Thread: On the Td5 alternator charging voltage issue ...

Correct!! And well done to sort it all out....

Thank you for the post

Mines reading fine at the moment. Getting a lovely 14.3v.
Just wondering what they are worth though?

Originally Posted by turps

Mines reading fine at the moment. Getting a lovely 14.3v.
Just wondering what they are worth though?

Think its a case of how many "first borns" do you have kicking around!

505 + delivery

Old one is 180,000km and 11 years old.

Sent from my iPad using Braille

here is the theory about parasitic drain caused by diode failure:

I'm not going to enter deep in scientific explanations cos they might be boring but it's good for everybody to know:
see the image, it's the alternator's scheme from RAVE, for those who dont know those 8 identical elements on the bottom are the diodes within the diode pack, the 4 "loads" are the motor's winding, those diodes are there to convert the AC into DC and in the same time they dont allow to any current to travel "bacwards" through the motor's winding to earth.

so, in a nutshell: there are at least 56 different ways(others than a "serious/total" failure) for a diode pack 'failure' without even notice a big difference in the charging voltage but inducing an up to 1A drain into the system... it can induce up to 4A but when it comes above 2A it's a total failure and it will generate mainly AC which will light up the warning. IMO it's not very common but it's good to know cos as we saw it happens and the only way to trace it is with an oscilloscope

Originally Posted by Fluids

This has been discussed in numerous posts in the past, but since I'm too lazy to back track and add to the relevant post I'll start a fresh one here ...

My D2a until maybe 12-18 months ago ALWAYS (by the Nanocom) showed 14.7-14.8 volts from a COLD start in the morning, and after 10-20min of driving the voltage would drop progressivley to somewhere between 14.1 to 14.32v ... it did this religously.

Then a couple of years ago I started to notice that after driving for a while the voltage would sometimes slip to below 14v ... sometimes hitting as low as 13.2v, with the usual range sitting between 13.6 - 13.9v ... but still with periodic dips below this range. When we purchased the camper last year this made it very hard to get the camper batteries charged when towing as the best we could get at the rear anderson was around 13.6-13.7v.

The Td5 alternator is NOT a temperature compensated unit. I do believe however that temperature was playing a big part in the reduced output voltage of my alternator .... OK when cold but lost voltage once up to operating temperature.

Moove forward to yesterday. Replaced the alternator with a brand new Denso Genuine unit complete with vacum pump (expensive little ****ers). It's marked 14v. Cold start, and it shows 14.7-14.8v and after around 10-15min driving voltage slowly drops to (by the Nanocom) 14.1-14.22-14.32v .... same as it used to do when I first purchased the Disco .... rear anderson shows 14.1-14.3v .... like it's supposed to be. Good for charging camper batteries, no DC-DC required ... as it should be.

Point of the post ... If your D2 is NOT running above 14v (the genuine Denso alternator is a 14v unit!!) then something is amiss. A few D2's I've Nanocomed for others over the years ALL running showed voltages above 14v. You may, like me, have been having no problems with keeping your D2 battery/s charged, and had no flat battery issues ... but it's not right. Others have posted that they have replaced the alternator and got no change and their charging voltages are, after a while running, sub 14v .... just like before replacing the alternator ... did they use a genuine Denso / OEM unit ??

Also to note, the battery voltages this morning were noticeably higher after sitting over night compared to what I've seen for the last several years (4yr old Optima Yellows) which leads me to the assumption that there was a percentage of back leakage from the batteries through the alternator due to partially failing diodes ... I have read this elsewhere on the net ... those who are more knowledgeable about such failures may be able to add to the discussion.

I'll keep watch and if it changes, &/or things change after I test with the Kamper connected (with 210A/Hr worth of batteries to charge) I'll add to this post.

So, fwiw ...

Re point of the post:

I fitted a genuine Denso in December last year as I suspected something was amiss with the old one. I have not seen any voltages above 14v with the new unit. Generally around 13.6v is the norm. When I bought the vehicle 9 years ago, I used to see voltages close to 15v after start in the morning, settling to 14.2 ish. Maybe it's time to chase the earths?

Hi Milton ... it's not right. Is your reading from a Nanocom or with a multimeter at the battery terminals ? The genuine Denso is a 14v unit so it MUST run above 14v.

I did a couple more checks yesterday and found that the 14.6-14.7v the Nanocom was showing equated to 14.48v at the starting battery (Optima D31) ... which goes 6BS to a Traxide USI-160 then 6BS to the aux' battery under the bonnett (Optima D34), then 8BS to the dual andersons at the rear which read 14.45v. (The 8BS cable with the chassis as the earth return was already in the Disco when I purchased it and I haven't got around to upgrading it to 6BS twin yet).

I couldn't get backed up to the garage close enough to connect the camper so I used a 10m 6BS extension I have, and get 14.38v at the camper batteries (andersons at the D2 rear reading 14.43v) ... they were already fully charged ... with the fridge running and lights on (5A approx') the voltage drops to around 14.2v at the camper and 14.35v at the anderson plugs ... happy with that compared to what it used to be ... take the extra 10m of 6BS out of the equation and camper batteries are now an easy charge ... no DC-DC charger require!

I need to run the camper batteries down a bit now and see how it reacts when it has more of a load to carry.

So, are there DON'T DO's which will lead to a diode failure ??

I'm thinking no'1 would be removing the battery leads while the engine is running ??

Anything else you shouldn't do ??

.. or do they just wear out with age and use ??