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Battery Drain

 
Old 02-09-2019, 03:01 PM
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Battery Drain

OK, I've never had an issue while parked for long periods of time, but with all the electronics on board newer cars, one has to wonder.

My RDX was parked for 9 weeks without a battery charger/maintainer (no power outlets were available) in a garage, yet it started like any other day. No hint of a weak battery.

Does the RDX have a circuit that partially shuts down the electrical system? When I bought my 2017 RDX, during the first year I used to get a message on my computer from Acura telling me that the vehicle is inactive and something about systems shutting down.
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Old 02-09-2019, 04:47 PM
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Maybe,I left the headlights on once, and the car shut them off,saving My battery.
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Old 02-09-2019, 04:49 PM
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When the car is turned off, it may take hours for the computers to shut down. The Acuralink will shut down when the battery voltage drops below a specific value. After all the computers shut down all that is powered is the KAM (keep alive memory), which should draw about 40 milliamps or less. The KAM is the power required to keep your settings like seat position, radio, clock and personal preferences. 9 weeks for a battery is not uncommon for a battery in good condition and your parasitic draw is low.
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Old 02-09-2019, 11:33 PM
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Originally Posted by dave08902 View Post
When the car is turned off, it may take hours for the computers to shut down. The Acuralink will shut down when the battery voltage drops below a specific value. After all the computers shut down all that is powered is the KAM (keep alive memory), which should draw about 40 milliamps or less. The KAM is the power required to keep your settings like seat position, radio, clock and personal preferences. 9 weeks for a battery is not uncommon for a battery in good condition and your parasitic draw is low.
Not to hijack the thread, but just wanted to say thank you to dave08902 for always making such great contributions to these threads.

Appreciate your insight and quick responses - just wanted to call that out.
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Old 02-10-2019, 01:24 AM
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Originally Posted by SandwichViking View Post
Not to hijack the thread, but just wanted to say thank you to dave08902 for always making such great contributions to these threads.
As always.

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Old 02-10-2019, 01:31 AM
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Originally Posted by dave08902 View Post
...which should draw about 40 milliamps or less.
0.04 x 24 x (9 x7) = 60 Ah

It must tapper off to almost zilch. I had booster cables in my on-board kit just in case. Funny thing is, I've never needed them on any car.



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Old 02-10-2019, 06:45 AM
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Thank you SandwichViking for your compliment. We are all here to help each other out and enjoy our RDX.

The 40 milliamp draw is the max limit that you should see, if it is above this then you need to look for a module that is not going to sleep.

This info was from my notes.

The reserve capacity of a battery is the number of minutes for which it can run at 25 amps of current without its voltage dropping below 10.5 volts. It roughly describes the amount of energy the battery effectively stores and technically specifies the battery's charge capacity. Voltage relates charge and energy by describing the amount of energy in each coulomb of charge. Ampere-hours is a different unit for describing the same quantity.

Multiply the reserve capacity by 60 to convert it to seconds. For example, if a battery offers a 100-minute capacity: 100 x 60 = 6,000 seconds.

Multiply this length of time by 25, which is the battery's amperage. Example: 6,000 x 25 = 150,000. This is the number of coulombs of charge in the battery.

Divide this answer by 3,600, which is the number of coulombs in an amp-hour. Example: 150,000 / 3,600 = 41.67. This is the number of amp-hours in the battery.

To test the actual parasitic drain on your RDX, follow this procedure. Remember to keep all doors closed and keyfob away from the car.

A safe and accurate method of measuring parasitic draw involves a 1.0-ohm, 10-watt resistor. The resistor is placed in series between the negative battery terminal and the negative battery cable to dynamically test parasitic draw. The key-off battery drain passes through the resistor, while battery voltage is allowed to stress the electronic components on the vehicle. Very little current passes through the meter, so there’s no risk of meter damage.

With the ignition off, placing the test leads of a digital voltmeter on either side of the resistor measures the voltage drop across the resistor. Using Ohm’s law, we know the measured voltage drop is a direct reflection of the current flow or parasitic draw that’s present. So a reading of .02 volt on our meter indicates a .02-amp (20mA) key-off battery drain.

Allow enough time for all modules to power down and make sure all lights are off. If parasitic draw remains high, remove fuses one at a time to isolate the source of the drain. Once you’ve narrowed it down to a single fuse, you may need to divide the affected circuit into sections to find the offending wiring or component.
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Old 02-10-2019, 09:33 AM
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Originally Posted by dave08902 View Post
When the car is turned off, it may take hours for the computers to shut down. The Acuralink will shut down when the battery voltage drops below a specific value. After all the computers shut down all that is powered is the KAM (keep alive memory), which should draw about 40 milliamps or less. The KAM is the power required to keep your settings like seat position, radio, clock and personal preferences. 9 weeks for a battery is not uncommon for a battery in good condition and your parasitic draw is low.
It really puzzles me why auto manufacturers don't just use a small flash-memory based storage solution for all memory settings. It would cost pennies, and will forever eliminate issues with losing personalized settings when disconnecting and/or replacing the battery, not to mention no power draw whatsoever when the car is off.
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Old 02-10-2019, 06:38 PM
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Originally Posted by dave08902 View Post
If parasitic draw remains high, remove fuses one at a time to isolate the source of the drain. Once you’ve narrowed it down to a single fuse, you may need to divide the affected circuit into sections to find the offending wiring or component.
That used to be the case and what I've always done (on other people's cars...never seem to have a problem myself ), until someone pointed the following VW Technical Bulletin out to me.

Taken from the attached PDF Technical Bulletin...

Due to the state of the CAN Bus communications in the vehicle, it is no longer acceptable to pull each individual
fuse one at a time to try and identify which circuit is consuming current. Removal/ reinsertion of a fuse while
vehicle is in a sleep state may wake the bus of the vehicle, and invalidate the test. Identifying "consuming" circuits
must be done by measuring a voltage drop across fuse and aligning with the value in matrix located at end of this
document.




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Old 02-10-2019, 07:41 PM
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Originally Posted by Tech View Post
That used to be the case and what I've always done (on other people's cars...never seem to have a problem myself ), until someone pointed the following VW Technical Bulletin out to me.

Taken from the attached PDF Technical Bulletin...
Thanks Tech

I learned something new today. I will be trying this on my next parasitic job.
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