Alternator Testing

[Niloc]

I recently had my 2.8CRD returned from a garage following timing belt change and rear crank seal replacement.

Now, the car is not charging it's battery. Garage said alternator is goosed, but i want to make sure. I've tested continuity between alternator and B+, alternator to B- and it's all ok. I've measured battery voltage on one side of the excitor coil connector, and 300mV (on multimeter) on the other side with the engine running. All i see is battery voltage on the alternator. Any other tests i can do?

[soupstone]

What voltage do you have over the battery +ve and -ve with the engine running, and does it hold steady when you switch on in-car equipment?

[Niloc]

The alternator is not supplying any current to the battery. Voltage continuously lowers, even more so when more equipment is turned on.

Thankfully, there is only a bit of electronics and fuel pump running when the engine is running so it can be used between charges

[mikebh8]

Hi, with the engine off, measure the battery ( you should have whatever is left,probably 12.something volts)

With the engine running, first of all if you have the small red battery light on the dash on it means the alternator won't charge, however if it's on its way out bit still workng you will get measurements with little voltage above the first reading. If it is on and is charging, you should get 13.80-14-40 volts steady.

Hope it helps.

[Niloc]

It isn't charging at all. The battery indicator is not illuminated. I'm going to try a couple of things today - disconnect excitor coil with engine running (to see if the battery indicator comes on). If it does, then likely the controller is working and seeing the coil.

I'm also going to try manually running the excitor coil with a test lamp.

[gordy]

Just a thought on work around gearbox. Has the earth strap been refitted...

[Niloc]

Continuity on positive and negative was confirmed on the original post.

I did try:

Removing the excitor connector with engine running - battery light came on so I suspect the ECU is seeing the coil and thinks it is regulating.

Measuring voltage on the excitor return wire - was at 200mV, so the ECU is trying to operate it at a high rate (the lower the voltage at this point, the more it is being dragged to ground)

Force the excitor coil with battery feed and test lamp to ground - light stayed lit and alternator gave nothing.

I have ordered a replacement alternator, so hopefully Wednesday I'll be back in action

Edited March 13, 2017 by Niloc

[Neilgibson]

If you check the exciter wire to the alternator with a dwell meter rather than voltmeter you will see not continuous voltage but a pulse width modulation signal from the body control module. I wouldn't go power probing it if I were you. The battery warning light is NOT connected with this " exciter" wire these days, it is turned on and off by the engine ecu. If it is on it doesn't necessarily mean the alternator isn't charging. It might mean it's overcharging or there is a fault in the smart charging system. Ever wondered why there is a battery temperature sensor in the battery tray? Smart charging. If you have any alternator issue the first thing to do is isolate it from the smart charging by disconnecting the sensor wire. It will then use its inbuilt voltage regulator and perform as a stand alone unit. Unless it's broke of course

[Niloc]

Neil, i understand the battery light is controlled by the ECU - i unplugged the excitor and the light came on which proved the ECU could see the coil and was most likely not at fault. In testing, i used a test lamp to provide some resistance through the excitor. I didn't want to ground it directly.

Without the equipment to view a pulse, a multimeter gives an indication of the pulse width. As it was, the measured voltage was low indicating the ECU was pulsing on more than off.

Anyway, i replaced the alternator with a used unit and it worked. I outlined the fault finding above to assist anyone else with alternator issues.