Pug 407 2.0HDi flat battery

Squealing Cat stuck somewhere?

is the alternator down the back? if so, disconnect it and see if the noise stops. otherwise remove fuses till the noise stops and work it out from there.

Damned bugger doesn't run out of air if there is one :)

Nope, the alternator is on the side. Removing/connecting the battery stopped the noise for now.

Current draw is initially 1.8A but drops to 200mA (without the noise), so I don't think that I have an issue there. Alternator output is 14V at idle, so OK too I guess.

Cheers, Mark

Make sure you have the radio code before you pull the radio fuse.

How much use does it get? Depending on intrusion detection, modern cars have quite high current draw even when off.

Do the current draw tests with a fully charged battery. I had a flat battery on a Mazda 323F BJ. Pulling fuses I found the door lock system was pulling current ~ 0.5A, I wasted quite some time looking for possible faults in this system. With a fully charged battery it stopped pulling current and performed the door lock self test sequence correctly. Clearly the circuit triggered as voltage dropped but voltage was insufficient to operate the door locks.

200ma is a lot. as the car sits unused things turn off, you should leave it for a couple of hours to see if the drain drops down. At 200 ma the battery will be seriously low on power in a week or two depending on battery size and condition

Many cars will have the odd thing running when woken up even when not started. You'd need to check the quiescent current after some time to make sure everything has shut down. Should be of the order of 50mA or less.

When using a DVM for this, start on a high current range - say 10 amps - to avoid blowing the DVM fuse. And don't switch anything else on. If that shows the reading to look about OK - but you can't measure it accurately on that range, change to a lower range, but short out the DVM for a few minutes to make sure things have gone to sleep then remove the short to get the accurate low current reading.

200mA quiescent is *way* too much. That would (in theory) totally flatten a 70 amp.hr battery in two weeks.

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Good advice. If super cautious, put a headlamp bulb in series with the DVM to start with. If the bulb doesn't glow, it's safe just to use the meter.

Chris

200mA represents about 200 hours on a 40 amp-hour battery. Given that the vehicle is in daily use this should not be a problem - but it is rather higher than I would expect. It's less than any ordinary lamp, but it might be the adapter for a mobile phone, or some part of the anti-theft system.

The voltage across the battery at tickover, with no electrical services on - I would expect more than 14v - and certainly something over 15v at a fast idle of about 1500rpm in the first few minutes after starting the engine when it replenishing the charge lost. This is dependent on temperature ...

Try it with all electrical services on - heater blower at full speed, rear window heater, all headlights & foglights - at tickover - the alternator should maintain about 13.2v across the battery, rising with engine revs. If it doesn't then probably an alternator or drive belt problem.

Fair enough. I didn't leave it too long before it dropped to 200mA, so maybe is not the final reading. It's a daily runner of around 100 miles per day, so I was surprised that it had discharged so much over night.

Will check quiescent current shortly.

Cheers, Mark

Funnily enough, I talked a mate through doing exactly that after he's had a new battery and alternator fitted to his car after it 'suddenly' started getting a flat battery after just a few days left unused.

I got him to take the (festoon) lamp out of the interior light and hold it in series with the battery lead and battery and if it lit up at all, to keep turning stuff off till it went out. He finally tried turning off the radio and the lamp went out. The 'problem' was the radio was broken but still drew power when turned on and the garage had tried to use it when it was in for a service, but not turned it of again. ;-(

Cheers, T i m

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If your DVM is not a reasonably decent one, low current readings may not be accurate.

If you suspect it's draining, disconnect the battery overnight and see if it spins over merrily in the morning when re-connected.

Chris

A VW Bug (new type) had a similar fault, but the (original) radio still worked fine, but drew some current all the time, no matter what. A new radio fixed the draining fault. The first 'mechanic' that looked at it said he couldn't find the problem.

The alternator is putting out a steady 14V to 14.5V regardless of engine speed or load. I think I'll head out tomorrow to have the battery and alternator tested and see what they come up with.

Cheers, Mark

Ideal way is one of those battery disconnect devices. Connect the meter across it, wait for things to stabise, and unscrew the knob.

Not so sure of that. I have a very accurate voltmeter connected direct to the SD1 battery. (although via a relay, so it only works with the ignition on, as it is LED and takes some current)

The alternator is a modern 100 amp Marelli, and the voltage almost never goes over 14. Under most conditions, it stays bang on 13.8v.

Cars with an ECU controlled charging system may well be different.

Ah - if it is used daily, 200 mA wouldn't be a problem. Once upon a time, old dynamo cars had to have a parking light on all night in some areas. Long before LEDs.

Many modern radios draw some current all the time. They lose their station memory if you disconnect the battery.

But usually less than 10mA. Other things draw current too at all times. The receiver for your remote central locking. Any form of alarm and immobiliser. And so on. And they all add up. Hence the need to measure the quiescent draw accurately.

It may not matter much if the car is used every day - but is a PITA if you leave it in an airport carpark when flying off on holiday, and the battery is flat when you return.