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Thread: Doesn't hold standby power if I crank the car right away

  1. #51
    Jesus Freak antimatter's Avatar
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    I got the replacement M4-ATX in today and I swapped it out with the old one. I will replace the battery this evening and will run for a while to see how things are doing after some real world tests.

    My assumption is that I still need some supplemental charging because of my driving habbits ie. taking lots of short trips through the day and long periods (2 or 3 days at a time) of just sitting.

    I will cross that bridge though after I replace the obvious.
    -Jesus- King of Kings Lord of Lords

  2. #52
    Jesus Freak antimatter's Avatar
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    So I just got the new battery all wired up and I took some numbers.

    @ the aux battery while idling it measures 13.51v (isolator connected)

    The Aux battery measured 12.75v (isolated)
    Standby current is roughly .3amps

    We will see how far it is drained when I test it tomorrow
    -Jesus- King of Kings Lord of Lords

  3. #53
    Jesus Freak antimatter's Avatar
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    When I tested it the next day (roughly 10 hours) it was at 12.46v which is a marked improvement proving that the battery was indeed bad. After a short trip with the alternator charging it was back to 12.6
    -Jesus- King of Kings Lord of Lords

  4. #54
    Raw Wave
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    As I just wrote in the Why is my voltage dropping? thread - and elsewhere if not in this thread - a battery just off charge should be up to ~13.6V due to surface charge which then drops over 12-24 hours (with no load) to its nominal full voltage (12.67V, but say 12.6-12.7V).

    13.5V is ok assuming that at idle, the alternator output has dropped. It certainly isn't discharging the battery, though long-term it is insufficient to charge it, and will wreck the battery without occasional equalisation charging (over 13.6V, usually ~14.4V) to blow away soft sulfation.

    A modern alternator (ie, after ~1960?) should charge the battery with 13.8-14.4V with 14.2V being a common set point. That's at the battery - the alternator may put out more.
    In theory, except for single-wire D+ alternators, the alternator should be sensing the battery voltage and hence the alternator compensates for voltage drops to the battery.
    But the second/remote battery may see a voltage drop due to its distribution current & resistance (ie, V=IR where V is the voltage drop; I is the current along the distribution (fuses, cable, relay/isolator AND ground path) which has a total resistance of R Ohms.
    As long as the remote batteries are generally near fully charged and occasionally see at least 13.8V they should be ok (assuming it isn't excessively discharged). (EG - normal batteries are discharged when cranking, but then have the trip to recharge. When the trip ends, its a fully charge battery. Audio-system batteries that are not fully charged are left in partial discharged states which cause sulfation.)

  5. #55
    Jesus Freak antimatter's Avatar
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    So it appears that i should have read all 27 pages of the "Everything you need to know about M4-ATX" thread

    Apparently on page 22 it states issues with the IGN line being flakey in regards to holding standby current. The solution... Diode and a Cap on the IGN line.
    Everything You need to know about your M4 ATX

    So far switching from ACC to IGN has worked out well for me but i still have some unresolved issues:
    http://www.mp3car.com/m4-atx/148142-...off-cycle.html

    I will be adding this soon (RMA'd my motherboard)
    -Jesus- King of Kings Lord of Lords

  6. #56
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    One problem with the diagram as shown on that Everything You need to know about your M4 ATX link is that the Standby Battery (and LCD and M4-PSU) get about 0.6V less than the IGN +12V.

    Not that that should be a major problem - it merely means the Standby Battery may suffer from inadequate charging.


    [ The cap should still hold sufficient voltage, though if the M4 can suffer because its IGN voltage is much higher that its + (Standby Battery) voltage, a diode should be inserted from the cap to the + (Standby Battery) so that it can discharge to the + voltage.
    And not that I understand why the relay is there - as I read it, it is on whenever the Standby Battery is connected (and with sufficient voltage) OR when the IGN is on - why not omit the relay entirely? ]

  7. #57
    Jesus Freak antimatter's Avatar
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    Thanks for taking the time read that. Ignore the majority of that drawing. Just the part of the capacitor and the diode on the ignition line was the part I was referencing.

    The purpose is to make the IGN line a bit more stable. IMHO if the IGN line is that sensitive than it seems like a good idea to me.
    -Jesus- King of Kings Lord of Lords

  8. #58
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    Phew!

    Yeah - just a diode to the cap which is at the IGN (sense) input.


    PS - I didn't read fully - just skimmed for and updated diagram else comments that stood out (but my 3D glasses detected nothing LOL).
    Last edited by OldSpark; 06-23-2011 at 05:27 AM. Reason: PS...

  9. #59
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    Argh terrible pun terrible!
    Lucky I haven't been keeping up with this thread so closely!

  10. #60
    Jesus Freak antimatter's Avatar
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    Quote Originally Posted by OldSpark View Post
    Phew!

    Yeah - just a diode to the cap which is at the IGN (sense) input.


    PS - I didn't read fully - just skimmed for and updated diagram else comments that stood out (but my 3D glasses detected nothing LOL).
    Picked up the cap and diode today, will be installing it shortly.
    -Jesus- King of Kings Lord of Lords

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