Battery problems, troubleshooting help needed


I have been trying to troubleshoot an electrical problem on my tractor (John Deere 300 with 16 hp Kohler single cylinder) and so far I am totally stumped. The problem is this: The battery seemed to be out of juice so I had to jump the tractor from my car. The tractor started right up and ran.... but as soon as I disconnected the jumper cables from the car, the tractor stalled immediately.

I am assuming the tractor should continue to run on its own power, so I started testing the charging system on it. The stator voltage was fine, around 30 volts AC. However when I went to check the voltage coming out of the rectifier, my multimeter went crazy and I could not get any consistent reading when connecting the negative of the multimeter to the engine block. It was as if something was interfering with the multimeter. But when I used the frame of the tractor for the negative, I finally got a consistent reading of around 0.3-0.7 volts DC. The negative battery terminal runs directly to the engine block and that connection was good. So immediately I assumed the rectifier was bad. After connecting a new rectifier still the same problem.

So next I hooked up the jumper cables again and shut off the car, keeping the cables attached.. and the tractor continued to run just fine. I checked the voltage across the tractor's battery and it was around 14.5 volts. I shut off the tractor with the key and the voltage dropped to around 13.5 volts. When I saw this I assumed the charging system was working and that my earlier assumption of a bad rectifier was incorrect. Then I removed the jumper cables and the voltage then showed 10.5 volts. Is it possible that the tractor's battery is bad or shorted, causing these issues???

Thanks in advance for any feedback...

-- Chris

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Hi Chris...

I suspect that you have one shorted (perhaps intermittently) cell in the battery.

A surefire quick and dirty test would be to switch the battery with another if one's available - but NOT with the one from your car, unless you have a car available that's older than the current computer ones.

Take care.


Reply to
Ken Weitzel

a characteristic of the kohler charging regulators is that on a totally dead battery, they won't do anything. when the battery voltage gets to about 8 volts if i recall correctly, they perform well. try charging the battery with a battery charger and check the voltage for proper charging. remember, there may be a current draw on the battery which is running it down over time.

incidentally, which type regulator is in your tractor? they come as a small heatsinked unit about the size of a deck of playing cards and also a larger unit about twice or 3 times that size.

the 16 hp magnum twins on up use a smaller unit mounted in the fan shroud with 3 push-on connectors. i use that type in an industrial app with a transformer to keep batteries charged. good luck, sam

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You have a 12 volt lead acid battery that reads 10.5 volts with no load on it. That battery is bad - no doubt about it. Replace it.


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Yes folks if the battery is low in power, you can't expect a sudden recovery, it will take at least 1.5 day to charge it. I am periodically charging my battery for my unused car in a garage.

Especially in winter, you need to keep the charge going or your battery could go dead, it happened to me before. Battery is like a human, it wants food, food, food. You can't leave it for 4-5 months without foods then give him foods again, it won't work.


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I think you lost the ground connection between the engine and frame. There ought to be a strap that connects them electrically.

I had this happen on a diesel, such that the only path to ground was back through the glow plugs. Put on the headlights and the engine overheats. Cute huh ?

Reply to
Rob Kleinschmidt

That says bad alternator/alternator path or bad terminal/connection... but since this is the third time I have heard this exact same problem in vehicles in two months, and each was fixed by replacing the battery... Shorted battery/bad post comes to mind. But onward into the post

That can 1) be a multimeter impedance problem. It can't read accurately if it's too low an impedance relative to the circuit being measured, or 2) be a directional problem in reading the rectifier (normal is it reads ok one way, doesn't read when the leads are reversed), or 3) the probe is inable to penetrate the corrosion, etc., on the contact point. (Scrape block before touching tip firmly to metal) or a combination of the three

or you were measuring the reference (negative) side of the alternator- which means no voltage. or you were trying to read AC on DC.

It was as if something was interfering

That level of voltage sounds like the voltage drop across poor cables/from high output from an alternator to a battery. It is also close to the voltage drop across an alternator diode.

You were not reading the battery, you were reading the alternator voltage output into the tractor circuit.

Alternators output around 14 volts, fully charged auto-type batteries around

11.5, give or take a few tenths

I shut off the tractor with the key and the voltage

Should have dropped to 11.7 if the battery had been accepting charge and no current was flowing in or out.

When I saw this I assumed the charging

First, remember that it's the rectifier path, not just the rectifier, and

second, voltage does not mean an appreciable amount of charge is going into/being accepted by the battery. It could be 14.5 volts and milliamps going through the battery

Then I removed the jumper cables and the voltage then

So before disconnecting, charge was still flowing from the car battery to the tractor battery, giving you an extra 3 volts until you disconnected the jumper cables.

Is it possible that the tractor's battery is bad or

Yes. It should read around 11.5/11.7 (memory here) when charged if the battery is ok.

But it also has to deliver amps as well - so just reading 11.5 is not enough - if it's outputting the amps of a watch battery it's not ok, but reading 11.5 and delivering rated amps does.

Reply to

Thank you for the quick response.

The regulator (rectifier) that I have is smaller one about the size of a small deck of cards (engine is a 16 HP Kohler K341AQS). It is mounted on the fan shroud, with 3 connectors, as you mentioned.

I have thoroughly tested everything I can think of as suggested in the other posts (checking ground, voltage, etc) ... so I will be taking the battery in to be tested and will post the results of what happens.

Thanks again!!

-- Chris

SAMMM wrote:

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I seemed to have found the solution to the problem I posted: a dead battery. After replacing the battery (load test failed at the store), everything is working fine. And, the output from the rectifier now shows about 14-14.5 volts DC, as it should. So it seems that the problem all along was that the dead battery was causing the charging system to not fuction at all, and made it seem that the rectifier was bad.

Thank you again for all of the feedback. I hope this helps others that may find this same problem. Now I have a brand new rectifier that i don't need... sounds like Ebay material!

-- Chris

snipped-for-privacy@group> Hello:

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Well, sounded like I thought it might have been. You left it without charging for a while, this might have killed the battery and there will be no way to bring it back. I test this theory on a brand new batter with full power; it did die one day for not charging it periodically.

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You were probably right about the rectifier. The tractor battery will, if still good, take more than a few minutes to recharge.

10.5 volts could indicate either a bad cell, (from the abuse delt by the bad rectifier) or a seriously undercharged battery, (from the inoperative charging system). Try leaving the battery on a trickle-charger overnight before trashing it. MadDog
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? ?????? ??? ?????? news:

Don't rechargeable batteries need 1/10 of their Ah rating for charging??What is the Ah rating of that tractor battery?

-- Tzortzakakis Dimitrios major in electrical engineering mechanized infantry reservist dimtzort AT otenet DOT gr

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Tzortzakakis Dimitrios

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