Is it my Alternator

[robbiefurn]

Merc Citan 2015 Van (Diesel) possible alternator issues?:
Battery when off :12V, Battery when on and with load (like heater, radio, lights etc) 14V . Battery is 2.5 years old
Lights flicker and heater goes low now and then usually at junctions or start up, slight burning smell very ocasionally only lasts 20s. Somtimes engine dips like its going to conk out for a fraction of a second. Performance is rubbish (might be unralated)
What do your recon ?
Many thanks

 

[Harry Bloomfield]

Battery when off :12V, Battery when on and with load (like heater, radio, lights etc) 14V .

12v suggests battery is faulty (but), 14v suggests alternator is fine. The burning smell, suggests something is amiss, and the 'amiss', might be discharging your battery. You need to check the discharge on the battery, when everything is supposedly turned off.

The 'amiss', might also be pulling your voltage down, causing the misfires too.

 

[Mottie]

Alternator overcharging intermittently?

 

[Burnerman]

I don't like the sound of this one particularly.........there is obviously a high current discharge somewhere, indicated by the fall of engine revolutions and the slowing down of other auxiliary items.
You can expect a bit of this if the heater plugs switch themselves back on under extreme cold conditions, but not to this degree.
The battery voltages are about correct.
Personally I'd slip off the alternator drive belt and try things again - don't run the alternator disconnected in any other way.
Re the burning smell.......any whiff close to the alternator itself? I guess you could try running the engine with the bonnet up and looking closely
but there will be a risk of damage to something.
Has any work been done to the van recently that could have upset the routing of the battery cables?
John

 

[robbiefurn]

Sound advice gents, so somethings possibly causing a high current drain. Potental Arc? albeit intermittant? one of the reg plate lamps is a bit iffy

 

[Mottie]

Alternator overcharging intermittently?

I have seen that happen a couple of times years ago and that was both on Cortina’s. When the alternator cut in and overcharged, the engine slowed down on tickover and the battery bubbled and gassed heavily. Maybe that’s the 'burning' you can smell?

 

[robbiefurn]

Quite possibly, i'll pop the bonnet and have a.wiff. No visible issues with the battery, new air filter fitted recently which is very close to the battery cables and would have certainly moved them a bit. Also worth mentioning i tried to jump start my car couple of months back from the van using jump leads( failed to jump)

 

[Harry Bloomfield]

Sound advice gents, so somethings possibly causing a high current drain. Potental Arc? albeit intermittant? one of the reg plate lamps is a bit iffy

Any fault on that, would take a fuse out.

 

[Harry Bloomfield]

I have seen that happen a couple of times years ago and that was both on Cortina’s. When the alternator cut in and overcharged, the engine slowed down on tickover and the battery bubbled and gassed heavily. Maybe that’s the 'burning' you can smell?

To eliminate that possibility, it might be a good idea to organise a meter, set up and able to semi-permanently, monitor the battery voltage as you drive.

 

[Avocet]

Loose battery cable? Or worse, a battery cable with chafed insulation, shorting against the chassis or engine block? Also maybe a broken engine earth strap, meaning the engine is getting its earth return by some other cable?

 

[Burnerman]

I don't like this burning smell scenario....I've had many an alternator fail (both electrically and mechanically) but never had one that smelt like burning.....maybe it was the drive belt causing this?
Wondering too if the vehicle has A/C, and the compressor is behaving itself.
John

 

[RevNomad]

The voltages you're seeing (12V off, 14V running with load) actually suggest the alternator and regulator are basically doing their job. If it was badly over- or under-charging you'd usually see bigger deviations (e.g. over 14.8V or stuck below 13.5V).The flickering lights + heater dimming + brief burning smell point more towards an intermittent high-current issue – possibly:

• A chafed or loose battery cable / main earth strap (common on these vans after work like air filter changes)
• Poor connection at the alternator output or battery terminals causing arcing
• A relay or high-draw component (e.g. glow plugs, fan, or even a sticky A/C compressor clutch) pulling too much current momentarily
• Or a small short that's only appearing under vibration/load

A couple of quick checks you can do:

1. Measure voltage directly at the battery terminals while the engine is running and someone wiggles the cables – any drop or flicker?
2. Check for parasitic drain with the engine off (ammeter in series on the negative cable, should be under 50-80mA after 30 mins sleep).
3. Remove the alternator belt temporarily and run the engine briefly (if safe) to see if the burning smell or dip disappears – this isolates belt/pulley vs electrical.
4. Inspect the main battery-to-alternator cable and earth points for corrosion or damage.