the charger will work with either but in truth you will get more charge current with 6V and also hold more discharge current in it too with a given size battery. Hook your charger source to the battery and don't worry about the charger creating noise. The frequency of the magneto is low (around 260 Hz at 50 MPH!) Easy for the battery to filter that but also easy for the current limiter bulb to soften any "spikes" that you might think are coming from the magneto toward the battery. Don't confuse ignition noise coming from your COILS as being caused by the magneto. Magneto is a source of power but the "NOISE" that makes digital meters go erratic is NOT from the magneto so much as it is from the coils.

Hope this helps.

[gtttrobinson]

Here is a sketch of my setup.
 
ISOLATION TO BRIDGE.jpg

Good evening BZB,

Would you have a parts list to go along with your drawing?

[BE_ZERO_BE]

Gerald,
My other hobby is Electronics.
I have a 50 year accumulation of parts.

Here is a suitable 50A 1000 Volt bridge rectifier.
https://www.mpja.com/50A-1KV-Bridge-Rec ... /31094+BR/

The isolation transformer was an unidentified one from my pile of transformers.

Here is a suitable transformer but you will need two of them.
It is a 115 VAC to 12 VAC, 2 Amp rated.
https://www.mpja.com/12V-4A-Center-Tapp ... 27840+TR/,

Here is how to connect two identical transformers back to back to make an isolation transformer.

This will give you about 48 VA of power to the rectifier.

[J1MGOLDEN]

Can you buy that little green strip all made up or do you have to make your own?

[BE_ZERO_BE]

Contact John Regan for that item.

[TRDxB2]

Can you buy that little green strip all made up or do you have to make your own?

The green strip is just a piece of circuit board. Most anything that provides electric insulation will work, like a wire junction box which also provides an enclosure and mounting

--

[speedytinc]

Homemade. Nothing fancy. Simple & functional.

[TRDxB2]

Homemade. Nothing fancy. Simple & functional. diode reg 3thumbnail.jpegdiode reg1thumbnail.jpeg

Yup, all that's needed. Good picture of how to wire as well!

[MKossor]

I noted the transformer Bob listed is out of stock and a bit expensive ($19 x 2 + 4.5 lbs Shipping ~$50). Here is another candidate 50VA isolation transformer that should work equally as well but only requires 1 transformer if you are looking for something to experiment with:

Available from Mouser: https://www.mouser.com/ProductDetail/Tr ... F80A%3D%3D

Available from Ebay: https://www.ebay.com/itm/-/252100975003

I just ordered one from Ebay for $23 shipping included to give it a try with a full wave bridge rectifier. This transformer has 2 primary windings and 1 secondary winding. The primary windings can be wired in parallel for a 115V input to 115V output isolation transformer (1:1) or they can be wired in series for a 230V input to 115V output isolation transformer (2:1). The series wiring (2:1 ratio) could be if interest if you have a hot magneto that produces too high of a full wave rectified output voltage for your 6V battery. The series connected primaries will effectively produce half the voltage output of the parallel connected primary windings.

[Steve Jelf]

I was recently reminded that it's best to keep high voltage (spark plug) wires away from other wires, especially if high voltage jumping to the low voltage wire can find its way to the magneto. I suspect that's why I can no longer start on mag and will need a recharge.

[ABoer]

To Day , I made this Thanks to John Regan .
Toon

[cslandry]

The bulb and single diode works just fine to trickle charge a battery. No need for a full rectifier. My battery is 12V and this has been working fine for several years. I did have the 6A diode that I originally got from FP overheat and burn out. I might have aggravated that as I had it enclosed in heat shrink tubing to look pretty. I replaced it with a 10A diode and made a heat sink to mount it and it has been fine.

[J1MGOLDEN]

You would need a transformer to make the full wave rectifier work, as one end of the Magneto Coils and the Battery goes to ground.

[Mountainrider]

Magneto to 1156 bulb in oil light
Bulb to Diode in battery box

[Fordwright]

I wouldn't risk connecting my phone to dirty power. Voltage spikes have an erosive effect on electronics, similar to the way gravel roads damage nice paint jobs. If I were serious about charging my phone in a Model T, I'd use a good power filter, an isolation transformer or a power bank.

[W Austen]

I don't know how much your time is worth, or your electrical talents, or caring about how the finished product looks. but my own experience is John Ragens can't be beat

[MKossor]

Half wave rectifying the magneto output is good but only uses the positive magneto voltage pulse so is not as efficient as full wave rectifying the output. Full wave rectifying the output makes use of both positive and negative magneto voltage pulses. The problem is the magneto output is referenced to ground and so is the load (the battery; negative ground). That shorts out one of the bridge diodes effectively resulting in half wave rectification.

But wait, there is a simple solution as Bob points out. Simply use an isolation transformer with 1:1 turns ratio (Vsecondary = Vprimary) to magnetically isolate the magneto from common ground, then you can Full wave rectify it and reference the negative output to common frame ground without issue.

ISOLATION TO BRIDGE.jpg (19.26 KiB) Viewed 8788 times

I found an inexpensive Triad N-68X 1:1 isolation transformer on ebay as mentioned earlier in this thread so figured I would try it out to see what the benefit would be in picking up the charge current. Its a simple, cleaver, straight forward, logical approach but unfortunately IT DOESN'T WORK!. There is no benefit to the added cost and complexity, in fact, their is a marked penalty imposed rendering the approach far less effective than the simple, tried and true, time tested half wave diode and 1156 bulb method. For those interested in learning why their electronics prowess failed them too, read on.

First of all, transformers are not lossless devices. They are designed for optimal efficiency at a specific operating frequency, voltage, voltage transformation ratio and load current. Core losses is a contributing factor but not the primary reason why this method fails to provide a viable means to full wave rectify the magneto output. For that, we need to look at the transformer model. Next we will use that model to create a larger model of two transformers connected back to back as Bob's schematic illustrates and lastly, we will make an equivalent model of that transformer which will expose the root cause it fails to produce the desired benefit.

25V, 1A Transformer Model
I had two Stancore 117V to 25.1V transformers (Model P-6469) on hand for measurements and experimentation I built a model for it shown in figure 1 below:
The transformer model has a primary coil L1, with resistance R1 and a secondary coil L2 with secondary resistance R2. Inductance L3 and L4 are leakage inductance that occur because the independent primary and secondary windings interact because they are wound on the same iron core. Capacitors C1 and C2 represent interwinding capacitance between the primary and secondary windings. L3, L4, C1 and C2 do not contribute significantly to the performance limitation that follows but included for completeness in building the model.

Back to Back Transformer Model
An isolation transformer is created by connecting the secondaries of two of these transformers together. Transformer 1 converts 117V to 25V then transformer 2 converts 25V back to 117V so Voutput = Vinput but Voutput is magnetically isolated from Vinput which is the property that permits us to then full wave rectify and reference what every output (positive or negative) to the input voltage without issue. Figure 2 illustrates the transformer model of Figure 1 connected back to back. The model is getting complicated so lets see if we can simplify the model by successively transferring the various resistances from each winding from input to the output until we have an equivalent transformer model with single equivalent output resistance. First we transfer the input resistance to the center connection (connected secondaries), add those series connected resistances into a total value then transfer that resistance to the output by adding it to the output (primary) resistance. The process takes a few calculations with the aid of the voltage transformation ratio N = Vs/Vp or N=Vp/Vs depending on which way we transfer the resistance; primary to secondary or secondary to primary. Since we have back to back connected transformers, we first use N=Vs/Vp and square the value (N^2) then we transfer that total resistance to the output using N=Vp/Vs and again square it (N^2). Note that the impedance transformation primary to secondary changes by the square of the respective turns ratio. Sounds complicated but really just a few simple calculations. The net result is illustrated in Figure 3.

Simplified Equivalent Model
The bottom line in Figure 3 is: The output resistance of the original transformer (1.8 Ohms) gets transformed into a much higher resistance (125) Ohms! Consider the voltages shown in Figure 3. The magneto (V2) is outputting 25V (RMS) If there were no transformer and half wave rectified, we would apply the 25V magneto pulses to the 25 Ohm load resistor R11 and have 25V/25Ohms = 1A pulses for every positive pulse from the magneto. Now look what happens with the isolation transformer. The magneto output is the same 25V gets applied to the primary of the ideal 1:1 isolation transformer so the secondary output at L10 is also 25V (RMS) BUT now we have a rather large voltage divider R10 and R11. Only 4.2V gets to the 25 Ohm load R11. The current through R11 is only 0.16A (RMS), surprise! All that work for lower output current. We can now full wave rectify the output but with the two diode losses and only 4.2V output, the battery charge current will be far far lower than the 1A half wave rectified pulses of the original, simple, tried and true, time tested method.

[dykker5502]

Mike,
don't you shortcut the ground and all your isolation transformers anyway? The battery still have the negative terminal connected to ground.

[BE_ZERO_BE]

I have since added a 6 volt starter and alternator to my ’16 T.
Let me offer my experience with the system I had.
I used a 1:1 isolation transformer feeding a bridge rectifier and connected to a 12 Volt lead acid car battery.
The transformer came out of my box of used transformers.
I have no data on it.
I had no voltage regulation system other than an ON-OFF switch to control the battery charging.
I monitored the battery voltage with a voltmeter installed where I could keep an eye on it.
As far as testing, I can only offer usage experience.
During normal driving, my battery voltage would rise from a quiescent 12.5 volts to 14.5 volts within a few miles.
At that point I would turn the charging system off.
The biggest stress test I put on my system was a 1½ hour night drive.
My headlights are 12 Volt, 50 CP.
The battery didn’t drop below 12 volts during the trip.
I was satisfied with the performance of the system for the five plus years that I had it on the car.

[speedytinc]

How many amps does the system put out @ 12v? That might give a better performance comparison over the simpler system. My single diode setup puts out 3 amps 12v.

[BE_ZERO_BE]

John,
I never did measure the current output of my system.
Bob

[Fordwright]

Never hook up modern electronics to the Model T electric system.
Like building a day care center in a lion cage.