Battery drain test procedure question

Multibeemer · #1 01-15-2011, 12:37 AM

This may be a dumb question, but I'll ask anyway. I think I may have a battery drain problem, so I want to test the amount of parasitic current flow in the car's electrical system. The procedure as I understand it is to disconnect the positive battery cable, and attach the positive (red) lead from an ammeter to the positive battery post, and the negative (black) ammeter lead to the battery cable I just removed. My ammeter only goes up to 250 mA, but my car violently pegs the needle, indicating I have a large leak.

However, here's my question. Since the X5's battery is located under the luggage area, I have to open the rear hatch to get to it. So, when I connect an ammeter across the battery post and lead as described above, doesn't that complete the circuit and attempt to engage all the interior lights that come on when you open the hatch? Or is the ammeter's internal resistance high enough to prevent that? If this is a problem, how does one actually test the current drain on a car such as the X5, whose battery is located in the interior of the vehicle? Thanks.

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diyanich · #2 01-15-2011, 12:44 AM

Quote:

Originally Posted by Multibeemer

This may be a dumb question, but I'll ask anyway. I think I may have a battery drain problem, so I want to test the amount of parasitic current flow in the car's electrical system. The procedure as I understand it is to disconnect the positive battery cable, and attach the positive (red) lead from an ammeter to the positive battery post, and the negative (black) ammeter lead to the battery cable I just removed. My ammeter only goes up to 250 mA, but my car violently pegs the needle, indicating I have a large leak.

However, here's my question. Since the X5's battery is located under the luggage area, I have to open the hatch to get to it. So, when I connect an ammeter across the battery post and lead as described above, doesn't that complete the circuit and attempt to engage all the interior lights that come on when you open the hatch? Or is the ammeter's internal resistance high enough to prevent that? If this is a problem, how does one actually test the current drain on a car such as the X5, whose battery is located in the interior of the vehicle? Thanks.

Hi there,not really the way it should be.
You have to put the multimeter's lead through the insulation and just after that remove the nut from the negative cable where it meets the chassis.
If you disconnect the battery and reconnect either putting the cable back or through the multimeter,the faulty module is gonna be reset and you won't find any draw signs.

Multibeemer · #3 01-15-2011, 01:06 AM

diyanich,

Thanks for the quick reply, but I'm sorry, I don't follow what you're saying. Been a long week, and I'm pretty tired, which is probably contributing to my inability to comprehend...

Which insulation are you referring to? Where exactly do you connect the multimeter's lead after putting it through this insulation? And which lead are you referring to for this, the red or the black one? What do I do with the other lead while I'm doing this? And I don't understand the purpose of removing the nut from the negative cable where it meets the chassis. What do I do after removing this nut?

Obviously, I'm completely lost. Could you please go through what you're proposing step by step, assuming I'm a complete ignoramus (definitely not a bad assumption!)? It sounds like you know what you're talking about; I'd just like to be able to follow the procedure you're recommending. Thanks, and sorry for being so dense.

diyanich · #4 01-15-2011, 01:08 AM

Quote:

Originally Posted by Multibeemer

diyanich,

Thanks for the quick reply, but I'm sorry, I don't follow what you're saying. been a long week, and I'm pretty tired, which is probably contributing to my inability to comprehend...

Which insulation are you referring to? Where exactly do you connect the multimeter's lead after putting it through this insulation? And which lead are you referring to for this, the red or the black one? What do I do with the other lead while I'm doing this? And I don't understand the purpose of removing the nut from the negative cable where it meets the chassis. What do I do after removing this nut?

Obviously, I'm completely lost. Could you please go through what you're proposing step by step, assuming I'm a complete ignoramus (definitely not a bad assumption!)? It sounds like you know what you're talking about; I'd just like to be able to follow the procedure you're recommending. Thanks, and sorry for being so dense.

That's ok

Look through the vinyl coating on the cable ,so you can reach the copper core .
Does it make sense now?

Multibeemer · #5 01-15-2011, 01:11 AM

OK, that answers my first question. So I understand I'm to connect the red lead of the ammeter to the copper core of the positive battery terminal. What exactly do I do with the other ammeter lead?

diyanich · #6 01-15-2011, 01:11 AM

I'm gonna write up in the morning.

Multibeemer · #7 01-15-2011, 01:25 AM

Perfect, thanks. I'm on my way to hitting the sack myself. Looking forward to your description. Thanks in advance for your help - I'm sure it will be helpful to others as well.

JCL · #8 01-15-2011, 01:55 AM

The problem is that you don't want to disconnect the battery for this test. You want to measure the current when you turn the key off, and then watch it over time, and see that it drops down as various modules go to sleep. Disconnecting the battery doesn't let you do this. Diyanich is saying to use the ammeter to keep the circuit connected. I would rather use an inductive (clamp-on) ammeter.