MTFCA Forum

What is the difference between a cut-out and a voltage regular for generators?

I hope John Reagan chimes in here. He's a real expert. But I can give you the basics.

If you connect a generator straight to a battery, the spinning armature will generate voltage and try to charge the battery. But if you shut off the engine, the battery will try to spin the generator. If the generator can't spin (as in tied to the engine), it will run the battery down or cause the windings of the generator to burn up.

So that's why you need at least a "cutout". It protects the battery when the engine isn't running. It's also called a "reverse current relay".

That's the essence of the cutout. Now for the voltage regulator.

When the generator is being spun by the engine, voltage is produced. The generator is set to provide enough voltage to provide a good charge to the battery. If you drive any distance at all, the battery gets fully charged. But then the generator kept hammering away at the battery because it doesn't know when full charge is reached. The water in the battery soon boils away, which is why we used to have removable battery caps and those little black water pitchers at gas stations. The life of the battery is seriously shortened by all this overcharging.

So some time in the late 1930's, the voltage regulator appeared. The regulator measures battery voltage and controls the generator such that it doesn't overcharge the battery. Suddenly the life of a typical battery jumped from one or two years to more like five years.

About 30 years later, solid state regulators came on the scene. The solid state regulators gave much more precise control of voltage and thus battery life was increased still more. Today it's not uncommon for a battery to last 10 years in a modern car.

Our Model T's are from the "cutout" era. The most primitive arrangement of all. There is a lot more to all this than I am qualified to explain, such as the different generator types, and alternators. That's why I hope Mr. Reagan steps in.

Dick

Well said Dick..
..A nice simple basic answer to a nice simple everyday basic question.. (Maybe not an everyday question)....n.

A cutout is better than nothing. A regulator will cost more, but will will pay for itself in longer battery life, longer generator life, longer accessory life, and less fuel wasted overcharging your battery.

TXGOAT2 wrote: ↑

Wed Oct 06, 2021 9:36 am

A cutout is better than nothing. A regulator will cost more, but will will pay for itself in longer battery life, longer generator life, longer accessory life, and less fuel wasted overcharging your battery.

Yes, if it was still available.

speedytinc wrote: ↑

Wed Oct 06, 2021 10:32 am

TXGOAT2 wrote: ↑

Wed Oct 06, 2021 9:36 am

A cutout is better than nothing. A regulator will cost more, but will will pay for itself in longer battery life, longer generator life, longer accessory life, and less fuel wasted overcharging your battery.

Yes, if it was still available.

Yep. It's been unavailable for quite a while now.

Thanks for the input. It was very informative.

Snyder's catalog doesn't list voltage regulators, but does have a "semi-conductor cut-out" on page T-61. It appears that this is an improved cut-out. I wonder if this would be basically as good as voltage regulator on T generator. Comments?

BLB27 wrote: ↑

Wed Oct 06, 2021 3:39 pm

Thanks for the input. It was very informative.

Snyder's catalog doesn't list voltage regulators, but does have a "semi-conductor cut-out" on page T-61. It appears that this is an improved cut-out. I wonder if this would be basically as good as voltage regulator on T generator. Comments?

It is an electronic cutout. Basically a one way flow valve for generator output. Way better than the cheap mechanical cutout available today. Fleabay has a unviersal tractor type electronic cutout for 4 $15-30.
A voltage regulator reads the battery voltage & stops adding unnecessary over charge, but will "turn on" as needed to keep the battery @ full charge.

A cutout, whether it's an old-style electromechanical unit or a modern, solid state unit, is simply an automatic switch. It is either OFF or ON. It cannot regulate current and voltage to meet the varying demands of the battery and the electrical system's accessory load.

John Regan is at Hershey, spoke with him about 3 hrs ago. Said he's not looking much at the Forum and that the purchaser of Funprojects has sold off most of the inventory and has made few if any replacement FP items since 2017. jb

Well, the good news there is that John is still alive and well. Shame that the new owner hasn't kept up with John's excellent product line.

jab35 wrote: ↑

Wed Oct 06, 2021 7:24 pm

John Regan is at Hershey, spoke with him about 3 hrs ago. Said he's not looking much at the Forum and that the purchaser of Funprojects has sold off most of the inventory and has made few if any replacement FP items since 2017. jb

It's too bad he can't share the design so we can reproduce it ourselves.

JBog: Here is a link to a blog that reports the reverse-engineered funprojects voltage regulator circuitry and parts if you want to try building one. I'm not aware of any patents involved but if you build any to sell you might check first. https://www.cool386.com/regulator/regulator.html

After burning up a generator when a diode failed, I switched back to the original cutout. I file the points about every 3000 miles and test its opening and closing voltage.
Never had a problem.
I have considered connecting two sets of diodes in series then connect the two sets in parallel. 4 diodes in total. If one diode failed the system would continue to function. If one in each series failed at the same time, you could burn up the generator. Just add another series set to the parallels. 6 diodes in total.
I would test each diode individually every year or so.

One disadvantage to the voltage regulators that you cannot adjust the voltage to your liking. You get what you get. I like to set at low output. I normally don't drive the car at night. If I do it is only for an hour at most.
Art Mirtes

There's a section in the mtfca Electrical System guidebook (pp 17-18) that describes a way to install a rheostat in the 3rd brush circuit of the generator to 'adjust' the charging rate on the go. Personally, I wouldn't do this b/c I think the risk of overloading the generator or overcharging the battery is too great but apparently some have done so, successfully. Of course, the VR does this automatically, but sourcing a VR is problematic. jb

It might be possible to use a later style, 3-element Delco 6 volt regulator on a T generator. The current setting would probably be too high, but that could be dealt with by limiting the output with a resistor in the field lead.

TXGOAT2 wrote: ↑

Mon Oct 11, 2021 10:59 am

It might be possible to use a later style, 3-element Delco 6 volt regulator on a T generator. The current setting would probably be too high, but that could be dealt with by limiting the output with a resistor in the field lead.

You need to be careful that any regulator you fit to a Model T or Model A standard generator is a shunt-type regulator. Series regulators will likely result in a damaged generator - T & A generators should not be run without a load. This is just a cautionary note as I don't know which Delco regulator you mean, it may be ok, but as most vehicle regulators are series types one should check first.

Out of interest; I was going to post a simple regulator design using common components, this would have been open source as with the 'FACT' coil tester, and people could have built it themselves or someone might have made a PCB such as Matt has for the coil tester.

However I was asked not to do so by a forum member who effectively suggested that my scruples would be in question if I did this. It was never completely clear to me why this would be so (maybe they didn't want 'competition'), but out of respect for the MTFCA I left it alone - not wanting to rock any boats.

That was some time ago and I may revisit my decision since there seems to be dearth of regulators available, yet they're really a very simple thing and something I believe people should readily have free access to. Mind you it happens that JohnH produced a simple design some years ago and although I've not trialled it myself it may be that someone here would like to try it out. More information can be seen towards the end of this thread: viewtopic.php?f=2&t=19562

You would need to determine how the field circuit is connected on the application the regulator was designed for. As I understand it, the T generator feeds the field circuit via the 3rd brush, thence through the field coil series, thence to ground. Many later generators had the field lead brought out to an insulated terminal on the case and the other end of the field circuit grounded. One or more of the regulator's elements controlled the field current/voltage applied to the field circuit, and the other element was a cut out. Something like a 1950 Chevrolet (6V /neg gnd) regulator might be adapted to replace the 3rd brush function as well as the stock cut out. Running the T generator with no load can destroy it. Running it with more or less added resistance in the field circuit ought not to. I think the later style regulator would see a light generator load, such as accessories off and a fully charged battery, as a condition requiring more resistance in the field circuit, which ought to limit generator output. The regulator field terminal would be connected to a lead off the third brush, or the third brush might not be needed at all, since the internal regulator circuitry would (I assume) energize and regulate the field circuit off the armature terminal once the generator "ramped up" if the ungrounded field lead was brought out to an insulated terminal and then connected to the regulator field terminal.