Battery drain test

[Andrew S]

Although this is about my day to day car, can someone please tell me what settings I need to use on this meter to test the drain amps. I have red and green and god knows how many selections. The car has been sitting for a week to 10 days and the battery is absolutely flat, 9v maybe and I had this before when the car sat doing nothing. I want to therefore test the drain and suppose I am looking for anything around 1-2 amps in order to drain it that badly.

I am presuming I put the black lead in the common as normal and the red lead in the 10A socket instead?

Any help appreciated
Cheers
Andrew

IMG_6961.jpg

[StagJonno]

Andrew,

Yes, use the Common & 10A and set the switch to 10A (once you know the demand is <2A, you could change from the 10A to the 2A socket and change the switch to 2A.

Very important (you probably already know, but just in case), the meter needs to be installed in series with the circuit. If you put it across any circuit live with voltage, you may destroy your meter as well as getting lots of sparks . Assume you're just planning on taking measurements with the ignition off.

If you want to see the total demand on the battery, then disconnect either the +ve or -ve (would recommend the -ve as the +ve is very close to metalwork) at the battery and connect your meter between the battery terminal and the lead you just removed from it. If you want to look at individual circuits, then you could use the fusebox, taking fuses out in turn and putting the meter leads across each fuse. (note, there are some unfused circuits, most notably, the fuel pump, ignition coil, most warning lights and voltmeter, but these are only on when the ignition is on). Of course, the wiring may have been modified by a PO - radio, immobiliser, tracker etc.

Remember to set the meter leads back to "normal" (ie Volts) afterwards to avoid any accidents next time you pick it up.

I prefer to use a clamp-type ammeter which avoids having to disconnect circuits - mine cost ~£35 and is pretty sensitive for this kind of troubleshooting on both dc and ac circuits and you avoid the risk of accidental short circuiting through the meter (don't ask me how I know!).

The above is based on my wiring diagram which is for a Mk2 - not checked for Mk1 or 1.5.

Hope this helps - let us know how you get on.

Jonno

[Andrew S]

Thanks Jonno. It's my BMW and there are 68 fuses ���� Will try try first and thanks for the guidance
Cheers
Andrew

[Andrew S]

I have just taken the following readings with the leads on 2A but I am unable to understand the t=reading outcome in relation to the selection I made to the green dial setting I chose. Does it show a drain of .78amps, if so, there is definitely a drain greater than the internal clock which I can only think is the only drain when the car is locked up. Its not a Stag so finding it is not so simple Maybe I should I put this in the non Stag section but the principal maybe helpful to others)

Any feedback appreciated before I start pulling god knows how many fuses

2016-08-07 10.54.02.jpg

Much appreciated
Andrew

[milothedog]

I have just taken the following readings with the leads on 2A but I am unable to understand the t=reading outcome in relation to the selection I made to the green dial setting I chose. Does it show a drain of .78amps, if so, there is definitely a drain greater than the internal clock which I can only think is the only drain when the car is locked up. Its not a Stag so finding it is not so simple Maybe I should I put this in the non Stag section but the principal maybe helpful to others)

Any feedback appreciated before I start pulling god knows how many fuses

[ATTACH=CONFIG]38232[/ATTACH]

Much appreciated
Andrew

Andrew[/QUOTE]

If you go to the lower scale 2A it should still read the same.

[Andrew S]

Hi Ian, thanks for quick response. It's connected to the 2A socket.

[milothedog]

Hi Ian, thanks for quick response. It's connected to the 2A socket.

Just seen that in your first post

[Andrew S]

One test I cant seem to do is putting say the interior light on, then disconnecting the negative of the battery and then putting the red lead of the meter on the battery earth strap and the then black lead on the neg of battery and get a reading. I was expecting that the light would come on as I am making a circuit and then it would tell me what it was drawing on amps.

All I have done so far is the above circuit set up and then pulled fuses. I think I was getting a 0.78amp draw down until I pulled the fuse for the central door locking and it dropped to zero on the meter. That door lock mechanism is very seldom used being the passenger door and could have caused some kind of short when I locked it and left the car for a week. It all works but occasionally it sticks. Wont do it now of course when I want it to but maybe this was my drain. Got battery on charge now and car unlocked to see what happens but still cant understand why I cant get a reading on the interior light as an example as I would imagine that would have been about the same amperage. I am not saying that the light is the cause, but in learning how to do this test, its good to make up some cases to see if test works.

Thanks
Andrew

[milothedog]

Just seen that in your first post

Just a thought, are you taking that reading with anything open,or on. Doors/Boot, ignition on etc

[marshman]

Andrew,

Firstly, yes it is a reading of 0.78 amps, but you should have the selector on the meter set to 2A not 10A. The 10A position is only for use when the leads are conndcted to the 10A socket. Some meters will read correctly, others won't. The correct procedure is to check the current with the leads plugged in the 10A sockets and 10A selected on the meter. If the reading is less than 2.0 Amps you can then move the leads to the 2A socket and select the 2A range to get a higher resolution reading.

Secondly on modern cars many electrical items are controlled by electronics and not switched directly so if you have the interior light turned on then disconnect the battery the electronics reset to the off state. This may not be the case in your car but if the light comes on when you put the key in the ignition, or comes on automatically at night when you turn the ignition off then it probably is controlled in this way.

As someone else said a far better way to measure current in a car is using a current clamp type meter. They have a much higher range, can't be damaged easily and best of all just clamp around a cable, so you don't have to disconnect anything.

One last thing, 9v is not totally flat. If an interior light is left on for that length of time the battery volts will go down to virtually 0. I know this as swmbo has done it several times in her mx5, not shut the door properly, interior light on all weekend, less than 2 v at the battery terminals the Monday morning!

Roger

[Andrew S]

Thanks Roger and Ian

I did select the 10a lead option first just in case it was a big pull. Then as I suspected just .078 I then switch leads to the 2A socket.
Ian, not, nothing is on at all.
Car is on charge for about an hour and then I can move the car away from a wall so I can get to the drivers door and see if operating the door lock, I can get the other lock to stick and then take a reading again on meter and then I will know it's the problem.
Thanks for all the advice
Andrew

[StagJonno]

Think you meant 0.78A, Andrew but, as Roger says, you can't assume this is correct or meaningful - the meter switch needs to be on 2A also.

"One last thing, 9v is not totally flat. If an interior light is left on for that length of time the battery volts will go down to virtually 0. I know this as swmbo has done it several times in her mx5, not shut the door properly, interior light on all weekend, less than 2 v at the battery terminals the Monday morning!"

I'm afraid I disagree with you, Roger. I'd consider anything below 11V (battery open circuit at room temp) to be flat. A lead-acid battery previously in good health will probably recover from lower voltages but its life will be reduced (particularly car batteries which are not designed for deep cycling). Best to recharge as soon as possible to minimise damage and an old (non-smart) charger may need to be used for the first part of the recharge at least.

Jonno

[milothedog]

I've posted about this before, We did a lot research work with the YUASA battery company (Who won our contract worth in excess of £250K annually at the time) It was their expert opinion that any lead acid battery that fell below a charge state of 10.5 volts would be irreversibly damaged and have a shorter working life.

Ian.

[Stagdad]

Andrew has it got full size blade fuses? If yes this is a great tool for testing circuits

http://www.ebay.co.uk/itm/Automotive-Current-Tester-Circuit-Meter-Standard-ATO-ATC-Blade-Fuse-Car-Vehicle-/400433639239?hash=item5d3bb46f47:g:pBMAAOSwPhdVBuki

[marshman]

Think you meant 0.78A, Andrew but, as Roger says, you can't assume this is correct or meaningful - the meter switch needs to be on 2A also.

"One last thing, 9v is not totally flat. If an interior light is left on for that length of time the battery volts will go down to virtually 0. I know this as swmbo has done it several times in her mx5, not shut the door properly, interior light on all weekend, less than 2 v at the battery terminals the Monday morning!"

I'm afraid I disagree with you, Roger. I'd consider anything below 11V (battery open circuit at room temp) to be flat. A lead-acid battery previously in good health will probably recover from lower voltages but its life will be reduced (particularly car batteries which are not designed for deep cycling). Best to recharge as soon as possible to minimise damage and an old (non-smart) charger may need to be used for the first part of the recharge at least.

Jonno

I agree the battery is discharged beyond the point where it will have the energy to start the car bug my point was there cannot have been something like an interior light left on for 10 days otherwise the terminal volts on the battery would be a lot less than 9v.

I've posted about this before, We did a lot research work with the YUASA battery company (Who won our contract worth in excess of £250K annually at the time) It was their expert opinion that any lead acid battery that fell below a charge state of 10.5 volts would be irreversibly damaged and have a shorter working life.

Ian.

I don't disagree that the conventional wisdom on lead acid batteries is not to discharge them below 10.5v otherwise their life can be shortened but if charged carefully and fully after a complete discharge most will continue to give good service. The damage made worse when they are left in a discharged state. Totally duscharging a battery is not guaranteed to kill it. The battery in my wifes mx5 is still the original and is 15, yes 15, years old. It has been totally discharged to less than 2v on three occaisions that I am aware of.

Roger