Strange electrical problem - no charge while on idle

[10mbc]

Hello,

Since the cold weather started I have some issues with my C5 2.0 HDI from 2003. If I let it idle in the cold, with the windshield defroster running on full power and rear window heater + mirror turned on plus headlights turned on (auto ligths), the charging indicator will show low charge and the measured voltage is 12.8v. If I rev the engine to 1500rpm, it's all good and, during normal operation on the road it works normal.

Is this a sign of an old alternator that is going bad? Is it possible I have a smaller alternator that normal? In the parts list available for my car I can see 2 type of alternators: a 90 Amps model and a 150 Amps model. Is there a rule for what car gets which alternator?

Thank you!

[GiveMeABreak]

Yes, the alternators used are based on factory equipment / option and engines fitted. But bear in mind use of any heated elements is going to put a higher demand on the battery and the charging system - but they are not intended to be used all the time - only to clear the windows / mirrors and that's why they are timed.

Most MK I C5 diesels were fitted with a 120A or 150A alternators - the 90A was only fitted to diesel models without Air Conditioning, but new replacement alternators were often 120A for these models.

Some 2.0 Petrol models were also fitted with 80A or 90A alternators
The 3.0 Petrol had a 150A fitted

[white exec]

At idle speed, the alternator will not be able to match the hefty accessory load you list, and so the balance will come off the battery - causing its voltage to slowly drop. Alternators need around 3000+ alternator rpm to achieve full output, and that isn't always provided by an idling diesel.

As you say, things look up when you raise the revs, or start driving.
Everything sounds normal.

[wheeler]

Are you using a proper voltmeter directly on the battery to measure this or a dash gauge?
When you say its not charging fully at idle does the drive belt look ok or flapping about?
If the drive belt is ok I probably wouldn’t worry about this if its only low at idle with a heavy load.

[10mbc]

I am using a multimeter to confirm, with the leads connected to the battery. Basically, each time the multimeter will just confirm the indicator in the dashboard.

I do not think this is normal for a couple of reasons:
1. I had another C5, the climate here is the same, never have I seen a battery voltage with the engine started.
2. My father has a Xantia 2.0 HDI, he does the same in the morning, no issues.
3. I had plenty of other cars, never had this kind of issue.
4. When a charging system is checked on a car (when replacing the battery), the check is done with everything turned on and the engine idleing. This car would fail this test immediate.

I am not sure why you confirm this is normal as this is far from normal. If the idle is not enough for the car to power everything, the normal thing to do would be to raise the engine RPM, not to quit powering the electrics. In other cars I used to stay inside with everything turned on and work on my computer for 30-40 minutes when I was a field technician and never had this kind of issues, even if it was winter outside (and, in some casese there were -22 degrees C)

The belt was changed as it was cracked but the issue predates the changing of the belt. The drive belt looks normal. Power steering works normally. I would assume the power steering would have issues is something would be wrong with the drive belt.

[white exec]

Just check that the alternator has the correct size pulley. It has been known for an over-size one to get fitted, which results in insufficient alternator output at idling.
Normally, the alt pulley is about 1/3 the diameter of the crank pulley, to give c3000 alt rpm at c1000 engine rpm at idle.
If idle speed is low, this will aggravate the problem.

Check that battery is receiving around 14.4v minimum when on charge from the alternator, major accessories off.

[10mbc]

I cannot compare it with the crank pulley as I cannot see it from above so maybe only from bellow, on a lift.

I took some pictures of the alternator, maybe it is apparent it's not the correct size.

Battery is receiving 14.4 when there is no load or I rev the engine at about 1500 - 2000 RPM.

Thank you!

[wheeler]

I wouldn't disagree with you that its not normal however if it was mines I wouldn't worry about it unless it changed any.
Can you recheck the voltage but this time connect the positive lead of the voltmeter directly to the alternator positive terminal & the negative of the voltmeter directly to the alternator casing to rule out volt drop on the cables. See if you get a different reading to what you get at the battery.