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Thread: POWER problem (inverter or battery related?)

  1. #1
    Variable Bitrate
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    POWER problem (inverter or battery related?)

    hey guys! . so first i must explain my install... i am using two battaries in the car. they are connected like that : the (+) is with the cable, a fuse and a switch. the (-) is connected through the cars grounding..
    the pc is powerd through a norrmal psu, that gets power from a 400 watt inverter... SO

    I suppose that when the car is working, both battaries should be at 13,8 V.. the cars battary is at 13,8 and the extra is at 11,8... (first clue)
    when i turn on the inverter, the voltage of the extra batary drops to 11,5..
    So here is the problem. everything worked fine, untill now. now when i turn on the pc. the fans just turn a bit and then they stop. from what i can get, when i turn on tyhe pc the voltage of the battary drops slowly to 9 where the pc shuts down.
    BUT the pc works perfectly fine in my house.... with the same PSU just with normal power source
    so what do you guys think ? is it the battery?(wich is prety old) or the inverter?? (witch is also ****ed up :P ) is there any way to test this??

    (etxra: the pc in the car does the same even with all its cables disconected from it (usb and stuff) also, the only change i made to the system the day before was that i used one of the usb cables to be the trigger to 5v relay, so that power from the battary would be sended to the car amp to start working. also the probelm sowed up like this: i tuned on the pc. it got into windows. then shut down. and the it always do the same!!) plz help!

  2. #2
    Low Bitrate
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    A possible reason for the discrepancy between the batteries is that there could be voltage drop between the main batt and the auxillary batt. Try a thicker gauge cable for the connection between auxillary and main batts. Also, get rid of the 400w inverter and use a dc-dc m2/m3or m4 atx psu as these type of psu's are designed to keep a consistent 12v to the pc even when battery voltage drops below 11volts or more and are more tollerant than a normal pc psu.
    Most desktop pc motherboards run on 12v dc anyway so having an inverter will only use more battery power to boost from 12vdc-240vac to your desktop psu which then converts the 240vac power back to 12vdc to the motherboard. So dc-dc psu is strongly recommended. It will make the system more stable and will use less power than inverter.

  3. #3
    Variable Bitrate
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    i know... i am not very proud about it:P i didint had much xp when i was making it... i was planing to change it assap. But the problem remains.. there is nothing else conected to the cable of the batteries exept the signal for the power up of the amp. (wich i dont think it drops voltage) maybe its becouse the (-) uses the cars ground and not a good cable... but the problem remains.. how can i check that the inverter works, or if the battary is finally dead??? Also, i checked the voltage outage of the inverter (without the pc working) and it was constand 240 volt... so i am leaning towards the battery...

  4. #4
    FLAC SNOtwistR's Avatar
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    Sounds like it's the battery to me. Most auto supply stores will test battery for you. SNO

  5. #5
    Raw Wave
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    With no load off the 2nd (and main) battery, the 2 battery voltages should be equal.

    If not, you have a high resistance interconnect.
    It may be a faulty 2nd battery (eg, collapsed cell) which is discharging the main battery and adding to that voltage drop.



    With no loads, both batteries should read 12.6-12.7V fully charged (and rested).
    Fully flat is somewhere below ~11.5V. (But generally discharges are limited to ~12.4V and 12.0V for cranking and deep-cycle batteries respectively. That's with no load and time for a bit of recovery (a few minutes?).)

  6. #6
    Variable Bitrate
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    i stick with batarry too. especially since i cant find a volt drop in the positive cable... will have it tested /changed and say the result

  7. #7
    Raw Wave
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    Check the GND path a well just to be sure.

    And measure from battery post-to-post with a load.

    If the 2 battery voltages are the same, there is no point looking for a voltage drop (der...?).
    But if one battery is lower than the other, there must be a voltage drop somewhere (assuming they are not isolated - but you should add a battery isolator for reliability, and up to 4x battery life).

  8. #8
    Variable Bitrate
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    the GND cable is the build in of the car... many other thinks are connected to it (the inverter, the amp.. ) but has it to do anything ?? also everything worked fine like that untill now... also what is an isolator?? :P

  9. #9
    Raw Wave
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    The GND connections have to carry all the return current from the +12V. If they break or burn out, you are likely to damage electrical & electronic equipment.
    But there are TWO main GND connections - battery to chassis/body/GND and alternator body (hence engine) to battery- OR chassis/body GND.
    The alternator/engine to battery- is usually ok to 200A or more (since it has to power the starter motor), but the chassis (and hence most car electricals) is usually rated much lower. Both must be capable of handling your max current demand from either source (ie, battery or alternator).
    When voltage drops are considered, the GND path/return should be included.


    Google for "battery isolators" or "UIBI oldspark mp3car".
    Many knowledgeable battery people will recommend NOT to parallel batteries (for long periods) when not being charged or required for the load. Paralleling TWO batteries when not in use infers replacing them FOUR times as often (or 9 times for 3 paralleled batteries) because if one fails, they all fail (eventually), or burn or explode.
    Most use a battery isolator to isolated/disconnect the 2 (or more) batteries when the alternator is not charging - UIBI & "smart isolators" (LOL!) refer. (Forget diode/MOSFET isolators.)
    The secondary - but most popular - reason for isolators is so that if whatever> drains your "secondary" (battery) loads, it won't drain you main battery, hence you can start normally.

    Some use IGN to energize a relay (the isolator switch), and that's fine if the aux battery and its fuses and interlink wiring can handle the shared or full starter motor and IGN current else you may blow the two fuses between the main and aux/secondary battery; or if unfused, the relay or wiring (ie, fire!).
    I consider it almost as easy to connect the alternator's charge light output (D+ or L) to the relay's coil (instead of IGN). That's the UIBI - a truly smart isolator with minimal cost yet exceeding the performance and adaptability of expensive voltage or "smart" (LOL#2) isolators. (That assumes an alternator with a charge lamp or similar circuit that can power the relay's coil.)
    The UIBI only connects the batteries whilst the alternator is charging. Manual switches and other triggers, delays, low-voltage disconnects, etc can easily be added.

  10. #10
    Variable Bitrate
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    yes, the two battaries are only connected when the alternator is working, through a manual switch. although i will search for what u sed about the relays!! i am off but when i return in two days i will search for what you sed about the grounding too see what might be causing the problem. But i get it that no one thinks that the inverter might be broken??

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