My 'rado keeps killing its battery

[MillSpeed 0]

Howdy folks. My KR 16V 'rado killed its second battery this morning. Luckily I had the one I took off before charged up and ready to go, so it wasn't too much of a problem. I was wondering if there are any common faults I should be looking for? The alternator appears to be charging ok (the charge light goes out and stays out, no flickering or anything). Nothing obvious is staying switched on that would drain the battery. The bastard always takes some cranking before she'll fire (which can't be helping matters) but every time she struggles on start-up I take her for a good run to try and put some charge back into the battery. I've got a spare alternator, might give that a try. Any other thoughts?

[dinkus 10]

My bet is the boot light is staying on. Trap a small child/midget/drunken friend in there and take a look to see if it goes out when you close the boot.

 

Or you could just take the parcel shelf out and peer in :)

[MillSpeed 0]

The bugger was staying on so I just took the bulb out and left it hanging. I then thought, maybe it'll go out with the main interior light (you know they got that delay on em after you shut the door). But now I've lost the bulb for the boot light so I couldn't test it.

[dinkus 10]

The boot light is related to the boot lid switch, and quite often the switch doesn't work properly so the boot light stays on all the time, even though the rest of the car isn't lit up.

 

But if you've taken the bulb out, then it's not that that's draining your battery :(

[davidwort 0]

Howdy folks. My KR 16V 'rado killed its second battery this morning. Luckily I had the one I took off before charged up and ready to go, so it wasn't too much of a problem. I was wondering if there are any common faults I should be looking for? The alternator appears to be charging ok (the charge light goes out and stays out, no flickering or anything). Nothing obvious is staying switched on that would drain the battery. The bastard always takes some cranking before she'll fire (which can't be helping matters) but every time she struggles on start-up I take her for a good run to try and put some charge back into the battery. I've got a spare alternator, might give that a try. Any other thoughts?

 

When they get old the Bosch alternators often get dodgy diodes, even if it appears to charge OK the battery can still discharge back through the alternator when the car is not running.

Sometimes you can feel the alternator is warm when the car has not been run, e.g. first thing in the morning.

You can check for current drain from lights etc, by putting an ammeter in series with the battery and then if you get more than a hundredth or so of an amp drain start pulling fuses to see which circuit is at fault.

 

David.

[MillSpeed 0]

Cheers for the advice David. Alternator feels pretty cool, maybe a bit of residual heat from the drive to work this morning but nothing to suggest something's amiss. Will have to get busy with the multi-meter this weekend.

[bcstudent 0]

Not strictly true...I've had some battery issues recently too so I had a poke around. The quiescent current draw was around 220mA, with 150mA accountable to my Alpine headunit even when it's turned off. I considered this high so I tested a friend's Calibra Turbo, which has the same headunit (along with an alarm), and his car was drawing a quiescent current closer to 600mA - he has had no issues with flat batteries. It's all very strange.

[RW1 0]

One of VW'a classics on the 8v/16v block engines is the earth circuit between the alternator and the block going high resistance. All appears normal with dash light out and the battery taking in some charge. But in fact the battery itself is only seeing a voltage of say 12.5 volts but the alternator sees 14 volts so the regulator backs off the charging. If you have significant current drain from ICE as such (ie. above the car's standard 100 - 150 mAmps for time clock etc.), then this will soon run down what is in effect only a quarter or half charged battery no matter how long the journeys are.

 

The way to check is to put a Digital Volt Meter on the battery earth and the alternator body (ie. it's earth). The DVM reading needs to be less than 0.1 volt. It's higher say 0.2 volts or higher then the earth circuit from the alternator through the engine block/gearbox etc back onto the battery earth has some resistance. The last car I worked on had 0.2 volts reading, when the bridging lead was fitted, the DVM read 0.095 volts and the battery charging was a lot better.

 

The usual place where the resistance exists is in the alternator mounting bracket and mount onto the engine block. Jump this area with an earth lead (from a local motor factors) from the alternator body (find some secure fix point) and attache the other end onto the engine block or cylinder head. The cable does not have to be substantial so one of the slender earth cables with eye ends will do fine or just make up a lead using something like 5 amp cable.

 

Every 8v I've had has had this problem. On the Golf Mk1/2s, some Golfs had an earth wire direct from the battery earth to the alternator body earth stud, fitted as part of the car's wring from new. VW have known about this one since the 1980's. Worth a check.

[MillSpeed 0]

Thanks for the tip RW1. Just tested it now with the volt meter and I'm getting 0.04v, that doesn't sound right does it? The engine has to be running yes? Might just run an earth wire direct to the -ve battery terminal like you suggested.

[dr_mat 0]

Pure maths says 600mA draw will drain a 64Ah car battery in 100 hours give or take, or around four days...

150mA is much more sustainable, if your battery is in top condition and is being charged well.

Check the voltage across the battery terminals when the engine is running. You should see most of the alternator's 14.2 or so volts right across the battery terminals. If you do, and the battery is still going flat very quickly, then it's probably time to swap the battery out.

[MillSpeed 0]

The battery was flat again this morning, that's 4 days. I've been swapping between two batteries, and charging up the flat one ready for the next swap. The voltage across the terminals was 13.74v with the enigine running.

[RW1 0]

Just tested it now with the volt meter and I'm getting 0.04v, that doesn't sound right does it? The engine has to be running yes?

 

0.040 volts with engine runing is very good for alt earth to battery earth. The 13.74 volts is not quite so clever. What are the volts across the alternator? If 14 - 14.2 then investigate things like the positive starter solenoid connection where the +ve alternator wire and the battery +ve wires connect. This can also go high resistance due to damp air getting to it from the road and thro' the rad.. (PS Disconnect the battery 1st!)

[Lippy 0]

hrmm this is interesting, would seem to explain a few probs I have been having.

 

I will report back my results soon

 

Lippy

[Toad 0]

If it's the alternator shoddying about, pop down and try a spare from mine, i've still got your old spare, and i should have the new car by the weekend. did have a recon unit, but my dad gave it away! (doh!)

[MillSpeed 0]

Ha ha, how's it goin fella? May well take you up on that. Gonna try cleaning the starter motor terminal. Found more evidence of wiring butchery, the buggers have been cutting wires to the ECU.

[bix 0]

Sure you dont just need a new battery? :wink:

[StormVR6 0]

Check the glove box light, mine often gets turned on by stuff inside. Only a thought.

[MillSpeed 0]

I measured a steady 14v across the alternator, suggesting that there may be an issue with the starter motor terminal. Will investigate this weekend. Checked the glovebox light, looks ok. Don't think it's the battery at fault, I'm switching between two batteries at the moment, unless they're both knackered!