My brothers focus ST broke down again. After replacing the alternator yesterday i went for a drive after about 50 miles driving the alternator possibly broke again. The battery doesn't charge and the battery light on the dash is on.

The first time (a week ago) my brother stranded with this car because of an empty battery. The alternator did nothing and the battery light on the dash was off!!!

what could this be that the alternator doesn't charge and broke again within 50 miles?

 

Pull the 3-wire plug off the alternator and check if it's charging.
If it does there's probably something wrong with the wiring.

 

it has 1 wire and it doesn't charge when it is off. it whines verry loudly now.

 

It could be a smart charge issue.

Martin

 

whining is an indication of stator/rectifier trouble, if it was a new
alternator it probably is a cheap Chinese one

 

Got a brand new Denso in it. Replaced the ground wires to the battery and the supplycable for the alternator.

But it charges with 100Amps. way too much for a charged battery with nothing on. Maybe it is the smart charging that gives the trouble.

Do you need to reprogram the battery with a ECU diagnostic when you replace a battery on these cars?
Have heard that BMW and VW will charge at max if you dont reset the computers after disconnecting the battery

 

The smart charge is a far too complicated system. Have you got the right calcium battery on it? It will cause grief if you use a lead acid.

 

It can't have that output, as you don't have that load. Smart charge just simply charges at a higher voltage, especially after startup, hence it requires Silver calcium (lead acid can explode!) no you don't need to change anything.

Martin

 

Exactly, that 100 amp has to go somewhere, if there is nothing asking
that amount the alternator won't supply it.
All modern cars have smartcharge alternators, no escaping that.
It's needed to lower emissions, it means the alternator will start charging at
full power whenever there is free energy, e.g. when you lift your throttle
going at a trafficlight, the engine on the overrun.
More modern cars need a AGM battery, these batteries can be left in a
partly charged state so that there can be "free" energy stored in it.

 

Also check the batteryvoltage, if it charging at too high a voltage
it could be that it is actually charging at 100 amps

 

It charges 100Amps with the orginal calcium battery (12.5V before i started it).
I replaced it with a lead battery (12.6V before i started it) and it charges 40Amps now. still a bit high i think, with no use of radio lights etc...

So i think the battery is dead. But does a diffrent battery lower that 40Amps?

The voltage is 14.3 on battery and 14 when plugging a OBD reader.

 

I think you should check it after running for an half hour or so,
right after starting the current is always high.
Voltage is OK.

 

i did let it run with the lead battery but still 40Amps.

 

Replaced the battery and the cables now, a new genuine Denso is placed. Has about 30amps now. problem solved