I was at my local airfield yesterday photographing some planes that were taking off to take part in an air show and waiting for them to return again, and as it was extremely hot and sunny, sat in the car with the blower on, engine off and as is normal for my car, the blower and anything else that happens to be on, switches off automatically after a few minutes and so it did, but as the car was then cooler, I never switched the fan back on. However, when I went to start the engine to drive home again, it just clicked and the dash lights and instruments flashed and the instruments switched on and off rapidly and nothing happened. I asked a friend who was also on the field to give me a jump start, however that was totally useless, I expect my leads simply were not up to the job.

 

Luckily there was a large Emergency Services repair centre on the field, and they repair Ambulances so I asked them if they could assist me, they did and their cables were far more effective and the engine sprang to life instantly, so I was able to drive home, some 20 miles in total and by the time arrived home the car started on the button again. Today I got my voltmeter on the battery and ammeter on the battery lead and I measured 14.2V on the battery and 7 Amps were going into the battery at idle, far enough. Now here is where it gets strange, unless I'm missing something here, giving the engine a little rev, the voltage remains constant, but the charging current drops to 1A and sometimes less, but as soon as the engine returns to a tick over again, the current goes up. I thought the alternator belt might be loose, no it is OK, so its not a case of the belt slipping.

 

Any ideas? I wondered if the battery monitor control unit might be faulty?

@Graham Butcher The last time I was buying jump leads (late 1995) the place I bought them from offered me el cheapo ones, "medium price" one at twice the cost of el cheapo specials, and professional ones at 6 (six) times the cost of the medium price. As a DIY type I bought the medium price ones, and the recipient vehicle (not always mine) has started first time every time in the intervening 27 years. Maybe worth considering?

 

i would check the alternator  pulley clutch.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

it

11 hours ago, Graham Butcher said:

Now here is where it gets strange, unless I'm missing something here, giving the engine a little rev, the voltage remains constant, but the charging current drops to 1A and sometimes less, but as soon as the engine returns to a tick over again, the current goes up. I thought the alternator belt might be loose, no it is OK, so its not a case of the belt slipping.

 

Any ideas? I wondered if the battery monitor control unit might be faulty?

 

Does your car have stop/start with AGM/EFB battery? - if so all sorts of strange things happen to (over) charge the battery with spare engine energy  eg on overrun. I spotted this with my stop/start as I fitted a split relay between the 12v boot socket and a cool box in my boot - this senses the input voltage and disconnects when it drops ie not charging. After a while I found it was turning off the coolbox every now and again. This is normal. I've found if I drive with the headlights on it doesn't do this.

 

 

 

Check your battery.  Check it hours after the car has been run so you're not getting the remaining high from it being charged, do not have the engine running, note the reading.   Then if you can note the reading whilst the car is cranking over from starting that'd be good.  Then start and stop the car immediately, about ten times and note what the battery reads at rest after that exercise.

 

I think it's best to start simple and cheap before moving on to complex, sexy and mysterious.

 

The very hot and extreme weather and humidity we had wouldn't have been kind to the battery (or charging system) and if the effects of that didn't show up straight away they could still be there to show up a bit later, particularly this autumn and winter (I'm getting shares in vehicle batteries).  Just driving the cars won't be enough a proper long, low, slow recharge, preferably off the car and in a more even controlled temperature if possible.

Edited 28 August, 20223 yr by nta16
spelling

Car has smart charging and above is acceptable  ( It charges then doesnt charge)

How old is the battery they are famously crap 

Get the battery tested with someone with the right equipment to do so👍

 

Edited 28 August, 20223 yr by DEL80Y

Unfortunately it's not only the right equipment but someone who knows how to use it and is trustworthy (not so easy in the motor trade I've found).

 

A proper recharge of the battery will help regardless but you do need to check it's not putting off the inevitable but be aware car batteries are probably still one of the most oversold car parts (RAC, cough) but also owners not looking after the battery is the most common cause of car breakdowns and roadside assistance.  A battery kept in a poor state will also make the charging system work harder - plus the VW computer programs will make the car owners suffer in all sorts of ways if they let the car battery go low, warnings, error codes and all sort of other punishments.  😆

 

Edited 28 August, 20223 yr by nta16

7 hours ago, KenONeill said:

@Graham Butcher The last time I was buying jump leads (late 1995) the place I bought them from offered me el cheapo ones, "medium price" one at twice the cost of el cheapo specials, and professional ones at 6 (six) times the cost of the medium price. As a DIY type I bought the medium price ones, and the recipient vehicle (not always mine) has started first time every time in the intervening 27 years. Maybe worth considering?

Yeah, those are the kind of leads that I opted for, sort of middle of the road, the leads have nice copper croc clips on them and the leads thick and flexible, feel good quality but perhaps the actual cable itself might be undersized, but then the cable would become rather warm to the touch, but it didn't. Maybe it was because I was unable to extract much power from the person providing me the loan of their battery. I say this because it was one of these more modern cars with a plastic distribution system on top of his battery so my clips were barely able to hang on. My main concern is the way that the alternator seems to be behaving, with the charge reducing with engine speed.

6 hours ago, Roots Supercharger said:

 

i would check the alternator  pulley clutch.

 

it

Thanks, I never knew that it had one, I know the AC pump has one.

4 hours ago, DEL80Y said:

Car has smart charging and above is acceptable  ( It charges then doesnt charge)

How old is the battery they are famously crap 

Get the battery tested with someone with the right equipment to do so👍

 

Yes it has the Stop/Start system with AGM battery which is about 2.5 years old but I seem to recall came with a guarantee of 4 or 5 years. The original battery lasted 6 years before it shuffled off the earth.

Except for you measuring voltages and being worried - has the car been fine since? I think the behaviour you mentioned could be normal as your car is stop/start. That's why I asked if it was.

 

 

 

 

Edited 28 August, 20223 yr by bigjohn

44 minutes ago, bigjohn said:

Except for you measuring voltages and being worried - has the car been fine since? I think the behaviour you mentioned could be normal as your car is stop/start. That's why I asked if it was.

 

 

 

 

Yes it is stop/start but when you have driven best part of 20 miles without the system kicking in once, you don't expect the battery to be drained sufficent to prevent the car starting after sitting in it with the radio on for about an hour and nothing else do you. I think it is the alternator clutch pulley at fault after Googling the problem, it does seem common for cars with 60,000 to 80,000 miles on the clock for this to start slipping in both directions and would explain why the alternator output drops so much when the engine revs pick up. There is nothing else switched on, radio, fans, AC and lights are all off but the output drops to 1A, even with the lights etc switched on, this does not increase.

 

The car is in the dealers on the 5th for seat belt replacement on the rear offside, brake fluid replacement, 80,000 mile service plus MOT so, I've asked them to check on the alternator pulley and replace if it is faulty. I'll report back with their findings. This is the second time I had issues with the charging, last time was a year ago after I had driven 80 miles in the daylight so nothing on other than radio and aircon, so you'd have expected the battery to have been charged enough after such a long drive 1hr 45 mins?

12 minutes ago, Graham Butcher said:

Yes it is stop/start but when you have driven best part of 20 miles without the system kicking in once, you don't expect the battery to be drained sufficent to prevent the car starting

Contrarywise, because the stop/start battery clearly is flat.

4 minutes ago, KenONeill said:

Contrarywise, because the stop/start battery clearly is flat.

I could accept that if the car had struggled to start at the beginning, but as it normally does it fired into life instantly, and on the journey from home to the airfield I did not have to stop anywhere along the route, it was a nice leisurely drive with me doing my normal style of driving, smooth and gentle, hypermiling to get the best performance because of the stupidly high fuel prices we are seeing now.

3 minutes ago, Graham Butcher said:

I could accept that if the car had struggled to start at the beginning, but as it normally does it fired into life instantly, and on the journey from home to the airfield I did not have to stop anywhere along the route

All this tells me is that you don't know how stop/start works. If the engine is hot, and the stop/start battery is well charged, then it will stop the engine and restart it if and only if the car is stopped and placed in neutral, clutch engaged. The initial start is on the main battery, not the stop/start one, and if you're not stopped stop/start will not cycle.

19 minutes ago, KenONeill said:

All this tells me is that you don't know how stop/start works. If the engine is hot, and the stop/start battery is well charged, then it will stop the engine and restart it if and only if the car is stopped and placed in neutral, clutch engaged. The initial start is on the main battery, not the stop/start one, and if you're not stopped stop/start will not cycle.

You make it sound as if there are 2 batteries in my car, I assure you, I only have the one. Also if you look at my details, the car is a DSG auto, so there is no clutch pedal to depress and the only way to start the car is with the transmission in park position and my foot on the brake pedal. If none of those conditions are not met, the starter is locked out of circuit.

 

The car had been parked at the airfield for around 2 hours so the engine was not hot, it was a cold engine, just as it was at the start of the journey. The car has regenerative braking system so when slowing down using the engine as a brake the alternator is designed to dump extra current into the battery, thus placing more rolling resistance to the cars forward motion.

1 hour ago, KenONeill said:

All this tells me is that you don't know how stop/start works. If the engine is hot, and the stop/start battery is well charged, then it will stop the engine and restart it if and only if the car is stopped and placed in neutral, clutch engaged. The initial start is on the main battery, not the stop/start one, and if you're not stopped stop/start will not cycle.

 

I'm confused. My 2014 tsi stop/start only has one car battery(EFB)

 

Hi @Graham Butcher your OP sounds similar to what I experienced when I had a cell in the battery fail.  I drove to work fine, but when I went to go home that day the car wouldn't start and the dash lights went on and off with a lot of clicking.

 

The battery looked like it was charging, voltage 13.8 - 14.something but wouldn't start the car.  Had to replace it (RA came out and did it there).  My Superb doesn't have stop start.

 

It must have failed during the trip to work.

If it was the battery failing or failed, I'd have expected to display these kinds of symptoms often, but since the jump start 3 days ago the car has been fine, and I have been to Southend and North Weald again since then as well shopping which are short journeys in town with lots of stop/starts with no hint of any problems. I'm going out again in few minutes on some short local trips and I'll measure the battery voltage again then, before I start the engine and after.

Odds are when you sat in the car with engine off, you simply drained too much from the battery on the day.

 

Now it has been charged up by driving, all will be good now most likely.

 

One to monitor for sure though, and have jump leads with you just in case.

Not important here, but. The engine can actually be starter in N if the car is parked with the shifter in N and not in P.   That is a unless the temperature is below something like -5*oC.       Useful if you are maybe working on the car, on a ramp ect and need to roll the car.  Left in N and able to start the engine.  

Thanks, I never knew that,  just tried it and it worked as long as I put my foot on the brake pedal. 👍

Edited 29 August, 20223 yr by Graham Butcher

40 minutes ago, varooom said:

Odds are when you sat in the car with engine off, you simply drained too much from the battery on the day.

 

Now it has been charged up by driving, all will be good now most likely.

 

One to monitor for sure though, and have jump leads with you just in case.

Doesn't the battery monitor the battery and instruct the Ecu to disconnect the item,  in this case the radio. I know the system does switch things off if you leave anything ON after a few minutes to prevent problems. 

If you have the key in position I (one) then many systems will be awake and talking on the canbus network, using up a fair bit of juice.

 

Position II (which allows your fan's to blow amongst other thing's) is an even higher state of readiness that will eat even more power.

 

 

Even if the car does tell the radio to power down via canbus, the network (gateway) will still be talking to various modules still using power.  The system doesn't even fully power down immediately after removing key and locking, it's still awake I think for 20mins before it leaves only alarm circuit.

 

I am sure someone who has really pulled a car to pieces can say for sure.

After letting the car stand for almost 20 hours, I tested the battery voltage, and it is 12.12V and started the engine a few times with no problem what so ever and just after starting the voltage reads 14.7V as the alternator tries to replace the energy that the starting took out of the battery. Then driving it a few minutes later around the City and the Start/Stop system was kicking almost from the start, just as it does normally in heavy city traffic. I think that is a sign of a bad battery, surely not?