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Parasitic drain - is 55 milliamps ok?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Charley Gosse, Mar 15, 2023.

  1. Charley Gosse

    Charley Gosse Junior Member

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    JohnPrius3005, yes, please let me know those Foxsur battery charger model numbers.
     
  2. rjparker

    rjparker Tu Humilde Sirviente

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    You have discovered that the easily replaceable fuses don't cover everything since your parasitic draw remains the same. The moderate capacity loss of your battery has nothing to do with causing the draw. If anything it is the result of the draw.

    The current is likely coming from the fusible links or the 5 amp fuse at the battery, assuming all normal fuses were removed. See attached where most of the fusible links are shown as triple fuse elements. They are actually single links, primarily in one big module.

    For example, one member found the eps electric power steering was a cause of parasitic draw. It has a fusible link.


    A7C1F995-302D-4DFF-B88F-038AAEBB8D39.jpeg 6409F5E3-67C1-485F-8BE7-A3F80EC2F4F2.jpeg
     
    #22 rjparker, Mar 18, 2023
    Last edited: Mar 18, 2023
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  3. Mendel Leisk

    Mendel Leisk Senior Member

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    This CTEK charger is roughly equivalent to what I'm using, near-constantly. Has worked well for me.
     
  4. JohnPrius3005

    JohnPrius3005 Active Member

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    FBC1207D 12V 7amp &-stage Smart Battery Charger. I use it on Moto setting - meant for small, motorbike bats. Amazon doesn't yield any results by model number. They are about $25 or less.
     
  5. bisco

    bisco cookie crumbler

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    if you'd rather not buy a charger, letting it sit in ready for 12 hours will work fine
     
  6. Charley Gosse

    Charley Gosse Junior Member

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    How do I test for these?!
     
  7. rjparker

    rjparker Tu Humilde Sirviente

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    Parasitic draws can be easy or they can be the most difficult of all auto diagnostics.

    Certainly 50ma should last several days and could be mitigated by constant use of a standby staged battery charger or by using a battery disconnect for longer durations. I would not like those solutions.

    An advanced method is to measure millivolts (mv) across individual fuses or fusible links. A draw will cause a very small mv voltage drop across the protection device. It requires a quality meter with high impedance. Not an analog (dial) meter or some cheap meter like the $3.99 Harbor Fright (Freight) or its clone. The fusible link module in gen2 is basically hardwired in but the plastic cover can be removed.

    Otherwise pulling connectors on the fusible link loads is the next order of business. This method requires good drawings from Alldata or the Toyota Information System (TIS). Both have costs and learning curves.

    Push come to shove, Pine Hollow Diagnostics in State College, PA might be worth a trip. He is one of the best specialists and has a youtube channel where advanced techniques are demonstrated. Sometimes he does road trips as well.

    In his latest video he runs down a similar draw using a custom wifi logger and mv tests. Other videos explain the mv method in more detail. He also hacks a solution for this customer without buying an $800 module.



    Be sure to wait for Bonus Footage he almost always includes after he signs off.

    While not exactly your issue, he sells a custom cylinder pressure sensor and in other videos, demonstrates logging starter current for electronic "virtual compression" tests. He also uses a pc based scope (picoscope) where he diagnoses variable valve and other timing or networking issues. He will use the wifi parasitic draw sensor to monitor intermittent draws over time. Sometimes he opens a bad module and repairs it.

    TIS
    https://techinfo.toyota.com/techInfoPortal/appmanager/t3/ti?_nfpb=true&_pageLabel=ti_home_page&goto=https%3A%2F%2Ftechinfo.toyota.com%3A443%2Fagent%2Fcustom-login-response%3Fstate%3DLTLZ0D3OC77sBJT4SwcvSOXlqHI&original_request_url=https%3A%2F%2Ftechinfo.toyota.com%3A443%2F
     
    #27 rjparker, Mar 19, 2023
    Last edited: Mar 19, 2023
  8. pasadena_commut

    pasadena_commut Senior Member

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    Also remember to try unplugging the brake related box which is right next to the battery. Several members have mentioned that it is often a source of parasitic loads.

    Regarding battery chargers - whichever model you get, be sure that when charging an OEM Prius 12V battery, the current in never exceeds 4A.
     
  9. Charley Gosse

    Charley Gosse Junior Member

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    Pasadena_commut, how do i unplug the brake-related battery next to the 12v battery? Is it the black box with the three white plugs? If so, which one?
     
  10. Charley Gosse

    Charley Gosse Junior Member

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    By the way, I charged the battery for 12 hours ending about midnight last night and this morning I got 12.62v when checking the car after it had been sitting dormant; I had left the hood open so I didn't need to wake up the car, following Mendel's suggestion. Mendel, you had said previously that 12.4-12.5 was iffy and 12.7-12.8 was 100% so at 12.62v what do you think? Keep this battery? I still haven't solved the paracite drainage problem, though.
     
  11. bisco

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    12. 6 is fine. measure again in the morning to see how much it's losing per 24 hour period.

    btw, 12.6 doesn't tell the whole story. only a load test can tell you if the battery is good or bad.

    you can try turning on the high beams and watching the voltage drop over 15 minutes, but that's a very simple test and not always enough load
     
  12. rjparker

    rjparker Tu Humilde Sirviente

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    12.6 is fine. The question is how long does it last? For battery validation it requires a load test, free at most auto supplies. But you are working the symptom and not the root cause.
     
  13. Charley Gosse

    Charley Gosse Junior Member

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    I have uploaded a photo showing the 12v in the rear hatch and what I think is the brake battery next to it and circled the one white connector I think you are suggesting I detach and then test, am I correct?
     

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  14. rjparker

    rjparker Tu Humilde Sirviente

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    Yes but it is supplied by the 15a ABS fuse you probably already pulled.
     

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  15. Mendel Leisk

    Mendel Leisk Senior Member

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    That module has constant-on power, solely to remember HVAC settings. In the "just have to vent" thread, I've been bemoaning the lack of ergonomic HVAC controls, which are typically mechanical. By default they "remember" what's set, basically because when you turn a dial or shift a slider, it stays where you left it, due to inertia, which doesn't require volatile memory, lol.

    Yeah interesting video, by revising the power to be ignition-on only, you have a system that goes back to (reasonable) defaults, a slight setback, but doesn't draw down the 12 volt.
     
    #35 Mendel Leisk, Mar 20, 2023
    Last edited: Mar 20, 2023
  16. Charley Gosse

    Charley Gosse Junior Member

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    I tested my 12v battery after it rested overnight and got 12.47v with my old meter and 12.43v with my new meter and then tested for milliamps, again in a totally quiet Prius, with the negative contact disconnected and with my old meter I still got 57 milliamps (first photo) but with new meter I got just 17 milliamps (second photo). Thoughts?
    IMG-0642.jpg IMG-0643.jpg
     
  17. pasadena_commut

    pasadena_commut Senior Member

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    Tens of mA currents are on the hairy low edge for what can be measured by a DC clamp meter. They are more often employed to measure much more substantial currents, which would burn up most inline ammeters. In order to measure a current that low accurately a clamp ammeter must be zeroed right next to the wire, with the jaws closed, and then the wire moved into the clamp, ideally without the meter moving at all. I could never do that with one of these battery cables, too thick, so had to move the meter. Anyway, since the newer meter returned the expected value, we should suspect inaccuracy in the older one. If you have access to a small battery and some resistors it isn't difficult to set up a wire with ~20mA flowing through it (measure the voltage on the battery and the resistance first so you know exactly what it should find) to test its accuracy. 1.5V and 75 Ohms would work for this test.
     
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  18. rjparker

    rjparker Tu Humilde Sirviente

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    Looks like the first meter was on ac amps rather than dc. But the second meter was using the 10 amp setting while plugged into the ma jack. So both have operator error.
     
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  19. Mendel Leisk

    Mendel Leisk Senior Member

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    Yeah 17 milliamperes is good, normal. (y)
     
  20. pasadena_commut

    pasadena_commut Senior Member

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    Good catch. It wasn't "on" AC amps, that model only does AC amps, and it only does it with the clamp, not the probes. There is no wire within the clamp in the photo. Relatively few clamp ammeters can also do DC amps. I use a UNI-T UT210E, which is about as low cost as it gets for a meter with this capability. Despite the reasonable cost, the UT201E is a pretty good meter with solid construction.

    Here is a review:
    https://lygte-info.dk/review/DMMUNI-TUT210E%20UK.html
     
    #40 pasadena_commut, Mar 21, 2023
    Last edited: Mar 21, 2023