Thread: TD5 Alternator charging fluctuation

Just about all alternators start off at 14.5 +- then reduce charging as the batteries increase their state of charge.

Mine usually sits around 13.7-13.9 with batteries charged but will drop down to 13.7 if the second battery has been depleted overnight and demands a high amperage input.

The alternator is not temperature dependent but batteries take less charge amps as they approach fully charged and the voltage should increase as full charge is attained.
This can take several hours of driving even with only a 750CCA starting battery and say a 95AH house battery . My experience with my previous RRC was that the batteries would reach say 90% in about 2 hours but another 4 hours to full charge. In my Disco I usually/always run my solar panels so the batteries are always near float charge so I don't see low volts.
Just a second thought. On a hot day over 28C with the aircon on and the electric fan operating , Mine sits on 13.7 as there is quite an electrical load. If you were driving along with low batteries and with air con on over 28C then You could expect a low voltage, maybe lower than 13.6.


In your case you have 3 batteries with maybe 200AH capacity and it would take many hours before you see full charge and recovery of volts to say 13.9. It may be that you will never see full voltage after 8 hours driving if your house batteries are both fairly flat.
Regards Philip A

To answer your question it is possible to change the regulator in alternators to achieve a higher output voltage. Not sure if you can do it to the alternator in the TD5. Luke Philip A said the alternator is doing its job by backing off the voltage. Alternators used to charge at 13.8 volts 25 years ago to preserve battery life. Why do you believe you have a charging issue?

The main reason was that I'm not achieving a full charge while I'm driving as it seems to back off the voltage and I get stuck with 80% charge (absorption charge stage). I thought if I could maintain a higher charge rate of 14.5v I would achieve a full charge in a shorter amount of time. I've seen other cars like patrols and landcruisers alternators put out a constant 14.4v and was wondering why my td5 wasn't doing the same.

Originally Posted by Rossco84

The main reason was that I'm not achieving a full charge while I'm driving as it seems to back off the voltage and I get stuck with 80% charge (absorption charge stage). I thought if I could maintain a higher charge rate of 14.5v I would achieve a full charge in a shorter amount of time. I've seen other cars like patrols and landcruisers alternators put out a constant 14.4v and was wondering why my td5 wasn't doing the same.

Your td5 isn't doing the same as a Toyota or Nissan because it's better than either

How are you measuring 80% charge? If you maintain 14.4 volts past 80-90% you can cook your batteries.

Originally Posted by Rossco84

The main reason was that I'm not achieving a full charge while I'm driving as it seems to back off the voltage and I get stuck with 80% charge (absorption charge stage). I thought if I could maintain a higher charge rate of 14.5v I would achieve a full charge in a shorter amount of time. I've seen other cars like patrols and landcruisers alternators put out a constant 14.4v and was wondering why my td5 wasn't doing the same.

I can see why you have come to this conclusion. What does each battery measure when isolated from the others and engine is not running? This is not a sure fire way to test them but give you an idea. Each battery should be approx. 12.6 volts in an ideal world.

Then check what the voltage is on each battery when the car is running and all batteries are connected, full load on the alternator. This is a little miss leading but you will soon find any voltage drop if it is present. You should measure the same on each battery.

Long story short if the current output of the alternator is large enough to charge all 3 batteries you should not have an issue and should not need to charge at a higher rate.

OK cool I understand a lot more now and it seems like everything is charging fine, I've got 12.7v at the two car batteries while the motor is not running, and the caravan battery is sitting around 13.1v (the solar system has been putting in 14v) . then when I start the car they all sit around the 14.4v for 10 mins then seem to settle around 13.6-13.9v.