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Old 06-27-2013, 06:44 PM   #1
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Odd 12V charging problem

So I bought this bobcat 773 to use around the farm. (OK, not TECHNICALLY an RV, but still a fun toy). It started maybe 2 or 3 times, then would not start unless jumped. It has a voltage gauge in the cockpit that reads about 14.5V when running, which as I understand it is the correct voltage for charging.

So, I figured charging system working, must be bad battery. So I go buy a new battery, install it, and it fires right up.... 2 or 3 times, then dead battery.

Now, the time span between the starts was weeks, so nothing is draining the battery when it's sitting.

So, I jump it off, and put my VOM across the terminals; 14.53VDC

This exhausts my knowledge of charging systems. How could I measure 14.5V at the battery when the engine is running, but not get any charge into the battery? I WAS careful to measure at the battery terminals, not at the cable ends, so dirty connectors are not the issue.
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Old 06-27-2013, 08:07 PM   #2
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I would suspect you have a bad ground. You can measure volts across a weak connection but when you put a load on the system to start it, you cannot get the Amps output.

I'd start where your negative battery cable is bolted to the frame
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Old 06-28-2013, 05:00 AM   #3
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Check ground connection from battery to frame and battery to engine.

Also do same for power.

Is it dead (nothing when key turned) or low (slow crank)

Could be bad ign switch or connector in harness.

Order the factory manual.

Have fun making attachments.

And do carry load low...
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Old 06-28-2013, 07:01 AM   #4
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Disconnect the battery when not in use. If you learn how to measure current you can disconnect the negative or positive lead and put the meter in series to measure any parasitic loads.
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Old 06-28-2013, 07:25 AM   #5
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Alternators can sometimes cause a weird problem like you describe. They have internal diodes and if one shorts out it will discharge the battery when not running but still charge when running. On a car or light truck you can sometimes hear one with this problem by carefully listening and you may hear a weak high pitched whine. If the short is bad enough you can feel the alternator housing and it will be warmer than surrounding parts. Just a thought and something to look for.
Good luck and safe travels!
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Old 06-28-2013, 09:16 AM   #6
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Thank all for your responses. I will check and clean aIl grounds and connections. I feel the need to clarify what the symptoms are:

1: Fresh battery installed sat for weeks before starting the engine normally, so parasitic loads are not a problem. Subsequent starts had periods of days between.
2: Each start was less energetic, until the engine wouldn't turn over at all, indicating to me that the battery was not being charged between starts. I used the machine 3 hours last time it started, shut it off for lunch, and wouldn't restart when I went back out, indicating that 'miller time' had arrived.
3: I put original battery on a charger, and it took the charge fine. I now use it as the jump battery, so $85 down the drain on the new battery.
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Old 06-28-2013, 12:42 PM   #7
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Well, sometimes you just have to substitute parts when troubleshooting. Somehow your charging system is either failing or you have a large draw while running and the simple stator type charger cannot keep up. I realize you measured the 14 volts with it running but once you start moving the increased rpm may cause a connection problem or the stator to fail. If you can do some temporary wiring of your meter probes directly to the battery and drive around you should soon see the story.
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Old 06-28-2013, 12:55 PM   #8
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Quote:
Originally Posted by YC1 View Post
Well, sometimes you just have to substitute parts when troubleshooting. Somehow your charging system is either failing or you have a large draw while running and the simple stator type charger cannot keep up. I realize you measured the 14 volts with it running but once you start moving the increased rpm may cause a connection problem or the stator to fail. If you can do some temporary wiring of your meter probes directly to the battery and drive around you should soon see the story.
There is, as I mentioned, a voltmeter in the cockpit that reads 14.5V when the machine is running. I did not notice it vary with rpm changes, though I did not specifically watch for it.

Maybe I should join a skid steer forum and post my problem there, but I know this forum is rich with 12V charging system knowledge and so thought it might be an obvious problem/solution to someone.
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Old 06-28-2013, 06:04 PM   #9
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Because the voltmeter is reading 14 volts does not mean that voltage is getting to the battery. That is why I suggest measuring at the battery with the thing running. Troubleshooting 12 volts systems and owning a service center that deals with those systems is difficult enough when you have hands on. Doing it over the internet poses some challenges and digging out specifics can be difficult. On some ocassions I have the OP call me so we can play 20 questions. Often a sublte clue or something the OP omitted because they thought it was not important is the clue. So be patient. There are some talented individuals here. I still suggest connecting a voltmeter across the battery while it is being run and in use. Either the battery is not getting charged or you have a load on it such as some headlights etc.
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Old 06-28-2013, 06:10 PM   #10
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I have had battery cables go bad before. Replacing the cable solved the problem. Couldn't tell the cable was bad by looking at it.
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Old 06-28-2013, 06:20 PM   #11
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Quote:
Originally Posted by YC1 View Post
Because the voltmeter is reading 14 volts does not mean that voltage is getting to the battery. That is why I suggest measuring at the battery with the thing running. Troubleshooting 12 volts systems and owning a service center that deals with those systems is difficult enough when you have hands on. Doing it over the internet poses some challenges and digging out specifics can be difficult. On some ocassions I have the OP call me so we can play 20 questions. Often a sublte clue or something the OP omitted because they thought it was not important is the clue. So be patient. There are some talented individuals here. I still suggest connecting a voltmeter across the battery while it is being run and in use. Either the battery is not getting charged or you have a load on it such as some headlights etc.
Thanks for your input. The bobcat has a manual throttle (kind of like a tractor) and so engine rpm does not vary much when its in use, only under load, etc. I revved it up to the position I normally run it at and checked the voltage, still around 14.5V both on the gauge in the cockpit and at the battery on my meter. This time I checked the center of the battery terminals, and the cable ends to see if there was a difference, there was none.

I would have to rig a harness to be able to run it and monitor the voltage at the same time, the battery is not near the seat.
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