Some of you might have tried this at home.
So i tried to make a magneto charger, i was told to use a light bulb and a diode. The diode used came from an old radio and i am not sure how many amps it handles but it is clearly not enough there is nearly nothing showing on the ammeter but the bulb glows brightly at speed.
Should i add extra diodes?
You'll need a pile of radio diodes to charge magnets.
I'm guessing an instantaneous draw of around a 100 amps or more.
Do you have a friend with a DC welder?
Kep,
You need a "full wave" rectifier which takes 4 diodes, see image below. The diodes should be capable of blocking the full peak voltage that the mag puts out plus some, around 40 VDC. They should also be capable of passing the current you are expecting plus some, say 20 amps. You can buy a full wave rectifier already wired up in one unit.
You will also need a way to control the voltage, which is the purpose of the light bulb. Measure the output DC voltage without it hooked to anything and then put different bulbs in series until you get the current and voltage you want. Use a meter.
Usually a capacitor is used across the output to smooth out the wave form, but the battery will act as a capacitor.
Neil
Radio Shack
NTE NTE53016 Silicon Bridge Rectifier 200V 50AModel: NTE53016 | Catalog #: 55052170
schuh
For those of us less informed, and totally oblivious to how the mysteries of electronics work...
Could someone who considers this stuff 'duck soup' please show a real schematic? Like mag post to battery and everything in between? That double 'in' and double 'out' shown in Neil's post just makes absolutely no sense to us uniformed.
(This from the guy who is pretty good at a lot of things but also still gets confused on third brush generator settings no matter how many times he tries to comprehend what is going on...a blown fuse he understands, needing wire sizes that don't get hot or don't have too much voltage drop he understands, using a voltmeter he understands, Ohm's law is plug-n-play, he can still read a resistor banding and know what he has...but when your Dad was the electronic guru for first Brewster Aircraft and then on the government payroll from '42 on for whacky things like the space program Centrifuge and for Listening Posts 'for the trail'...he made so much of this stuff 2nd nature 'duck soup' around the house that I never wasted brain matter to understand and this guy now has no comprehension on this sort of 'stuff' )
On the surface I would say it would likely be much cheaper, make more sense and easier to use three 12 volt auto batteries or a DC welder. Charging a mag is not a regular maintenance procedure but a rare operation to get a weak mag operating till proper repairs can be made at a later date.
However I see that the 200V 50A that schuh listed can be bought for $4.72 on eBay.
http://www.ebay.com/itm/NTE-NTE53016-Silicon-Bridge-Rectifier-200V-50A-NTE53016- /160882249381
I don't know if it would work.
Jim
George
Looking at Niels diagram above:
Connect the bottom "in" wire to ground and the top "in" wire to the mag post.
Connect the bottom "out" wire to ground.
The "top" out wire is then pulsating DC and can be connected to some sort of regulator to keep the battery charged.
For 12v systems any kind of modern solid state voltage regulator (read as cheap !)would work well. I have little experience with 6v regulators but they should be available.
Cheers
schuh
Kep
You need one diode, a light bulb, some wire and an appropriate bulb socket. All this is supplied in the $25 FunProjects battery charger kit.
A bridge rectifier is a waste of money and enhances your chances of diode failure by a factor of four AND if you selected the wrong bulb (that limits reverse current into your magneto) discharged go the magnets.
This is a simple circuit, but proper engineering of the components is important for reliability and safety.
Ron the Coilman
Craig & Jim - this is not about charging the magneto magnets, it's about using the output from the magneto to charge a battery while driving if you haven't got a generator
Thanks Roger, that would make more sense. Here is an old thread on that subject:
http://www.mtfca.com/discus/messages/29/23876.html
Jim
A schematic for hooking up a rectifier and regulator.
Cheers
schuh
Ron
Modern full wave rectifiers are very reliable if sized correctly and the Radio Shack unit should be way overrated.
The bulb mentioned is only a crude current limiter. A modern solid state voltage regulator is more efficient and will ensure that no mater what the load, voltage will never exceed 13.8 volts (approximately).
The components are relatively cheap.
schuh
Bud
From an engineering point of view the "best" electrical circuit for any application is the one with the fewest number of properly sized components and accomplish the required task.
In my view all the bridge rectifier and regulator do is add cost, unnecessary complication and increase failure rates.
Ron the Coilman
schuh, your circuit is not as good as the Fun Projects design for a couple of reasons. One, yours is shorting 1/2 of the cycles of the mag to ground. These may be needed for ignition. Two, yours is shorting any voltage over the voltage regulator voltage of the other 1/2 of the cycle to ground. The Fun Projects design only diminishes 1/2 of the cycles, and only to the extent of what is pulled through the current limiter (the lightbulb).
I believe there are two separate issues being discussed here - a magneto powered battery charger and a magnet charger ?
The only way I can see to set up a full wave rectifier on a T mag would be to isolate the mag ground somehow from the chassis ground... Just not practical. The best one can achieve is a half wave output, which might charge a battery if engine speed is kept high enough.
The problem with using a bridge rectifier is that 'more' is not always 'better'. Using a bridge rectifier as Ron said increases your failure rate. Usually, when a diode fails - it fails as an electrical short. In other words, it turns into a straight piece of wire. Now you have a possible short on your magneto and using said bridge increases the chance of problems. Diodes may also fail open-circuited but that will be due to a manufacturing issue and it won't cause your engine to stall - but the battery you're trying to charge won't get a charge. So keep it simple. Why the lamp is on the circuit ... it's a current limiter and a fuse, and if it's somewhere visible, you may be able to shut off the engine before something lets the magic smoke out.
Garnet
Tom
Its just the opposite. A bridge rectifier uses both halves of a ac waveform. A single diode uses only half the cycle and is not as efficient.
Those who believe a bridge rectifier is more prone to failure had better not buy any more electronic equipment. Virtually every quality piece of electronics with a power supply in it uses bridge rectifiers for efficiency.
Modern day alternators use between 9 and 12 diodes in a modified bridge circuit.
If simplicity is your object then the old diode and bulb circuit is the way to go. If efficiency and better charging are your object a bridge rectifier and solid state voltage regulator will do a better job of keeping battery levels up.
BTW last time I bought a VR it was around $15 & $5 for the bridge. Prices may have changed but certainly competitive with the fun projects system and certainly more efficient.
Cheers
schuh
There's quite a difference in the power requirements of a vcr and a Model T powered battery charger Bud. I'm sure Kep isn't trying to run a big screen TV in the backseat for the kids and he just wants a simple charger to keep a battery topped up without drawing excessive current from the Ford magneto.
Adding more diodes gives you less voltage Kep, as each diode causes a voltage drop depending on the diode's construction (germanium or silicon). If your bulb is glowing, you're drawing too much current through it for your purpose.
Garnet
(30+ years electronics and dangerous)
Wow i was not expecting any where near this much response, thanks guys. Maybe one day i will get the proper fun projects charger but for the moment i was hoping i could use the 5 odd diodes laying around in parallel. With a bridge rectifier and a big power diode in series i guess i could take advantage of the full wave output.
Used to be good at this electronics stuff 15 years ago, Haven't even seen a book on it since then.. guess i have some catching up to do.
This guy used just a diode and a light bulb http://youtu.be/Bw8TDDGmYcs not sure if he used 6 or 12 volt. Maybe i should use 12?
Like how he starts it?
schuh said:"Tom
Its just the opposite. A bridge rectifier uses both halves of a ac waveform. A single diode uses only half the cycle and is not as efficient. "
That can be true, but not the way you've shown it. What I said was correct.
Tom
You ARE correct in this instance. The circuit will NOT work as shown because one end of the magneto is grounded.
In order for it to work the way I described it the other end of the magneto winding would have to be directly connected to the bridge, as it is in a modern alternator.
Mea culpa, mea culpa .............
schuh
If you want a full wave rectifier from the mag then you need to isolate it with a transformer. Such a transformer will need to cover the frequency range of the mag, which would be a 400Hz device. That should be possible. Think the half wave, non isolted approach is best.
Shuh,
I have been there - done that - smoked it.
The reason a bridge rectifier will not work on a Model T is because the mag is grounded on one side. In order to take full advantage of both sides of the sinewave you must use an isolation transformer as I did on my 1916.
Be_Zero_Be
Another advantage of B0Bs design with the transformer is, that the coils in the transformer will limit whatever spikes are generated by the ignition coils.
I've toasted a LED lamp because of them.