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Thread: Battery drain

  1. #1
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    Battery drain

    I've been noticing that my car has been "reluctant" to start often since my install. I did some testing and find the following:

    Battery is a panasonic 46b24l(s) rated at "45ah"

    Stock = 40ma
    Arduino circuit = 24ma
    OBDSX = 9ma

    I'm seeing right around 73ma with everything hooked up and the car off. The stock drain is higher for a few minutes after you close the door for timers and dome lights and stuff but settles to 40ma with all of my stuff disconnected.

    So it seems like I have about doubled my consumption (kinda stinks about the OBD... any thoughts there?) I have to keep the arduino powered as it must be initially powered via usb or else it cannot communicate with the computer.

    According to a calculator I found online, stock should last bout 33 days before dead stock and 16 with my mods. Of course that is DEAD... ability to crank is lost long before those figures.

    So I guess my questions are, should that obd really pull so much? is there any easy solution that people know of? and does it seem normal to have a weak crank after 12 hours of being off.

    It has only failed to start once and that was about 5 minutes after I sat with the engine off and the system on for about 10 minutes.

    Oh and before people suggest second batteries, I'm not going that route... it is an MX-5... I barely have room for my lunch.

  2. #2
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    Just tested it again after about an hour and it dropped to about 45ma with everything hooked up. That suggests that without my stuff it would be around 12ma.

  3. #3
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    pulling 40mA you should be able to last much longer than 12 hours, 400mA would probably drain a battery near dead after 12-15 hours. Are you sure you're not off by a decimal point somewhere?

    As for the OBD, 9mA is nothing, I'd be more concerned about the Arduino circuit pulling so much, that's a massive amount, my Arduino barely pulls 10mA when idling.

    Oh and don't trust calculators online. A LOT of factors go onto the actual capacity of a battery, much more than an online calculator could ever figure.
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  4. #4
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    I'm certain on the decimals. It lasts 12 hours no problem, just sounds a bit weak when trying to start. Always starts though. (temps are low though and this is my summer car... perhaps I'm just not used to the starter sound again.) The battery always reads above 12v when I test it prior to starting even after sitting for the night.

    What do you mean by idling. It is always in a loop... it just checks once per loop if the ignition is on. If it isn't, it skips everything else in the code(simplistic explanation). I know there is a method for putting it into a sleep mode of some sort but I never got around to figuring that out and I read it didn't save much if any as most of the draw is the 5v regulator. I will have to look at my wiring notes (short memory here) and see what is pulling off of the 5v pin if anything when it is idling. Perhaps I also need to tweak my code to ensure all go low on power down. I might also be going low to turn ON an opto...

    The 24 is an educated estimate. I placed my meter inline with the negative on the battery and checked with the arduino switched on and off (I have a switch for it in the kick panel). I didn't actually isolate the arduino circuit as I would have had to either cut wires or rip out half the dash/console to get at it. I did the same for the OBD scanner. I just wish there were a way to keep the scanner from taking ANY power when the car is off. I may unplug it for a while. I know I read on the scantool forum about console code to get it to go low without usb power or something... I'll have to look that up again.

  5. #5
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    OK, so my battery was dead yesterday morning. I took the car to Mazda as I question the battery. They tested it but said the machine said charge and retest which they couldn't do before close. I go back tomorrow to have it rechecked. In the meantime, I shut everything down and removed the fuse from my 8 gauge line to my amp. I got home at 2:30am from a 30 minute drive on the highway. The battery had 12.85 volts. I slept and checked it again at 11:15am about 9 hours later and it was at 12.45.

    When I bought the car a year ago, it had been sitting most of the winter in the dealer lot. The battery was of course dead. It was also about 0F out. For the following 3 or 4 days I had to jump it every morning. I took it back questioning if the battery had been damaged sitting dead in the cold. They shrugged it off, charged it with their fancy charger and sent me home. It has been "fine" since then but something doesn't seem right.

  6. #6
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    When ever a battery is "not full", it deteriorates.
    Of course, a little bit "not full" is fine, but he flatter it gets AND the longer it remains there, the shorter the battery life. (Sulfation refers; both hard & soft.)
    And a battery is "not full" as soon as its charging is removed and its surface charge has dissipated (hence full-time "float" charging).


    The shorter a battery is left discharged, the better it can recover (especially with high current and/or equalisation etc charging, and certainly above 13.8V - the old vehicle/12V standard voltage).
    And some batteries can improve with exercise. (New batteries usually do.)


    TIP - if a battery is weak coming into summer, it may get thru, but replace it if heading into winter. (Lower temperature = less capacity.)


    Your battery's inability to hold charge is an indication of its age.
    Your dealer shrugged off your question because they were irresponsible etc.
    My previous 40AH battery was able to crank after a night with the 10W (~800mA) dome light on in snow (-1C/30F).
    LEDs (20mA) should be ok for a week or weeks. (Noting the accelerated life-demise of the battery though modern charging at 14.2V - 14.4V etc reverses much of the demise.)


    And IMO, you were right to say "about doubled" your consumption. Doubling the current more than doubles the effective discharge of a battery (total Wattage output decreases with increasing current).


    Rather than an Arduino for a supervisory function, have a look at PICAXES - eg, the PICAXE 08M2; ~10uA stand-by current as I recall. Use that to connect the Arduino (or even replace it).
    Last edited by OldSpark; 04-11-2012 at 09:12 PM. Reason: added lower temp = less capacity

  7. #7
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    Well, I'm headed in in a few minutes to drop the car off to have them go over the battery again. I really suspect the battery. This is a summer only car and has about 11k miles on it. The battery spent from October to March in my basement sitting on a board. I put a trickle charger on it but it accidentally got unplugged at some point and I didn't notice it for a while so that may have caused some problems.

    I have left all of my equipment unplugged for the last couple of days and it still is having a hard time starting in the morning.

    As for the PICAXE... I waffled back and forth between PICAXE and arduino and specifically chose arduino for some reasons. At this point it would be VERY time consuming to switch as I would have to basically re-do everything (fairly complex circuit as well as a very complex vb.net application that interfaces with it). In standby the nano pulls 10ma which from what I read is the 5v regulator. The PICAXE would need a regulator as well but I'm sure a more efficient one could be chosen.

    All that to say, the 25ma I'm pulling on the arduino shouldn't cause my problem from what I'm gathering.

  8. #8
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    Sorry, but you misunderstood. I meant merely for the PIC to monitor/supervise to then power up the Arduino.
    Of course, that depends on what supervision processing is required...

    I too chose the Arduino over PICs for numerous reasons. However with the 08M2 now having the program space etc of the larger PICs, I'm starting my detailed PICAXE learning curve.
    Since I program in assembler, I too know what a pain cross-platforming is. But the 08M2 has the capabilities once only available to its larger brethren, and though falling short of my DIY self-learning EFI/EMS, I reckon it can handle simpler "add on" sequential ignition as well as ignition timing mods (from OEM dizzies or fixed dizzies etc) and anything simpler - and it's certainly cheaper else simpler (and more configurable) than old logic circuits for combinational logic and switching. I'm even thinking of using an 08M2 instead of 2 extra "logic" relays (SPDT) for hibeam/spots/lowbeam combinations, not to mention dimmer applications (whether driving lights or LEDs) etc.


    As to its PSU, a simple resistor and zenor should be fine.


    IMO 25mA is a reasonably significant additional battery load, but that depends on battery age, capacity, and recharge intervals. (As I recall, Optima had an example or case study relating to a 17mA parasitic draw. That translates equally well to any lead-acid battery.)


    But your battery is definitely stuffed (with >95% confidence).
    Space permitting, it could be used for the Arduino etc in a dual battery with isolator set up, though any appropriate aux battery could be used if cranking reserve is to be reasonably guaranteed. (A smaller aux battery could remain connected to the main cranker until some "low voltage" threshold is reached - eg, 12.5V etc. Again, a 08M2 for that unless using some other low-power circuit (ie, NOT a 555 timer - they draw 10mA in standby).


    Optional ramble....(UIBI)
    Speaking of battery isolators, the UIBI-Mk2 was to be a FET front end for zero alternator chargeLight-circuit loading and for use on EMS controlled alternators (with an RC filter). In fact a $2 MOSFET could replace a 100A battery isolating relay...
    Anyhow, it looks like the UIBI-2 will be ditched in favor of the UIBI-3, and alternator (charge-light) controlled battery isolator that uses a PICAXE for its sensing. And since it's a PICAXE, why not add user configurable delays if required (including for fools that believe in "priority charging" except in rare specialised circumstances.
    In fact, the UIBI-3 may include a voltage-sensing or "smart isolator" option for marine & stator alternator applications, or where fools think they are "superior" except in certain rare or specialised applications. Of course unlike most "smart" isolators, the UIBI-3 would have user-configurable voltage thresholds AND delays. The user would just add a relay of their choosing unless the UIBI-3 MOSFET could do the switching, though it's likely instead to have it ground-switch the isolation relay(s) for up to 100A of relay coil/solenoid current, ie, ~500 typical 30A relays, or 50 typical 200A relays etc.
    Now that would be smart wouldn't it?
    (The UIBI is an alternator chargeLight-circuit (aka D+ or L) controlled battery isolator. Using the alternator D+ or L to control the battery isolator(s) results in superior and less risky operation (with few exceptions) than expensive "smart" isolators. Being the mere addition of a relay, it was dubbed the Ultimate Intelligence Battery Isolator (UIBI). But if the UIBI-3 were to include the option of a user-configurable "smart isolator", where doe that put other "smart isolators"? LOL!)
    Oops - I digressed...

  9. #9
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    I don't think that would work. The arduino must first boot from USB power or else computers won't recognize it. (must be a limitation of the serial to usb chip) I could possibly run the arduino off of the USB power only so that it boots from the USB every time the computer starts. The problem there is it might not be reliable that way.

    All that to say, I'm looking at a different screen possibly which the screen dimming circuit and steering wheel control was the #1 reason I did a micro controller to begin with. If I change all this up, I'm already up to my eyeballs in rebuilding the circuit.

    Resistor and Zenor? I'm going to ask for clarification. I assume it needs 5v? My limited EE knowledge isn't allowing me to understand how that would work.

    A second car battery really isn't an option as I have a very small car to begin with. What about a capacitor or small battery for the arduino only?

  10. #10
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    Mazda just called. It's official. Bad battery. It is holding 275 out of 340 amps. Rat bastards tried to charge me $60 pro-rated value of the battery. I'm like.. hey, I brought this thing back 2nd day I owned it complaining it was dead. He gave me the battery I suspect my arduino problem will mostly go away. I drive this car an hour a day during the week and usually at least some on the weekends. At worst it would sit from Friday night until Monday morning.

    Definitely still consider the PICAXE route if I have to rebuild my circuit but might wait until next winter while it is in storage.

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