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I have a 300tdi Defender, was fitted with a 65Amp Alternator, this Alternator required a healthy blip of throttle to get the Alternator to charge, this blip was required at every start irrespective if the engine was hot or cold.

Now I have a new Alternator 100Amp, to get this Alternator ready to fit on the landy I had to remove its original pulley and replace it with the original alternators pulley, this also required grinding down the flange on the back of the pulley and also a tool needed to be made to extract the bolt from the Alternator shift.

Upon fitting the new Alternator, charging failed even with the mandatory blip of throttle, I then removed the Alternator and bench tested it, on the bench it works and charges a connected battery as it should, when fitted to the Landy the dash light stays on with no charge from the Alternator, the battery (This battery is an Optima Red Top) which read 12.6v with ignition off, the warning light feed wire (brown and Yellow) had 2.5v with the ignition on (10 Volts less than what it needs to excite the Alternator) any ideas why its not charging once on the vehicle?

As said the Alternator is brand new, off the vehicle the Alternator works and charges as it should, New Alternator pulley has been replaced with the old alternators Pulley (the original pulley off the new Alternator was too big) and the pulley nut is tight and the Alternator inards are rotating as expected.
 
freelance said:
Is it rotating in the right direction, if so it’s probably a fault with trigger wire
Click to expand...

Hi freelance yes, if I am correct the 300tdi engine rotation is clockwise if standard in front of the vehicle while bench testing the Alternator, the operation was also clockwise.
 
Have you connected the trigger wire to the correct terminal assuming that your replacement alternator is for a Discovery?
The Discovery alternator has an extra terminal for the rev-counter.
The pulleys should interchange between 300tdi alternators, if the pulley does not have a flange, there will be a spacer behind it. Rather than grind the flange off your pulley, you could have removed the spacer, although they can be fiddly to get at.
The larger pulley is for the later vehicles, it was an improvement to help charging at low revs, as you have discovered, later 300tdi's have a longer serpentine belt.
 
Rougharse Racing, thanks for your reply, the Alternator was listed as being for the Defender 300tdi models, my Defender is the 1994 300tdi, as for the trigger wire/excitor wire, the connection on the new Alternator is the same connection on the old Alternator, both had the 3 connections 1st is battery, 2nd warning light, 3rd tachograph, the placement of both wires as I don't have a tachograph fitted was checked during bench testing, it was rigged in a similar fashion as it would be once fitted to the vehicle and rotation was done with a drill, which also included a 12v Bulb for the dash warning light, as stated, testing on the bench resulted in the Alternator charging the connected battery and the de-illumination of the connected bulb once the charging process started, as for the removable flange I'll check that tomorrow but it didn't look like the flange could have been removed.

I am thinking that the issue may be with the exciter wire, as with the old Alternator the Alternator wouldn't charge the battery unless the engine was revved up at engine startup.
 
I think the wattage of the warning bulb might be an issue, 4w rings a bell?
On of my 200s has always needed the blip to get it to start charging, this was pretty much standard years ago, so common no one batted an eyelid.
 
300TDI CHARGING.png
MAY HELP View attachment 261564
 
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Just been out today and changed battery to an optima yellow which is fully charged, cleaned all connections, earth and + battery wires that are connected to the battery prior to fitting, disconnected the exciter from the Alternator and tested with multimeter, at this point with the ignition on, the voltage reads same as battery voltage (this shows the necessary voltage is getting to the Alternator's exciter connection), now when this brown/yellow wire is reconnected back to the Alternator, with the ignition on, the voltage then drops to 2.6v even with the engine running this voltage only increases by 0.30v (2.90v), now as a test I used another battery (the one I removed) connected the negative to the Alternator body and the positive to the brown/yellow connector on Alternator started the vehicle and the dash light did go out, but the Alternator still won't charge.
 
Maybe try a bypass circuit, ie your own bulb and test wire to the alt
Not something silly like the alt body needs its own earth?
 
Why do you need to blip the throttle to get the alternator to charge? I've never heard of this before.
 
OK I've located the issue, one thing I did forget to mention is the landy does have a split charging system fitted, have again checked and tracing the B+ wire from the Alternator to the split charging system there is a connection made with nut and bolt, the heavy duty spade connector had come away from this connection on the split charge end, this is most likely why the throttle blip was required as the vibration most likely allowed that connection to be made, I have now connected the battery cable directly to the Alternator until I can source a heavy duty cable, or until I can check all the connections on the split charge system, throttle blip is also no longer required to get the charging system working, also thanks for all your help.
 
Al2O3 said:
Why do you need to blip the throttle to get the alternator to charge? I've never heard of this before.
Click to expand...

Mine needs it. If I just start the engine and leave it ticking over the charge warning light stays on. I need a few RPM to get it to go off and the alternator to send out a charge
 
miktdish said:
Mine needs it. If I just start the engine and leave it ticking over the charge warning light stays on. I need a few RPM to get it to go off and the alternator to send out a charge
Click to expand...

My JCB needs this too. It takes a little acceleration to get rid of the warning light.
 
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