Flat battery: one to watch out for!

shamwari

Over the weekend, I was asked to look at a car which was flattening its battery. The story goes like this.

A new car stereo was purchased from a "German" supermarket and fitted to the owners car - an aged Opel Corsa. The owner purchased the radio as it was fitted with bluetooth and he was using it as a "hands free" unit for his phone.

Not long after the stereo was fitted, the owner noticed his car was turning over quite slowly first thing in the morning, but was ok during the day. He decided to fit a new battery. A week or two later, the slow early morning starting syndrome returned, and the owner reckoned he might need an alternator. At this point I was called in.

The usual checks around the alternator revealed everything was ok and nothing was amiss. I checked the amount of current being drawn with the car stopped and everything switched off an I was surpised to see several hundred milliamps being drawn. I disconnected the alternator suspecting that leaky rectifiers might be causing a parasitic drain on the battery, but the current draw persisted. I then pulled the fuses on by one, and one fuse on a constant live (which served the radio) killed most of current draw. This led me to the new radio which was fitted, which it transpired was not faulty!

The setup in this Corsa allowed the radio to run even with the IGN key off. With the key off and radio itself also off, the bluetooth function was still active. The owners phone was still shown as connected to the car, and when I rang his mobile, the radio in the car sprang to life to take the call!! The owner then commented that he was having problems with receiving calls sometimes and had too manually change his phone settings after being in the car.

The solution was to remove the radio and change wiring in the ISO socket so that a switched live was used instead of a constant. It meant that the IGN had to be on to use the radio when stopped, but it put and end to the battery being drained.

Rovi

Good tip, thanks.

It's a variation on the old 'sloppily fitted handsfree equipment' thing that often appears, where the 'engineer' that fitted it twists the switched and permanent live feed wires together and connects them to a permanent live on the vehicle. This results in the bluetooth being always 'On', with obvious consequences for the vehicle battery and peculiar phone behaviour when within range of the vehicle.

thewintermute

The War Departments '99 Clio is doing this and it has my head wrecked.
For some reason the battery flattens overnight.
No new equipment installed though, her mechanic has had it for over a week and keeps fobbing her off that an auto-electrician will look at it, but he hasn't been in yet.
Any advice is appreciated. I'm reasonably handy with most mechanicals, but electrics aren't my strong point.

shamwari

thewintermute wrote: »

The War Departments '99 Clio is doing this and it has my head wrecked.
For some reason the battery flattens overnight.
No new equipment installed though, her mechanic has had it for over a week and keeps fobbing her off that an auto-electrician will look at it, but he hasn't been in yet.
Any advice is appreciated. I'm reasonably handy with most mechanicals, but electrics aren't my strong point.

Assuming there isn't a light left on in either the glovebox or the boot, and that the battery isn't kaput, I'd disconnect the alternator. The rectifiers inside it can go leaky and discharge the battery. Make sure any disconnected cables are covered and secured so that they can't short circuit anywhere. Leave the car overnight, reconnect and restart it. If she fires up ok, I'd wager the alternator is the cause.

If you feel uncomfortable or uncertain doing this, get your mechanic or autoelectrician to do this for you. It is simple enough for them to do.

thewintermute

Cheers,

took the bulbs out of the lights to make sure they weren't draining.
The mechanic reckons the alternators fine, I guess I better wait for the magic of the auto-electrician to appear.
Thanks for your help.
Bloody annoying though, pretty sure its something simple.

R.O.R

Rovi wrote: »

Good tip, thanks.

It's a variation on the old 'sloppily fitted handsfree equipment' thing that often appears, where the 'engineer' that fitted it twists the switched and permanent live feed wires together and connects them to a permanent live on the vehicle. This results in the bluetooth being always 'On', with obvious consequences for the vehicle battery and peculiar phone behaviour when within range of the vehicle.

My CK7W Nokia kit has been fitted in the above fashion. Thankfully it's not a huge drain on the battery. Untouched for 2 weeks there was almost enough to turn over the engine, but not quite.

Don't actually use the Bluetooth on it as my work phone is so old and cr@ppy that you can plug the cable straight in to the bottom and it sits nicely in the passive cradle I aquired.

shamwari

thewintermute wrote: »

Cheers,

took the bulbs out of the lights to make sure they weren't draining.
The mechanic reckons the alternators fine, I guess I better wait for the magic of the auto-electrician to appear.
Thanks for your help.
Bloody annoying though, pretty sure its something simple.

The funny thing about this particular fault I described is that the alternator can produce what appears to be a normal output when in use. if your mechanic put a voltmeter on it, he'll still see around 13V.

When the alternator is stopped and is idle, the rectifiers gradually leak the charge away. You can use the car perfectly during the day, and the problem usually shows after it's been laid up overnight.

Owen

Before you go disconnecting the Alternator, there's a much more fundamental step you should take. Disconnect the negative lead from your battery, and put a multimeter between the negative terminal on the battery and the negative lead, switch the multimeter to current. With the ignition off, see how much current is being used.

Open up the fusebox in your cabin, and pull the fuses one by one watching the meter all the time to see which one stops the current drain. If none of the cabin fuses being pulled show you an issue, then go to the ones under the bonnet.

It's a pretty foolproof method, and allowed me to diagnose the current drain on my 75 in 10 minutes.

shamwari

That's what I did in my opening post above. However, in the case of wintermutes situation, he acknowledges he is handy mechanically and not electrically. That's why I advocated disconnecting the alternator to eliminate it first. He may not have the understanding and the equipment needed to isolate a leak based on pulling fuses.

mathepac

If The War Department's '99 Clio above uses a maintainable battery, carefully check that the electrolyte in each of the cells is topped up to the mark.