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OT: Magna battery draws 0.08 Amps when not running

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  • darryl
    replied
    This particular camper/trailer has a fairly long boxed-in area to carry the battery. I don't know if two Trojans will fit here side by side, but it looks as if they would. That was my recommendation anyway- two 6v Trojans. The other option would be a second deep cycle battery and a disconnect for each one. That way you could have one fully charged battery available in a pinch.

    The low voltage cutout is a good idea- I don't know if this particular unit has that feature, but there's no circuitry visible to suggest that. In any event, if a battery is discharged to that low level, it should be brought back up to full charge as soon as possible.

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  • PStechPaul
    replied
    It would be good to have a low voltage cut-off that completely disconnects the battery from the vehicle circuitry (except starter) when the voltage goes below 11 volts or so. Another option would be a separate battery for accessories and ECU. RVs often have such a system.

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  • darryl
    replied
    One of my jobs today was to troubleshoot a camper/trailer for draining the battery too quickly. Turns out the fridge needs 750 ma to remain in operation, and the battery had been drained enough times that it didn't have anywhere near the capacity it should have had (mostly trying to keep the fridge cold). It's an LP fridge, but has a control module to sense when the burner is working. It also runs a gas valve. Between the two the drain on the 12v system is considerable.

    Considering also that the on-board charger is voltage limited (to prevent boiling off the battery) it doesn't ever deliver enough voltage to bring the battery to full charge. This is probably a reasonable trade-off in this use, but you do lose something of the full capacity. I'm going to put it on a trickle for a few weeks to see if it helps- I've had some luck doing that with other batteries.

    There's also some leds that remain on in the system- not much loss here but it's still a drain. My Land Cruiser could sit 6 months and still have a good charge- enough for an extended cranking to get the old engine running- but there were no parasitic drains. Sometimes simpler is better-

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  • PStechPaul
    replied
    The battery has become indispensable to the running of modern car engines. When the battery in my 1999 Saturn totally died, I got a hot-shot that allowed it to start and idle, but as soon as I put my foot on the brake to get ready to drive, the engine died because of the additional load of the brake lights. When the battery failed in my 1989 Toyota pickup, it ran terribly and overheated in the 2 mile trip to my mechanic, probably because the fuel injectors were screwing up the mixture.

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  • Norman Bain
    replied
    Thanks to all for engaging on the topic.

    I like the option adding in the battery isolator as described by PSTechPaul ... will order one of those as it lets novices turn off the draw on those occasions when needed. I am not concerned about turning "off all electrics" and restarting same as this has happened many many times over the years without issue.

    I do note that the motor does get a little ragged at idle when the battery is close to dead ... but comes good as soon as good power supply is restored.

    The battery is (now) new so there should be no "wicking" directly across the terminals causing leakage. That does not mean that wicking is not occurring elsewhere.

    My multi meter has a 10AMP plug point and that is what I have been using to get the reading thus far.

    The car has had a couple of runs with new battery since I posted the question. Today I setup the multi meter before detaching the battery cable in an attempt to get a "fresh and settled" reading. Did not work ... clip fell off and dropped the connection ... however I do note that it is now 12ma for about 30 seconds or so then drops immediate to 5ma and stays there.

    I think from the posts that all is good for me. Thanks again for providing analysis and instilling confidence.

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  • danlb
    replied
    I was surprised to find that our car does some emissions based self tests after it's shut off. Don't quote me, but I recall that one was a vacuum leak-down for the fuel system. I became curious and looked into it after my wife pointed out odd noises after the car was parked for a while.


    Dan

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  • Willy
    replied
    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.

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  • Paul Alciatore
    replied
    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?



    Originally posted by Willy View Post
    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.

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  • Willy
    replied
    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.

    Leave a comment:


  • Paul Alciatore
    replied
    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.
    Last edited by Paul Alciatore; 07-31-2017, 02:10 AM.

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  • RichR
    replied
    Originally posted by PStechPaul View Post
    ... 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.

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  • PStechPaul
    replied
    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.





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  • darryl
    replied
    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.

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  • danlb
    replied
    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

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  • lakeside53
    replied
    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

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