No announcement yet.

Battery drain

  • Filter
  • Time
  • Show
Clear All
new posts

  • 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
    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
      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.
      "stop with the REINSTALLS, what do you think we got some lame-o installer!!!" - mitchjs
      My Shop


      • #4
        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
          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
            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, 09:12 PM. Reason: added lower temp = less capacity


            • #7
              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 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
                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
                  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
                    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.


                    • #11
                      Whilst in storage, your battery should be on float charge.

                      For a typical unloaded and fully charged and good condition wet lead-acid battery at normal room temperature, recharging is generally recommended at no less than 3 monthly intervals. (Though a mate has a great wet cell battery that stood uncharged for 2 years! There are always freaks and exceptions...)

                      For any battery with a load, sulfation builds. And soft sulfates turn hard after about one week.
                      A loaded battery with infrequent charging and maintenance (equalisation etc) may last a season or year etc, but not the expected 4-6 years.

                      LOL. If "275 out of 340" is it's capacity, 275/340 = 80.9%...
                      80% (of original capacity as opposed to "rated" capacity) is the "normal" criterion used for an end of life battery. Sorry - I just LOL'd at the coincidence. (FYI - I retired my last crankers at an estimated 10% remaining capacity.)

                      And I'm glad that they replaced it. IMO they should have upon you first flattery experience... (Imagine being stranded somewhere... Sue the pricks!)
                      And BTW - don't buy batteries from automotive dealers, find a reputable battery shop.

                      But to answer your previous post - and possibly save a premature battery failure....

                      Re the PIC, again, it depends on your setup. The PIC could sequentially power up a few devices and can sense various inputs, whether voltage, or diode-connected etc interrupts or state changes, etc.
                      The 8-pin (leg) PIC08 has 6 inputs/outputs, but bigger PICs have more, however I was only considering the PIC08M2 for its $3-$5 price and small size (especially if SMD). For more inputs etc, I'd go CPU but only because my many I/O applications IMO are easier with a CPU and their expandable memory (rather than single wire RAM etc) and other peripherals. But the PICs have many of those peripherals internally (counters/timers, ADCs, DAC(s), etc).

                      Zener regulators:
                      For a 5V supply, a resistor would feed a 5V Zener (or whatever Zener is close; 4.7V, 5.2V etc).
                      The resistor drops the voltage from the supply (eg, 8V-16V) but must carry the current required by the load.
                      Its Wattage is its voltage drop time the current thru it. EG, for 16V in and 5V out, it drops 11V. For 0.5A, that's 11V x 0.5A = 5.5W, hence a 10W resistor though 5W might do if the voltage is rarely above (say) 14.5V (hence 9.5V x 0.5A = 4.75W hence 5W is ok if the resistor wattage is conservative and it doesn't get too hot (for practical purposes) OR the normal load is under 0.5A OR additional heatsinking is added.
                      (And the resistor value: for a 11V drop at 0.5A, V=IR hence R=V/I = 11V/0.5A = 22 Ohms which is coincidentally one of the preferred resistor values, so a 22 Ohm 10W resistor.

                      The Zener must be able to "dump" the max current through the resistor - eg, 0.5A. For a 5V Zener, that's 5V x 0.5A - 2.5W, hence a 5W Zener. (Zeners are often 400mW, 1W & 5W. Bigger than that gets rare and expensive.)

                      Hence Zener regulators are suited only for small current applications, and the 0.5A example above is probably too high current wise for practicality.
                      Besides, an LM317 is only a $few and has internal thermal limitation, regulates very accurately, and there is no trickiness involved in selecting its resistor. (2 low-power resistors required where one is 120 Ohms to ensure the minimum required load of 10mA for a stable output). Zener voltages vary a bit depending on their current (as with all diodes).

                      They are both linear and waste about the same amount of power, eg, "burn" up to 11V @ 0.5A in (5.5W) for an output of [email protected](2.5W), hence an efficiency of 2.5/(2.5+5.5) or ~30% at 16V in; 50% at 10V in etc.

                      A regulator for the Arduino etc:
                      For power conservation, a dc-dc converter is recommended. They are almost 100% efficient (typically 95% or more), and hence for 12V to 5V will more than half the current as used for a linear regulator.
                      Mind you, that depends on their overhead (or standby) current. If that's ~equal to the average load current, then overall efficiency is ~50%. If it's higher than the load current, then linear regulators may be more efficient.
                      IOW, dc-dc converters are NOT used for low current applications if power conservation is critical (eg, uA and maybe mA loads etc).

                      In your case, for an Arduino battery, maybe a CurrentLogic PCB-mounting CLD5-12S05 (9~18VDC input; 5V 1A (5W) output) for ~USD$10.50 ($9.50 + $1 for 5W output).
                      [ Note - unfortunately they do not state their standby currents, but assuming "typical efficiency >80%" applies to 50% load and higher, that could mean up to 20% inefficiency x 50% load x 5W = 10% x 5W = 0.5W or 0.5/12V = 40mA overhead, though I'd expect far less. You'd have to confirm with them. Maybe >80% efficiency covers a mere 10% of rated load etc. (Max efficiency is usually at ~80% of rated load and is hence easier to calculate, though how much is current-dependent circuit loses as opposed to mere no-load "idling" overhead/drain is just as tricky...) So ignoring its idling overhead... ]
                      Hence a normal 12V battery whose AH rating you can probably calculate (based say on max 20% discharge; I'd recommend the Yuasa NP range.
                      [ Quick quesstimate: (24+9)mA = ~35mA => ~15mA @ 12V => 15mAH => 20x15 = 300mAH for 20hours (C20) x 1/.2 for 2-% discharge => 1.5AH. Hence an NP1.2-12 for ~20 hours to 80% capacity, or NP4-12 for a guesstimated 3 days, or NP7-12 (usually the best bang for bucks (~$25-$35)) for 6 days etc. But please check my guesstimates - I could be wildly wrong!. And those reserve times multiplied 1/3 to 1.2 for linear regulators. ]
                      And an isolating relay. (For small batteries, current limiting is desirable, but that might not be a problem if not too discharged.)

                      Capacitors - forget it. Not for mA loads for more than a few seconds or minutes.


                      • #12
                        Originally posted by OldSpark View Post
                        Whilst in storage, your battery should be on float charge.

                        And I'm glad that they replaced it. IMO they should have upon you first flattery experience... (Imagine being stranded somewhere... Sue the pricks!)
                        And BTW - don't buy batteries from automotive dealers, find a reputable battery shop.
                        If they hadn't backed off of the cost I would have purchased it elsewhere. After the warranty wears out and I need a new one (my 2k3 mx-5 still had the stock battery when I sold it last year but it was a gel), I'll buy elsewhere.

                        I hadn't thought of a battery like those Yuasa. I can probably get one from a buddy who has a bunch. I just really don't want another car battery sized thing.

                        I'm not sure I follow the need for the regulator. There is already one built into the Arduino. I'm not up on the dual battery setups and will need to read some but would think you need a relay that would hold open when the computer(or ignition) is on and slam immediately there after to keep from draining the main crank battery. Sounds like you suggest a current limiter to keep from smoking the little guy when it starts charging? I assume it would just charge like normal off of the charging system. I would also guess a GOOD diode is in order.


                        • #13
                          A regulator is needed if the load does not handle the typical 8-16V range of a car's electrical system. At least that is my own traditional "design" spec plus some high voltage (spike) suppression, though some cars may not exceed 15V etc and good batteries or low current starters may not cause dips as low as 8V. (The M2 & M4 dc-dc PSUs are spec'd down to 6V!)

                          If the Arduino handles car voltages, then fine. But if it is merely a "12V input", then it probably only handles ~11.5V to maybe 14V or 14.5V - the typical range for a battery with bench charger - if that (ie, it may require regulated 12V). I know the Arduino can be powered via USB, but I don't remember its higher voltage input spec.

                          The isolating relay is to prevent batteries being in parallel when not being charged (otherwise 2 parallel batteries can fail FOUR times as often as a single battery; one failing battery drains the other battery, etc etc).
                          The relay is not to open during cranking - that would require a 2nd power source, ie, a 2nd battery.
                          But normally, battery isolators are open during cranking - they should only be closed when the system is charging. (Hence one possible flaw with voltage sensing or smart isolators - if they have a minimum connect time with no immediate disconnect when the vehicle cranks (however that may be determined!), then the 2nd battery also powers the starter, and pop go the one or both of the 2 interlink fuses or circuit-breakers (else the inter-wiring or relay if not protected).

                          Batteries have a specified maximum recharge current which is typically 10% to 20% of their AH rating - eg, a C10 or C20 rated 40AH car battery might have spec'd max 10% or 20% of "40" - ie, 4A or 8A.
                          But that is for warranty purposes and optimal life but is otherwise usually a semi-long term spec to prevent battery overheating and demise.
                          My 38AH cranker (a Yuasa UXH38-12 UPS battery) typically takes 40-45A after a very long crank or headlight discharge (maybe 10% discharged???), but that drops to under 10A within ~30-60 seconds though that is still above its likely 20% = 8A "max" charge current (I'd have to check its spec). And being AGM, it has no fluid to boil off to keep cool.
                          However, despite it being a 13 year old battery with a 10-year UPS design life - replaced from the UPS after 35 years (a typical preventative measure) and used for 3 years in my vehicle (which IMO is a totally unsuitable application for it!) - it is still behaving ok. Maybe that's because I am underestimating its spec (compared to other UPS batteries), or that that Yuasa battery is so bluddy good. (I liked Yuasa from my early biking days.) (Did I mention my mother's house alarm? It had a Yuasa NP4-12 that lasted 23 years before failing its yearly reserve test. As I recall, they have a ~4 or 5 year design-life spec.)

                          If my UXH38 translates to a "small"(?) 7AH NP7-12, it means a ~10A initial charge current acceptance, hence at least a 10A diode (and I'd suggest self-resetting circuit breakers) and such diodes can get expensive and uncommon - especially if Shottky types.

                          But the diode voltage drop is undesirable anyway. IE - if the charging system suits the main battery which is also lead-acid whether wet cell, AGM or gel, then it is NOT optimal after a diode's voltage drop.
                          Besides, a flat 2nd battery can still drain the main battery though the diode - it only needs to drop to a voltage below that of the main battery minus the diode's forward voltage drop, and a collapsed cell means a voltage drop of ~2V. And charging a collapsed AGM battery at several Amps can cause thermal runaway and (or) a possible fire or explosion. (Same for wet cells, but they boil off their water and acid before thermal runaway. Not that its surroundings like its acid vapor!)
                          I did initially include a diode as an option to a relay, but I deleted that (I think!) for those reasons. Likewise, diode isolators that were once not uncommon for vehicle dual-battery installations have since virtually ceased to exist. (Or they should have! Some installations expressly forbid them due to battery life considerations as well as safety issues.)
                          POST EDIT: Commercial diode isolators for dual batteries use TWO diodes (a diode between the alternator and each battery) hence one batter will not discharge into the other (nor share any loads) unless a diode shorts. I was referring a single diode used for dual-battery isolation, however the same problem of different battery charge-voltages occur (diode voltage drops vary with current), and that the alternator must sense one of the batteries (hence zero wire or "single wire" D+ only alternators are unsuitable without appropriate modifications. /end POST EDIT
                          And don't confuse the (Zener) diode regulator with a battery isolation diode - that's a totally different application.
                          Last edited by OldSpark; 04-12-2012, 08:34 PM. Reason: POST EDIT - 2 diodes in "commercial" battery isolators.


                          • #14
                            The regulator on the Arduino is to convert 4-12vdc to 5vdc for the Atmega chip and other components on the board. The pixaxe board would have the same thing. You should be able to put the Arduino into sleep mode though, and have it use a fraction of the power... and then just watch for some signal (Ignition line/wifi rx pin, whatever) to turn itself back on.
                            "stop with the REINSTALLS, what do you think we got some lame-o installer!!!" - mitchjs
                            My Shop


                            • #15
                              Originally posted by malcom2073 View Post
                              The regulator on the Arduino is to convert 4-12vdc to 5vdc for the Atmega chip and other components on the board. The pixaxe board would have the same thing. You should be able to put the Arduino into sleep mode though, and have it use a fraction of the power... and then just watch for some signal (Ignition line/wifi rx pin, whatever) to turn itself back on.
                              From what I read it pulls 10ma for the regulator alone so sleep is ill advised. Have you put yours to sleep? The only difference would be you could possibly choose a more efficient regulator for the picaxe than is used on the arduino. (oh and the article I read from:

                              Input voltage for the arduino is listed as 6-20v

                              My house alarm battery is years old and still goes. Hey, I think my brother in law has a system that all the copper was cut off before he bought his house. I wonder if he has the battery I once ran my entire house alarm on the battery including 4 smoke alarms for about a week or 2 when I unplugged it for a reason and forgot to plug it back in.
                              Last edited by dmcdlrn; 04-12-2012, 03:05 PM. Reason: added supporting documentation.