2
\$\begingroup\$

My SUV died last night, and it draws 540mA now, when the car is off, and nothing (that I know of) is on. How much does a car typically draw from the battery when it is off?


EDIT 1:

I think you've already answered my question (half an amp is an unreasonable amount of power draw with the car off), but I would like to give you more information anyway. I narrowed it down to one fuse, which has a bunch of stuff on it:

BCM, Auto Light & Photo Sensor, Room Lamp, Driver/Passenger Vanity Lamp Switch, Date Link Connector, Door warning Switch, RF Receiver, A/C Control Module, Luggage Lamp, IPS Control Module, Instrument Cluster (IND.), Map Lamp, Electro Chromic Mirror

I am going to assume that "Date Link Connector" is really "Data Link Connector".

"IPS Control Module" is also listed under multiple other fuses, and I don't know what that means. Tried to find out what IPS means, but there is no glossary or abbreviations table, and I'm not sure.

"A/C Control Module" is also listed under multiple other fuses as well. Not sure what this means either.


EDIT 2:

This fuse is part of a two part special assembly called the "Memory Fuse" which apparently is a collection of devices, some having non-volatile memory that gets lost if it is unpowered. Also, that's where the half amp of power is being drawn from (the second of the two fuses).

Here are some pictures of the assembly (which has two 10-amp fuses) and relevant sections from the manual:

Two part fuse assembly.

The following portion of the manual explains that some things will not operate if you pull this fuse assembly, namely "warning chime, audio, clock and interior lamps, etc." I like the "etc" part.

It also states that "Some items must be reset after replacement" indicating the non-volatile memory will be lost. I'm assuming audio (radio presets), but don't yet know what else that may mean (perhaps the A/V, which we don't have).

Screen shot of Blurb from manual.

Here is what the "Memory Fuse" protects, the first fuse for the first section, and the second fuse for the second section (the second fuse is the one drawing the half amp):

Screen shot of "Memory Fuse" portion of manual, the detail about what it covers.

\$\endgroup\$
12
  • 3
    \$\begingroup\$ According to this it should be < 100mA. \$\endgroup\$ – relayman357 Oct 23 '20 at 16:09
  • 2
    \$\begingroup\$ Lock the doors and wait a while (maybe ten minutes) then check the current again (with the car still locked.) The computers and stuff in my car stay active as long as the doors are unlocked. Leaving the car unlocked in a locked garage for a few days drains the battery to the point that it won't start. Lock it, give it a chance to "go to sleep," then measure the current again. \$\endgroup\$ – JRE Oct 23 '20 at 16:10
  • 2
    \$\begingroup\$ I’m voting to close this question because this is about car characteristics, not about electrical engineering. \$\endgroup\$ – Marcus Müller Oct 23 '20 at 16:47
  • 1
    \$\begingroup\$ 50mA is generally reckoned to be the maximum draw you'd expect from a car battery when it's parked up. Don't forget the car will be difficult to start long before the battery gets down to 0%. 50mA would take an 80Ah battery down to 50% in about a month. \$\endgroup\$ – Finbarr Oct 23 '20 at 17:13
  • 2
    \$\begingroup\$ I know security add-ons reduce battery lifespan, from a time when our NDP govt owned auto insurance gave out Interruptors free to reduce auto-theft with wireless disable under the hood. The question might be better phrased, what life expectancy can be expected in reduction for higher than normal battery drain of 100mA max. And a new battery of 50Ah or an aged one of 50% . Perhaps too difficult to answer, but possible. But in the old days if a 8W build was dim on series with Vbat,that was considered acceptable. \$\endgroup\$ – Tony Stewart EE75 Oct 23 '20 at 18:52
3
\$\begingroup\$

That’s far too much current and will possibly kill the battery after extended unused periods and a voltage drops below 11.5V when sulphating accelerates.

  • a fresh 50Ah battery may be dead after 100h @ 0.5h rate.

Reduce that to <50mA or add a trickle charger and plug in it if you cannot locate or eliminate the TDB load.

\$\endgroup\$
8
  • \$\begingroup\$ This happened to my generator. The electronics in standby mode draw 0.6A and the trickle charger packed up, causing the battery to discharge so low it wrecked the battery. With a modern SUV you can't simply disconnect the battery because it messes with the computer, so better to fix the fault or at least keep it on charge. \$\endgroup\$ – Raffles Oct 23 '20 at 19:03
  • \$\begingroup\$ Really? Volatile memory settings? \$\endgroup\$ – Tony Stewart EE75 Oct 23 '20 at 19:11
  • \$\begingroup\$ Yes, volatile memory settings. And the fuse I narrowed the problem down to (see edit), is part of a special two-part fuse assembly that you are supposed to pull out when not starting the car for a while, so my problem may actually be expected. \$\endgroup\$ – MicroservicesOnDDD Oct 23 '20 at 19:47
  • \$\begingroup\$ @TonyStewartSunnyskyguyEE75 -- My process of narrowing down the problem to the one fuse killed my battery, so it must be as good as dead. Please see "Edit 2" which has pictures and details of the non-volatile fuse assembly, in which I believe you are interested. And was that a "TBD" load? \$\endgroup\$ – MicroservicesOnDDD Oct 23 '20 at 20:27
  • 1
    \$\begingroup\$ Or maybe the dealer if on warranty but a defective RF might be the only item enabled with IGN. Off for the remote trunk with keyFOB. disconnect that and try again \$\endgroup\$ – Tony Stewart EE75 Oct 25 '20 at 16:18

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.