Expected alternator behaviour?
 

With a fresh MOT on Val, it's time to look at a few of the quirks she has, including the idle which has a mind of its own most of the time.
Whilst warming the car this evening I thought I'd do some experimenting, channelling the Gary Sinise character from Apollo 13 by adding load during the power up sequence.

So from a cold start it idled nicely just about 1000rpm for a few seconds and then settled down below that. With each extra electrical load I switched on the idle got lower and lower until it was really struggling sitting at just above 500rpm. Blipping the throttle didn't change the idle - straight back to 500rpm once off the throttle.

Power up sequence was:

Side lights
Dipped beam
Full beam
Heated seats
Stereo
Blower (on full heat)

The straw that almost broke the camel's back was the front and rear fogs going on. That took it down to 500 and a whole lot of shuddering going on.

Each load I removed bumped the idle up a bit.

Is this normal behaviour or a sign that the battery or alternator is struggling a bit?

On other cars I've owned the ECU has bumped up the idle to cope with extra electrical load - e.g. my Golf Mk4 adds 150rpm to the idle if I switch on aircon.

Car is starting fine - first time every time, even at -4C this week - and driving fine (well, other than the aforementioned haunted idle and ABS issues)

I know Luke barely saved my battery when he popped the recon engine in so maybe it's struggling a little?

What Voltage is it showing ? It should be around 12.6v and somewhere between 13.7 to 14.7 with the car running.

If you don’t have a multimeter to tell you the voltage of your battery, you can do a test of your electrical system by starting the car and turning on the headlights. If they are dim, that indicates the lights are running off the battery and that little or no charge is being produced by the alternator. If the lights get brighter as you rev the engine, it means the alternator is producing some current, but may not be producing enough at idle to keep the battery properly charged. If the lights have normal brightness and don’t change intensity as the engine is revved, your charging system is probably functioning normally. If you’ve been experiencing problems with your battery system and the headlight test checks out okay, you should check whether or not the battery is holding a charge, or if something on the vehicle is discharging it.

I suspect your battery is knackered :teeth_smile:

It sounds very much like your alternator is putting out plenty of power (and to produce that it saps power from the engine, hence the lower idle speed etc) but also that the battery is either pulling too much current from the alternator or isn't providing enough of a back up power source as it should.

I'd suggest keeping an eye on the battery, try and find an autoelectrician to do a drop-test on the battery and advise accordingly - no gravity defying exercises are involved with this.
My suspicions in short are similar to Marks, your battery is weak and/or at the end of its useful life. Try to find a Halfords HB096 to replace it with, it's a traditional lead-acid battery without calcium or silver-calcium in it which need a much higher voltage to charge than your alternator puts out.
Also the HB096 is the heavy duty battery for yours so should have plenty of reserve power for starting etc.

If you maintain more than one car and can afford it I’d recommend getting a modern battery tester. I have always suspected they were nowhere near as good as a traditional load tester. However, I watched a (non-advertising) video online about them and decided to get one.

I have got a Yuasa battery in one of my 940s which came with a car I bought in 2011. It has never let me down and I condition it on a Ctek charger periodically so I was minded it would last forever. However, I tested it the other evening and the results have disavowed me of that idea. See picture!

If you can get an 096 type battery in the battery tray then that is certainly a heavy duty option. Personally, I prefer 027 or 075 size batteries as they are easier to manoeuvre into position. I find either nowadays comfortably exceeds the original specification in the owner’s manual.

The 027 is the standard 9xx battery (except for diseasels that use an 096) and the 096 fits nicely as would a 100 battery (same size as an 096) and the 075 is more or less the same size as an 027.

The reason i recommended the Halfords HB096 is it's the only battery i currently know of that still uses lead-antimony on the plates instead of silver calcium so will work and not be subject to premature sulphation as a result of undercharging.

https://en.wikipedia.org/wiki/Silver...alcium_battery

That mostly explains it although from experience and research i would say calcium batteries need 15.1-14.7V to charge with the 14.7V being the threshold where they actually start charging. Just to really confuse us all, the fully charged voltage remains at 12.7V after letting the battery rest for an hour ish after charging to disperse surplus battery voltage. The higher charging voltage is simply to overcome the silver-calcium coating on the plates in the battery. :err:

As for a battery tester, IMHO there isn't a substitute for the traditional drop-tester as it puts real world loads on the battery to see if it will cope with starting. It's not without risks in use though and for the number of times a home mechanic would use one, even the cheaper traditional ones never mind the new digital varieties that don't put a real load on, difficult to justify in terms of cost.

Each to their own and i must confess i have some "vanity tools" as i call them - tools that are difficult to justify buying in terms of cost Vs use but are handy to have for their occasional use or to boast about saying "I've got one of those!" - hence my term "Vanity tools"! :thumbs_up:

Hi all is a good multi meter good just to read the battery and alternator out put so you can move forward from there I wouldn't be without mine now very easy to use

It's normal as don't think the idle system compensates for those loads. It only increases for autos or aircon equipped cars as they send a signal to the idle valve ecu.

Putting in a massive battery won't change that. When it's running the alt is powering everything.

You don't say what car it is. The LH2.4 will absolutely load compensate during idle. You can drive the car without touching the accelerator if you engage the clutch slowly enough.

The load compensation baggy is talking about is immediate signaling. The auto drive and AC put on huge loads which might otherwise stall the engine, so they are signalled directly to the ECU and it immediately changes the fueling and idle valve setting. For the rest of the loads the ECU uses the rpm feedback from the ignition ECU and this provides a slow feedback.

Either your idle solenoid is stuck or your idle switch isn't working and the ECU doesn't know it is idle mode.

It seems your constant Idle valve isn't working or not adjusted properly More likely throttle blocked with carbon around the edges not allowing enough air through.

If this problem has gradually got worse suspect a dirty throttle plate and housing inside .
if it suddenly happened , maybe an electrical problem.
If it happened after you did something perhaps throttle and position sensor need setting up from scratch again.

The idle valve and ECU will compensate for carbon build up, this problem only happens shortly after starup. If it doesn't stall the ECU will compensate. Like I say above the ECU compensation isn't kicking in for some reason.