Charging problem

So, the battery light decided to come on and it soon became apparent that the battery wasnt charging. Managed to get home, left it for a few hours and it started no problem,put a meter across the battery and got quite a high reading of about 15 volts. Everything seemed fine until the voltage suddenly dropped to about 11.5v , alternator going round all belts fine. Just stopped charging, cant figure out why. Is the charging circuit controlled by the ECU or is there a seperate reguator/rectifier? Is 15v a normal charging voltage? seems a bit high to me.
2001 TD4, just hit 150,000 miles.

Any pointers gratefully accepted. Bob

Had a similar problem on my MGB !!!
Note that your meter is reading what it 'sees' - in my case a diode had packed up and a large component of the output was AC (alternating current) which is what the alternator produces before the rectifier changes it to DC.

So - the reading being high may be misleading, try measuring the AC voltage. This may reveal the problem. The regulator is part of the alternator. Taking it to an auto elec for test or substituting it with a known good un is simplest solution.
Small chance that there is a high resistance connection between the alternator and the battery, but would guess alternator is to blame.

Good luck.

Hi, Tanks for the info, will have a look tomorrow. I am measuring the voltage at the battery, so should be D.C.
What is confusing me is the fact it charges for a few minutes then stops.....
I was wondering if it the voltage was too high the ECU decides its too high and cuts the circuit.
Auto elecs are expensive.......and Im afraid Im a tight wad !!
I will dig out my RAVE manual and get my head round the wiring diagram

i had this problem earlier this year 2001 td4 145k miles, charging light started to flicker then stayed on just got home before everything went dead, , mine was a denso alternator, it was the brushes on the regulator unit had worn , cost £15 for a new regulator very easy to repair

I like the sound of that £15.......
Think I will get the alternator off and order a new regulator. Will let you know if it works.
Just discovered a fuel leak too, busy weekend.

Bob1974 said:

I like the sound of that £15.......
Think I will get the alternator off and order a new regulator. Will let you know if it works.
Just discovered a fuel leak too, busy weekend.

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Have a look at Gold Lion autoelectrics on eBay. They even have vids showing you how to fit the bits.

just for info, i was an hour into a 4 hr journey when my alternator light started to flicker then stayed on, late evening driving with the lights on, as i was getting closer to home the lights were very dim indeed, as i got a mile from home the radio cut out and then all the dash lights lit up but the engine still continued to run i just got home quite amazing really, i guess about 3 hours with no alternator charging .

Bob1974 said:

I like the sound of that £15.......
Think I will get the alternator off and order a new regulator. Will let you know if it works.
Just discovered a fuel leak too, busy weekend.

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Just a note though - if the issue is an issue with the diode pack then changing the regulator will do nothing. However, in the case of a single failure of one of the 6 power diodes (which is the most common diode failure) you will get SOME charge - just not a normal charge. Rob's advice to check for any ac component in the output is valid.
try revving the engine and seeing if the battery voltage increases and if so - to what. If it does nothing it is almost certainly the regulator.
If it is reaching 15v and dropping back instantly it will definitely be the regulator. !. Check you battery fluid as well as a matter of urgency - if the unit has been knocking out 14.5 - 15v for a while you may well have a cooked battery.
11.5 volts on a battery is also way too low and I would caution against the condition of the unit - you may well need a new battery as well.
Wet cell units are prone to damage at such a low voltage, AGM / gel types are usually able to withstand such a deep discharge ok.
A 'sealed for life' battery is often wet cell lead acid.
Hope you get it sorted.

I will get under the bonnet this weekend and do some proper testing, will post results. The thing that puzzles me is it charges to begin with and then after a few minutes stops.
Will update at weekend

Bob1974 said:

I will get under the bonnet this weekend and do some proper testing, will post results. The thing that puzzles me is it charges to begin with and then after a few minutes stops.
Will update at weekend

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Hi Bob,
The regulator usually has a final limiting circuit inside it that is designed to cut all current to the field coils of the rotor (the current through the field coils controls the output voltage effectively) when the voltage rises to a certain level , 15V would be about right for the safety cutout. 13.8 / 14.2 is a normal nominal output voltage but can peak at 14.8 (ish)
What you are probably seeing is the regulator overvoltage protection kicking in. - this is part of the regulator but is in addition to the actual standard regulator function of monitoring the B+ output voltage and controlling field current to stabilise at the required level - an add on 'safety' feature if you will. I used to design and program advanced external regulators that offered multi stage charging that used 14.8V for the initial boost for wet cell - but still had a 15V overload cut. The regulators used internally in modern alternators are extrrmely capable (when working lol )
It must be extremely rapid in your case as the battery voltage is so low when the regulator drops out -in other words - it is, in effect - not charging at all as it rapidly drops back. (hence the VERY low and heavily discharged 11.5v)
The batteries in cars are thin plate units (as opposed to 'leisure' or deep cycle' batteries) hence the voltage on the plates will rise extremely rapidly as the alternator regulator winds up the output. (the delay you are seeing before trip out is the inability of the alternator to push the plate voltage of the battery up to 15V immediately - even with full field coil current!) - the battery will 'absorb' most of the current for a short time with alternator output at maximum. It acts like a huge capacitor in reality.
Unfortunately, the thin plate design (a necessity in vehicles for an appropriate CCA) is the very reason the battery can be damaged in an overvolt situation.
Can you get the battery on a good charger with trickle charge facility ? - it may save you the expense of a new battery as every start is damaging the battery further.

edit - IF the voltage across the battery is more or less immediately falling to 11.5 from 15 as the reg trip kicks in then the battery is toasted as well.
Joe

@Joe_H could he measure the AC ripple by just switching his meter to the AC setting, or would he have to put a cap in series with it? Or is it a scope-only job?

Either way, what range of values would be considered good?

guineafowl21 said:

@Joe_H could he measure the AC ripple by just switching his meter to the AC setting, or would he have to put a cap in series with it? Or is it a scope-only job?

Either way, what range of values would be considered good?

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Hi GF, It is a difficult one really - on AC, any real value evident would be considered abnormal as the battery itself acts like a huge smoothing capacitor for the half wave rectification of the triple phase AC produced by the stator and diode pack.
The AC 'ripple' would be noticeable via a discernible ac voltage additional to the DC reading.
Normally - there would be nothing.
A scope would be great - but not needed here.
The key to the 3 phase dual diode per phase rectifier diode failure - as opposed to regulator failure is usually as simple as a slightly glowing alternator warning light (if field excited via the bulb) - or a glowing warning light with some output of the alternator but well below expected - ALONG with warning light glow - however dim .

It is more a case of identifying differential symptoms of diode pack (rectifier) or regulator (both completely independent of each other.
In the above case from the OP, then the issue certainly sounds like reg failure without a doubt.
The reg does not tend to fail in a 'semi' range output way.
A reg that is functional is almost always a constant output when stabilised.

Hope that helps ?
Maybe not -
A SCOPE WOULD BE SUPERB, BUT 99,9999999 % do not have them.

Cheers mate - Joe

PS - how is the DC clamp going - almost finished here after getting the toroids from China.

Thanks Joe, I have a decent charger, Amazon product,
I will take the battery off and put it through the recondition stage and see how it goes.

I have another battery in the garage, slightly smaller, which I know is good, will try that one and see how it performs.

Joe_H said:

Hi GF, It is a difficult one really - on AC, any real value evident would be considered abnormal as the battery itself acts like a huge smoothing capacitor for the half wave rectification of the triple phase AC produced by the stator and diode pack.
The AC 'ripple' would be noticeable via a discernible ac voltage additional to the DC reading.
Normally - there would be nothing.
A scope would be great - but not needed here.
The key to the 3 phase dual diode per phase rectifier diode failure - as opposed to regulator failure is usually as simple as a slightly glowing alternator warning light (if field excited via the bulb) - or a glowing warning light with some output of the alternator but well below expected - ALONG with warning light glow - however dim .

It is more a case of identifying differential symptoms of diode pack (rectifier) or regulator (both completely independent of each other.
In the above case from the OP, then the issue certainly sounds like reg failure without a doubt.
The reg does not tend to fail in a 'semi' range output way.
A reg that is functional is almost always a constant output when stabilised.

Hope that helps ?
Maybe not -
A SCOPE WOULD BE SUPERB, BUT 99,9999999 % do not have them.

Cheers mate - Joe

PS - how is the DC clamp going - almost finished here after getting the toroids from China.

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Reading through your reply, the battery charges and car performs normally for a few minutes, no battery light. After a few minutes it stops charging and battery light comes on, bright.

I may be able to get clamp and scope on it but I could do with it on the road asap,

Bob1974 said:

Reading through your reply, the battery charges and car performs normally for a few minutes, no battery light. After a few minutes it stops charging and battery light comes on, bright.

I may be able to get clamp and scope on it but I could do with it on the road asap,

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Hi Bob,
I wouldn't bother too much, you have absolutely classic symptoms of reg failure !
replace reg or whole alternator - job sorted.
Nothing you have said would lead me to believe it is anything apart from a reg failure mate
Joe

Brilliant, thanks for the advice Joe.

Well, have replaced the regulator on the alternator and all is fine !! A nice consistent 14.0v and not the 15v it was before.
Picked up the regulator from a place called Agan car parts in Birstall near Jct 27 M62, very friendly and helpful.

Also replaced fuel filter as it was leaking. We now have a noise coming from front left wheel area, maybe because it was up on axle stands for a few days??

Thanks for all the advice.

Bob.