battery drain test

[Joderest]

Hi All
Not going to bother you all with the issues with my ML270, as documented to death on other threads. I cannot have anyone look at the car for a few weeks due to my work and their workload, so, against my better judgement i am going to try and do a leak/drain test on the battery, and need a bit of help.
I have a small digital meter, it has a 10amp setting, if i disconnect the negative pole of the battery, connect black side of meter to the battery pole and the red side to the battery lead, will this give me the amps reading i require ? (meter set to 10amp setting)
What am i looking for as unacceptable, and what is acceptable. I have already done voltage, seems to drop to 12.4 volts overnight, its a new Yuasa battery only fitted this week. Engine starts really well.
Any advice ?

 

[Dec]

parasitic draw test - Google Search:

See diagrams in link above. Before you start you could clamp the door pins closed, see video below.

Dec

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[Major774]

Do this and let us know your resting amp draw.

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[190]

if i disconnect the negative pole of the battery, connect black side of meter to the battery pole and the red side to the battery lead, will this give me the amps reading i require ? (meter set to 10amp setting)

It will but be sure not to do anything that will draw more than 10 amps like turning the headlights on or it will overload the meter. The usual technique when using a meter in this situation is to start on the highest range and then turn down to lower ranges if required to increase sensitivity.

The other option instead of disconnecting the battery is to remove fuses one at a time and then use the meter to check the current flow at each fuse holder. This has the advantage of narrowing down the search for the culprit.

 

[Joderest]

Great, thanks to you.
I was going to pull each fuse in turn to see which circuit is pulling power.
I have to wait a few days as ordered some new leads with clamps for meter.
Of course I will update.

 

[markmifsud]

Its easier to measure the voltage running through the fuse to check for current drain as pulling and inserting fuses will wake the car up.
Most fuses have a small access hole at the top of each leg. Probe these on the millivolt range and look for any fuses that are showing more than a few millivolts. These are your main points of interest.

 

[sturgeon]

I wonder if there is actually a problem. All cars have a continuous current drain in the form of the alarm/monitoring system. That, coupled with the battery self discharge is one element. So it sits all night being discharged by the alarm etc, then you unlock it and open the doors. Motors activate, lights come on, the battery dips, then recovers slowly. If it was at 12.7V when you went to bed , it wouldn't be in the morning and that's before you unlock it.

It might be worth trying this. Unlock it in the morning, open the bonnet, then lock it (bonnet open) and leave it for an hour, then check the voltage. Do the same in a few days time and see if it has changed. A new battery will cope with this. A failing one won't. I'm giving ours a charge once a week as I'm not driving it enough to replace the losses at the moment. Ours opens the wing mirrors and spins up the Comand HD when you unlock it too.

 

[Joderest]

Erm, you could be correct. Since fitting new battery I only drove it a couple of miles, and then started testing again, battery dropped below 12.5 volts. However, better half used it yesterday to take her horse for a gallop, and do shopping, so got a good run. Tested again this morning, 12.8. started and all worked as it should. Put meter on and left it on for three hours, did not fall below 12.7, I even reconnected the alarm. I wonder if I did not give the new battery a chance.

 

[sturgeon]

Sounds perfect! As good as you get!

 

[Major774]

You still need to work out the resting amp draw.

I am current doing this to my car. Initially I had a resting amp draw between 0.29-0.31a. After pulling fuses and relays I have found that 1x fuse and 1x relay were still draining the battery. I went ahead and replaced the relay as it was a cheap option to try and reduce the drain, this reduced my resting draw between 0.26-0.29a.

So my resting amp draw is between 0.26-0.29a.

Voltage drop test - The millivolt reading across the fuse gave me 0.04mV which equates to 0.087a. However, I know that this fuse is related to my electronic lowering control module. So I am prepared to live with this as it is wired permanently on.

Pulling the relay equated to a drop between 0.10-0.12a. So a consumer unit is still live and not going to sleep. I found out that the relay is connected to the OEM iPod kit. So when I get a chance I am going to try and disconnect the iPod control module.

If the iPod control module is the culprit I should expect a resting amp draw between 0.073-0.083a (not including the lowering control module). This is slightly high but I assume the Keyless Go option will have a small drain as well.

 

[Joderest]

Thanks for that, good info. I am going to do the test anyway, as have never done this and you are never to old to learn.
Car been stood at work this afternoon since 12.30, just gone out and battery voltage at 12.9, so all good. THERE IS ONE POSSIBILITY. The better half used the car yesterday, first time since this problem started, and of course, she moved the drivers seat. I wonder if the seat controller was stuck on and not shutting down, and moving the seat has done this. I know, clutching and straws, but its a thought. I am glad not alarm unit pulling voltage.
I will do the test Friday as waiting for new leads for meter with clamps on the ends.
Thanks all, real good help and info

 

[Joderest]

Honest, you could not make it up.
Was going to do this draw test today, however, Mini overdue service, so thought quick oil change, no issue. Drained oil, removed oil filter cap, but hang on, why has filter stayed in bowl, and what's that sitting on top of it ????.
Turns out the pressure switch in the oil filter cap has dropped of, so sitting on filter, looked in cap to see a plastic tab broken off, oh god, if it's in the engine, but looking closer at filter, saw it lodged inside, got hold of it with long nose pliers.
4 hours later, managed to find one up country, over night delivery. Even BWM did not have one. So 1/2 hour job turns into over a day.
As now have time, removed air filter, air box stuffed with leaves.

 

[Major774]

That’s some oil change... lucky it turned out ok.

 

[Joderest]

Morning all.
Ok, have now done tests.
Voltage, rest overnight 12.9 volts.
Leak test, done 1/2 hour after disconnecting battery. Draw is 0.05 amps, fluctuating to 0.04 amps.
I think this is 40 to 50 milliamps.
If correct, then yippee, all is good, can someone confirm my readings.
Now, just got to wait for oil filter cap for Mini, then back to work tomorrow for a rest !!!!!!.

 

[Major774]

At 0.04-0.05 amps you are good to go, no major battery drain. So any low battery warnings will be your driving habits and battery age/condition.

 

[Joderest]

Thanks, not auto electrician just wanted to be sure

Thanks

 

[cheddar]

0.04 amp is still above acceptable levels for battery discharge, however should not drain a large battery down to non-start level for a good few days (assuming it was in a good state of charge to start with).
If the car is used at least every other day it may be fine, but like you said, it could be something that’s taking more power intermittently.
Seat control units were always a common culprit.

 

[190]

I haven't tested the car I have now but a previous one was 34mA with the alarm on. That equates to 5.7Ah per week and it used to survive 2 weeks in an airport carpark without problems. And so it should as 11.4 Ah is not going to drain a big 85 Ah battery. There would be the internal self discharge rate on top of that which is a variable dependant on battery type, age and ambient temperature.

 

[Joderest]

Thanks all, battery is very good now, 12.9 volts over night.
It could have been the seat controller not sleeping, or just simply my battery was no good.
Time will tell