Komatsu PC210LC-6K alternator wiring harness resistor

[husabetunia]

Hi!

A new owner of older Komatsu excavator here and struckling with alternator wiring harness.


The machine has an aftermarket alternator (Prestolite 66021507) and it does not start charging without little 'kick', meaning that I have to excite the alternator a litle extra with a voltage testing pen to get it doind it's job (by testing between the battery positive and indicator lamp connector).

So, I checked on the wiring schematics and found out that the charging indicator wiring has a resistor unit in it and I wonder if that unit is faulty. At the moment I am reading only +2 VDC at the indicator pole before engine start up.

Do you happen to know where exactly this resistor unit should be located at the machine? Somewhere in the engine bay or inside the cabine maybe? According the schematics it should be inside the engine bay, before the SWP connector, right?

Thanks a lot!

 

[007]

I am assuming is 24V system.
I cannot see a resister in the circuit you provided so how are you determining there is one?
Typically the alternator is excited by a charging light globe or a fixed resister.
The globes were typically 2watt and have approx 0.083Amps flowing to excite the alternator in 24V system.
This would have been a 288ohm resister approx.
If the globe was to small you might have a problem but a larger globe no problem so the values are not that critical.
Typically you would see about 2Volts at the ign terminal on the Alt with the key turned on engine not running.
So the voltage you are seeing sounds good.
There can be huge tolerances in some alternators so yours might just need a slightly larger bulb or lower ohm resister.
A second problem could exist in that one of the internal diodes in the alternator is bad.
There are nine in there and one can go open and the alt will still charge with reduced output and be hard to excite due to that bad diode.
Its hard to hear on the machine but on the test bench the alternators often have a squealing sound when it has issues with the diodes.

 

[husabetunia]

Thank you, very useful information indeed!

Yes, it's a 24V system. The resistor "resistor for shut-off valve" is marked with green in the schematics, located next to the fuel pump shut-off valve. I think this is where the indicator wire is powered from. The resistor seems to consist of two parallel 390 ohms resistors, so it should be approx. 195 ohms together.

About the second possible problem, good call! I'll try to measure if I can spot a broken diode in the alternator. Yesterday we got the alternator charging at 25 - 28 Amps after a kick in the indicator pole. It was with pretty empty batteries and about - 10 degrees of Celsius, so maybe it's a bit low-ish, but not sure because of the low ambient temperature.

Anyhow, I have purchased a brand new alternator, I'll try it on the machine and see if it wakes up with the + 2 VDC the indicator wire has to provide. The first attempt with the new alternator was a miss, because I didn't spot it has no wire between battery negative and field negative poles as OEM.

Thanks again!

PS. the manufacturer states that the incidator post voltage reading should be max. +3 VDC, so maybe I need to crank the voltage up by fixing the resistor package. That is if I cannot spot any broken diodes in the alternator.

 

[007]

I do not think the resisters you reffer to have any thing to do with alt.
It is a 55amp ALt so should have pushed out more than 28amps?
If you pull the alt to pieces i can help with tests but no need since you have new one coming.
Yes specs say alt is fully insulated so you need to earth the alternator properly.
Cheers

 

[LACHAU]

I saw another diagram of the PC210LC-6K!!!

 

[husabetunia]

Very good, thank you Lachau!


I am afraid the wiring diagram I am using is for the PC210LC-6 -version, not for the British made -6K I have... So there might be physical differences indeed!


The main difference between those two diagrams seems to be that according to my diagram the alternator warning light pole is powered / excited via the fuel pump shut-off valve. The shut-off valve is powered when ignition is ON. In addition to that, the D poleo is connected parallel to starter solenoid negative signal pole to prevent cranking when the alternator is charging.

In Lachau's diagram the the D-pole of the alternator is powered directly using starter's / alternator's battery positive directly. So once the main battery relay is connected, the alternator will be excited.

So, bringing it all together, a resistor unit is being used for alternator excitation voltage. I asseme it's because there is no traditional bulb for the charging indicator, but a electronic user LCD-panel / monitor instead.

Cheers!

 

[007]

Yes i think you are correct.
Is very confusing when you have more than one diagram.
I am not sure i agree with your starter lockout description, but from the second diagram it seems clear they are just forcing the alternator to excite using the two resistors 195 ohm.
Which is fairly heavy start up current but no big problem.
The alternator might start ok with one resister but they double it for redundancy?.
The only way you can test such things would be to remove the excite wire from the alternator and short to ground through your multi meter and you should get aprox 0.123amps flow.
Ether way the 2V connected you are seeing is normal so i expect your new alternator will resolve this issue.
Cheers