Maximum Third Brush Setting Allowed

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Model T Ford Forum: Forum 2016: Maximum Third Brush Setting Allowed
Top of pagePrevious messageNext messageBottom of page Link to this message  By James A. Golden on Friday, May 20, 2016 - 07:44 am:

The Model T Ford Service Instruction book provides a Third Brush setting procedure and notes the brush can be set to a 10 to 12 amp charge rate, if the vehicle is doing frequent stops.

This setting is done with the engine running at a fast idle.

An alternate procedure is described elsewhere that suggests turning on the head lights and setting the ammeter to show ZERO with the engine running at a fast idle.

There is a big difference in the amount of current the head lights draw with original bulbs and 50 candlepower bulbs.

A friend's car has sealed beams installed and the ammeter shows about 16 amps when they are turned off.

While the car is seldom driven at night, the 16 amp charge has not hurt the generator for over 5 years that I know for sure.

Volts times Amps equals Watts.

The voltage measures about 8 when the amps measure 16.

That makes the generator about a 90 to 100 Watt device.

I have always suspected it to be a 60 to 75 Watt device.

Does anyone know for sure if the 16 Amp setting is dangerous?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dave Dufault on Friday, May 20, 2016 - 08:55 am:

Good Morning Jim,

Until someone else comes on, here's the words from Ron & John from years ago...

http://www.mtfca.com/discus/messages/179374/181231.html?1294463308

(Last 2 posts on this thread) - 100 watts max.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Royce in Dallas TX on Friday, May 20, 2016 - 09:12 am:

Yes, the 16 amp setting will boil the water out of the battery. You need to set the amperage to around 2 amps with the battery fully charged, if you insist on using a cutout.

A better plan would be to use a Fun Projects voltage regulator. It will top off the battery and then maintain it without overcharging.

If you drive around much with the battery boiling like that you risk an explosion. Seen it several times. Makes a big mess. The good thing about Model T's is they can drive home on MAG without a battery.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jerry VanOoteghem - SE Michigan on Friday, May 20, 2016 - 06:24 pm:

I try for 6 - 8 amps. Never a problem with batteries or generators.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Wayne Sheldon, Grass Valley, CA on Friday, May 20, 2016 - 09:41 pm:

I like low charging rates. About 5 amps max with the lights off. Let it discharge a bit with the lights on unless you are going to do a crazy amount of night driving. A couple hours of night driving won't hurt the battery under normal conditions.
Much higher charging rates can damage both the generator and the battery and may not warn you until the damage is done.
What Royce said is all very good. I had a battery explode once. It was nasty!


Top of pagePrevious messageNext messageBottom of page Link to this message  By Steve Jelf, Parkerfield KS on Friday, May 20, 2016 - 11:52 pm:


It makes a big noise and pieces go flying.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Craig Anderson, central Wisconsin on Saturday, May 21, 2016 - 01:05 am:

One can put in Scat cranks and Roof heads and Chevy rods and and and.......but the BEST money one can spend is for John's solid state cutout/regulator!


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kevin Whelihan Danbury, WI on Saturday, May 21, 2016 - 07:07 am:

I agree with Craig, the Fun Projects regulator is some of the best money I ever spent on my car. Set the 3rd brush and forget it. I keep all the connections in the system clean and never worry about over-charging or catastrophic battery failure. That kind of piece of mind is priceless.


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