alternator

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Originally Posted by drivesafe

Hi Rich, it is unusual for the voltages to swing some much in as short a time that those reading were changing.

The D3 alternators are big enough to cause those sorts of readings, particularly if the reg is stuffed.

BUT, and this may sound like a stupid question, have you check the battery in the DMM, because this can cause similar type readings. Also loose connections can also produce the same effects.

Another test would be to measure the voltage on another vehicle and see if it is constant or jumping around like you had.

It is most likely your alternator, but it may save you some messing around if you test your DMM.

Just a suggestion but I have been through this very scenario quite few time lately with customers and low batteries have caused the erratic readings.

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It was a brand new duracell battery in the DMM and I hardwired the leads to the battery too. On the way home after that video it settled back to a steady 14.1v. Interesting to watch to say the least.
Yes I definitely think the replacement alternator will fix it. (Finger crossed though)

Another consideration is that the Engine Management ECU is a player in this game and it seems to vary the voltage outpoint setpoint for the alternator depending on a few operating variables. If you look at the charging wiring circuit you will see 2 wires coming from the Engine Management ECU. Land Rover provides an explanation on what the variables are and what voltage levels to expect.

DISCO3.CO.UK - View topic - Alternator overcharging?

So, apparently, brief rises to around 16 volt with a cold battery may not be reason to panic. I suggest that people research the Land Rover data before condemning alternators.

It's the quick fluctuations that's causing impact as in the video, not so much the actual voltage.

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Originally Posted by ~Rich~

It's the quick fluctuations that's causing impact

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Hi again Rich, and its those rapid LARGE voltage changes that lead me to thinking the problem is not your alternator but something to do with the DMM and/or its connections.

I'm not ruling out the alternator as the problem, but when you have a massive capacitor, like your battery, connected to the system, I would have expected a MUCH slower change between those LARGE voltage reading differences.

Do you by any chance have access to another DMM, and if so, try put them side by side and see what you get?

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Originally Posted by ~Rich~

Strike 4 - New Genuine L/R alternator fitted last Friday, on Monday leaving work I noticed on startup :
Dashboard displays pulsating, Radio cutting in & out and the Handbrake light flashing orange!....
Well I spoke to both Auto Electricians - Faulty Alternator!!!!

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I think the possibility of a faulty DMM is nil. A faulty battery connection or earth is a possibility though.

Yep, checked all them.
Got it back at 3.30pm another new alternator fitted.
Packed & ready to hit the road tomorrow. Yeehaa ;)

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Originally Posted by Graeme

I think the possibility of a faulty DMM is nil. A faulty battery connection or earth is a possibility though.

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This is what I am thinking, particularly with the known mounting problem the D3s have with their motor to body earth cable, where the cable mounts to the body behind the plastic wheel guard.

But we wait to see, hopefully, that the problem is finally resolved with the replacing of the alternator.

Tiboburra now, all good.