OT: Magna battery draws 0.08 Amps when not running

[Norman Bain]

I have an oldish (approx year 2000) Mitsubishi Magna that has been handed down thru the family and has recently been resurrected, literally from under the tree, for use by 18yo daughter.

The battery was flat, but after a charge it worked ok for a day or so ... then needed charge again.

After a bit of this the battery needed a charge every time car was used ... then eventually it died while we (self and daughter) were parked while collecting some online auction goodies I had purchased.

Needed to persuade a fellow traveller (also collecting from same pickup) to give us a jump start. I could ask, what is it with folks these days that they are reluctant to jump start another vehicle ... but I won't, they are just daft and live in their own wee worlds.

On the way home I purchased a new battery and installed it when we got home. Noticed that it arced a bit when I put the positive lead on ... expected that somewhat as there is need to run all those things that cars have these days ... but it was quite a spark. Anyways decided to check the amperage draw and it is drawing a steady 0.08 Amps after the draw settles down.

I also checked the charging voltage ... all good ... goes from around 12+ Volts when not running up to 14+ Volts with motor running. These are ok numbers; so alternator is ok.

My question; is this 0.08 Amp draw "normal" or do I have "a something" that is drawing more than it should and needs investigating?

[dave_r]

You might need to do further testing. Many vehicles take 5 or 10 minutes (or longer) after you turn off and exit the vehicle before the various computers in the vehicle will power down.

[rdfeil]

Hi Norman,

.08A draw is most likely normal for a 2000 car. The newer cars have to keep a lot of things alive even when the car is off. Ford Crown Victoria police cars of the 2000 and up will draw between .05 and .10 amp from the day they were delivered from the factory. The engine control computer 'learns' how the car is driven and adjusts accordingly. The radio keeps its memory alive and don't forget the clock and if equiped, the remote door opener. I would not worry about a .08 draw as long as the car is driven on a regular basis. If the car is going to be unused for weeks or months it would be prudent to disconect the battery during storage periods or install a battery maintence charger and keep the car pluged in. Hope this helps.

[Hopefuldave]

That's a total of about one Watt of power being drawn, not a lot... Does it have an alarm, immobiliser etc? Clock on the dash? Fancy radio/CD with memories etc.? All of these will draw a little current, all the time, and it adds up.

If you're determined to find what's drawing the power, once it has "powered down" try pulling a fuse at a time, then look see what the fuse supplies - I once had a car with a faulty switch for the lamp in the glovebox, it would flatten the battery in less than a week: I ended up taking the bulb out, no more problems That was a 70's Vauxhall, no electronics in it (coil and points ignition, carburettors, only 3 fuses) so the 5 watts of lamp was Obvious!

A decent battery will deliver 40 Amp-Hours, call it 500 Watt-Hours near enough, so at that rate it'll be getting too flat to start after at most two or three weeks, is it used less regularly than that? Other side of that coin, most alternators will deliver 45 Amps so from flat the car needs to run for at least an hour to get a full charge (there will be other loads while running, of course!)

Dave H. (the other one)

[skarven]

I think the 0.08 is too high. I might be wrong, but I do not think I have seen higher than 0.03 on any of my cars.

I would check if there is a light in the "rear luggage compartment" (probably not the right term :-)) or in the engine-room. 0.08 at 12V is app. 1W. These lamps are normally 4-5W but could have been replaced with an LED.

To check if the alternator is OK you will have to disconnect the B+ on the alternator. This is directly connected to the battery, so remove battery ground connection while doing this. If one of the diodes in the alternator is leaking, it could charge OK, but still drav current when not running. The alternator is not very robust in the Japanese cars from this period. I have seen them fail if engine running while jumpstarting another car.

Another test is to remove the fuses one by one till the current disappear. This will not work if it is the alternator as it is directly connected to the battery.

Hope this helps
Kai

[Noitoen]

Ultimately you can install a little solar panel on the dash to deal with this current in case you cant eliminate this power draw.

[lakeside53]

It's pretty normal for that era. At that rate a fully charged 100 amp/hr battery will last about 1250 hours. My 1990 truck with virtually no electronics is about 50ma.

Some Mercedes models were drawing 300 ma... That caused a few flat batteries

[danlb]

If you resurrected a 17 year old car that has not been used for a very long time (a year???) there is a good chance the battery is no longer good. Lead acid batteries are damaged by being run down and left that way for a very long time.

I have used one of the little 1.5 watt solar battery maintainers on all my cars since the late 1990s. The wife's car was driven so little that the battery was dead every time she went to use it. My pick up truck was used once every month or two, and it had the same problem. Both cars had around .75 watt of drain when everything was off. After adding the solar charger the batteries lasted for many years and always started quickly and reliably. One battery lasted over 10 years.

Dan

[darryl]

There's a fair amount of capacitance in a modern car stereo system, and these caps need to charge from the battery voltage- especially an amplifier where there's no disconnect between the battery and the initial power supply caps. They can draw a pretty good spark, then when they are up to battery voltage the current flow ceases. This is an interesting case because those caps will also discharge through the power wire if the battery voltage drops- as it does when you're starting the engine. The caps will discharge into the starter at the same time the battery is trying to run the starter. The result for me more than once has been that if a battery terminal has gotten a tad loose, the fuse for the amp gets blown. You can get a few current surges through this fuse if you're having an issue trying to start the engine.

At any rate the 80 ma draw does seem high to me- and could be due to some discharge tracks across the battery or across the contacts in switches which are always live- the starter solenoid would be one of these. I would suspect that because of the environment it's in, so a test would be in order. Just remove the heavy lead from the solenoid and see whether it makes a difference in the parasitic current drain. That's pretty much the basic procedure to test for leakage current drains in any vehicle. If the device you're testing has an inline fuse, such as add-on car stereo components, then just pull the fuse and see whether the drain stops or changes.

Many meters have current ranges which are fuse-protected, and this can interfere with your mental ability to figure out what's going on. It's so easy to blow this fuse, especially if you're using a less than 2 amp full scale range, and you're hooking into a circuit which needs a current rush to charge its caps. If your meter has a high current range, say 10 amps or more, then it's probably not fuse protected. But this can mean that you don't have the resolution to read low milliamps, so you tend to switch to a lower range- and potentially popping the fuse without even knowing it. Once the fuse pops, you'll either see a full range reading or OL, or no reading at all, potentially misleading you.

I've gone slightly off track here, but I wanted to shed some light on some measurement issues that can come up when you're trying to find out where a drain is occurring.

[PStechPaul]

I also think 80 mA is a bit high, and that will drain an 80 A-h battery to nothing in 1000 hours or 41 days, and thus dangerously low in 2-3 weeks. A safe and effective way to measure the current is to use a 1 ohm power resistor in series and read the voltage. 80 mA will read 80 mV, while the 1 ohm will limit surge current to 12 amps. Remember that a sustained current of 12 amps will cause 144 watts of heat in the resistor.

For a vehicle used infrequently, a battery cut-off switch may be a good idea, but it will reset the clock and the ECU may lose self-calibration information which can cause less efficient operation.

[RichR]

... but it will reset the clock and the ECU may lose self-calibration information which can cause less efficient operation.

Plus you'll have to enter a code into your radio to make it operational again.

[Paul Alciatore]

Automotive batteries generally are rated between 75 and 275 AmpHours. So, lets say 150 AmpHours for argument's sake.

150 AH / 0.08A = 1875 Hours

That's 78 days or 2.6 months.

Lets say the battery will start a vehicle with half of a full charge remaining. That's 39 days.

You should be OK if you run it every week or two.

That being said, 0.08A does sound like a lot to me. Memory chips do not need a lot of current to keep their data. They use coin cells for that purpose and they can last 10 years or so. A clock? Still sounds like a lot. One AA or AAA cell lasts for months in them. So what?

I think you have a small problem somewhere. If you want to find it, you can use a modern, clamp on Amp meter to trace DC currents as well as AC ones. Start at the positive battery cable and measure it. Find where it starts to split and follow the current.

[Willy]

Parasitic current draws vary greatly from one automaker to the next, even from model to model and from the same manufacturer depending on component and circuitry design. I've measured some at 15-20 ma. draw others as high as 110-120 ma. and all was good. The exceptionally high ones were a certain makers model with a tach drive module that typically ate up a lot of juice while parked, and this was normal! Worked out fine as long as the car had a good battery and didn't sit for more than a few weeks.
Later models were however changed due to complaints. Lets face it there's just no reason for this situation other than cheap shoddy circuit design, however it happens to various degrees even today.

I believe I read that Ford is happy with a design if the car can sit idle for one month and still have enough reserve battery capacity left to start in freezing temperatures, this of course with a good battery.
Also many cars (probably most today) are equipped with body circuit timers that drastically cut parasitic current drains after a preset time interval after shutting off the engine. The one Ford I have in the yard today takes 40 min. to reach this threshold, other makes and models vary greatly in this respect.
Keep this in mind when taking current draw readings, and if one wants to get a truly accurate reading do so after an hour or so. It takes a little bit of extra work work to do so without disconnecting the battery out of the circuit momentarily but it's a very simple process really and results in a more indicative reading.

[Paul Alciatore]

OK, I can see the radiator fan running for a few minutes to cool things down. And it is nice at night if a light will stay on for a minute or two. But just what benefit does running what accessory for 40 minutes after parking? And just why would it take dozens of milliAmps? Memory chips can maintain their data with microAmps.

I would expect that after two to five minutes everything, except some memory chips would be shut down. The current drain at that point should be mainly due to leakage across the battery's own cells.

Just what is drawing that current? Anyone have any real numbers?

Parasitic current draws vary greatly from one automaker to the next, even from model to model and from the same manufacturer depending on component and circuitry design. I've measured some at 15-20 ma. draw others as high as 110-120 ma. and all was good. The exceptionally high ones were a certain makers model with a tach drive module that typically ate up a lot of juice while parked, and this was normal! Worked out fine as long as the car had a good battery and didn't sit for more than a few weeks.
Later models were however changed due to complaints. Lets face it there's just no reason for this situation other than cheap shoddy circuit design, however it happens to various degrees even today.

I believe I read that Ford is happy with a design if the car can sit idle for one month and still have enough reserve battery capacity left to start in freezing temperatures, this of course with a good battery.
Also many cars (probably most today) are equipped with body circuit timers that drastically cut parasitic current drains after a preset time interval after shutting off the engine. The one Ford I have in the yard today takes 40 min. to reach this threshold, other makes and models vary greatly in this respect.
Keep this in mind when taking current draw readings, and if one wants to get a truly accurate reading do so after an hour or so. It takes a little bit of extra work work to do so without disconnecting the battery out of the circuit momentarily but it's a very simple process really and results in a more indicative reading.

[Willy]

Just what is drawing that current? Anyone have any real numbers?

I just gave you some real numbers from just one component that was a very heavy drain, constantly. This is just one example. There's literally a hundred different components in a new car car that could be at fault, probably more, as each car is unique in this respect. As I stated previously there is simply no need for most of this parasitic loss.
It's simply not a perfect world, not in the automotive sector at least.