Parasitic drain - what’s normal?

Pinkythelabrat

Pinkythelabrat

A2OC Donor
My battery has been going pretty flat pretty quickly during lockdown - charging it once a week and it’s below 12v every time. I normally drive 70 miles a day, five days a week, so this hasn’t really been an issue before.

It’s an 18 month old F18 85amp hour battery. A good un. I’ve got a TDi 75 2002.

I measured the battery current drain with the doors all locked and the boot latched - alarm set and it settled to 100mA drain steadily.

At this rate - 17 amps per week - my battery is pretty much going to be half way flat every fortnight! It feels faster but I probably am charging it at least fortnightly if not weekly.

100mA seems to be pretty high but does anyone have their own parasitic drain in a TDi to compare it to?

Thanks awfully!

Alex.

Ps I do have a solar panel trickle charger but it can’t keep up...


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Evening Alex.

Ive had a battery drain issue in the TDI. It was there when I purchased it and thought it was something to do with the stereo. I finally worked out it was the CCCU starting to fail when I purchased it. It just got worse and noticed other electrical issues which helped point the problem the said CCCU.

I’ve now changed the CCCU and I no longer have a flat battery after a few days.

I’m sure this is something for @timmus to comment on as it really is his area of expertise.

Kind regards,

Tom
 
Oh dear.

Thank you Tom. I really really hope it’s not a CCCU issue...

More than likely it’ll be some of the bodged electrical installations I’ve put in myself... I’m almost certain but wanted a baseline before checking.

I’ve installed two additional 12v sockets and a permanent live 5v for my dash cam. I’m thinking maybe there’s an led or something in the gubbins.

I’ve fitted a connects2 music thing I’d to give me usb input.

I’ve fitted heated seats and controls from an A3.

One of my doors shows a ‘won’t desafe’ error. And clunk clunks an extra time when locking.

I’m sure one of these things will be at fault.

Alex.


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right, reading the runes from the Germans, 100mA is OK but you should be measuring after the systems have been shut down (i.e. locked and all doors closed!) for two hours, and not before. The CAN Bus takes some time to wind down.
If you want to eliminate the CCCU, remove fuses 36, 37, 39, 41, 42 and 280.

- Bret
 
Some useful info on battery drain diagnostics in this old thread - https://www.a2oc.net/community/index.php?threads/battery-drain.42505/post-386902

As Bret indicated it's important for all the systems to shut down and the alarm to be activated. A convenient way to do this is to disconnect and extend the battery earth terminal using a jump lead. I looped the jump lead over the back seat then positioned a clamp meter for easy viewing through the window and finally locked the car then waited until the reading stabilised

Cheers Spike
 
Another thing to be aware of; for each start (cranking) the engine must be running for 10 to 30 minutes (depending on battery) in order to recharge battery back to the same level as it was before the cranking
 
Olerype said:
Another thing to be aware of; for each start (cranking) the engine must be running for 10 to 30 minutes (depending on battery) in order to recharge battery back to the same level as it was before the cranking
Click to expand...
Reference? If that were true, stop/start wouldn't be of much use on any car!

RAB
 
RAB said:
Reference? If that were true, stop/start wouldn't be of much use on any car!

RAB
Click to expand...

Using google translate:

www.testfakta.se

Bästa bilbatteriet i vinterkylan - Bäst i test | Testfakta

Test av bilbatterier 2015. Testfakta har testat vilket startbatteri som presterar bäst när temperaturen dyker. Bra om du vill slippa bli stående med bilen i vinter.
www.testfakta.se www.testfakta.se

When you start a car, about an hour of amperage disappears from the battery if you include lighting and some other electronics. The results of the test show that the Banner battery only requires eight minutes of running time in the cold to recharge to the level it had before starting. It can be compared to nearly 14 minutes with the Varta battery or 13 minutes with Extreme.
- This is a very interesting parameter that has extra importance for the person who drives many short distances, typically for city traffic, when traveling and shopping or leaving the children in day care, says Viktor Ekermo.

Start and stop normally disables under a certain temperature, or if being engaged too many times during a short period of time.
 
Olerype said:
Start and stop normally disables under a certain temperature, or if being engaged too many times during a short period of time.
Click to expand...

Start/stop never disables under a certain ambient temperature (if that's what you mean) but is mainly dependent on battery state of charge and coolant temperature. The only time I experience suspension otherwise, is in very heavy traffic with very frequent stops, but nothing like your "ten minutes" never mind thirty! If the running time between frequent stops is not too short, say less than 20 secs, suspension doesn't happen. I'm not sure that the person you quoted knows what he's talking about!

RAB
 
RAB said:
Start/stop never disables under a certain ambient temperature (if that's what you mean) but is mainly dependent on battery state of charge and coolant temperature. The only time I experience suspension otherwise, is in very heavy traffic with very frequent stops, but nothing like your "ten minutes" never mind thirty! If the running time between frequent stops is not too short, say less than 20 secs, suspension doesn't happen. I'm not sure that the person you quoted knows what he's talking about!

RAB
Click to expand...

See link which parameters that typically disables the star&stop; https://www.vwwatercooled.com.au/forums/f197/disable-stop-start-vcds-tweak-94276.html

Ok; the mentioned 30 minutes was maybe too long (when writing by memory on the fly), lets say 8 to 15 minutes depending on alot of variables.

Anyway; the point was just to consider this if you use the car for a 5 minutes trips to buy your daily bread&milk
 
Thanks peeps.

I very rarely do short journeys. Very all or nothing.

Brett, Thank you for the German perspective. I was aware that the CCCU needed a while to ‘settle’ after shut down but I’m parked in a street so couldn’t figure a safe way to do it. And I didn’t fancy locking the car with a battery that might accidentally disconnect and leave me stuck outside.

Spike, thanks for the solution. I already had an extension lead to my meter but if I drop the rear seat then I’ll be able to lock the car, leave it 2 hours, then check the meter. And if it pops off the leads I can manually unlock the front door and crawl into the boot!

Thanks fellas.

Alex.


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A resolution to my problem. Hopefully.

My battery went from fully charged to 11.8volts in just over a week. With a solar trickle charger and the sun on high.

I decided I didn’t need an exact measurement, just find out what reduced drain. So I hooked up an Ammeter in the circuit to measure the current drain and latched the boot and locked the car.

As suspected, when I disconnected an auxiliary 12v and usb charger module that I fitted in the rear coin tray, the semi-resting drain dropped from 0.1A to 0.03A. I think I have found my culprit.

I had removed the standby led and thought I’d stopped it drawing power at rest by fitting a switch - which is always off. It looks like the dc-dc buck converter circuit wasn’t affected by the switch and was still drawing current.

When there’s a problem... assume I caused it myself!

Fingers crossed.


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RAB said:
Reference? If that were true, stop/start wouldn't be of much use on any car!

RAB
Click to expand...

Stop start cars usually have much higher rated (and spec: e.g. AGM) batteries for this reason (ask my Volvo how I know this :rolleyes: ). Also, re-starting a hot engine is completely different from a stone cold engine. Finally, many cars fitted with stop start have auxiliary batteries to run systems during shut-down to preserve the main starter battery.
 
As a sidenote; some Volvos also has a dedicated auxiliary battery for the Webasto heater, to ensure that you still can start the car after running Webasto for a long time
 
Rusty911 said:
Stop start cars usually have much higher rated (and spec: e.g. AGM) batteries for this reason (ask my Volvo how I know this :rolleyes: ).
Click to expand...
That's true but the capacity used still has to be restored by the alternator, so it's not really relevant. I have been stuck on the M25 many times in heavy traffic but as long as the engine runs for about 30secs between stops, suspension of stop/start never happens. Nothing like 10 mins!
Rusty911 said:
Finally, many cars fitted with stop start have auxiliary batteries to run systems during shut-down to preserve the main starter battery.
Click to expand...
No different really from a larger battery. See above.

RAB
 
But if you do that for a week, your battery will be flat at the end. The start&stop software in 1.2TDI or any car, is not that advanced. Are you still running factoryoriginal battery?
 
RAB said:
That's true but the capacity used still has to be restored by the alternator, so it's not really relevant. I have been stuck on the M25 many times in heavy traffic but as long as the engine runs for about 30secs between stops, suspension of stop/start never happens. Nothing like 10 mins!
No different really from a larger battery. See above.

RAB
Click to expand...

As above, hot engine restart takes a fraction of the amps of stone cold start, perhaps after overnight or a few days. AGM stop-start is often linked to higher capacity alternator to reflect extra demands of S/S. I.e. we're not comparing like with like. If you fitted S/S to an otherwise completely standard A2, it would operate for fewer cycles than a full S/S built car reflecting the need to recharge a standard lead-acid battery at a lower rate (with smaller alternator).

To use the existence of S/S on a different era of car with a different specification doesn't address or diminish @Olerype 's original point: if you are suffering low battery voltage and are only doing short journeys, it's entirely possible you may gradually eat into your capacity reserves. This would be particularly true in the winter of course.

As it happens, Alex had already said he drives 70 miles a day in post one, so short-journey drain didn't apply this time, but the general point made surely still stands?
 
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Rusty911 said:
if you are suffering low battery voltage and are only doing short journeys, it's entirely possible you may gradually eat into your capacity reserves. This would be particularly true in the winter of course.
Click to expand...

My wife's drive to work is about five miles (in a Lupo 3L). It involves at least three engine stops there and as many as seven or eight on the way home. We never have to charge the battery, winter or summer. It might be a problem IF the battery was in a less than optimal state.

RAB
 
Let’s see you go flat now Mr Battery!

e647bd91c00f83a18b489cdef229afe0.jpg



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