parasitic draw on a 420 positive ground generator system

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Paul Buhler
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parasitic draw on a 420 positive ground generator system

Post by Paul Buhler » Mon Mar 20, 2017 10:25 am

Hi
I seem to have developed a parasitic draw meaning my battery goes dead when the tractor sits
The battery has been checked and holds a charge well
It shows about six and a half volts when out of the machine
and six and a half volts in the machine with the switch off
At the distributor I am showing about four and a half volts with the ignition switch off which confuses me
I would not expect to see any current there when the ignition is off. So for the short term I unhook the positive strap from the battery when I am done using it and keep the battery on a trickle charger
This works, but I want to fix this
I am assuming that there is a problem with the ignition switch but before buying a new one I thought I would ask for thoughts here
Thanks in advance
Paul
Paul Buhler
Killington, VT
420c 5 roll with 62 blade, FOPS, and Gearmatic 8a winch

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Lavoy
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Post by Lavoy » Mon Mar 20, 2017 2:32 pm

Check for wiring harness short, regulator is a common draw when they fail.
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Parts and restoration for antique and late model John Deere crawlers.
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Paul Buhler
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Post by Paul Buhler » Mon Mar 20, 2017 3:01 pm

Thanks. Harness was replaced two years ago. Regulator is quite old; I have a spare waiting to be installed. Only the start switch will be original if I swap out the regulator. That said, I never rule out a loose connection, cut insulation, something shorting out, etc.
Paul Buhler
Killington, VT
420c 5 roll with 62 blade, FOPS, and Gearmatic 8a winch

mini kahuna
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Post by mini kahuna » Mon Mar 20, 2017 5:04 pm

I will suggest the regulator as well, I have had more than one do exactly what you are describing....one would only do it intermittently.
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Stan Disbrow
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Post by Stan Disbrow » Tue Mar 21, 2017 4:57 am

Hi,

Inside the regulator box, there are two relays. One is the actual regulator which switches current on and off to the generator field. The other is the Cut Out relay. That is meant to open up when the ignition switch opens. When the ignition is on, it will be closed.

The cut out relay may have an issue where it lets some current thru when open. That can be a weak spring, gunked up contact points, bent contact arm, or even a carbonized bug.

If the cut out is at fault, you should see voltage on the gen field terminal with the machine off.

But, you mentioned voltage at the ignition points. That comes from the ign switch, which is rotary and so might have some wear which now lets it have a poor path when in the off position.

My 420 has a bad ign switch, but it is opposite: poor current in the first position. Cuts the machine off sometimes. So, I added a bypass switch and left the old switch in place since the lights sections are still fine.

Stan
There's No Such Thing As A Cheap Crawler!

Useta Have: '58 JD 420c 5-roller w/62 inside blade
Useta Have: '78 JD350C w/6310 outside blade
Useta Have: '68 JD350, '51 Terratrac GT-25
Have: 1950 M, 2005 x495, 2008 5103 (now known as 5045D)

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Stan Disbrow
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Post by Stan Disbrow » Tue Mar 21, 2017 6:46 am

Hi,

As long as we are on the subject of regulators.....

These kind are electromechanical. They have two relays inside the can. One is there to cut out the generator from the battery once the ignition is shut off. Even the three-brush generators (M series) have one. If it were not there, the field would stay energized with the switch off.

So, if the cut out relay fails to open, the field coil will stay energized with the ign off. If it fails to close, the generator will not charge. This relay is Normally Open, so it needs power applied to it from the ign switch for it to Close.

The other relay is the voltage regulator. It is Normally Closed. It will supply power thru the cut out relay contacts to the generator field coils. This makes the generator operate and charge the battery.

As the battery voltage rises, power passes thru a ballast resistor in the VR housing to the VR relay coil. The resistor sets the regulated voltage level. As that is reached, the VR coil pulls on the contact arm and opens the circuit to the gen field. That shuts down the generator until the batt voltage drops some and the VR relay coil lets the contacts make again.

The VR coil, when everything is operating normally, sort of buzzes as the voltage drops from the load (usually the ign coil) and rises from the generator output. It is opening and closing the entire time the machine is running.

There can be several problems with relays. First, the coils can go bad and so will not work at all. The contacts can crud up and not make, even though they close. They can pit and/or carbonize and sort-of make when they are supposed to be open. Finally, that ballast resistor can have an issue where the voltage regulation point changes.

So, now that ought to be enough info to help someone troubleshooting charging issues with the voltage regulator.

Stan

And I just added a couple of empty posts due DeBug due to my using contractions again!
There's No Such Thing As A Cheap Crawler!

Useta Have: '58 JD 420c 5-roller w/62 inside blade
Useta Have: '78 JD350C w/6310 outside blade
Useta Have: '68 JD350, '51 Terratrac GT-25
Have: 1950 M, 2005 x495, 2008 5103 (now known as 5045D)

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Paul Buhler
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Post by Paul Buhler » Tue Mar 21, 2017 10:06 am

Thank you guys. Always appreciate your thoughts and time.
If the cut out is at fault, you should see voltage on the gen field terminal with the machine off.
Stan that is easy to check. Thanks for the test. I try not to be a parts replacement mechanic - costs too much to replace good useable parts needlessly. I suspected the ignition switch when I found juice at the distributor when the switch was off. If your test proves that the cut out is not at fault, I will start with the switch.
On the home stretch as far as the electrics are concerned. Over the years I have gradually rebuilt, repaired, or replaced almost all of it excepting the switch and regulator. Either could be tired at this point.
Paul :D
Paul Buhler
Killington, VT
420c 5 roll with 62 blade, FOPS, and Gearmatic 8a winch

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Stan Disbrow
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Post by Stan Disbrow » Tue Mar 21, 2017 1:23 pm

Hi,

Yes. A good meter (like a Fluke 70 or, better yet, 80 series) meter is costly, but it then allows you to not buy unnecessary parts. I call that shotgunning, and in this case, shells are costly!

I just used a Fluke 87 DVM to t-shoot an apparent transmission issue in a 1999 Dodge with a Cummins. How can a good meter shoot transmission trouble you ask? Because it has a fast analog bar graph along the bottom of the display.

The issue was that at 45 MPH or so, once the thing had run a while, then set about an hour, then was run again....the lockup clutch would start locking and unlocking in rapid succession. This, until it had gone about 10 miles then the action slowed until it stopped doing it.

So, heat soaking of something was at fault. And, the trans is controlled by a computer. It seemed to me that the heat soaking was towards the front end. Hmmm. Alternator?

In this iteration, the regulation is via the controller. So, I stuck the Fluke leads into a cig lighter plug and went off. When the trans was acting up, that bar graph on the meter showed me a lot of variation at high frequency. Switching to AC showed how much, and switching to Frequency showed how fast.

The only thing better would have been to hang an oscilloscope on, but I had enough to go by with just the good meter.

The culprit turned out to be badly worn slip rings on the alt rotator shaft. Since in an alternator this is the field coils, their mag field was noisy as a result. And, that noise has to come out the back end of the alt and then all thru the electrical system.

And, into the controller, which is then misreading every sensor. It only affected the transmission because none of the diesel engine is run by that controller. If it had been a gasser, it would have quit and then restarted and run fine until it quit again.

Alternator a lot cheaper than any other parts it might have been. So, once again the good meter pays for itself.

The bottom line: be happy you are shooting a 420!! :P

Stan
There's No Such Thing As A Cheap Crawler!

Useta Have: '58 JD 420c 5-roller w/62 inside blade
Useta Have: '78 JD350C w/6310 outside blade
Useta Have: '68 JD350, '51 Terratrac GT-25
Have: 1950 M, 2005 x495, 2008 5103 (now known as 5045D)

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Paul Buhler
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Post by Paul Buhler » Wed Mar 22, 2017 9:34 am

You forgot to mention the experience and skills you have to know how to use these tools. I am still just above the continuity or no continuity stage of using a multimeter.
Paul Buhler
Killington, VT
420c 5 roll with 62 blade, FOPS, and Gearmatic 8a winch

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Stan Disbrow
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Post by Stan Disbrow » Thu Mar 23, 2017 10:46 am

Hi,

Time to teach you about the voltmeter part, then. You have two: DC and AC. Use the DC one on the old 420.

You have a 6.3 volt nominal system there. That means neither charging or discharging. The only major load you have is the starter. That will pull the battery down to around 4.5 volts. Charging will see about 6.8 volts or so.

All you need to do is hang the positive lead onto ground and poke at things with the negative lead and see what is where. Of course, with it off, there should be nothing anywhere beyond the input side of the ILDB switch.

You can save the AC voltmeter for working on house and shop wiring. There will be no AC anywhere in a generator system. You use the AC side sometimes on alternator systems because when they have issues, there is usually some unwanted AC riding on top of the DC. But, that is not on a 420.

Stan
There's No Such Thing As A Cheap Crawler!

Useta Have: '58 JD 420c 5-roller w/62 inside blade
Useta Have: '78 JD350C w/6310 outside blade
Useta Have: '68 JD350, '51 Terratrac GT-25
Have: 1950 M, 2005 x495, 2008 5103 (now known as 5045D)

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