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Discussion Starter · #1 ·
I have the pleasure of repairing and maintaining a 2015 Bobcat 3650 with a Kohler engine. This thing has non stop problems and we are close to trading it in. I now have most of the problems fixed except the charging system. When the engine is first started, it will not charge until it is driven. It will sit and run on only battery until it is down to 8 volts or so. It doesn't matter if it is at idle or high engine speed. Our local dealer isn't much help. They replaced the alternator a few months after we got it but it still has issues. Does anyone have a similar problem or is this the way they are? I have never experienced a charging system that doesn't start charging as soon as it is started. Thanks for the help.
 

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Do you have "Chapter_15_Electrical.pdf"?

The service manual states:

OfficialServiceManual said:
With lights and other electrical loads off, the “break even” point should occur at approximately just above idle RPM.
I have a Bobcat 3650 (with the Yanmar engine), and it "breaks even" at idle; if I idle for a long time with multiple aftermarket accessories running, only then does Brutus draw down the battery.

 

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Discussion Starter · #3 ·
Thank you for the information. I will try this test but the thing I don't understand is why doesn't the alternator charge until engine RPM comes up. The guys that run the 3650 will start it and let it idle to warm up for over a half hour before moving it. This seems to be when we are having the problem. Once it starts to charge, it maintains 14.1 volts until the engine is shut off.
 

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The guys that run the 3650 will start it and let it idle to warm up for over a half hour before moving it. This seems to be when we are having the problem.
Why so long? I usually pre-heat the engine with the block heater, then just 2-5 minutes of idling (and cycling the hydraulics for the plow) before getting rolling.


Can you train the guys to idle shorter, and advance the engine speed control lever to raise the RPMs slightly while it sits idling (as instructed in the Owner's Manual under "Starting the Engine")?
 

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Discussion Starter · #5 ·
I've asked them multiple times to only start the engine a few minutes prior to using the 3650. I am going to check the amperage being used while at idle tomorrow. I have repaired a few loose connections already but there may be more. I like the machine and all of the features but I just need to get the kinks worked out. I will update tomorrow with the "break even test" results.
 

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Discussion Starter · #6 ·
I performed the break even test this morning. The thing that I noticed is that it will not charge at all until engine RPM hits 3300. After that, it will charge at 14.2 volts and put out over 30 amps even at low idle. Is it normal for the charging system to need the engine to run at 3300 RPM before it will charge? I've been repairing electrical system for a long time and this is the first time I've come across an alternator that doesn't charge as soon as the engine is started.
 

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Anybody have updated manuals for Kohler engine or for 2015+ models?

The thing that I noticed is that it will not charge at all until engine RPM hits 3300. After that, it will charge at 14.2 volts and put out over 30 amps even at low idle. Is it normal for the charging system to need the engine to run at 3300 RPM before it will charge? I've been repairing electrical system for a long time and this is the first time I've come across an alternator that doesn't charge as soon as the engine is started.
This can happen if the incoming alternator supply voltage isn't energizing the field coil appropriately.

I don't know if they've updated the manuals for 2015 or for the Kohler engine, but parts catalog shows 2015 Brutus HDPTO uses the Polaris MPN3040001 alternator, it's a newer Bosch model than mine.

Does this match your alternator? Can you get mfgr specs based on the maker's model #?
 
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