Battery Drain!

smyrk · Nov 23, 2015

Hi there I've owned my R reg 300tdi disco for over a year now and hardly used it because the battery drains off after a couple of days standing. Finally found bait of enthusiasm. Bought a new battery and researched how to check for a parasitic drain.
Tested it and I've got a reading of 0.72. pulled all the fuse and this then drops to 0.05 when i remove fuse A12.
if i remove B6 it also drops to 0.05
Then with either of these removed if i remove C6 my reading drops to 0.00
Can anyone tell me if anything links all these fuses together. A mutual earth etc.
(also had a problem with the mfu, no intermittent wipers, no fog light, unbolted it to check part number order a second hand working unit. bolted old one back in placed whilst waiting for new one to arrive and everything was working again for a short while and then stopped. So new one arrives i bolt that in place everything works for a while and then stops again. not sure if this is related or not.)

biolandy · Nov 23, 2015

I would check your diode pack in the alternator is not leaking-remove large connector from alt(be careful as +12 volts) and then repeat your drain measurement.If this is the problem,sometimes cleaning all the carbon crap out of alt will fix this.

smyrk · Nov 24, 2015

biolandy said:
I would check your diode pack in the alternator is not leaking-remove large connector from alt(be careful as +12 volts) and then repeat your drain measurement.If this is the problem,sometimes cleaning all the carbon crap out of alt will fix this.

Cheers mate will check that. Also after id posted yesterday i noticed that the initial drain is 0.03 and then jumped to 0.72 after about 2 minutes?

sierrafery · Nov 24, 2015

The hint with the diode pack is spot on IMO, it's the most common cause of parasitic drains and not noticeable while driving cos the alternator will still charge normally from voltage point of view measured with DC voltmeter(providing it's only one or max two diodes from the pack which has 8 in it), it will be a sine wave component in the charging feed which is damped by the battery detectable only with oscilloscope... that 2 minute delay might be the time while the p/n junctions are getting ''loaded'', something to be ruled out exactly like biolandy said

smyrk · Nov 25, 2015

Thanks sierrafery although most of that went right over my head

.
The other day i pulled the fuse to the mfu (A12) and left it out. check the battery next day and it was down to 11.4v.
Reconnected everything and still had a drain of about 0.70 so left it connected as i removed the large alt lead. The multimeter wouldn't then stabile but was jumping from 0.30 to 1.1ish.
So i removed the other 2 alt connections cleaned them all up and replaced them all. Took my meter out of the way and then started the disco. let it run for a minute and then switched it off and reconnected my meter (on the earth side if it make any difference) and now I've got a 0.03 draw which reduces to 0.01 if i remove fuse c6.
And now i have no mfu i don't think as the int wiper, fog light etc are not working.
I can feel the little bit of enthusiasm i had slipping away again!

sierrafery · Nov 25, 2015

IF the diode pack is the problem and more than 2 diodes are shot the sine wave component can hurt sensitive electronic systems and the MFU can be considered that... as you released the battery's backfeed to the diodes then gave them the voltage back it's possible that some more diodes were hurt, also with all those tests you've made maybe at one point the contact between the battery and the alternator output was interrupted while the engine was running then the output can jump up to 20V and if that happened the MFU might have had it, better not start the engine again with this alternator as it is, or put another known good one, or fix this one to be sure it's OK then try with a known good MFU...it's possible that some main harness is chaffed too then the whole thing is messed up, i dont envy you at all

smyrk · Nov 25, 2015

Sorry mate the MFU was intermittent before, id swapped it for another 2nd hand one and it was doing same thing. it worked for a short while and then stopped. This had stopped working before i touched the alternator and i didnt touch anything or have the multi meter in place whilst the engine was running at all. Does that change anything you've said? Is there anyway to know 100% its the alternator before swapping it as id hate to swap it if thats not the problem?

discool · Nov 25, 2015

smyrk said:
Is there anyway to know 100% its the alternator before swapping it as id hate to swap it if thats not the problem?

So what happened when you did what biolandy advised, post#2 ?

smyrk · Nov 25, 2015

discool said:
So what happened when you did what biolandy advised, post#2 ?

My multimeter wouldn't give a good reading it kept going up and down and was doing the same when i removed the alt lead. Then after i restarted the engine with it all back together its showing a draw of 0.03 and isn't showing any sign of returning back to 0.7 even after I've left it for a while it hasn't gone back up.

sierrafery · Nov 25, 2015

smyrk said:
Sorry mate the MFU was intermittent before, id swapped it for another 2nd hand one and it was doing same thing. it worked for a short while and then stopped. This had stopped working before i touched the alternator and i didnt touch anything or have the multi meter in place whilst the engine was running at all. Does that change anything you've said? Is there anyway to know 100% its the alternator before swapping it as id hate to swap it if thats not the problem?

i misssed that the MFU made tricks before too, that info changes things cos it seems very like a chaffed harness issue then,... especially after the last results with the alternator as you explained to discool

smyrk · Nov 25, 2015

no worries mate i find it hard making myself clear on these forums, no matter how long winded i make my replies!
Originally because of the big change when i removed fuse A12 which is for the mfu i wondered if maybe there was a separate earth for the mfu or maybe something shorted in this which was causing the drain. OR if for instance say the wipers had a short and were draining tha battery would this be indicated by a drop in current when the MFU fuse was pulled? Another issue the disco has has is that the hazard lights flash 3 times every now and again. say every half and hour or so. (possibly the sounder would go out but its been disconnected) It might not be linked but just incase that helps point to anything else that could be the issue

sierrafery · Nov 25, 2015

You have to follow that wire from A12 then

smyrk · Nov 25, 2015

Been back to it swapped the MFU for my old one and have fog lights and heated rear screen again for now, removed the interior bulb near the back door, as that seemed to come on when the mfu was back in, stripped and cleaned the trailer socket because thats what fuse b6 is for and its reduced drain down to 0.05 - 0.03 i think mainly due to removing the bulb. Now how quickly would that flatten the battery? will i ever get it down to 0.00? or will it always have a drain due to the alarm etc? thanks for all your input guys

sierrafery · Nov 25, 2015

That up to 50mA drain is not something to be scared of especially if there are some retrofitted things on it which are maybe not 100% well wired, for example with that kind of drain a good 100AH battery will go to 70% of power where it's still good enough in 600 hours but as long as the MFU is missbehaveing IMO there's some problem with one circuit to it which triggers some functions.... i dont have too much experience with D1s to tell you more

smyrk · Nov 25, 2015

Brilliant mate thank you for your help. I think like you say its time to find where the wires from the fuses go and see if i can isolate it. thanks

discool · Nov 25, 2015

There's a dianostic program available, it's more of a function test, you will find how to set the test in motion on the www.
As Sierrafery said 50mA is not sad, I suspect you are taking your readings just after you had unlocked therefore the security system, MFU are not in their quiescent state so waking up charging up components etc ready for what is their next command... so to speak... So there will be a higher reading, also using a digital multimeter, readings will bounce around, use a anolog multimeter for a steady meter reading.

Battery Drain!

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