My alternator is not charging. So, a little background on what was going on and what happened. On my 299d xhp battery was old and the colder weather was killing it so i bought new battery and installed it. prior to the install the alternator was charging i was seeing approx.14V on the screen. I installed new batter started the cat up and now only showing 12.2V and of course it drops the longer the unit is running because not charging. I put another alternator on the unit had same issue so took it back and put the old one back on. I have checked all fuses inside cab all good. do not know if there are fuses somewhere else, I need to check. The wires on the back of the alternator i have the main wire going to the battery have a plug with a white wire in it and a single plug which is a green wire. With the switch on I get about the same voltage on the white wire as I have on the battery, I do not get any voltage on the green wire. If someone could help me out it would be great.
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CAT 299D XHP Alternator not charging
- Thread starter S.Fox
- Start date
Did you check voltage output right at alternator terminal? White wire is voltage sense wire, it controls output of alternator based on load. Its correct to have 12v on it with key on. I think Green wire is field excitation wire, it gets alternator to start charging. But it could also be for tach. If its for the field excitation, it should have 12v. Do you have a tach? You could have got a crappy rebuilt alternator, its common. Hopefully someone will be along and decipher your serial number.
Nige
Senior Member
Sounds like your wiring checks out. You probably got a bad rebuild. That, or your excite wire is compromised, (green crusties), and is failing under load.
Simon C
Senior Member
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- Jul 1, 2015
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How about 3 simple test with multimeter:
#1- With Engine running and revved up 1/2 throttle and Lights on and Heater Fan on Stab the Red Output post of Alternator with RED test lead. Stab the dead center of the Positive post of battery with the Black test lead. Any reading over 0.5 volts means cable is compromised.
#2 Same engine running stab the Side of the Alternator Steel Case on clean steel with the RED meter lead, and the BLACK test lead on the dead center of the Battery Negative terminal. Any reading over 0.5 volts DC indicates a compromised negative cable from Engine Block to frame back to battery. If you have a master disconnect switch it has to be on obviously. If the number is higher than 0.5 Volts DC put your meter leads on the master disconnect switch if you have one ( one test lead on each stud ) . What does that small test reveal ?
#3 Same engine running while revved and loaded up with fan and lights stab the R-Terminal of the alternator where the white wire goes in with your Red Meter lead and Stab the Dead center of the Negative post of your battery with the Black meter lead. What does it read.
Start with these three tests to eliminate bad cables under load. They can test perfect with no load and fail under load.
Simon C
do have a RMP (tach) but i was told that the green wire should have 12 volts to start the alternator to start but do not have it. don't know where it comes from in the system. Also, I did check at the alternator and still nothing.
According to diagram, field is controlled by white wire, R terminal. Tach is driven off off P terminal. You have your 12v at R, however, that does not have any load on it. You need to verify the integrity of that wire under load. If it’s impossible to access terminals with alternator in place and running, remove alt. and connect a 12v bulb (2-3amp) in series to white wire. Ground one side of bulb and turn on key, if bulb stays lit, you’re good to go. If it goes dim or goes out, you have a bad wire somewhere in harness.
Simon C
Senior Member
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- Jul 1, 2015
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- Rocky Mountain House , AB., Canada
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- Heavy Equipment Mechanic
Very good test to do to eliminate whether the computer is sending the signal consistently without dropping out because of a poor connection somewhere.
Wanted to say that owner said all the non-charging started after he changed the battery, makes me wonder if something happened to one of the connections in there while manhandling the battery out of the compartment. If he checks all we have suggested, something will come up as a weakness.
Simon C
Nige
Senior Member
Unfortunately that information is incorrect. The wire 403 GN to the alternator is not used in your particular machine application. The wire goes from the alternator into one side of the first major (31-pin) harness connector after the alternator but there is no corresponding wire coming out of the other side of that connector, instead there is only a blank hole.
I would imagine the harness is a "standard" one and it was easier to leave the wire in there than it was to build a different one without the green wire using a different Part Number.
Nice of Cat to add confusion, with phantom wires that lead no where. Where is tach signal pulled from?
Nige
Senior Member
Engine ECM - crank speed sensor.
Ok I was able to perform 2 of the three test you ask the third one i am goi g to have to build a some sort a lead i can not get to the white wire with it hooked up.
first test positive lead .08 Vdc
Second test negative lead .07Vdc.
I will complete the third test he ask about the white wire as soon as I can. My question is there another fuse that may have something to do with the voltage on the green wire somewhere under the cab. I have not raised it. I have checked all fuses in the cab and they are all good.
Third test 11.89 Vdc
Nige
Senior Member
You didn't see my answer above. The green wire connected to the alternator goes nowhere. See Post #11.
There is the main fues in the engine compartment. But if it was blown the engine would not even start.
I did see your I am just wondering what it would be there for. I was told that it was to enable the alternator to start charging. I was also told to put 12 volts to that spade and see if it would start charging but did not do that I did not want to cause more issue then I already have.
Nige
Senior Member
Whoever told you that was also not correct. it seems as though you have been getting some bad advice.
To excite an alternator that does not want to come out to play and start charging battery + voltage should be applied to the R Terminal, not the P Terminal. It says there right on the illustration (note on the bottom RH corner)