I’m having a problem with the charging system on the Focus, I replaced the alternator as I thought that was the problem but it’s still doing the same, it’s all over the place. I have a live feed of the charge rate and it can be anywhere from 12.2 volts to 13.4 volts, on start up it will usually rise up to 13+ then drop back down to 12.2 where it can stay for the rest of the journey, other times it will drop down to 12.2 then go up to 13.4 when I put the lights on and stay there for the journey, other times it’s done this but after a short while dropped back down to 12.2 ish. It rarely ever goes above 14 but will sometimes do that on first start up then as usual drop back down to 12.2.

 

I’ve removed the connector that goes to the alternator, it is a single wire feed which in my mind I had it as just a 12v supply that was there to excite the regulator within the alternator, it shows 8v. When I seen this I presumed this was in fact the fault. So I removed the connector and using a jump wire I applied voltage directly to the pin taking the feed from the car battery and it did not work, in fact the reading I was getting now was as if it was not charging at all, just showing battery voltage and no charge rate. I tried a few various methods just in case the connection was poor and each one came back as above.

 

I then exposed the wire that goes to the original connector and applied 12v directly to that to see if that would make a difference but no, it just done the same as above where it would be no charge at all, as soon as I removed the 12v feed it went straight up to 14+ before coming back down to 13.4 where it stayed before I shut the car down.

 

Any ideas? Thanks all.

 

 

You do know that your vehicle is equipped with a Smart charging system ?

What you are describing is exactly how the charging system is intended to work. It will change the alternator voltage to try and maintain the battery state of charge at 80% (never more). The alternator is a 3 phase brushless design and disconnecting the Smart plug from the alternator will  cause it to go in to the standard emergency charging voltage of between 13.6 and 13.8V

Are experiencing a problem that you battery State of Charge is low ?

13 hours ago, unofix said:

The alternator is a 3 phase brushless design

Are you quite sure about that? Alternators are normally controlled by varying the excitation in the rotor by pulsing the current on and off so slip rings are used to make the rotating connection, which still need brushes. If it was truly brushless the rotor would need permanent magnets and it would be a lot more difficult to control the output.

110% sure. 

There are no brushes and no slip rings. They were last used in the 90's

Here is a link which explains the operation of a brushless alternator:

https://speedalternators.com/brushless-alternator

I have a disassembled 150 amp Focus MK3 alternator of a 1.0 ECOboost and it definitely has carbon brushes and sliprings. 

Through the years I repaired/overhauled several of these 120/150 amp OEM Denso alternators of both the Focus MK2 and MK3. All of these had carbon brushes and sliprings. 

 

I am currently on holiday but of people want I can post pictures of the disassembled alternator in about 1.5 week.

Likewise I can post countless photos of brushless 3 alternators

As I never have seen one myself I would be interested to see such a picture. 

 

To be honest I only serviced the Denso alternators and never touched a Bosch, Visteon or Valeo alternator. 

 

23 hours ago, unofix said:

Here is a link which explains the operation of a brushless alternator:

https://speedalternators.com/brushless-alternator

Interesting. I can see how this works from the circuit diagram but the description is simply appalling :

".....This interaction causes the rotor to spin,"  It's not the 'interaction' that's causing the rotor to spin is it? The rotor is being driven.

".....which causes the stator to rotate. The rotation of the stator creates an alternating current (AC) in the coil wire." - Since when did a stator rotate? (obviously this is meant to refer to the magnetic field rotating relative to the stator).

In the description of a conventional alternator: "The brushes in a brushless generator help transfer electricity from the rotor to the stator. The windings in the stator are connected to three rings’ slip," - What???

".....The AC current flowing through the wire coils is then sent to a load, such as a light bulb or a motor. The load converts the AC current into DC current"

I could pick out many more but you get the gist. Total rubbish.