Alanb Posted March 7, 2021 Share Posted March 7, 2021 rayc - 2021-03-07 10:25 AM ================================================================================== ================================================================================== The D+ terminal is 'shorted' to earth via the alternator diodes when the ignition is on but engine not running [ i.e. the alternator is not producing charging volts]. ================================================================================== ================================================================================== Perhaps I am too pedantic, but I do not like to see incorrect statements which may cause confusion. The D+ connection is the alternator field connection, and connects to earth (chassis) via the internal alternator regulator and field winding (rotor) which is connected by the brushes. When the alternator starts generating, a dedicated diode pack supplies the D+ node. To expand slightly, the small current passing through the indicator lamp provides an initial field current, which enables the alternator to start generating. Connect too many items to D+, and the alternator will be reluctant to start generating. Alan Link to comment Share on other sites More sharing options...
DEL Posted March 8, 2021 Share Posted March 8, 2021 Related, but not likely to be very helpful to the OP (Sue) who will probably not want to lie under her van! My 2009 Ducato X250 3.0L 160 rewarded me for its recent inactivity by displaying similar symptoms – no red light but an increased tick-over. The tick over increase was very deliberate, the van started at its usual 800, thought about it for a bit and stepped up to 1000, thought again and stepped up to 1400 and there it stayed. Searching on here, the earth strap was highlighted as a possibility but I had already added one of those and a temporary additional link with a jump lead made no difference. I checked the Alternator output at the starter battery and found the first time no charge at all, it was actually running on the battery (11.9v) and then a second time it managed (12.2v) – it was time to look at the Alternator? Searching again I could not find a lot of info on the 3.0L Alternator other than it was down the offside bottom of the engine at the back. There was one (only) YouTube article that suggested “rather than removing the half-shaft and aircon pump to gain access, you could just remove the front end of the exhaust and its related pipework”!! Neither option filled me with much enthusiasm and it may be that others on here can tell me that is wrong and the Alternator will come out without all that work (in which case don’t bother reading on from here) but coupled with the problems of removing and replacing the serpentine belt and the stretch Aircon belt, I looked for another solution. Securely up on ramps and sliding under from the front (I did remove the undertray) the Alternator can be quite clearly seen and access to the rear of it is (relatively speaking) quite good. Having done some research on repairing Bosch alternators on You Tube and seen that the Voltage Regulator/Brush assembly was a single unit designed to be replaced I thought I would give it a try with the Alternator still in situ. Unplug the D connector plug in the Alternator end cover and there are three 13mm nuts that hold the Alternator black plastic end cover on, the first acting as the cable clamp. This is live direct to the battery so disconnect it at the battery end first or have an insulator to hand as you undo the first nut, then remove the other two 13mm nuts. There is also a cross head screw that just secures the cover situated down in a recess which I could not undo but I could flex the end cover sufficiently to get at the three cross head screws that hold the Regulator assembly in place and out it came. In my case there was a label on the Alternator giving the Model Number of it, and part numbers printed on the Regulator which enabled me to source an exact replacement for £42.40 from a very efficient SED Ltd (01483 538038) an Electromotive specialist. Beware of eBay in this case, I wasted a lot of time with an unknowledgeable supplier, and Bosch themselves were not much more helpful. Reassembled, tick over was back to normal and plus 14V at the battery. There was nothing wrong with the brushes so it had to be the electronics. Link to comment Share on other sites More sharing options...
Alanb Posted March 8, 2021 Share Posted March 8, 2021 1. Almost immediately after making my previous post onthis thread, I decided to add postscript. Due to some temporary aberration of the forum systems, manifested by the lack of an EDIT button I was unable to edit the post as I wanted to. I wished to add the comment that on more recently manufactured vehicles, alternator voltage is computer controlled, and the provision of a D+ connection is significantly different (switched negative). I think that this applies from the intruduction of Ducato x290, where a converters panel is fitted at the base of the RHS "B" pillar. Can some person with more knowledge in this area, please confirm/correct? 2. May I thank DEL for his informative post. However for safety I most strongly advise disconnecting the starter battery negative, before working near the alternator, or battery positive connections. This is the standard advice given in eLearn, for any work in the engine bay. Alan Link to comment Share on other sites More sharing options...
colin Posted March 8, 2021 Share Posted March 8, 2021 From posts made by 'eddieandsue', it is quite obvious that all the technical explanations are beyond what is needed. Lets keep it simple. The most likely problem is a faulty alternator or wiring from this. Any competent garage or motor electrician should be able to sort this. Whilst checking this, it would be a good idea to change the engine earth strap for a better quality one, many on this forum have already done this as a preventative measure. Link to comment Share on other sites More sharing options...
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