We just bought this 279d3 Cat skid steer with 38 hrs from a private owner. We found the alternator problem once we got it home. The alternator we removed was melted on the inside where the voltage regulator is. We bought an aftermarket alternator and it won’t make power, the exciter wire ( white ) has battery power. Everything looks as it should, I mean the machine is almost new, I read that the ecm can adjust how much voltage is pushed into the battery so that it’s not always at 14.4 volts , does that have something to do with it? Im pretty frustrated at this point, I’ve checked the connections as well as the ground next to the battery on the frame. I checked the ground on the frame down inside on the ground strap that comes from the engine but not on the engine side of it. I checked the fuses that go to the alternator. Weird thing is that the alternator would start charging after doing some checks and taking off and putting on the white wire but once we shut it off and start it then it won’t charge anymore. The battery is good, we removed it and charged it then reinstalled it and it takes a charge and stays charged for a while but eventually gets low. The only other thing that didn’t work was the radio which had a blown fuse in the back of it. any ideas would be appreciated, Cat wants $1000. For an alternator, is it really necessary to spend that much for an alternator? Is there something special about it? thank you in advance.
Just for the sake of confirming, did you check the voltage on the 123 white wire when it was connected to the alternator or unhooked?
Unhooked
Check it with it hooked up, could be a bad spot in the wire causing it not to carry the load when connected.
Ok, good idea, could I just run 12 volts from the battery to the alternator with the white wire off just to see if the alternator is working?
Yep that will tell you that the alternator is working correctly.
Thank you
we had a similar problem with a CAT CTL. the solution ended up being: switch it on and let the display do the complete self test. after that you started it and it would charge just fine. but when started without the self test, it would not charge. might be worth a try.
Thank you I appreciate that information very much.
This is an update for anyone who cares. We tested The aftermarket alternator and decided it was defective, we received another alternator from the company as a replacement and that one doesn’t work on the skid steer either. While that was going on we took the original alternator (mitsubishi) to a professional rebuilding shop. These people have been in business for decades. They cannot get the alternator to work after rebuilding it. He brought in the guy that does the field work for the company and the 2 of them have spent too much time on it but cannot figure out why it won’t work. is there some kind of computer chip in these caterpillar alternators? This is weird, once we get the final word from the rebuilding shop we plan to order an OEM alternator and try that. If that doesn’t work it’s going to the Cat dealership.
There is only 2 options here, and keep in mind an alternator is just an electric motor (generates power vs consumes) 1 - windings are shot and the "motor" must be rebuilt 2 - voltage regulator (which yes, has compact and semi-complex circuitry) has failed