Parasitic current draw on tow vehicle

It's been my understanding that newer vehicles draw a little power to maintain computers that are used within them.

Dusty

Looking beyond a good meter, a parasitic drain can be really difficult thing to accurately chase down....

I had one once that, after chasing it for a long time, turned out to be a bad diode in the alternator. It was allowing a little current to dribble through when the vehicle was shut off.

SHRED wrote:
Any recommendations for a quality VOM? I'm tired of cheap junky ones.

Uni-T UT210E. $50 on Amazon

This also includes a current clamp so you do not have to disconnect the battery !

Another way to test for current draw is check the VOLTAGE across each fuse. Most cars have 2 fuss boxes. One under the hood and one under the dash.

FYI this info may be of benefit to others having start problems on the road or in remote area and is for all not just the OP situation.

In recent years I have used this small but powerful lithium power brick/booster to jump start my V-8 Ram trucks more than a few times when having electrical start problems and a dead battery. They instantly start the truck and will fit in the glove compartment or backpack and weigh almost nothing. Actually have a larger other brand for the other truck. They both hold 100% charge for a long time even after use and have a USB port to charge laptops and phones. Can charge them with a truck DC outlet/adapter that comes with them. Bought the Type S on sale at Costco for $50.00. Just for backup I carry standard jumper cables as I have plenty of room. Very cheap insurance for many years of use in remote areas with no help available. Cheers

CA Traveler wrote:
FYI Once you disconnect and reconnect the battery electrical resets may occur and you no longer have the drain perhaps until driving and turning off the car. That is just one reason why a clampon ammeter is so useful.

Sounds like you meter is not working.

Just tested my VOM fuses with my other VOM. Both were "OL".

Operator error.
I ordered new ones.

wa8yxm wrote:
Sounds like either the VOM is bad or the operator (you) is... Yup that can happen.. I have multiple VOMS and sometimes get confused as to how they work. (No two alike type thing)

Suggestion is a Jump Starter. they make two types (I of course have one of each) one is a Lead Acid (AGM) battery in a big HEAVY box. about 25 Amp horus usually with battery leads Some of these have air compressors, work lights and other features.. NOTE when hooking up it is suggested the NEGATIVE (Black) wire NOT go to the battery but rather the block or other unpainted metal part (This is for US cars with Negative ground.. If by some strange chance your car is positive ground that's the RED wire).

The other is a LI tupe... way lighter. 10 AH but about the same Kick Start power.

I use, or rather used, the big one as a "Portable car" for powering 12 volt stuff that plugs into the accessory outlet.

:R

So, the "fix" is to ignore and bypass the problem with a portable jump pack?

:E

Something draining a car battery in a day or two is not something one really should ignore. It is not normal and depending on what is draining the battery could very well end up with the OP stranded somewhere at the least and at the worst 100% charcoaled vehicle and or home.

Some things stay hot (not switched off with ignition), silly things like Ford had with the pressure switch located on the Master Cylinder which if the seal failed allowed brake fluid to enter the switch and cause a fire type of catastrophes have happened..

Brake switches do go bad, modern versions have multiple switches which do fail in odd ways..

Sounds like either the VOM is bad or the operator (you) is... Yup that can happen.. I have multiple VOMS and sometimes get confused as to how they work. (No two alike type thing)

Suggestion is a Jump Starter. they make two types (I of course have one of each) one is a Lead Acid (AGM) battery in a big HEAVY box. about 25 Amp horus usually with battery leads Some of these have air compressors, work lights and other features.. NOTE when hooking up it is suggested the NEGATIVE (Black) wire NOT go to the battery but rather the block or other unpainted metal part (This is for US cars with Negative ground.. If by some strange chance your car is positive ground that's the RED wire).

The other is a LI tupe... way lighter. 10 AH but about the same Kick Start power.

I use, or rather used, the big one as a "Portable car" for powering 12 volt stuff that plugs into the accessory outlet.

Shred,

Stop working so hard. Get a very small 12V bulb, two alligator clips and some wire. Make the wire long enough so you can see the bulb from the area of the fuse panel. Make it up so the bulb is between the two clips and disconnect a battery cable. When you put the bulb between the battery and it cable, if it lights, you have a problem.

Modern vehicle keep-alive power for the computer should not light the bulb. So, if the bulb lights, start pulling fuses. If you have had anything like a sound system added to the vehicle, be sure to include that in the fuse pulling.

When the light goes out, you found the problem.

Matt

Gdetrailer wrote:

SHRED wrote:
Any recommendations for a quality VOM? I'm tired of cheap junky ones.

It isn't your cheap junky meter.

It is how you are using it.

10A setting you must use the input marked 10A.

On 10A setting you will have a very low current resolution of .1A at a time which will not reveal very low current draws.

Your DVM should have a MA (Milliamp) setting (may look like 1000 (1000 is 1A), 100, 10) which has a higher resolution. That setting will use your normal DVM "Volt/resistance" input lead.

Choose the highest range on the MA setting then switch down..

Have to very careful when using the MA setting as it is to smoke the meter..

Good to know.
Thanks

SHRED wrote:

Is the allowable amp draw about 0.3 amps?

thanks

No. .3A is 300 Milliamps, that will drain any car battery in a matter of a couple of days.

Should be more like .01A (10 Milliamps) or less (.001A (1 Milliamp) and your vehicle should be able to sit for a month or two without being started or charged.

Most vehicles have a "power management" system which is supposed to go into a sleep mode after a period of inactivity which may need investigated. Check to make sure you have no USB chargers or anything plugged into the 12V power ports since those may or may not be managed by the power management system.

Make sure all lights like interior lights (including under hood and trunk if equipped) are turning off (sometimes interior lights get accidentally turned on via dash light control) or your door switches may not be working correctly.