Thread: D2a TD5 - low voltage when driving - sick battery or alternator?

Originally Posted by harro

Intermittent voltage drop is usually the brushes in the alternator.
Thay are worn down and starting to fail.
Haven’t kitted a td5 alternator before but it shouldn’t be that different to most alternators.

Assuming that is the problem.

Paul

I’ve replaced the alternator on our 2003 td5 D2 and it is a real pain. Very tight squeeze in and out past the radiator. Undoing the fan was interesting too.

The original alternator failed due to oil ingress onto the commutator and brushes. I made a post some years back about that and solar powering a D2 to get home.

The source of the oil was then and still now remains a mystery.

The good folk at MR Auto are an excellent choice if you’re in Brisbane.

Originally Posted by trout1105

I had a good look at the bearings and they seemed to be Fine so I am hopeful that this fix will last, However I bought another working alternator Cheap on eBay for $85 as a backup plan.
DISCOVERY 2 V8 ALTERNATOR | eBay

I will fit new brushes and bearings in this one So that it will be "Good to Go" if I need to replace the one I have just fixed for any reason.

Interesting comment you have quoted there.
I have fitted brushes in numerous alternators over the years and never had a problem.

Yes, bearings can fail and a quick spin of the alternator tells loads ‘no pun intended’.
Brushes are IMO a consumable in alternators as they will eventually wear down while bearings are a bit of a mystery and can last seemingly forever or fail in a relatively short time.

Paul.

sorry I didn’t get the quote you used in my reply.

even when fully charged the alt/battery should be reading at least 13.6/7

The D2 takes around 30A to run,, or so I read

Six cells x 2.1 per cell equals 12.6 so that's a fully charged battery. Readings above that are a surface reading which falls when the battery is placed under load.
At idle you must be reading the battery, not what the alternator is making. If you stick a voltmeter in your dash cigarette plug you'll get a reading close to what your alternator is making, minus some minor voltage drop.
Do D2s have smart alternators which adjust the output to the need, as found on D3/4s?
My Defender doesn't have a smart alternator and it just flows 13.9-14.0 through the vehicle all the time, whether driving or idling.

Not sure about Smart Mick,,,

but yea,, the charge voltage will vary depending on load, from 14.2/3 down to 13.6/7
From a cold start mine drops from 14.2 down to 14 in around 7 minutes,, only around two minutes of that is normal engine temp..

Originally Posted by harro

Interesting comment you have quoted there.
I have fitted brushes in numerous alternators over the years and never had a problem.

Yes, bearings can fail and a quick spin of the alternator tells loads ‘no pun intended’.
Brushes are IMO a consumable in alternators as they will eventually wear down while bearings are a bit of a mystery and can last seemingly forever or fail in a relatively short time.

Paul.

sorry I didn’t get the quote you used in my reply.

I have changed brushes in lots of different alternators and power tools and the process is pretty much the same, Some of the power tools I have bought even came with a set of spare brushes.
I bought the other alternator as "Insurance" because I didn't know the condition of the bearings and the rest of the alternator that was in in the truck, Luckily there was No issues with the original alternator other than the brushes were worn right down to a "Stub" and replacing the brushes has done the job.
The other alternator that I bought on eBay will most likely sit on a shelf in the shed for a few years after I have refurbished it But at least I will have a replacement "Just in Case"

Originally Posted by twr7cx

Three days ago I noticed that the voltmeter on my D2a TD5 HSE was reading lowish - 11.9 volts while driving - I confirmed with a multimeter that the gauge was accurate, it was. Over a two day period this dropped down to a low of 10.4 volts which started to cause electrical issues with the car such as random chimes and then the SLS amber warning illuminating etc. During this time I drove around 200km or so with the stereo, AC, headlights, driving lights and even at times the seat heater on - if the alternator was not working I would have expected the power to die much earlier. When the engine revs the volts would increase by .3 or so and then drop back down at idle when stopped.

Last night I left it on charge with the Ctek charger in Recon mode. This morning it was at around 12.5 volts and when I was driving down the road it reached up to 13.9 for a short while but then back down to 11.9 for the bulk of the drive to work.

I'm unsure how to diagnose if the alternator and/or rectifier are at fault or the battery (i.e. dropped a cell).

The car still starts perfectly fast in the cold in the morning which makes me wonder if the battery is ok and the overnight charge got it back up to above 12volts.

The alternator must still be working at least somewhat for the vehicle with it's electronically controlled engine and gearbox and all the HSE electrics to run for three days and a couple hundred km before getting low enough to cause issues.

Ideas?

I would put a meter on the back of the alternator first. Earth on the alternator body and positive on the lead where it power comes out of the alternator. If you have more than 13.5 there then check at the battery for voltage drop from the lead to the battery. If so just give it a good clean both ends of the power lead and don't spray anything like DW40 on it

The alternator that I bought on fleabay arrived today and instead of the genuine LR 130a unit arriving I got a no name unit with an extra spade connector at the back of it with a "W" or "M" stamped next to it.
Any idea if this will still work on my D2a.
alternator1.jpg