I tried to recharge my Model T magneto in place today

[Rata Road]

Latest arrival - The magneto was working fine except at about 800 - 1,000 rpm range the motor would die off slightly when switching from Batt to Mag (12 v battery in this car).

In my other T's the motor speeds up slightly when switched to Mag (one 6v other 12v) around this rev range.

So today I put a Magneto voltmeter on to check. Book says 5 V at idle and 20 to 30 V at high revs is the target. Mine was putting out exactly this but I wasn't happy with the drop off in revs so I decided to recharge.

I used the compass on the Hogshead method which I find really hard to get the correct north, tried for ages and must have got it wrong.

I have used this method twice before over the years with great success even though I struggle to find North exactly. As before I placed 3 good 12v Batteries in series.

 

Didn't work this time as I completely removed the charge from the magneto! 

Like no reading on the meter and the motor cut out when switched from Batt to Mag!

Oh no, I was gutted.

I remember reading a different method from on the T forum so I tried that.

Removed the trans cover and turn the motor over until you get 2 brass screws on the mag inline & parallel to the floor. That was easy to do compared with the compass method.

Then spark the Trans the same way as before except remove the Mag post and place a insulated bolt in the Magneto post hole. Gave it 6 sparks, then refitted the magneto post in the hole and screwed it down and gave it another 6 sparks on the Trans.

Both times placing the positive lead on the bolt (then mag post) and sparked with the negative lead.

Fingers crossed I got it ready for a test and wow what a reading.

It doesn't die off now at any revs.

Video link attached. At normal idle it is 10v (drops back at close to stall idle) and it goes off the gauge at high rev.

Went for a test drive and the car now drives better than before, perfect!

 

 

[Fordy]

So.... For the non-T Ford guys is this like flashing a generator to re magnetize the pole shoes for negative / positive earth? Are the spark plugs fired directly off that voltage? I have never understood T Ford ignitions - where do trembler coils etc come into play? Indulge a village idiot on the subject please?

Steve

[Pete O]

2 hours ago, Fordy said:

So.... For the non-T Ford guys is this like flashing a generator to re magnetize the pole shoes for negative / positive earth? Are the spark plugs fired directly off that voltage? I have never understood T Ford ignitions - where do trembler coils etc come into play? Indulge a village idiot on the subject please?

Steve

Kind of.  The Model T magneto has V shaped  magnets attached to the flywheel and coils attached to the back of the engine block.  As the flywheel turns and the magnets pass by the coils it induces an AC current as the + and - poles of the magnets pass the coils.  It's just like a modern lawnmower, but there's like 16 magnets and coils rather than just 1 set.  The permanent magnets can loose their magnetism over time.  They can lose them right quick of you mistakenly hook up a power source to the magneto and cause the coils on the back of the block to become energized.  That produces a magnetic field in them that can wipe out the magnetism in the V shaped magnets. 

 

The trembler coils can be fed by a battery or by the magneto (there's a switch on the coil box).  Lots of T guys crank-start their car using a battery to power the ignition and then switch to magneto after it's running because you really have to give it a good twirl to build up enough voltage in the magneto.  The magneto can produce something like 20 volts at a high rpm which is why you get a better spark running the magneto vs. a battery.  All 4 trembler coils are always energized when the ignition is on,  fed from a common bus under the coils (from the battery or magneto).  They're hot but they are not grounded.  There is a commutator driven off the front of the camshaft which is just a rotating  ground for the trembler coils.   Each coil has a set of points on top that are operated electro-magneticly.  When each coil is sequentially grounded by the rotating commutator, the juice already in that coil begins to flow to ground, and the current sets up the magnetic field in the primary winding, and that magnetic field also causes an electro-magnet to pull open the points which breaks the circuit,  inducing a high voltage in the secondary winding from the collapsing magnetic field, and directly off to the spark plug that high voltage goes. The collapsed magnetic field turns off the electro-magnet so the points on the coil close, which sets the whole  cycle in motion again.  You can get a few sparks each time the commutator grounds the coil, but the first one is strongest (because the coil has had more soak time for that first spark) and most critical for proper spark timing. Those quickly opening and closing points causes that trademark buzz you hear in the T ignition.

 

[Mark Gregush]

Not like changing the polarity in a generator. This is actually rebuilding the magnet strength keeping the same polarity. Depending on engine speed, the magneto output can be anywhere from 0 to 30+ volts AC.

The plugs are fired off the coils just like any car with a single coil/points setup. Charge is built up in the primary winding, electromagnetic force opening the points when the charge reaches about 1.5 amps in the primary, dumped into the secondary windings and fires the plug. It's just that there are 4 coils and 4 sets of points instead of single coil and points on cars with a distributor. 

[Rusty_OToole]

Model T was the first car with an alternator. A permanent magnet alternator as found on many motorcycles. There are permanent magnets in the flywheel, that produce electricity when they swing past coils of wire that surround the flywheel.

The magnets lose their magnetism over time. You can recharge them by putting them in a strong magnetic field. This is done with electromagnets. The coils in the car will act as electromagnets if you feed DC electricity to them. I mean the coils of the alternator, these are completely separate from the ignition coils.

You have to have the magnets lined up exactly right with the electromagnets or it won't work. This is what crossed up  Rata road at first.

[Jack Bennett]

Hi Rata Road…….Thanks for your highly descriptive, end very detailed recount of your encounter with the magneto of your Model T.

When I read posts of this nature I always leave with a taste in my mouth sort of like…”Golly, I learned something I may never use, but it sure is good having it in my mental library”.

In this case, I got a taste like “Golly, I learned something I am now certain I will never use, but, it is likely to get stuck on the shelf of my mental library”.

I engaged in an argument with myself as to whether I should buy a Model T, or stay with a hopelessly destroyed, but more conventional, model of car to undertake as my next reanimation project. 
Your post confirms my decision to go with the hulk of a 1929 Fargo Packet Panel truck, and reminds me as to why I have not bought a Model T.

Just kidding of course. There is no information which isn’t valuable to us old car fans and I do appreciate you sharing it.

BUT, that doesn’t even imply that I will ever own a Model T.

Jack

 

[Rata Road]

Hi Jack - I have 10 classic/vintage cars all drivable. 3 of them are Model T's for a reason.

They are easy to work on, very reliable, lots of fun. The real benefit is every part is available new and from several suppliers plus the parts are cheaper than any of my other cars. The Model T forum is excellent for guidance.

I realize my post will not help members with other makes but could be a huge help to a T owner going forward and perhaps owners of other Veteran brands. I have met one guy who paid thousands to get his motor/trans removed to allow access to get his Magneto recharged when it can be done to a high quality for free.

I enjoy reading posts about cars I will never own, they are all interesting to me.

 

Kevin