My terrible magneto-battery charger

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Model T Ford Forum: Forum 2018: My terrible magneto-battery charger
Top of pagePrevious messageNext messageBottom of page Link to this message  By kep on Monday, August 06, 2018 - 03:15 am:

Folded & soldered some of the legs on a bridge diode down & soldered them together.

Screwed to the generator and magneto wires, after this I put a screw through the hole that held a layer of insulation on the firewall side & an aluminium heatsink on the other. No thermal paste, wouldn't even know where to find that.

Most of the time I see nothing on the ammeter. At flat out speed I was getting 4 amps charge.
Probably one small problem... Should the diode burn out & short internally the battery would discharge through the magneto & kill the magnets, and flatten my battery.
I might add a light bulb, but where to put it that it won't be in the way i'm not sure..


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jim Davis. Tomball Texas on Monday, August 06, 2018 - 10:59 am:

Thermal Compound! Most electronic supply houses such as All Electronics carry it. some auto supply houses may also have it as well. used between regulator and alternator heat sink in older alternators.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jay - In Northern California on Monday, August 06, 2018 - 11:22 am:

Light bulb?? We don't need no stinking light bulb!!

Put one of these on your dash and your magneto will be fine. :-) :-)


All joking aside I wouldn't risk toasting my magneto running without the light bulb in the circuit.


Top of pagePrevious messageNext messageBottom of page Link to this message  By kep on Monday, August 06, 2018 - 04:16 pm:

That heat sink gets rather warm....


Top of pagePrevious messageNext messageBottom of page Link to this message  By John F. Regan on Monday, August 06, 2018 - 06:48 pm:

Its worse than just demagnetizing your magnets when that diode shorts and that is for sure the way it will fail if/when it fails. If you are using a 12V battery and it is more than a very small storage battery, the peak current could hit a value over 50 amps and that could heat up your mag ring enough to cause the windings to fall off the frame and get into your motor. Magneto ring DC resistance is about .25 ohms TOTAL so 12.6 Volts could provide 12.6/.25= 50 amps reduced only by the resistance of the wires that you have in the connection. A single diode with no fuse is playing very very high stakes poker. Adding a fuse only allows the damage to be magnet discharge unless the fuse is too heavy in which case you probably end up with discharged magnets, open or damaged mag ring and boiled battery due to excessive discharge rate. It is not far fetched to even suggest the wires could turn red hot and fire up the T with a whole new meaning to the word fire. Not something to try let alone make jokes about. I would implore you NOT to proceed but I suspect some simply have to learn the hard way.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Neil Haywood on Monday, August 06, 2018 - 07:56 pm:

Add the bulb like I did. Use the rear light



Here is the diode in my battery box


Top of pagePrevious messageNext messageBottom of page Link to this message  By kep on Thursday, September 06, 2018 - 12:00 am:

Finally found one.

Where can I put this light socket that doesn't look like a senior citizen duct taped a random light on their dash? Want to be able to see it when I shut the engine off but not have it in my face.

Also, if I use the bulb as a current limiter for if the diode fails, I could use a diode to turn it on only when the current is flowing backward. But the problem is if both diodes fail I would never know, and wouldn't know which one had failed first...


Top of pagePrevious messageNext messageBottom of page Link to this message  By John F. Regan on Thursday, September 06, 2018 - 12:49 am:

Kep:

Bad idea since the added diode is shorting out the bulb during the "normal" operation so you don't have any current limiting action by the bulb. Keep it simple and park the bulb fastening it to the dash under the floor board but down where you can look through a pedal slot and see it.


Top of pagePrevious messageNext messageBottom of page Link to this message  By kep on Saturday, September 15, 2018 - 03:27 am:

Found this gauge. How do i wire it up?
Currently tried wiring it between the magneto post and the terminal block produces 18 volts at a high idle when feeding the battery via the diode, and when turned to magneto the needle swings wildly from 0 to 30 and almost no spark is produced, the engine backfires & winds down to stop.
As my magneto isn't healthy i'm guessing i have this wired incorrectly. How does one normally wires these?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Neil Kaminar on Saturday, September 15, 2018 - 08:07 am:

I don't think the mag was ever meant to charge a battery. A friend had a battery charger conversion on his car and it never worked very well. It did not put out enough current, especially to charge the battery and run the lights. He finally went to a belt driven generator on his 1915 engine, which as you know does not have the generator mounting front plate.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Steve Jelf, Parkerfield KS on Saturday, September 15, 2018 - 10:08 am:


I used John's design for my battery charger and mounted it here. I've never had to use a separate charger for my little six volt battery, which powers only the coils for starting and my phone charger as I drive. The only trouble I've ever had with the setup was a wire that became frayed and got hot from grounding. That was only because of where I routed the wire, not the charger. I will be adding a fuse at the battery to make sure that doesn't happen again. If I get caught out after dark I use the mag headlights, which are almost adequate. :-) I do have magnetic trailer lights converted to LED for tail lights, and they do run off the battery. Again, no problem so far keeping the battery up. I don't care for night driving, and I do as little of it as possible.

Here's my page about the battery and the charger.

http://dauntlessgeezer.com/DG102.html


Top of pagePrevious messageNext messageBottom of page Link to this message  By Gene Carrothers Huntington Beach on Saturday, September 15, 2018 - 01:51 pm:

Steve, I use John's recommended location for my light bulb. The white light up in your face would certainly be distracting your vision. I always get a kick out of remarking to passengers at night about a fire under the floorboards though.

BTW Thanks for all your posts about your recent trip and hope your car is back on the road!

YMMV


Top of pagePrevious messageNext messageBottom of page Link to this message  By John F. Regan on Saturday, September 15, 2018 - 02:23 pm:

Neil:

You are correct that the simple magneto charger will NOT keep up with "typical" DC headlight bulbs that are running off the battery that is being charged. Most 6V DC headlight bulbs are in the 8-12 amp range and 12V bulbs are about half of that. Both setups exceed the charge capability of the magneto simple charger. The assumption with the simple charger is that there must be enough unused power from the magneto left over for the coils. If your needs are not steady and you drive most of the time during the day then on my son's car we simply put a group 1 regular model T 6V battery in the car for starting and lighting. There is no way you can run that battery down on one evenings drive if the battery is fully charged when you start out. We found that on typical week long tours that the battery was always "up" at the end of the days drive (typically 60-100 miles) and even when we did operated his headlights during the evening before when we went to a local restaurant after dark, the simple charger restored his battery to full charge by the end of the next days tour. Only if you use the lights just before you put the car away for awhile do you then need to put an external charger on that battery. Right now that battery is well beyond 5 years old and has not needed anything in the way of attention and every time I have checked it - it is always fully charged. So it really depends on your driving and whether you "regularly" drive at night or "rarely" drive at night.


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