Alternator dead -300tdi

[Oberon 110]

Hi all, as per the title it looks like my alternator has died (300tdi in a 110).

I was parked in town and the car wouldn't crank - got a jump from an RACQ guy, and he got "nothing" off the back of the alternator when he tested it. Obviously it would follow that the alternator has had it, however the alternator is not more than 2 years old so I'm a bit surprised. Also worth mentioning is that the battery warning light on the dash used to always iluminate for a few seconds on startup, but has recently stopped doing so - I'd assumed a blown bulb.

So, I'm wanting trouble shoot any and every possible cause of the above without replacing the alternator, if at all possible! I haven't been able to put a multi meter on the alternator myself so not sure exactly what voltage it's outputing.

Thanks in advance

[TonyC]

Hi Oberon,

I'm no auto electrician, but my understanding is the dash warning light is part of the the field winding circuit.
So if the lamp is blown, or the circuit is open, the alternator won't charge.

Tony

[Tins]

Hi Oberon,

I'm no auto electrician, but my understanding is the dash warning light is part of the the field winding circuit.
So if the lamp is blown, or the circuit is open, the alternator won't charge.

Tony

Pretty sure that's correct on a pre "smart" alternator, pre CAN BUS car. Replace the globe and see what happens.

[Old Farang]

Yes, a 2 wire alternator of that vintage needs a battery voltage to excite the field windings. That voltage source is via the "ignition" lamp on the dashboard. It works in a similar way to the old "dynamo" DC generators.

[Oberon 110]

Thanks all for your replies, very helpful info. Have swapped the bulb with the one in the high beam slot. Still no charge or battery light illumination, but the high beam indicator doesn't illuminate anymore, so obviously the battery light bulb blown. Not sure what's happening but I'm still hopeful the alternator is fine and there's some other simple fault in the circuit

[Oberon 110]

Thanks all for your replies, very helpful info. Have swapped the bulb with the one in the high beam slot. Still no charge or battery light illumination, but the high beam indicator doesn't illuminate anymore, so obviously the battery light bulb blown. Not sure what's happening but I'm still hopeful the alternator is fine and there's some other simple fault in the circuit stopping excitation of the stator.

[Old Farang]

On some of those alternators the field connection terminal (the small terminal), can develop a high resistance. It is usually a bad crimp joint, or corrosion. Carefully undo the nut on the terminal, remove the lug and make sure that the lug is tight on the wire and clean.

Ah, your explaination is a bit confusing? Are you now saying that the high beam lamp does not work anymore? If that is the case, then there is either a ground fault on the field wire, or the alternator has an internal fault, which blew you test lamp.
How are you testing the output to know that it is not charging, or does it have an ammeter?

Scroll down a bit:

add link: Alternator Exciter Wire Light | Electronics Forum (Circuits, Projects and Microcontrollers) (electro-tech-online.com) (https://www.electro-tech-online.com/threads/alternator-exciter-wire-light.148372/)

[Oberon 110]

On some of those alternators the field connection terminal (the small terminal), can develop a high resistance. It is usually a bad crimp joint, or corrosion. Carefully undo the nut on the terminal, remove the lug and make sure that the lug is tight on the wire and clean.

Ah, your explaination is a bit confusing? Are you now saying that the high beam lamp does not work anymore? If that is the case, then there is either a ground fault on the field wire, or the alternator has an internal fault, which blew you test lamp.
How are you testing the output to know that it is not charging, or does it have an ammeter?

Scroll down a bit:

add link: Alternator Exciter Wire Light | Electronics Forum (Circuits, Projects and Microcontrollers) (electro-tech-online.com) (https://www.electro-tech-online.com/threads/alternator-exciter-wire-light.148372/)

Thanks for the tip regarding the field connection wire, I'll check that out.

Regarding the dash lamps, I was saying that I had swapped the high beam bulb (has always worked) for the battery bulb (stopped working shortly before the battery went flat, no charge since); after doing this, no high beam light on the dash when high beams are on, but also still no battery warning lamp.

Now with all this being said, today the battery light came on, and then went off after a few moments of higher rpm - just as it should. I put a multi-meter on the battery and it was charging normally - sitting at around 13.5V, dipped to 12.8V or so when I turned the lights on but then came back up to more than 13V after hitting the throttle (although I suppose the voltage should come back up at idle too?). Then when I started the car this eveing, no battery light at all. So my thinking at this point is that the alternator is fine, but there's an intermittent fault somewhere. Perhaps the field conmnection terminal?

Bit of a confusing one, but again, appreciative of all your responses. Cheers

[Oberon 110]

Just to close this one out, after trouble shooting a few things, the issue seems to have been with the brushes - pulled the brush/reg pack out to get the part number, and when I put it back in the alternator charged (mostly) fine. Output was still a bit low, and I measured around 840mV across the alternator when I did a diode test (which I belive is just a bit higher than it should be). So obviously the alternator is not helathy - ordered a new 100 amp Hella one, will be going in when I get a free weekend.

The excitor wire get's a relatively healthy voltage, maybe .5V less than the battery, and I haven't had any issues since. Dirty brushes? Anyway, hope anyone with the same symptoms as me finds this thread helpful. Thanks all for your responses.