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The return of the discharged start battery

Discussion in 'Generation 1 Prius Discussion' started by anon61, Jul 2, 2012.

  1. anon61

    anon61 Junior Member

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    I posted a few months ago about my start battery Discharged start battery | PriusChat. I replaced the battery, and things seemed to be OK. Yesterday, the battery was flat.

    It was exactly a week since the car had been driven. A forgotten light is the most immediate explanation, but I could not find anything that was switched on.

    Before I changed battery I tried to measure the current, and I think it was about 50mA. Would that be enough to discharge the battery? The car is driven 1-2 times per week, mostly short shopping trips.
    Could the battery be slowly discharged? Finally, is there any reason that the car would sometimes require more current? E.g. the key remote system? Or the hybrid battery fan?

    Also, we were going to leave the car for 10 days at the airport. Is is OK to disconnect the battery
    that long? I was thinking about the hybrid battery fan.

    (Also I would like to change my handle from anon61 to fstx)
     
    #1 anon61, Jul 2, 2012
  2. anon61

    anon61 Junior Member

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    I've measured the currents through the fuses, and I get zero everywhere, except 0.03A over DOME, 0.01A over DOOR, and 0.06A over ECU-B. Measuring current at the battery I get in total 0.06A. Obviously my multimeter is not very accurate.
     
    #2 anon61, Jul 2, 2012
  3. Patrick Wong

    Patrick Wong DIY Enthusiast

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    You need to decide whether your meter is accurate or not. If not I suggest you purchase one that can be relied upon.

    For now I will assume it is accurate. A drain of 60 mA is around double what it should be. 60 mA x 24 hours/day x 7 days = 10.1 Ah.

    If your battery was fully charged and in new condition it might have a capacity of 30+ Ah. You can see that it won't take much time for the battery to get to the point where it is seriously discharged and will not start the car.

    I suggest that, until you can figure out why your car has excessive current drain, you use a battery charger to fully-charge the battery weekly. Yes, if you are going to park the car 10 days you should disconnect the battery. The hybrid battery fan is not going to run for a very long period after the car is IG-OFF.
     
    #3 Patrick Wong, Jul 2, 2012
  4. anon61

    anon61 Junior Member

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    Is 30mA what it usually draws?

    I paid for an hour on toyota-tech.eu and downloaded the wiring diagram, but I can't find any information on expected idle currents.

    According to the owners manual, the DOME fuse leads to audio, info window, roof lights, bagage light, power windows, and remote key. The current here was 30mA.

    I had the drivers door open when I measured the fuses in the dashboard. Also, I probably had the ignition key in my pocket. The DOOR fuse leads to central locking system. The current here was 10mA. The ECU-B leads to a/c, running lights, powersteering, immobilizer, rear fog lights. I assume they mean to a control unit for those systems, since 7.5A seems a bit small for all those things. Anyway the current was 60mA.

    I got 60mA in total on the battery, not the 100mA that the above sums to. That could be that
    my multimeter is not accurate, or that there is some addtional draw when the drivers door is
    open.

    I'll get a new for fuse for the low A range for my meter :) and 600 Ohm resistor to check with.
     
    #4 anon61, Jul 3, 2012
  5. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Yes, I recall that my 2001 had a quiescent current draw of around 30 mA. The 2G is lower, around 20 mA or less.

    An excellent idea to use a known voltage and resistor so that you can develop a known current flow and compare to your meter reading.
     
    #5 Patrick Wong, Jul 3, 2012
  6. joedirte

    joedirte Member

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    I will warn you that measuring currents at different voltages than normal will result in weird readings. ie. the ECU will draw different current at 11.2V versus 12.6V. Each ECU probably has it's own voltage regulators down to 5V and who knows what is going on inside the MFD. So I just want to mention it is possible if you are checking a dead battery the current might be very large (and not some short) compared to the same system when it is at 12.6V or so.

    But this shouldn't apply to any of the lights which are linear with voltage..
     
    #6 joedirte, Jul 3, 2012
  7. anon61

    anon61 Junior Member

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    I measured the current with the start battery connected, at 11.7 volts. The DOME fuse had an initial flow of 70mA, but after a few seconds it went down to 30mA. I have recharged the battery, and it does not seem to be totally damaged.
     
    #7 anon61, Jul 4, 2012
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