Alternator getting hot.

[Les Harrison]

Hi Guys.
I have a 2005 Mitsubishi Pajero 3.2 turbo diesel and it started chewing out the inner alternator belt. I have discovered the alternator was getting so hot it was literally melting the inner belt. I hope I am correct in beliving the regulator is built into the alternator so I have changed the alternator but still after running a couple of minutes the alternator starts getting to hot. I have tried taking the positive wire from the alternator off, and then it will run cool however if I then connect the output of the alternator to the positive battery terminal it will run hot again. The alternator is indeed putting out voltage. I have checked all connections and battery terminals to make sure they are clean and connected. Bearings are free and easy. This is perplexing to say the least. I really have no idea what would cause this. Anybody been there done that.

[DibbyDibbyDJ]

With alternator connnected,and engine running, try connecting voltmeter between output of alternator and battery positive.

This will check the integrity of the battery cable.

Less than 0.3 volts is acceptable. If it is higher then the cable is compromised in some way

[Les Harrison]

With alternator connnected,and engine running, try connecting voltmeter between output of alternator and battery positive.

This will check the integrity of the battery cable.

Less than 0.3 volts is acceptable. If it is higher then the cable is compromised in some way

Thanks for the reply Dibby. I am helping a mate who is not so comp savy, he is working down Townsville at the moment and has the rig at his place in Babinda. As soon as he gets back we will try that. I see what you are doing is hitting the alternator output and the battery positive to measure the potential difference between them. So if there is a few volts difference the cable is putting up resistance, correct. However if I take that wire right off the alternator it dosent get hot at all.??

[DibbyDibbyDJ]

Thats correct. With the main cable off there is no output as alternator is self excited, and as soon as it sees 12v at that terminal it starts charging. i have seen over 70v at that output terminal with a high resistance cable.

[old Jack]

Most high resistance are caused by the cable terminals at each end of the wire and the adjoining 100mm of wire under the insulation where you can not see the problem.

OJ.

[erad]

How tight is the alternator drive belt? If it is slipping under load, it will soon heat the pulley up. And when you remove the 12V reference wire, there is no load and therefore the unit will run cooler than when it is loaded.

[Les Harrison]

Good point I will be checking that as well. Thanks for the input. Erad.

[Les Harrison]

Thats correct. With the main cable off there is no output as alternator is self excited, and as soon as it sees 12v at that terminal it starts charging. i have seen over 70v at that output terminal with a high resistance cable.

Dibby, Now you have my interest, you said the alternator is self excited. I was not expecting that. I was assuming apart from the charging wire to the battery the other two smaller wires were the alternator light through the ignition and the exciter wire. If the alternator is self exciting what is the other smaller wire doing. Is it that the alternator is indeed self exciting but the other wire is sensing battery voltage to control the regulator.?

[DibbyDibbyDJ]

i would have to check wiring diagram to 100% sure, but you may have regenerative charging on that model. When You lift off throttle and ECU knows car is travelling at speed the alternator CAN output more power to the battery. Whilst the engine is on overrun this would be less noticable. The other wire may be this wire to ECU.


I will try to check Diagram on monday to be sure

[Les Harrison]

I would appreciate it because this is getting confusing.

[DibbyDibbyDJ]

For some strange reason i thought you had a 2010, but then i re read thread. i will look at 2005 tomorrow.


This is 2010 diagram. https://imgur.com/nHOMMSL How many wires going in to your plug?