Generators - I learned something new today.

[Been Here Before]

Here are a few crude schematics showing the 3 brush generator and some common hookups. Note that these schematics avoid showing the starting system which, in practice, you will likely find between the battery and the ammeter.

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https://www.yesterdaystractors.com/articles/artint4.htm

[Scott_Conger]

they avoid showing the starting system, because they are showing the charging system

the starting system in no way involves or is connected to an ammeter and is an entirely different circuit

since the article you pulled these from, was describing the difference of 2 and 3 brush generators and their regulation, including a starter would in no way affect the charging system or add to the readers understanding of the charging system

[Been Here Before]

they avoid showing the starting system, because they are showing the charging system

The starting system in no way involves or is connected to an ammeter and is an entirely different circuit

since the article you pulled these from, was describing the difference of 2 and 3 brush generators and their regulation, including a starter would in no way affect the charging system or add to the readers understanding of the charging system

The electrical diagrams I have seen, show that there is a direct circuit from the battery to the starter, via a switch. There apparently, in early design to show current draw of the starter. Too should the ammeter malfunction there would be no current to the starter. So there was a direct circuit to the starter. Besides the starter is not part of the charging circuit. Unless the starter and generator are one unit, as related to an early Dodge or Buick, or even aircraft related. The possibly the ammeter is in the circuit.

[jab35]

The schematics shown are for + ground, Just FYI.

The article cited is a good read for background knowledge and it presents correct information in a straight-forward manner. While the principles are applicable, some important 'details' are different in the Model T. Model T is (-) ground with 3rd brush grounded inside the generator (the top figure) but with (-) battery ground.

Note that in the mtfca Electrical System handbook (pg 17-18), reference is made to a generator circuit modification that allows the driver to vary generator output by varying the resistance in the 3rd brush connection. The mtfca author suggests installing a 25W, 25 Ohm Potentiometer in the 3rd brush circuit to permit adjusting charging rate externally, without adjusting the position of the 3rd brush. This modification replaces the 'light switch' resistor circuit shown in the bottom figure, with a variable resistor (rheostat). I'm not recommending such a modification, would NEVER do it to my T, just reporting. YMMV, jb

[Scott_Conger]

Too should the ammeter malfunction there would be no current to the starter.

Really?!?
Honestly, you really think this?
Does the ammeter also read +/- 0-200A?

I edited my last post on cut-outs, because it was pretty unflattering and did not meet the spirit of the Forum, but when you come up with statements like this...woof...

[Been Here Before]

Too should the ammeter malfunction there would be no current to the starter.

Really?!?
Honestly, you really think this?
Does the ammeter also read +/- 0-200A?

I edited my last post on cut-outs, because it was pretty unflattering and did not meet the spirit of the Forum, but when you come up with statements like this...woof...

Now I know I missed the MEMO! All things being equal, the amp gauge of a Ford T does not go to 200 +/- amperes. If the current and voltage of the starter pass through the meter, and the meter burns out the circuit is open and no voltage to the starter. And I like you are offering an opinion based on life experiences. So

[Jerry VanOoteghem]

George,

You state, " If the current and voltage of the starter pass through the meter, and the meter burns out the circuit is open and no voltage to the starter."

What you say is technically true, however it has nothing whatsoever to do with a Model T, since this is NOT how a Model T is wired. To state what you do, really confuses things for those trying to learn about their cars.

[John kuehn]

My 54 NAA Ford tractor is a positive ground system sort of what is being shown.
Model T’s have a negative grounded system like is mentioned in the article.
It would be a good idea to read the Ford brochure that in the post that states Model T’s have a negative grounded system. When in doubt always read the instructions.

[A Whiteman]

Hi George,
Thanks for posting the diagrams.
Like Scott says, the forum is great for new owners to learn about their Ts and helps chaps like me to learn more and correct some mis-understood things too. In that spirit, instead of saying why something is wrong, here is an attempt to explain how it is for new owners:

As explained above, the starter circuit is independent from the charging circuit, and starter current does not go near the ammeter or generator wiring.

What MAY cause some confusion is that there is actually a physical interface between the starter and charging circuits. Yes, indeed.

The power comes from the battery to the starter switch by way of the heavy cable.
The wiring for the ammeter 'live' side does go directly right to the battery as shown in the simplified diagrams posted above, but in physical terms, it does so through being connected to the post on the 'live' side' of the starter switch.

While this may appear to connect the starter and charging system physically, in electrical terms, they remain separate. Ford probably used this hook up as it meant only 1 wire had to go right back to the battery, and shortened the ammeter 'live' wire by a couple of feet. That would add up to a lot of wire over the production life of the T. (pennies saved here and there helped lower the price).

Sometimes simplified drawings are good to get an idea across, but should not be relied upon for 'accuracy'. Looking at the above diagram that shows the starter and charging systems, you can see that the starter wires (thick black lines lower left) go from battery to the starter switch to the starter motor and back to ground only. They don't carry current with the charging circuit.

In the drawing you can see where the charging circuit draws its 'live' side from the starter switch 'live' post, which is in electrical terms is the same as carrying the wire right to the battery even though in physical terms it shares a common live cable with the starter - ONLY as far as the starter switch. Pushing the starter switch does not affect the circuit to the generator in any way, nor can the generator circuit affect the starter in any way.

Hope this is helpful to anyone not familiar with the topic..

As an afterthought, if you want to install a fuse in the T wiring, then the ammeter lead from the starter switch to the 'live' side of the ammeter is the place to do so, as it covers the complete electrical system with one fuse (except the starter!). You can put the fuse near the starter switch so it can be easily got to under the floor board.