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M2ATX shuts off while starting engine: SOLVED

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  • M2ATX shuts off while starting engine: SOLVED

    this problem occurs for numerous people with the m2atx. if the pc is on with the engine off, and you try to start the engine, the m2 will shut off completely and then turn back on a second later. of course this borks your windows machine, and youre lucky if it boots back to desktop without problems.

    it has been said by some (oldspark if i remember?) that its not a problem with the m2, its a problem with your electrical system (battery is crappy)

    it has also been suggested that it IS the m2, that its low-voltage threshold (which is about 9v) is simply losing its integrity and after awhile it just wont survive the engine cranks.

    well, in my case anyway, its 100% the battery's fault. just a regular interstate megatron II battery. 540cca, which is spec for my truck. battery is only a year old, and hasnt showed any signs of degradation, but recently its been hitting 30F at night and i notice that the battery has a hard time starting the truck in the morning. angry (because this is my 4th battery in 6 years) i finally stormed down to sears and made them sell me a diehard platinum absorbed glass mat battery (they didnt want to sell it because it technically doesnt fit my truck).

    the new battery is 880cca and 1/4" too long for my battery box. super big hammer took care of that, now it fits great. jump inside the truck, pc running, and fire up the engine. pc still running, no hitches. shut off engine, turn back on. pc still running. no matter what i tried, the m2 never drops out anymore, it stays on through multiple consecutive engine starts. no more "rrrr, RRRR" struggling noise on the starter. no more delay on the starter (which i know is a sign of solenoid going bad though), and no more dimming dome light when i shut off the engine. this battery is kick ***!

    so like i said, here is proof the m2atx is probably completely innocent of failure. wet lead acid batteries suck, period. yeah, it cost me $220 after tax, but for the first winter in years i wont be jumpstarting the stupid thing in 2 feet of snow, and my computer might actually last awhile.

    this battery is claimed to be made by the same factory that makes batteries for the us military. AGM batteries are the real deal, theyre in a whole different class from regular lead acid's.

  • #2
    Wet lead acid batteries have approx twice the internal resistance of AGM batteries, hence AGMs have half the internal voltage drop under load.
    The higher the current, the higher the voltage drop.
    EG - if internal resistance (ESR at full charge) is 3mR (0.007 Ohm) and cranking current is 250A, then the battery voltage is 12.7V (full charge) - IR = 12.7 -(250x.007) - 12.7 - 1.75 = 10.85V.
    For a wet cell it would be 12.7 - ( 250 x .014 ) = 12.7- 3.5 = 9.2V.

    The less charged the battery is, the higher its internal resistance, hence a larger voltage drop for same current. (From a lower internal voltage, but that is similar for both wet & AGM batteries - ie, 12.7V full; 11.3V fully discharged.)

    In the above example for a 250A starter motor, we compared a 1.75V difference due to battery alone.
    But cables can also make a big difference - hence the "Big 3" - especially for the starter the battery +12V to starter, and the battery -ve to engine ground.
    For other loads, the battery +12V to the load, and the battery -ve to the chassis/body to the load (ground).

    Hence why PC (and audio) supplies are often dedicated add-ons that avoid voltage drops though "least cost" cabling, ignition switches, various fuses and connectors.

    Fuses add resistance (especially near rated capacity) - far higher than the cable they are protecting.

    Why mention the above?
    Because voltage dips at PC PSUs can be overcome by good wiring (the Big 3, and dedicated cable via a fuse and perhaps a relay)..
    Or a second battery for the PSU (which is only connected when the vehicle is charging; hence ensuring independence from the main battery in case the PC etc drains its battery when not charging).

    That may overcome the need for expensive AGM batteries as cranking batteries. Deep cycle batteries are not designed for cranking. And whilst some say AGMs are good for both deep cycle and cranking, what they really mean is "all AGMs provide good cranking current" by virtue of their lower internal resistance - it doesn't mean they like doing it. (How often do you see CCA etc for AGM batteries? Not often? They usually provide short circuit current or internal resistance instead don't they? Certainly if they are deep-cycle or slow-rate alarm etc AGMs.)

    If you can only have one battery, then fine - AGM.

    But I prefer a standard wet cell main/cranker, and then whatever other battery I want for the application - whether deep cycle; a small AGM in lieu of an inferior stiffening cap; or a big AGM for thumping audio or winches. (With automatic isolator of course!)


    • #3
      Originally posted by trader007 View Post
      the new battery is 880cca and 1/4" too long for my battery box. super big hammer took care of that, now it fits great. jump inside the truck, pc running, and fire up the engine.
      If at first you don't succeed, get a bigger hammer.
      2008 Ford Mustang GT/CS CARPC(99%)
      Software: Ride/Road-Runner, Digital FX skin 5.x, iGuidance 2011, GPSgate on Win7 64bit


      • #4
        i honestly think the biggest difference with this new battery is how well it will hold up under multiple discharges. wet lead acid degrade after you flatten them out a few times. from my experience, if you flatten your battery more then 6 times (leave something on overnight, starter wont even turn over in the morning) you already have lost a good chunk of its capacity (battery wont hold a charge for nearly as long as it did new). all of this is greatly amplified in cold climates too... like in my case where the battery right now works fine in the warm weather, but noticeably sluggish when temps are around freezing.


        • #5
          Actually - as a general rule - AGMs are worse if abused.
          Their big killers are charging and discharging out of range - ie, above 14.4V, and below their designed discharge level.
          And most AGM instructions stress to recharge ASAP after high discharge. (They cannot be rejuvenated like wets cans.)

          Some decades ago Exide introduced the perfect car battery - the TorqueStarter range.
          They were AGMs and were pulled fro the market within 12 months.
          Why? A high rate of failures & returns.
          Why? AFAIK - over 14.4V charging, and forgetful headlights etc.

          With modern chargers and headlight reminders or circuits, I reckon the TorqueStarter story would have been very different.

          AGMs discharge & recharge at higher rates due to their lower internal resistance.
          Their lower leakage resistance also means a much longer shelf life.
          And the don't sulfate the same way as wets (though that is usually recoverable in wets).

          Other than that, they are effectively the same battery.

          My wets last typically 6-8 years despite several extreme flattenings (well over 6!).
          That is more of a quality or design issue. (EG - many UPS AGM batteries only survive about 6 full discharges, or 10 years - whichever occurs first.)


          • #6
            Originally posted by OldSpark View Post
            Actually - as a general rule - AGMs are worse if abused.
            Their big killers are charging and discharging out of range - ie, above 14.4V, and below their designed discharge level.
            And most AGM instructions stress to recharge ASAP after high discharge. (They cannot be rejuvenated like wets cans.)
            thats not what ive studied over the years... unless im not understanding what you mean by abuse?


            • #7
              AGMs do not tolerate over-voltage charging or excess-discharge without prompt recharge. (Compared to flooded.)


              • #8
                over voltage charging is rare... my alternator and onboard charger are both in top shape. ill keep that in mind about the discharging though, thanks. (battery has a 5 year warranty, not to worried!)


                • #9
                  Over charging may be rare for you (and me - I have a dash mounted battery voltmeter), but it isn't for others.

                  And whilst wets can boil of liquid, AGMs do not have that luxury.

                  Your 5 year warranty is void if you over discharge it.
                  PS (8Jun11) - and over charge it.
                  Last edited by OldSpark; 06-08-2011, 03:46 AM. Reason: PS...


                  • #10
                    well i just wanted to update after the winter and now some hot summer use. this battery is balls-out awesome. i cant even believe the difference, its like i added about 10 of my old batteries.

                    a few weeks ago i accidentally left the pc on overnight after doing some vnc maintenance. about 8 hours just sitting on the desktop and the truck still started like a full charged battery. even the cellphone died from trying to run vnc for that long (i have it running adhoc wifi so it drains a little faster then it can charge).

                    then today i just fired up the pc while my truck was out in the parking lot. i went inside and did some frontend updates through vnc again, then transferred about 10gb of data over the next 6 hours or so. i didnt even care if my battery went flat, i would have just charged it right away anyway. i thought for sure actually using the pc for 6+ hours would kill the battery at least a little, but the m2 never even shut off while cranking, and the truck started like nothing ever happened.

                    the capacity of this thing just makes an absolute joke of my stock sized interstate. i would be lucky to start the truck after an hour with those interstates, it wouldnt matter if they were used or new. this diehard though, it can be 20 below outside, truck sitting for 10 days straight ill remote start it like its been on the charger. its more then a night and day difference from what i had...

                    i dont think im worried about over-discharging. the price of it did bother me at first but it now seems cheap... ive went through 3 interstates over the last 7 years. a lot of battery pack jumps during that time too. i dont hardly need my onboard 20amp battery charger anymore either. still great for camping though, i can have all my entertainment bumping all night no worries.

                    one of these days this summer i will see how long it will run the stereo and subs with the pc on though. i have a feeling then it will still go for a couple hours.


                    • #11
                      Good to hear, though total life span will be interesting.
                      Like I (think I) said, my wets lasted 6 years but were retired after 8 years and both had had a few total flattenings in their early years. Same with my mum's - 2 or 3 totals (not detected for a week or 2) plus half a years use per year (left in car open circuit; sometimes with a 3 month top up charge) - it was retired after 8 years.

                      My flooded battery was replaced with a 10-year design Yuasa UXH38-12 UPS AGM battery (38AH). It was discarded after 5 years (preventative maintenance) which is when I, er, acquired it/them. They sat for ~ 5 years with occasional checks (maybe charged every 2 years or so), and then I started using 1 as my main battery (and another as a spare). So 12 years old and it is still going strong despite it not supposedly being suited to cranking, though I have a 140A reduction starter as opposed to the 240A standard starter.
                      I'm waiting for it to die - it should have considering the abuse it gets.
                      But so far I', that impressed that I reckon I'd get the cheaper UXH100 or 110 (AH) which would probably last forever... well I reckon a good 10 years judging by the UXH38 performance.
                      The UXH100 is about the same price as 75AH Optima yellows & reds etc (they retail here for $550 though can be obtained for $450; UXH100 (or UXH110?) is about $500), and I know which brand I trust.


                      • #12
                        do you live in the south oldspark? we see a lot of flooded batteries last about 4 or 5 years old in the shop, but not much more then that. we go from 100F to -30F year to year though.

                        but yeah ill definitely be expecting 5 years from this battery, yet i have a feeling it will last double that. especially since it could probably lose about half its rated capacity and i could still use it just fine for my needs.


                        • #13
                          I'm in the south, but Australia. We have warmer temperatures here...
                          Up north nearer the equator, for UPSs they use to use gel cells (specifically Sonnenschein) because others would not last (AGMs and wets).

                          My AGM life comment is because many confuse an AGMs ability with it's liking - eg, just because it can supply high current does not mean it is good for it!

                          I presume by "in the shop" you do not mean sitting on the shelf and topped up (or trickle charged) every 3 months max?

                          My wets after 8 years were probably about 5AH capacity instead of their original 40AH, but that was fine if she started withing 15 seconds. (Though then I got the reduction starter and a reluctor/electronic ignition and she'd cold-start as low as 5.2 battery volts! YEs - it's a 12V system.)


                          • #14
                            i grew up working in my dads auto shop. in general, most batteries we saw were garbage. i do agree if you buy a good quality wet cell they can be plenty good... but i was so sick of battery problems i just splurged. it seemed to work too, like i said its a heck of a lot better then even i was expecting.