How to guide to investigate parasitic drain

[Doc007]

Is there a "How to investigate parasitic drain" Guide anywhere?

My 2016 car loses charge over the course of a couple of weeks. It has a Banner battery which I generally keep on a CTEK but if you take it off it loses charge relatively quickly.

I'm contemplating fitting a cut-off switch but if it is a simple fix then that would be preferable.

I have an multimeter and am not afraid to use it, BUT would require VERY basic instructions!

I called an automotive electrician to take a look at it a while ago and he took one look at it and said he couldn't do it!

[Jonathan Kay]

There are some *measurements in the archives, but I don't think that I've seen a guide.

While we're waiting for the experts...which engine and ECU, and do you know which alternator?

And do you need a wiring diagram?

Jonathan

* With a lot of variation between Sevens.

[aerobod - near CYYC]

The security system definitely puts a parasitic drain on the battery. With the battery having quite a low capacity, you typically don't want to leave the car unused for more than a couple of weeks to ensure there is enough charge in the battery to start it next time it is used.

I haven't measured with my car, but a few 10s of mA is not unusual for parasitic drain (I know BMW normally specifies up to 75mA as being normal). If your want 50% of charge in the battery at all times and the car is shut off with say 90% of charge, then with the Banner battery having 30Ah capacity, only 12Ah of parasitic drain would be desirable. This would equate to 36mA of parasitic load as a maximum over a 2 week period.

You can remove the ground terminal off the battery and put a multimeter with amps selected in series with the battery terminal and cable end, just ensure the car isn't started or any significant load put on the battery when connected like this to avoid blowing the meter fuse. This should give you the parasitic drain when the car is sitting unused.

[revilla]

2016 won't be a K but this may still be relevant ...

A lot of Ks drain the battery on that sort of timescale. People always say it's the immobiliser but when you measure it that's a small contribution.

The major cause in many cases is leakage through the ECU drivers for the injectors and ignition coils. They're solid state switches to ground. On some cars the Main Relay on the MFRU is wired in and allows the ECU to cut the 12V supply to the injectors and coils when it powers down and these cars tend to be a lot better. But on a lot of cars the loom just omits the Main Relay entirely and the injectors and coils get a permanent 12V supply, with leakage then flowing through the ECU to ground.

[Golf Juliet Tango]

Thank you Andrew.  I knew the 21 would drain the battery in about 10 days, so added a battery isolator. I didn't know the cause and didn't think it worthy of investigation, better to add a useful anti-theft device.

[Doc007]

It's a Duratec with the OE ECU/alternator.

[Benton]

Because of this thread I thought I'd try measuring my parasitic drain just for my own reference.

For context it's a 2018 620R fitted with standard factory immobiliser (though it's on its second one!, the last one being too effective ) and standard factory fitted battery isolator.

1. in theory with just the immobiliser active:- average 41ma 
2. Plugged in a cigar socket USB adapter,nothing connected, just for curiosity  :- additional 5ma draw
3. Finally turned off the battery isolator :- 13ma draw​ still being recorded (interesting!)

​In case 3.  I only kept measuring this for a few minutes until I got cold and decided it was time for a coffee   so whether the 13ma draw would continue ad infinitum (well at least until the battery went flat!) or tail off I don't know.

Since the car when not "out and about" is always hooked up to a Ctek, none of this is going to give me sleepless nights but I thought it might be useful info to share/compare.

[Roger Ford]

Using your multimeter to measure the parasitic drain is very easy. Connect the leads to the currrent sockets of the meter (most meters have a common negative and then one socket for most measurements and one socket for current, often marked "10A"). Set the dial to amps (if there's several choices 1A should be sufficient). Disconnect your battery earth and then connect the red lead of the multimeter to the earth lead and the black to the battery terminal. Your multimeter will now read the constant parasitic drain. If it's - say - 0.1A and you have a 30AH battery you can expect the battery to be drained in around 300 hours (12.5 days). It's possible that you might need to cycle the ignition and immobiliser to get a true reading.

[SM25T]

#7 ... point 3 ... the battery isolator isnt switching everything then !

[Benton]

Apparently so, when I can be bothered I'll try pulling individual fuses to see if I can track it down or maybe try to figure out how the switch has been implemented.  Since it came as factory fitted I assume it was installed correctly(?) 

[Doc007]

Roger Roger.

I'll try this.

[John Vine]

I've just measured my R400D (MBE 992 ECU and FIA master switch).

The sequence is: 230mA at start (accompanied by a click from the MFU), dropping to 130mA after 3 secs (with another click from the MFU), then around 20mA after a further 7 secs.  The reading then fluctuates in sync with the little red LED on the dash: Off 19.4mA, On 20.9 - 22.4mA.

JV

[Geoff Brown]

I have been through a few Banners with three Sevens & parasitic drain is usually caused by the immobilser exacerbated in cold weather.

In cold weather or winter lay over disconnect the negative lead.  From my experience Banners do not like being permanently connected to a trickle charger such as a CTEK. Experimentation with my latest car proved that so over several winters. Therefore I only connect the battery once a month to top up during winter lay over. 

IMO Banners are notoriously fickle in the way they are charged & looked after.

 

[Hampshire West AR]

Interesting experience Geoff. I have always wondered why the Banner only lasts about 3-4 years when people have told me their experience.  My previous Blackbird had a Vidor battery that lasted over 10 years on a Accumate with no issues.  I replaced it with a Bosch one that seemed to be doing well until I sold the car.  My new R500D has the Banner  and based on your experience and the drain of the immobiliser of up to 22mA the charger could be disconnected for a few weeks(32 days max if the Banner is 17Ah?) to see if it would extend battery life?

Nick

[Jonathan Kay]

"I have always wondered why the Banner only lasts about 3-4 years when people have told me their experience."

It seems to be very variable. Of course that variability could be related to different charging patterns..

Jonathan

[Jonathan Kay]

Thanks for all those measurements. Very interesting. Please keep them coming.

We'll have something to compare with when problems occur. And might even be able to spot some risk factors...

Jonathan

[Beagler]

When I installed a new battery I heard the fuel pump in the tank run for a second or so when connecting the battery. The key was not in the ignition. I thought it only came on with the ignition. There must be power to it continually when switched off so surely will add to battery drain along with alarm system.

[revilla]

If it only ran for a second or two, then I suggest there was only power to it for a second or two. If there was power to it continually, it would run continually. It won't add to the battery drain. There's probably just something in the ECU's power-on code that runs the pump briefly.

[andy_harries]

@Beagler

I have the same engine (1.6 Sigma) and hear the fuel pump run for a second when I turn the battery isolator to 'on'.

It's actually very helpful as its an audible cue that I have turned the isolator in the right way and everything should now be working.

[Geoff Brown]

#15 JK - In my case Banner life is not that variable:

First car owned for five years - one replacement Banner at year four.

Second car owned for eleven years - replacement Banner at year four & year eight.

Third car owned for nine years & counting - replacement Banner at year four & year seven.

So a round average of every four years.

[Jonathan Kay]

And if you had the same pattern of use throughout that consistency would support my suspicions...

: - )

Jonathan

[John Vine]

My present (I almost wrote "current") Banner is now over 7 years old.  When not in use, it lives hooked up to the Accumate.  

However, I suspect that it's well into its dotage, as it was very churny when I started the car the other day at about 5C.

JV

[Jonathan Kay]

Can I encourage you to track that minimum voltage during cranking? Better to know that it's failing while you're at home...

Jonathan

PS: 

"I almost wrote "current""

Resistance is futile.

[John Vine]

Will do, Jonathan -- as soon as tomorrow, if it's sunny for a blat.

JV

[lincslotus7.club]

This maybe of use... My battery experience pretty much mirrors Geoff Brown. Last year when needing another I went for a JWM LiFePO4 Battery Kit. As these really don't like parasitic drain nor long trickle charge I also fitted a Master Cut-Off switch (thanks to Jonathan Kay for info etc) job done! Just checked the battery reading 13.4v not been used or charged since October. The engine now turns over much better too.

Fitting the switch is tricky however, but worth it, good luck with a fix.