Charging correctly????

Used John T?s trouble shooting guide to check charging system problem on MF 35 Perkins diesel with 12V generator. New voltage regulator was bad. Installed another new voltage regulator and amp gauge is showing charge. When you rev the engine up to 2/3 to 3/4 throttle the needle on the amp gauge goes wild swinging back and forth rapidly. Any ideas as to why this occurs and how to fix.

As always all responses are appreciated.

May not appreciate this response but you are finding out why many old tractors have been changed over to 12V alternators,probably buy a 12V 1 wire alternator cheaper than those regulators and never have to worry about it again.

Could be a few different things.

Most likely, a poorly functioning regulator, arcing contacts.

A failing generator.

A worn amp gauge.

A bad connection, bad regulator ground.

If you have an analog volt meter, check the voltage. If it reads steady and around 13v or so, it is charging. Could just be the damper is worn in the amp gauge and it is over reacting to the regulator contacts arcing, or vibrations. If the lights are steady, and the voltage steady, just try it and see what happens.

Be sure the regulator base is grounded, all connections are tight, no intermittent shorts to ground.

Two things...

1. By nature old-fashioned mechanical regulators don't operate as "smoothly" as we have become used to with solid-state charging systems over the last 50 years.

2. Good old production ammeters were "damped" to hide the crude behavior of the mechanical regulator from the operator.

As long as the charging system is keeping the battery "up", teach yourself to ignore the flopping of the Ammeter.

By necessity the regulator must sense the battery voltage and notice when it is below a certain threshold. When this occurs, the regulator calls for the generator (or alternator) to "give it some juice" and the output will be only limited by the regulator cutout. When that happens the ammeter goes to the full charging amperage. Now the regulator senses that the battery voltage is too high so it cuts the generator off and the needle of the ammeter returns through zero and as soon as the regulator senses the voltage to have dropped below the threshold it calls for the generator to give it some more juice and the cycle repeats. An ammeter that has dampening will respond more slowly so you don't see the fluctuation.

tl, good question, when I was a used tractor dealer back in the day I saw many ammeters act that way, there's a ton of possible reasons.

1) Ammeter is showing its age or just faulty,,,,,,,,,,genny brushes may be worn or there excess carbon (or oil) on the commutator or the brush hold down springs are weak or the commutator insulator segments need undercut (more apt to cause poor charging but had to throw it in),,,,,,,,,,,,,Voltage regulator contacts may be coated or be burned or carboned or its just not perfect matched to the system,,,,,,,,,theres a loose resistive ground connection,,,,,,,,,loose resistive wiring connection,,,,,,,,and a ton more Im forgetting lol.

BOTOTM LINE if the battery is still charging and all else is working I wouldn't worry much, maybe check and clean all grounds and wiring connections. If it ant broke don't fix it lol

John T

Traditional Farmer - Over 60 years ago most every small town had a starter/generator shop to rebuild/repair generators and voltage regulators, and the occasional starter. Slightly bigger towns would have 2-3 or more shops. Then automotive companies and finally tractor companies all switched to alternators with solid-state voltage regulators. And eventually those small starter/generator shops almost all disappeared. Takes a good sized town/city to keep one small shop in business now. I've had SEVEN alternators fail on me on 16 cars/trucks plus 2 Farmalls, and 15-20 trucks I drove for various people over the years. I've had two alternators fail after 200,000 miles each rebuilt by a shop over 60 miles away, they did have a shop locally for a short time, but now you take your part to another shop and complete the paperwork and their truck picks it up and you get a phone call the next day from the rebuilding tech with the firm price on repair, next day you can pick your starter/generator/alternator up repaired. I had the 6V starter on my Super H rebuilt 2 yrs ago, it starts on 12v, first time I started it it scared me it spun the engine so fast!

I really don't see why ANYONE would want to continue using 6V and generators that the tractor companies replaced with 12V in the mid 1950's and alternators in the 1960's. The joy of having a "period correct restoration" lasts until the first time it doesn't start!

(quoted from post at 08:31:28 03/14/20) By necessity the regulator must sense the battery voltage and notice when it is below a certain threshold. When this occurs, the regulator calls for the generator (or alternator) to "give it some juice" and the output will be only limited by the regulator cutout. When that happens the ammeter goes to the full charging amperage. Now the regulator senses that the battery voltage is too high so it cuts the generator off and the needle of the ammeter returns through zero and as soon as the regulator senses the voltage to have dropped below the threshold it calls for the generator to give it some more juice and the cycle repeats. An ammeter that has dampening will respond more slowly so you don't see the fluctuation.

Click to expand...

dditionally, the on/off/on cycling is generally many times per second on a battery that is near full charge, but with time/wear & maybe a bad clone VR design, the cycling may be much slower & thus more ammeter flutter.

For a show tractor I can see using all original equipment for sure.I use my old tractors as farm tractors and one of the best updates on an old tractor to make it user friendly for me is to
switch it over to an alternator.Fought the generator/regulator issues for years growing up they were always a source of aggravation guess that was why there were so many places that worked on them now that I think about it.