420c charging problem

[redkneckracer]

hello ive got a mid 50's 420c with winch , last owner converted 6volt system to 12volts machine always starts and runs good but if i'm pushing snow or winching logs in the dark while running her work lights after a while she'l shut off and won't crank.... battery goes dead. so obviously she probably isn't charging. but what im wondering is does the points system on the 2cylinder need 12 volts to keep power to the distributor for spark? or should she still run with a dead battery?

[boler76]

I would say if it has an alternator that it wont run with a dead battery, but a good generator will keep it running with a low battery I think

[Stan Disbrow]

Hi,

If you're thinking that a 6v system ought to run with a 12v battery that won't crank a 12v starter, that seems to make sense but really does not.

When you stick a 12v battery into a 6v machine, you have to also add in a current limiting resistor in the ignition line. That drops the 12v to 6v so the points don't fry.

So, when the 12v battery drops, so does the 6v at the points just as if it had a 6v battery and no resistor.

At this point, you need to either correct the charging fault, or don't run the lights. The battery can run the ignition for hours without the lights.

It's also possible that you have enough charge current to cover the load of the points and coil, but not enough to cover the additional load of the lights. Of course, this means you still have to fix it to work after dark....

Later!

Stan

[Willyr]

A 12volt gmc/chevy alternator should run as soon as the engine turns over. But the problem may have occured the last time the battery was installed. And yes, it too will run with out a battery. One of the tests of the older alternators was to remove a battery connection. if the car stalled the alternator needed servicing.

Alternators run on NEGATIVE ground only! People with these older tractors will have some one tell them that the tractor is positive ground (the diodes fry with positive ground instalations, the effect is immediate) and will burn the regulator in the alternator from hooking up the battery wrong.

Its about $50 to repair, less if you know what you are doing inside there (dont for get to pin the brushes to re-assemble). Otherwise just buy a replacement from a junkyard for $20.

Another item is sometimes you need to use the spade holes on the side of the alternator to tell it when to turn on. The pic below will help figure it out. Normally you oonly need to hook up the power and make sure you have good ground.

[boler76]

Were does the field get its current when there is a dead or no battery?

[markvdh]

The Delco alternators (like the one depicted in the schematic, internally regulated) had three notable configurations.

1. Regulated and triggered (these require three wires as the schematic shows)
2. Unregulated, but still triggered (these have to have at least two wires, and they charge at a preset rate when energized)
3. Unregulated and untriggered. These only require one wire; the large one to the battery. (these were used in many marine and stationary power plant applications, and had fields that were permanently magnetized so that at a certain RPM they would self energize and produce a determined rate of charge).

So it is possible to have a Delco internally regulated alternator with only one wire that will still charge appropriately.

Hope this helps,
Mark V

[Stan Disbrow]

Hi,

Ironically, an alternator that has permanent magnets to self-energize it's own field coils is called an AC generator.

Later!

Stan

[markvdh]

You're right, Stan. And actually all of the alternators generate AC voltage. The internal bridge rectifier converts it to DC voltage before it gets shipped to the battery.

Hopefully, we're not totally confusing you in regards to your 420C problem. The bottom line is, whether a system is nominally 6 volts or 12 volts, when it is running at operating RPM with lights on and any other normal operating electrical load (air conditioning, surround sound stereo...JUST KIDDING) the generator or alternator must be capable of putting out approximately 110% of nominal voltage (measured at the battery) or the system will slowly loose voltage and eventually the coil will not have enough voltage to transform primary voltage to secondary voltage, and the coil will quit firing the plugs. On a 6 volt system, you should have at least 6.6 volts when measured at the battery. On a 12 volt system, you should have 13.2. 6.9V or 13.8V is considered ideal.

Mark V

[markvdh]

Sorry for the back-to-back post, but after reading your question again, I still don't think I answered what you where asking.

The ignition system (points, condenser, coil, etc.) on these tractors will NOT run without voltage from the battery/generator (charging) system. It is not like some older tractors (and most airplanes) that have a magneto ignition system. A magneto generates its own voltage, and doesn't need the charging system to supply it, so they will run or start (if you can crank it by hand) even with a dead battery, and they'll keep running without a battery or an alternator/generator. Your 420C is not that way. When the battery starts going dead for whatever reason, and the voltage drops below a certain point, the ignition system will quit firing and your engine will die. Like Stan said, you need to fix your charging system in order to use the lights because of the additional electrical load that they are demanding.

Mark V

[Gil]

Redkneckracer,
You might also be thinking about a diesel engine. Once they get started you can remove the battery. But diesels fire their fuel by compression and do not use spark plugs and an ignition circuit like a gas engine does. However, to run lights on a diesel crawler you still need a battery and need to keep it charged with a charging circuit.
Gil

[Stan Disbrow]

Hi,

Well, I was making one of those odd EE distinctions once again.

I was pointing out that an Alternator is dependent on an external source of power for it's field coils, whilst a Generator is capable of producing it's own field coil excitation.

So, there are AC alternators, most commonly seen in automotive applications, and AC Generators, the best known of which are sold in hardware stores.

Silly me.

Later!

Stan

[redkneckracer]

i after posting my problem i went down in the woods with a fully charged batterry , hooked it back up , ran her at high idle and checked my alternator with multimeter and im gettin 14.6. so i know my charging system is fine. but what im noticing now is sometimes i have to frig around with my light switch to get my lights to shine bright. if the light wiring is shorting or grounding somewhere a guess that could run my battery down no? also i wondering if anyone got any info on points adjustment? latley shes been getting gutless when pushing uphill. im not getting that good flame from my exhaust when i rev her up like i used to. thanks boys