Battery Drain

[Gun Runner 5]

I have a 1997 Lexus LX450 that is having a battery draining issue. If it sets for several days the battery will almost completely drain. ( new battery ). The vehicles charging system appears to be functioning normally ( 3/4 scale on the volt gauge ).
Any thoughts.........

 

[CJF]

New batteries can still be bad.

 

[george_tlc]

Search. There's quite a few threads in the 80 section on recommendations on how to measure parasitic drain and how to isolate various circuits (pulling fuses etc) to narrow down the area of high current drain.

You do have a multimeter?

cheers,
george.

 

[91 4runner]

(pulling fuses etc) to narrow down the area of high current drain.

that was the old way of doing this, not very accurate, as it could be a control module not going in to"rest" mode, pulling the fuse would temporarily reset the module and hide the problem and cause you to miss the malfunction.

the proper test would be a "voltage drop" test on the fueses, that way you can do your test without disturbing the current state of the electrical system.

 

[PDoyle]

What kind of battery and how old is it?

 

[george_tlc]

that was the old way of doing this, not very accurate, as it could be a control module not going in to"rest" mode, pulling the fuse would temporarily reset the module and hide the problem and cause you to miss the malfunction.

the proper test would be a "voltage drop" test on the fueses, that way you can do your test without disturbing the current state of the electrical system.

Really, voltage drop across a fuse - a fuse has very close to 0 ohms resistance. You won't measure anything of any consequence and without knowing the resistance of the fuse you'll have no idea what the current flowing through that circuit is (V = IxR). Assuming most parasitic draw that causes a flat battery over a few days is of the order of hundreds of milliamps, explain to me the voltages you will need to be measuring across the fuse that would indicate some problem?? What is the resistance of a 10A or 15A or 20A fuse?

If you want to get really fancy then you would put a sensitive DC current clamp over each wire fed from the battery to each circuit. From what we've seen on cruisers, typical parasitic current draws are from alarm systems, radios and various after market stuff added on by the PO or owner etc.

The first step is to measure current draw from the battery, then isolate each circuit. Well proven and easy to do.

cheers,
george.

 

[Gun Runner 5]

Thanks guys .......
Isolating the problem is at the top of my Monday morning to-do list.

 

[alia176]

I have a drain on the '96 that's been an interesting problem to solve. Using a DC current clamp, I found out that the 30FL (pink fuse) is where the drain is coming from. After poking around this circuit, it turns out that the driver seat is pulling about 0.3amps.

Ideally, all three fusible links should not be drawing any appreciable current, as evidenced on the '97. So, I'll need to sort this out eventually but for right now, the seat harness (under the seat) has been unplugged.

Good luck in trying to find the source of your draw. It could be something very simple but having the proper diagnosis tool is very important.

 

[Gun Runner 5]

I have always found that whole "electrical" thing to be a little baffling but fortunately I have a close friend who is the "MacGyver" of electrons and I am confident he can figure it out. I will pass along the information gathered on this thread.
Thanks.....

 

[Funner]

I had this problem after performing a mod that enabled power windows to function anytime. The mod resulted in an additional 90 micro amps to draw down the battery. Mine is not a daily driver, so sitting a week or two at a time eventually killed the battery. I replaced the mod or reverted back to stock and replaced battery.

 

[george_tlc]

90uA wouldn't have been a problem... maybe you meant 90mA....

90uA x 24 hours x 30 days = 0.065Amp.Hour Even some AAA batteries could deal with that

cheers,
george.

 

[CRUISER TIME]

I have the same problem. My first find was the Door switches found in each the doors on my rig. Over time, they corrode, and even though interior light was not on, arching was taking place and letting a small amount of current to be drawn, but not enough contact to set off the interior dome light. I replaced all 4 doors and rear hatch. Got the switches from Toyota Dealer. Amp draw went down enough to not drain the battery in 2 days, now "when warm outside" i can go as long as 1 week.

When I pulled out the switches from the door jams, they were all corroeded and fallen apart.

My next find was the EFI relay and system. I got a small constant current draw from that circuit as weel, even with the key out of the ignition. Have not done anythin yet. Getting new relays, might not fix the issue, but as our cruisers age, everything helps.

My rig was used in water crossings by the previous owner, so i have some bad relays and contacts time to time, changing things out little by little.......... as my wallet allows,,,,lol


CRUISER TIME

 

[91 4runner]

Really, voltage drop across a fuse - a fuse has very close to 0 ohms resistance. You won't measure anything of any consequence and without knowing the resistance of the fuse you'll have no idea what the current flowing through that circuit is (V = IxR). Assuming most parasitic draw that causes a flat battery over a few days is of the order of hundreds of milliamps, explain to me the voltages you will need to be measuring across the fuse that would indicate some problem?? What is the resistance of a 10A or 15A or 20A fuse?

If you want to get really fancy then you would put a sensitive DC current clamp over each wire fed from the battery to each circuit. From what we've seen on cruisers, typical parasitic current draws are from alarm systems, radios and various after market stuff added on by the PO or owner etc.

The first step is to measure current draw from the battery, then isolate each circuit. Well proven and easy to do.

cheers,
george.

not to start any debates but heres a good article for you to brush up on, this is what they teach in school and what i use almost every day as a professional mechanic.
http://www.motor.com/article.asp?article_ID=1701

 

[george_tlc]

not to start any debates but heres a good article for you to brush up on, this is what they teach in school and what i use almost every day a professional mechanic.
http://www.motor.com/article.asp?article_ID=1701

They mention 0.8mV (for nominal 178mA) most folk here don't have meters that can resolve down to 10mV with any accuracy and have HF meters or similar...

I happen to have a Fluke 87III (amongst other meters) and I can measure such levels (when set to 4 1/2 digit resolution).

They say 178mA for a 0.80mV reading. I just tested on the bench (yes, I'm an EE) and measured 200mA with 0.80mV and another fuse at 0.91mV and 200mA (both 15A fuses). So, the method works, albeit not with any accuracy, to spot a higher current draw fuse when searching for parasitic draw - IF you can probe the fuse from above and have some idea of how to correlate the measured voltage with nominal current flow across various value fuses. I did warm a fuse up and saw about 10% increase in voltage measurement from cold.

Anyhow, I'll agree, it's one method to identify suspect circuits, IF you have a good meter and IF you know how to measure low voltages reliably. Hunting 50mA circuits means you're looking at measuring 250uV.

cheers,
george.

 

[Gun Runner 5]

Fairly confident we have narrowed it down to a interior lighting issue. More troubleshooting to do tomorrow.

 

[kblomquist]

Mine ended up being something with the radio. I had a draw that would kill battery after 3 days. I pulled radio fuse and have not had a problem. Haven't researched past this. Plan on putting aftermarket sound system in soon. I think I read somewhere that the cd player can often be the culprit. Just my .02