630 Jumpy Ammeter Needle

GlenT · Sep 16, 2009

I got the 630 running after two years of rebuild and lots of new parts including new aftermarket gauges. The ammeter gauge jumps around a lot but does show a good charge. I have turned the 2-brush generator commutator and cleaned between sections and changed the voltage regulator with a new one I had. The generator brushes are good and the bearings are good. I'm not sure about the fields or armature since I have no way to test them but like I mentioned, it does charge okay. I am wondering if it is the generator or cheap aftermarket ammeter that is making the ammeter so jumpy. I didn't like the way the one terminal on the ammeter wouldn't tighten. Also, I wonder if there is an internal capacitor in the better ammeters to keep the needle from being so jumpy.

Thanks for any ideas you may have.

ET · Sep 16, 2009

Stuck generator brushes can do that, even new brushes will sometimes stick. Take the cover off the regulator and check the contact points on the cutout and current regulator. With the tractor running do you see an arc on either set of points idicating poor contact?

Bob · Sep 16, 2009

Has the commutator been turned and correctly undercut?

(If the commutator is not perfect the brushes will bounce.)

Is the regulator well grounded?

Also, these old "vibrating contact" VR systems do not produce the precise charge control we are now accustomed to and a certain amount of ammeter jiggle is NORMAL.

An ammeter and VR made in "the land of almost right" don't help the situation any.

Bottom line is if the commutator is in good condition, you are probably going to have to live with the situation as it is, or try a NOS ammeter or a QUALITY new ammeter (Steward Warner, perhaps?) and/or another voltage regulator.

Anonymous-0 · Sep 16, 2009

There is very little voltage drop across the ammeter so it would take a very high value capacitor to dampen the meter movement. Its better designed into the meter with a magnetic damper. Like a slab of copper next to the rotating magnet to let the moving magnet induce shorted eddy currents into the copper. Probably got left out of the inexpensive ammeter to save on cost.

The connection that won't tighten will cause jumping and will only get worse. I think you need a different ammeter. Hold it up and shake it and pick the one that's not so free at moving.

I added an ammeter to my gas 4020 and it bounced from peg to peg from the slow regulator. With a new generator regulator about $35 (ten years ago) I put up a little more money for a one wire alternator and now I have a steady ammeter and much better charging. I didn't like the change from original, but the generator charging system was badly designed.

Gerald J.

John T · Sep 16, 2009

I wouldnt take a cheap ammeter out of the equation. Ive seen a ton of those systems work WITHOUT any jumpy meters.

If its NOT a non concentric commutator,,,,,,,or raised commutator insulator segments,,,,,,,or a poor VR ground or other bad connections,,,,,with brushes plenty long,,,,,you may wanna insure the brush hold down springy assemblies are free and tight and not sticking etc which a cleaning and light lube and excercising may help cure.

Other thoughts are oil or carbon on the commutator or brushes or brushes backwards from previous wear and slant patterns

John T

hojon_1 · Sep 16, 2009

Did you polarize the generator? Search past Posts and you'll find out how to do it, when and why.

Whewn you say it's jumping mine did that until it charged up the battery then started acting right.

Keep in mind that the Regulator has relays that will cut in and out depending on battery volatge and current draw while charging.

At higher RPM's mine wouldn't charge (Needle went to 0) but at lower RPM's it showed around 10 amps. Once the battery finally charged up (13.5vdc using a volt meter) everything was normal and even at higher RPM's it shows 2 amps or so depending on the state of the battery.

Bob M · Sep 16, 2009

Good chance the problem is the ammeter itself.

If the needle is insufficiently damped an ammeter will dance even with a 100% healthy generator/regulator.

A quick test: With the engine stopped turn the lights on and then back off again. If when the switch is turned off the ammeter needle swings beyond center one more times before coming to rest you’ve found the culprit.

Unfortunately there’s nothing you can add to increase ammeter damping (capacitor, etc). Rather it’s a matter of simple friction in the needle suspension bearings. The only fix is ammeter replacement.

Kruse · Sep 16, 2009

I'm suspicious of the gauge also. But because the battery acts as a huge capacitor, I'm also curious as how your wiring is between the gauge and the battery.
With that being said, I've done some rewiring from scratch on tractors and off-road vehicles and when I do, I keep the ammeter out completely. Instead I put in a voltmeter. If your vehicle's battery voltage stays in the area that you want it to, you know your charging system works. Amp meters tell you that the system is charging (or discharging), but little else.
There is a reason that auto makers moved away from the amp meter and went to a volt meter. Of course, my opinion is completely different if you are keeping every stock looking, which you are not. My $.02 worth.

Anonymous-0 · Sep 16, 2009

I disagree with taking out the ammeter. The ammeter tells you current is REALLY getting to the battery. A voltmeter tells you that the voltage is right that IF the battery was connected, it would take current and charge. The voltmeter won't tell you the battery isn't taking charge from a bad connection or being sulfated.

Gerald J.

Anonymous-0 · Sep 16, 2009

Meter damping doesn't come from friction, it comes from designed for damping. Many a cheap meter has been made without damping because it takes more material and design time.

In the simple moving magnet meter used for a 12 volt vehicular ammeter, there needs to be a copper sheet that the magnet moves past to be a damper. In good designs thats probably a wide flat current carrying conductor. In the cheap meter that current wire is probably just a wire. Reads the same, but bounces like crazy.

And on a tractor not designed for an ammeter like my 4020, it could be the regulator is designed to vibrate slower to give a longer life. But it bounced my new ammeter from peg to peg, giving me no information. The alternator with solid state regulator fixed that problem.

The only cure for the bouncing ammeter is a better quality ammeter. Shake the prospects to see if they move freely and after being shaken they oscillate to settle back at zero. Those are the bad ones.

Gerald J.

Kruse · Sep 16, 2009

To each his own, but how many new cars or trucks have an ammeter? Zilch.

Anonymous-0 · Sep 16, 2009

And how much information is there on that voltmeter. Maybe that the igntion is on is all that the "voltmeter" in my '98 F150 tells me. For sure I can't judge battery charge with two calibration marks, one at 8 and one at 18 volts. I don't see it change with cranking or charging or lights on or off, engine running or stopped. Its just like the oil pressure "gauge" that shows mid scale for all conditions because the oil pressure sensor is an idiot light switch. These "gauges" are nothing but decoration. Totally useless for watching out for trouble or for learning all is working properly.

Modern cars don't have an alternator because it costs $50 to provide a decent ammeter shunt and remote indicator, and $25 to run the 140 amp circuit to the dash for a simple direct connected ammeter.

Gerald J.

Kruse · Sep 17, 2009

You say that modern cars don't have an alternator? Okay......

Anonymous-0 · Sep 17, 2009

Don't have an ammeter.

Gerald J.

GlenT · Sep 18, 2009

I installed a new ammeter from my JD dealer, made by Stewart Warner, and it is rock solid.

So, the cheap ammeter (made in India) I originally installed that jumped all over the place was the culprit.

Thanks for all the info. and suggestions.

630 Jumpy Ammeter Needle

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