replacing alternator

bucknbuzz · 27-03-2021, 03:42 PM

It seems my alternator is knackered on my 2010 tdci 2lt diesel. I've connected the multimeters neg lead to the neg battery terminal and positive lead to the postivie terminal of the alternator and I get a reading of 12.34amps, which is the same when both leads are on the battery terminals. When the engine is running, there is no charge going to the battery. I'm on the verge of trading this unit in so am looking for a standard unit to keep it going. Where would I find a reliable recond unit, or even 2nd hand unit? I've found the video online showing the process, that's not an issue, just the sourcing of a replacement unit.
cheers
B.

GTLEGEND · 27-03-2021, 05:13 PM

Does your negative terminal have a battery monitoring sensor? If so then your vehicle is fitted with smart regenerative charging, meaning the PCM will only turn on the alternator to charge once the battery state of charge falls below 80%. So if the state of charge is above 80% then the PCM to save fuel turns the alternator off, thus not charging the battery and you will get normal battery voltage. This is normal operation.

bucknbuzz · 28-03-2021, 03:55 AM

no, this is the 2010 model, it is not fitted with the sensor. If the alternator was not charging, shouldn't the battery warning light come on?

bucknbuzz · 28-03-2021, 09:11 AM

Quote:

Originally Posted by GTLEGEND

Does your negative terminal have a battery monitoring sensor? If so then your vehicle is fitted with smart regenerative charging, meaning the PCM will only turn on the alternator to charge once the battery state of charge falls below 80%. So if the state of charge is above 80% then the PCM to save fuel turns the alternator off, thus not charging the battery and you will get normal battery voltage. This is normal operation.

My mistake, it seems it does have something attached to the negative terminal which I now take to be the BMS, was never aware of it and never noticed it in the past. This morning I attached the multimeter to the car, started it and got the revs up. At idle, the battery continues to slowly drain, no charge. At 1500rpm the battery does charge little by little. @ 2000rpm it charges a bit quicker but it took a few minutes to get from 12.21v to 13v. So, battery is holding charge so can assume is still good, alternator is working, battery is charging, albeit slowy. Turned A/C on, very slight drop in battery v, not an issue. turn lights on, battery V drops noticably then settles when revs increased. Dying diodes on alternator? Can you make sense of this?
thanks for your reply re the BMS, never knew of it.
cheers
B.

marg99 · 28-03-2021, 09:55 AM

voltage is low if the alternator is working it should be about 14 volts to charge a battery

bucknbuzz · 28-03-2021, 10:11 AM

Quote:

Originally Posted by marg99

voltage is low if the alternator is working it should be about 14 volts to charge a battery

yes, thats what I would have expected, 13-14v @ idle. What is it telling me, diode's need replacing?

foxtrot3 · 28-03-2021, 11:51 AM

Quote:

Originally Posted by bucknbuzz

yes, thats what I would have expected, 13-14v @ idle. What is it telling me, diode's need replacing?

Hi. More likely the brushes need replacing, they will be at that point where they are just touching the slip ring and pass a little current for the field windings but not enough to produce a full output. The power diodes tend to last for ever and I think I have replaced about 2 exciter diodes in 50 years. Cheers MD

GTLEGEND · 28-03-2021, 12:05 PM

Quote:

Originally Posted by bucknbuzz

My mistake, it seems it does have something attached to the negative terminal which I now take to be the BMS, was never aware of it and never noticed it in the past. This morning I attached the multimeter to the car, started it and got the revs up. At idle, the battery continues to slowly drain, no charge. At 1500rpm the battery does charge little by little. @ 2000rpm it charges a bit quicker but it took a few minutes to get from 12.21v to 13v. So, battery is holding charge so can assume is still good, alternator is working, battery is charging, albeit slowy. Turned A/C on, very slight drop in battery v, not an issue. turn lights on, battery V drops noticably then settles when revs increased. Dying diodes on alternator? Can you make sense of this?
thanks for your reply re the BMS, never knew of it.
cheers
B.

Sounds like its working normal to me. Suggest leave lights on for 20 mins or longer when car is turned off to drop the battery state of charge below 80% which would only drop below if you don't drive the car often. Then start and see if the alternator charge rate is up.

bucknbuzz · 28-03-2021, 12:36 PM

Quote:

Originally Posted by GTLEGEND

Sounds like its working normal to me. Suggest leave lights on for 20 mins or longer when car is turned off to drop the battery state of charge below 80% which would only drop below if you don't drive the car often. Then start and see if the alternator charge rate is up.

great thinking 99!