Parasitic current draw.

Discussion in 'Gen 2 Prius Technical Discussion' started by Don Holtz, Jun 19, 2020.

  1. Don Holtz

    Don Holtz New Member

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    Hello,

    I'm working on a 2005 Prius which has an intermittent problem that causes the 12V battery to drain in a couple days.

    My question is a simple one, what is the typical parasitic current draw on the 12V of a Gen 2 vehicle?

    I've measured it with an in-line ammeter with everything off, doors closed and locked, all lights off (including in trunk, etc.), SKS key far away, and a waiting time >20minutes so that everything is shut down. Battery is in good shape.

    I need to know an actual measurement value, please.

    Thanks,
    Don
     
  2. sam spade 2

    sam spade 2 Senior Member

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    I don't have access to the exact information that you are asking for.

    Are you aware that a failing battery will "self discharge" when not in use at a rather rapid rate ?
     
  3. Don Holtz

    Don Holtz New Member

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    Yes, thanks. I am aware of that. That is not the problem in this case.

    As I said, I want to know what the parasitic drain should be as actually measured on other normal Prius vehicles.

    Thanks.
     
  4. edthefox5

    edthefox5 Senior Member

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    One of the battery drain suspects is the brake power back up box. It a box full of caps that hold enough charge that if you lose power you should have enough to do some braking. Its the vertical box metal box that's right next to the 12 volt battery. The box could have some corrosion or the caps have dried out and are now esr'ing.

    But almost everyone who comes on here thinking they have a phantom power draw usually just have a bad 12 volt battery that has become sulphated or they do not drive enough to properly charge that battery. You have to drive a significant distance to charge the 12 volt battery.
    Like 10-15 miles a day hopping around town for 20 mins wont do it.

    Almost everyone who comes on here does not own a modern battery charger with recondition mode that they put on there battery regularly to see how it does. .

    Hope your not saying the dealer tested the battery as the dealer is incapable of testing a 12 volt battery based on what i see here.
    if you own a DC voltmeter theirs a simple test you can do to see how capable the battery is.

    A healthy 12 volt battery should be at 12.6 volts at the front jump points with the car off.
     
  5. Don Holtz

    Don Holtz New Member

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    Hi edthefox5,

    Thanks for responding. I've read in various other threads that the capacitor bank can be a potential current draw problem.

    Before I head down that road though, I need to know, for reference, what other people are actually measuring as their normal parasitic current draw. I've searched high and low for an actual specification but can only find vague references to 20mA, 50mA, etc. I need an actual number that someone has measured on their vehicle.

    Thanks,
    Don
     
  6. davecook89t

    davecook89t Senior Member

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    I remember someone on here saying it should be no more than 30 milliamps with everything turned off.
     
  7. Mendel Leisk

    Mendel Leisk Sand Pounder

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    On a 3rd gen I measured 16~18 milliamperes with spikes (every 5 seconds or so) to around 40~45.
     
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  8. Don Holtz

    Don Holtz New Member

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    Do you happen to remember where that value came from? Was it an actual measurement or just a rule of thumb?
     
  9. dolj

    dolj Senior Member

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    Just got to love people who have never even owned a Prius Gen 2 hijacking every thread that mentions "battery" and offer often irrelevant information that derails a thread. I have seen pages and pages of irrelevant and often semantic nonsense clutter up a thread. Sheesh! Interestingly, they never seem to have the direct answers to the question(s) asked, but rather just go off on their own hobby horse. Anyway, I digress, sorry about that.
    Mendel's Gen 3 information (in this particular case) is pretty close. I would guess that the spikes would be the SKS waking to check if there is a fob nearby. On a Gen 3, I believe this SKS activity will automatically shut down after a number of no-fobs hits (or is it after a time period, I have no idea) to reduce the quiescent draw. In the Gen 2, there is a "Key" button below the steering column that, when pressed in, disables the SKS function to achieve this same objective. Another press toggles the button to the out position to re-enable the SKS function.

    To put into perspective what is the effect of the quiescent current draw and out of interest I conducted a little experiment when required to isolate for COVID-19 and after reading of so many 12 V battery woes.

    By way of background
    • The car is a non-SKS Prius with a 6-year-old 55 Ah AGM battery that is in very good condition.
    • The car had the hatch open, but all interior lights were switched off.
    • The "Door Open LED" was illuminated.
    • This battery has had a lot of love.
    • The battery was still connected to the car.
    The experiment parameters were reasonably simple.
    1. Charge up the battery to full.
    2. Bleed off the surface charge, then let it sit for 30 min.
    3. Measure the voltage across the terminals.
    4. Measure the battery again after 3 weeks.
    Results:

    Initial reading 13.1 V
    After 3 weeks 12.9 V

    This is obviously not a double-blind study nor even a statement that every battery/Prius combo should act this way. It is, however, an observation and documentation of something that really happened.

    Is it a placebo effect? No, because I really expected that the battery would drop more, so I was pleasantly surprised.

    Leeming effect? No, I never read of any other similar experiment, so I had no preconceived ideas at what outcome to expect.

    Result of hope or any other psychological effects. No, I went into this out of interest and with no preconceived idea to the outcome.

    Is it anecdotal? Sure, but hey, I think it is useful. YMMV.

    I hope others find this as interesting as I did.
     
    #9 dolj, Jun 20, 2020
    Last edited: Jun 20, 2020
  10. ydpplqbd

    ydpplqbd Active Member

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    When I get a chance later today, I will measure draw on my 12V in my 2006 Gen2. And then get back with the info for this posting.
     
  11. TMR-JWAP

    TMR-JWAP Senior Member

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    @Don Holtz

    On my 2007 Prius:

    I used a Fluke 115 with heavy gauge alligator clips leads.
    I connected one alligator to the 12v battery positive terminal clamp. The other lead was connected to about 20' of doubled up 16ga speaker wire that I terminated at the underhood jump point. Once it was all connected, I unplugged the large and small car harness plugs at the positive terminal assembly so all current would pass through the meter.

    With my meter outside the car, trunk closed, interior lights in off position, hood closed. After few moments, it was showing 70-80 ma and after several minutes, the meter was oscillating between 21 and 24 milliamps. If I did it with the trunk open, it was in the 500-700 range.
     
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  12. Mendel Leisk

    Mendel Leisk Sand Pounder

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    Yeah I had hatch closed, leads connected between neg cable (connected to battery post) and ground. Ran leads out hatch threshold, closed hatch on them. Waited about 20 minutes, fob away, other end of the house.
     
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  13. sam spade 2

    sam spade 2 Senior Member

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    And we have seen hundreds of posts from members here complaining about other members......which sometimes stirs up really nasty feelings......as opposed to people who offer a few well meaning comments and cause no real trouble at all.

    If you were REALLY sorry, you would CUT THE CRAP.

    Even the rest of your post contained a LOT more useless information that all of the other well meaning posts combined.

    Pot.....kettle.......BLACK.
     
    #13 sam spade 2, Jun 20, 2020
    Last edited: Jun 20, 2020
  14. davecook89t

    davecook89t Senior Member

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    Rule of thumb. Others have since provided more specific information. I would think if you are seeing more than 30 milliamps consistently you would want to investigate further, otherwise maybe not.
     
  15. Mendel Leisk

    Mendel Leisk Sand Pounder

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    What measurement did you get?
     
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  16. Albert Barbuto

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    Don, I also have a 2005. I've measured by undoing the positive cable at the battery, and letting the current flow through the meter. 16 to 18ma is the magic number. Open the hatch, with all lights switched off, and it will be just a tad under 500ma.
     
  17. Don Holtz

    Don Holtz New Member

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    Hello folks,

    I've done some more current measurements with my Prius in the off state, key fob far away, 20 min sleep delay, etc.

    My vehicle consistently draws ~50mA to ~80mA all of which is on the dome fuse circuit. It constantly varies with a period of a second or two. I was hoping to see <20mA as Albert Barbuto measured (thank you for that Albert!).

    I have further measured the current draw of various components that are connected to the dome fuse circuit. The budget that I see is:
    • 20mA-50mA (varying) supplying the Smart Key ECU on pin 1 (S11 on the Toyota wiring diagrams, also known as certification ECU)
    • 25mA (constant) supplying an aftermarket iPod interface device that was hidden under the dash near the radio.
    • 5mA (constant) for all other components connected to the dome fuse circuit.

    So, ignoring the current taken by the iPod device, my Prius has a draw of 25mA to 55mA which is much higher than the normal <20mA.

    I think the Smart Key ECU is not going to sleep properly. Does anyone have any ideas why this might be happening?

    I'm thinking about disconnecting Smart Key related devices like the oscillators. My thought is that if one of them is malfunctioning they could be keeping the Smart Key ECU awake. Then again, maybe having things disconnected might be keeping it awake? It would be nice to have some detailed information about this ECU and how it plays with other parts of the system.

    Thanks,
    Don
     
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  18. dolj

    dolj Senior Member

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    This actually sounds about right. Look to see if the iPod accessory can be made to power off when the car is IG-OFF. Otherwise, you are stuck with it. It is, in and of itself, reasonably insignificant.
    Maybe, but I'm not so sure. In the Gen 2, the SKS does not fully quiesce, so there is an SKS disable button (marked 'Key') below the steering wheel that you can press in to disable the SKS exactly for this reason. The owner's manual advises disabling the SKS any time the car is not being driven for an extended period.
     
    #18 dolj, Jun 30, 2020
    Last edited: Jun 30, 2020
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  19. Don Holtz

    Don Holtz New Member

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    Hello dolj,

    On my vehicle, the current draw of the Smart Key ECU of 25-55mA doesn't change when the SKS enable/disable switch is toggled.

    I'm going to look at it more today to see what else I can figure out.

    Thanks.
     
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  20. dolj

    dolj Senior Member

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    Interesting. I'll be watching to see how this turns out.
     
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