MTFCA Forum

I need some help - I'm not much on Model T charging circuits.

Our 1924 T has two 6-volt batteries, and runs on six volts. She always runs on the battery, my not yet being ready to tackle the non-functioning magneto circuit. She is starting and running well, but the ammeter reads negative about 5 amps, with no lights on, and stays at negative 5 amps independent of the RPM. After half an hour or so the voltage drops to the point that she will not restart if stalled. This change was sudden; charging was until recently dependent on RPM, although I had noticed that turning on the lights made a positive ammeter reading hard to obtain.

Is there any alternative to the generator being bad? Could the cut out switch be stuck? Is there any possible cause that is repairable before she is due to carry the Grand Marshal in a parade Saturday?

Thanks in advance for any assistance.

does it show a 5A discharge constantly or only when running?
why does it have 2 batteries?

a fully charged automotive battery should run a "T" for hours with a 5A discharge...there are more things going on with this car than has been described

What sort of batteries are you using, and how are they connected?
It sounds as if your system has quit charging. That could be due to a problem with the wiring, the generator, or the cutout relay. It's not out of the question that it cold be a battery problem.

tkeithlu wrote: ↑

Mon Feb 20, 2023 2:45 pm

I need some help - I'm not much on Model T charging circuits.

Our 1924 T has two 6-volt batteries, and runs on six volts. She always runs on the battery, my not yet being ready to tackle the non-functioning magneto circuit. She is starting and running well, but the ammeter reads negative about 5 amps, with no lights on, and stays at negative 5 amps independent of the RPM. After half an hour or so the voltage drops to the point that she will not restart if stalled. This change was sudden; charging was until recently dependent on RPM, although I had noticed that turning on the lights made a positive ammeter reading hard to obtain.

Is there any alternative to the generator being bad? Could the cut out switch be stuck? Is there any possible cause that is repairable before she is due to carry the Grand Marshal in a parade Saturday?

Thanks in advance for any assistance.

I am confused by this part of your description.s. ". She is starting and running well, but the ammeter reads negative about 5 amps, with no lights on, and stays at negative 5 amps independent of the RPM. .... until recently dependent on RPM, although I had noticed that turning on the lights made a positive ammeter reading hard to obtain." The ammeter should read positive while charging and negative when filament lights are turned on (LEDs take a lot less). The recommend setting for a generator is 5amp output & no more than 10amps. So your description sounds like the ammeter is hooked up backwards. Check the wiring diagram, you may just need to reverse the leads to the ammeter

However that doesn't account for the starting issue, battery drained. You say you have two 6 volts batters - are they both hooked up to the generator, how do you use them? and is it stock one or do you have an alternator or 12 volt gen

If the cut-out switch was stuck it would run your generator like a motor when you shut off the engine.

".... [ showed 5 amp charge rate] ....until recently, dependent on RPM, although I had noticed that turning on the lights made a positive ammeter reading hard to obtain."


I take it that the charging rate USED to show around 5A, dependent on RPM, and showed near 0 with lights on, and that now it shows a 5A discharge, regardless of RPM.

The battery on a T is negative ground with the positive terminal connected through the cutout to the generator. If you installed the battery backward with a positive ground, the generator could be discharging the battery.
Norm.

To test if the generator or cutout is not functioning use an analog voltmeter. (necessary if running on coils.)
Take the negative probe to ground while running. Touch the positive probe to the battery side of the cutout.
Should read a bit higher voltage than when not running.(Gen & cutout is working)
Touch the positive probe to the gen output terminal. If voltage is quite a bit higher than battery voltage. the Gen is working, but the cutout is not.
@ this point the motor should not be run without grounding the generator terminal, lest you burn up a working gen.
If there is no voltage, the gen is not working. If you are going to drive it still on battery voltage, you should ground out the gen terminal to be safe.
If your cutout is NOT a fun projects regulator, whall running, take a wire or pair of pliers handles & momentarily bridge the gen terminal & cutout hot terminal. Does the ammeter now show a charge? If so gen is glitchey.

Thank you very much, and particularly thank you speedytinc for ways of testing to isolate the problem. Our T has two ordinary type 65 6 volt batteries that normally operate in parallel, A pair of relays, controlled by the starter switch, connects them in series for the few seconds that the starter is running. Then, back to 6 volts for the whole system. Assuming reasonably charged batteries, the engine starts readily. No smoke/burning insulation or other excessive heat has shown up in this - just -5 amps while running, independent of RPM. Everything is just right, except she is not charging.

Timothy,
As I understand, you have two 6v batteries wired in parallel, that switch to series for starting, with relays at the starter switch. So I guess you have a 12v starter. My head is starting to hurt. I would bow out of the parade at this point. The real solution in my opinion, is to convert back to the Ford 6v electrical system, which is very reliable, and the parts are affordable, and available.

tkeithlu wrote: ↑

Mon Feb 20, 2023 6:00 pm

Thank you very much, and particularly thank you speedytinc for ways of testing to isolate the problem. Our T has two ordinary type 65 6 volt batteries that normally operate in parallel, A pair of relays, controlled by the starter switch, connects them in series for the few seconds that the starter is running. Then, back to 6 volts for the whole system. Assuming reasonably charged batteries, the engine starts readily. No smoke/burning insulation or other excessive heat has shown up in this - just -5 amps while running, independent of RPM. Everything is just right, except she is not charging.

To fully charge a 6 volt 100 amp-hr battery with a 5amp charger would take 20hrs. So since you 2 connected in parallel to a Model T generator (recalculating recalculating....) never while driving. No way for the batteries to get enough once they get low. So I believe the amp reading is indicating its charging but the batteries are too low.

Model T' coils don't take much (not sire why you need two six volt batteries since you start one).
What I would do is use just one six volt fully charged battery connected per the wiring diagram to see what you got. Back in the day, none starter cars used those old round dry cell battery to run one.

What's interesting in your setup is some would set it up so 12 volts hit there declining starter

The head lights normally need about 12 to 16 Amps.

Your Generator can only charge 10 Amps for a long time.

Maybe 12 Amps for a few minutes.

So, the Ammeter should show about a 5 Amp discharge with the generator charging and the lights turned on.

The last time I helped a guy with this similar problem, I got rid of his 12 Volt 4 Gauge cables and replaced them with the correct 0 Gauge cables.

I also eliminated the weaker battery that was taking, but never giving.

Then everything worked fine.

Well, when diagnosing Model T issues, it is easier and more productive to know the totality of what is going on. Now we know that the car has extensive modifications, some of which I would not doubt for a second, that we still do not know about.

Providing advice to fix a Model T which is not put together like a Model T is pretty difficult to do over the internet. No matter how well meaning, any advice you get from someone who is not laying their eyes on the patient is going to be pretty much meaningless.

When this is all behind you, and I suspect that time will be well past your parade obligation, you will be doing yourself a big favor to find out why your car needs all of the modifications that it has, and revert to how it was designed to operate. From that baseline, you will have lots of useful tips and advice from anyone familiar with Model T's.

FWIW, a T with two 6V batteries in parallel should be able to start and run for several days without a generator or being recharged. That is an enormous amount of spare "oomph". Since it won't restart (on 12V!!!) after a couple hours, and it is showing a discharge (which you still have not defined as continuous or only while running) of 5A, it sounds as though you are trying to motor your generator through a stuck cutout. If that is the case then with the car not running, if the discharge continues, remove the yellow wire to the cutout...the discharge as shown on the ammeter should cease and the meter will sit on "zero". Again, if I am right and you get that result then the reason your generator is not "genning" is because it is cooked.

If you were running a belt drive generator without a belt and the relay was stuck closed the generator would motor if it was workable. It cannot on a model t asit is gear driven and cannot turn the engine over. Take your generator off and onnect a 6 volt battery with the positive terminal to the generator body and the negative terminal to the generator output terminal. It should motor if it is working.
It is not difficult to build a test bench setup to test generators. If you belong to a local club, maybe they would like to take it on as a club project and several of you could use it.

It appears that your generator has been adjusted to provide 5 amps output at moderate car speeds. If you have 2 batteries in good condition, connected in paralell, but significantly discharged, it may be that the current draw of the 2 discharged batteries is sufficient to absorb the generator's entire available output, and maybe more, thus keeping the batteries discharged. You might try charging the 2 batteries for 24 hours or more, then seeing how the system behaves. If either or both batteries have issues, one or both may not be capable of taking a full charge or holding it. Discharged batteries in good condition can absorb a considerable amount of current, and your generator's output is limited. Given enough load, the generator's output voltage could fall below the batteries' required charging voltage. Good batteries go bad, sooner or later, and often sooner.

Thinking about this a few days, makes me reflect on the remarkable irony of using 12V to start and 6V to run, is that this arrangement provides maximum damage to the Bendix and ring gear while simultaneously providing minimum spark from the coils. If this car is in fact running coils at the very least I'd want the tradeoff of a hotter spark if I was determined to beat the he!! out of the starting system.

When making modifications to the electrical system as has been done, the inevitable failures that result will hopefully encourage the adoption of the original system... considering that the original system was used successfully millions and millions of times and so far, this version, not so much.

Fixing things right will take more than a weekend, but when done right, it will only need to be done once. And if done well, it will almost always outlast the owner.

If you don't own the Model T Service Manual, the "bible" of Model T's, do yourself a huge favor and pick one up. It will provide invaluable insight to the car, how it was made, and how to maintain it. Best of luck.

The ignition system, and therefore, the engine, will perform best on magneto. The original Ford system offers several advantages, besides being quite reliable, economical, and easy to service.

As for your non-functioning magneto system, it may be a simple matter to get it operating again. Several common faults with the magneto can be corrected without major work.

With the original Ford system fully operational, you can start the car with the starter, or with the crank, or by pushing or pulling it. Often as not, you can "free start" it simply by turning the ignition key to Battery.

If you encounter a dead battery situation, or have no battery at all, you can still start the car by cranking it, or by pushing or pulling it.

In the past I used two hunting type 6 volt batteries (about $7 each at Walmart) connected in series to power the GPS. With the new GPS, I found that it would operate on the car 6 volt supply. The old GPS wouldn't work on 6 volt.

Starting a T with 12V is a patch to cover a poor starter/starting system. IMHO

Regarding the OP's system with relays that presumably add the extra voltage AFTER the bendix is engaged & turning the flywheel is way less destructive compared to direct 12V or than those fooled into thinking a bendix spring as a resister will be easier on the system.
I am also impressed that the T doesnt have a full 12V conversion with an Itchiebushey alternator & starter.

There is much we dont know about this T. Maybe it is running a distributor reliably on 6V with just a weak starter.
If running coils on 6V without a good magneto, maybe the owner isnt aware this T is running poorly & a max speed of 35 is normal.

A true 5 amp loss running is a high for just an ignition system. Is a fuel pump involved also?
A T will go a long time @ a dead loss on a battery without a lot of starter/head light use.

I hope the charging issues can be easily resolved & get her back on the road.

Let us know, did you get your charging problem reaired?