MTFCA Forum

I have a Model T that came with a new 8v battery. The cutout just died and I happen to have a spare 12v cutout. I've been reading past forum posts, but only seem to confuse myself (easy to do). I know options 3 and 4 are the ideal solutions, but can I get away with option 1 or 2 for now?

1) install my spare 12v cutout for my 8v battery
2) buy a 6v cutout for my 8v battery knowing in 4-5 years I'll replace my 8v battery with a 6v battery
3) buy a 8v cutout
4) buy both a 6v battery and a 6v cutout

Thanks!
Chad

You'll be pumping about 13V into your 8V battery with a 12V cutout. Uh-uh.
This is a bad area to be playing games

I thought the cut out was no more than a electromagnetic switch, the question would be if the 8v battery would energize the 12v cut out? With the cut out system the battery voltage was the regulator, amps mattered not voltage, true?
I have no problems with running 6v cut outs on my 8v batteries.

Is the 12v cut-out positive or negative ground; solenoid or diode?
A cut-out should not be confused with a voltage regulator, so what ever the generator is putting out will be used to charge the battery less any equipment draws like headlights. By the way voltage regulators also incorporate a cut-out as part of their function. A solenoid cut-out is a simple switch to make contact, close, when the output of the generator is greater than that of the battery and to disconnect, open, when the battery voltage is higher than what is coming from the generator so it doesn't run it like a motor. However the solenoid is an electromagnet with an iron core and winding, so it is likely the coil is designed to trigger at about 12v. So it would stay open until the generator put out 12volts or more and you would be using your battery. A diode basically just lets the voltage flow in one direction and have similar parameters. The suppliers sell one rated for Model T use. I would just buy the diode that they sell for about $6 and retrofit the cut-out you have. An keep your 8volt battery. Here are instructions
https://www.snydersantiqueauto.com/Reso ... t-5010.pdf
This recent discussion references 8 volt usage. https://mtfca.com/phpBB3/viewtopic.php? ... lt#p103608

The generator on a Model T is a current-controlled device; you set the current delivery via the 'third brush' and I'm sure you'd find lots of information on that here.

If you want to voltage regulate the output of the generator you can use a voltage regulator, but note that it should be a shunt regulator as you don't want to run the generator into an open circuit.

I made an electronic regulator, using some parts from an old PC PSU, but I'd hesitate to put that detail up here, and it's not really the focus of the question. In my view a 'modern' 'cut-out' (in reality a schottky, or even conventional high-current diode) would be fine to replace what just failed. You could probably also dismantle the present unit and simply replace the internals with a >20A schottky diode and then just check that the generator is set to deliver not much more than 5A or so. Incidentally many PC PSU's contain just the right diode

The reason for the 'cut-out' is to prevent the battery supply back-flowing into the generator. Diodes do this job admirably, I'd expect a so-called 6V 'cut-out' would probably work as well, but if it's a 6V regulator it shouldn't be used.

Appreciate the comments! My generator is set to about 8amps. Apologies for interchanging the terms cutout and regulator! This is an important distinction.

Correction, I have a 12v regulator, not a cut out.

Noting the correction, it seems option 3, 4, or 5 are my best options. Correct?

1) install my spare 12v regulator for my 8v battery
2) buy a 6v regulator for my 8v battery knowing in 4-5 years I'll replace my 8v battery with a 6v battery
3) buy a 6v cutout for my 8v battery knowing in 4-5 years I'll replace my 8v battery with a 6v battery
4) buy a 8v regulator
5) buy both a 6v battery and a 6v regulator

Thanks!

Budreau wrote: ↑

Tue Jun 30, 2020 7:18 am

Appreciate the comments! My generator is set to about 8amps. Apologies for interchanging the terms cutout and regulator! This is an important distinction.

Correction, I have a 12v regulator, not a cut out.
Noting the correction, it seems option 3, 4, or 5 are my best options. Correct?
1) install my spare 12v regulator for my 8v battery
2) buy a 6v regulator for my 8v battery knowing in 4-5 years I'll replace my 8v battery with a 6v battery
3) buy a 6v cutout for my 8v battery knowing in 4-5 years I'll replace my 8v battery with a 6v battery
4) buy a 8v regulator
5) buy both a 6v battery and a 6v regulator

Thanks!

6v regulators for a Model T have been unavailable for over a year and their future is suspect, but would be the best choice if found. You just can't use just any 6 volt voltage regulator like from an early VW (mods needed).

The least expensive way to go now, option 3, is to just purchase a diode from a Model T supplier and mod your dead cut-out. It a simple modification. https://www.modeltford.com/pl.aspx?t=s&v=diode&page=1
Here are some references about 8 volt batteries
http://www.mtfca.com/discus/messages/50 ... 1426597940
http://www.mtfca.com/discus/messages/50 ... 1451270644

Thanks all. Based on the advice, I'm getting a 6v cutout and adding a diode as an extra precaution. I'm finding 6v and 8v regulators are out of stock anyway.

I've been in the hobby for 12 years, but I'm always learning. Do I understand correctly my 12v regulator will try to charge my battery until it hits 12-13 volts. Since I have an 8v battery, I will experience boil over, especially on a long run, but a standard generator cutout could also overcharge my battery.

Chad

Budreau wrote: ↑

Tue Jun 30, 2020 6:58 pm

Thanks all. Based on the advice, I'm getting a 6v cutout and adding a diode as an extra precaution. I'm finding 6v and 8v regulators are out of stock anyway.

I've been in the hobby for 12 years, but I'm always learning. Do I understand correctly my 12v regulator will try to charge my battery until it hits 12-13 volts. Since I have an 8v battery, I will experience boil over, especially on a long run, but a standard generator cutout could also overcharge my battery.

Chad

So your are getting a 6volt, diode version, cutout and a diode for your old cutout?
https://www.modeltford.com/item/5055.aspx or Ford Script https://www.modeltford.com/item/5055FS.aspx
Diode https://www.modeltford.com/item/5055DIO.aspx to fix your old one (really all you need to buy)

@TRDxB2, I misread your earlier reply and suggestion to buy a diode.

I'm only getting a cutout with diode. I'm not buying a diode to repair my cutout, but may try to add it to my order and see if I can salvage my old cutout.