Hi all, my MK2 is currently running fine (famous last words) but I suspect my high capacity Varta battery and daily long motorway runs is hiding a fault somewhere in the charging system.

 

When I initially start my car it starts up no problems (I've got a battery tester and it confirms my battery is delivering the CCA it should be for it's official rating), my concern relates to the voltage being delivered by the alternator at idle and low revs.  If I immediately turn on the quickclear windscreen after starting the engine the voltage drops from 13+ volts to below 12 volts, I'd not previously monitored it so I'm not sure what the normal/expected behaviour is.  If I rev the engine to about 2000 RPM the voltage rises to about 13 volts but I don't think the neighbours will appreciate me holding the revs at 2000 RPM for 2 minute each morning at 6:30!

 

Does anyone know what the correct voltage range is for the alternator output when it's under heavy load but at idle revs?  I'm sure it should be greater than 13 volts and certainly above 12 volts!

Few points to look at:

- age of your present battery, if over 5yr check for the electrolyte transparency, Focus is notorious for increased battery cells corrosion (it's when electrolyte from the cell is all dark, muddy). check the electrolyte specific gravity in each cell (Varta should have plugs on the top). This is the best indication of the battery condition.

- how is the auxiliary belt condition, could be stretched (from my experience, Conti belt stretched and developed cracks after 12 kmiles)

- how is the alternator pulley/clutch, freewheeling ok or not

- try to charge the battery with an external charger (longer the better, with Ca-Ca batteries there is no overcharging) and than check for the voltage when car is running. TBH since voltage rises with increase in RPM I would say that the  alternator voltage regulator is fine. At idle, immediately after start, voltage should be btw 13-14 VDC, depending on the battery state of charge. When nominal op.temperature is reached voltage should be 14.3VDC or so....

Iirc the heated screen is a huge power draw - I'm pretty sure my voltage dropped to 12ish at idle.

8 hours ago, Ned_Mk2_1.8tdci said:

Few points to look at:

- age of your present battery, if over 5yr check for the electrolyte transparency, Focus is notorious for increased battery cells corrosion (it's when electrolyte from the cell is all dark, muddy). check the electrolyte specific gravity in each cell (Varta should have plugs on the top). This is the best indication of the battery condition.

- how is the auxiliary belt condition, could be stretched (from my experience, Conti belt stretched and developed cracks after 12 kmiles)

- how is the alternator pulley/clutch, freewheeling ok or not

- try to charge the battery with an external charger (longer the better, with Ca-Ca batteries there is no overcharging) and than check for the voltage when car is running. TBH since voltage rises with increase in RPM I would say that the  alternator voltage regulator is fine. At idle, immediately after start, voltage should be btw 13-14 VDC, depending on the battery state of charge. When nominal op.temperature is reached voltage should be 14.3VDC or so....

Battery is approximately 1 year old (silver series) and has been tested by a garage who confirmed it was in very good condition.

 

I suspect from what you've mentioned for points 2 and 3, as well as further research on my part that the alternator itself is probably fine and the culprit is likely to either be the belt or the clutch/pulley.  I ploughed through a few threads on here and found several relating to the alternator pulley on the 1.8 TDCi misbehaving as they get older and the current symptoms seems to better fit those items as being the likely culprit.

 

At the moment it's an inconvenience rather than a issue because the battery gets a good charge twice a day (2 hours motorway driving) so I'll have a poke around and see if anything is obviously not right and see where I go from there.

 

Thanks the responses so far!

Battery is silver-calcium, this chemistry is resistant to high temp under the bonnet, hence corrosion is out of question

Check the belt as well as the clutch. Also if you are able to take alternator out, than connect it in series with the battery and a voltmeter. Spin the alternator by hand in CW direction, voltmeter should show more than 12V, hence alternator is good.

One more point to check is ground connections to the chasis and gearbox, getting rusty overtime. 

Battery should be put on the external charger at least once a year. BTW what is the voltage after you finish the 2 hour drive?

On 11/6/2019 at 10:18 PM, 1979Damian said:

If I immediately turn on the quickclear windscreen after starting the engine the voltage drops from 13+ volts to below 12 volts, I'd not previously monitored it so I'm not sure what the normal/expected behaviour is.  If I rev the engine to about 2000 RPM the voltage rises to about 13 volts

I haven't got quickclear, but my charging system is a bit similar after a start, at idle it stays below 13v for a minute or so. After a bit of driving, then dropping to idle it stays at about 14v. I wonder if it is protecting the alternator charge system against trying to deliver high current to re-charge the slightly depleted battery at a start. High current at low rpm is possible with an alternator by running it at full field current, but is quite a stress (high torque) on the drive belt and alternator.

Big, powerful batteries, especially when in good condition, will demand a very high charge current if you try to push them up to over 14v immediately after a start. All the charge taken out will want to go back in again very quickly.