Using 12v battery to run small air pump

Discussion in 'Gen 4 Prius Main Forum' started by RoadNoise, Nov 8, 2018.

  1. RoadNoise

    RoadNoise Active Member

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    Just purchased an air pump that uses the lighter socket for power. Thinking this little compressor likely pulls a fairly heavy load, I was concerned it could deplete the charge of the 12v battery while topping off all 4 tires. So I put the car in "ready" mode before pumping and later noticed the hybrid battery had drained by 2 ticks. This led me to believe the 12v battery gets its charge from the hybrid battery, and "starting" the car before pumping was the correct way to handle this, right?
     
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  2. bisco

    bisco cookie crumbler

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    exactly, well done(y)
     
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  3. Since2002

    Since2002 Senior Lurker

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    If you are in an enclosed space like a garage you can also use ON mode which you get to by pressing the power button twice without stepping on the brake. ON mode also draws from the hybrid battery but it will keep ICE from coming on. The next time you go into READY mode the hybrid battery will be recharged from ICE. Just keep an eye on the battery level while you are in ON mode to make sure it doesn't get near the bottom, although just airing up your tires shouldn't be a problem.
     
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  4. alanclarkeau

    alanclarkeau Senior Member

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    I've got one too. I "START" my PRIUS before using it, turn off Climate Control, and I've not noticed it changes the hybrid battery level - it only takes maybe 30 seconds on each tyre if that.

    Just don't leave it in "N" - as it doesn't recharge the 12v in "N".
     
  5. Elektroingenieur

    Elektroingenieur Senior Member

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    The engine won’t start in ON (Ignition ON) mode, but the hybrid battery is isolated. The three system main relays that connect it to the inverter with converter assembly are closed only when the hybrid system is in READY.

    See the HV Battery High-voltage Line Circuit and Terminals of ECU pages in the Hybrid Control System section of the Repair Manual (more info). Keep in mind that the service literature uses the term “on (IG)”—as opposed to “on (READY)”—for the state described in the Owner’s Manual as “ON mode.”
     
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  6. Since2002

    Since2002 Senior Lurker

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    I was apparently misinformed in the past, and also thrown by the owner's manual stating that the power shuts off after 20 minutes in ACC mode but after one hour in ON mode, which seemed to affirm that ON mode was powered by the traction battery, especially since ON mode uses more power than ACC mode since a bunch of other things are powered up when in ON mode. If ON mode is powered by the 12V battery you would think it would be reversed and that it would shut off sooner in ON mode than in ACC mode.

    That being the case that ON mode is powered by the 12V battery, then in the situation of powering 12V devices in an enclosed garage it would be better to use ACC mode even if it does shut off sooner. Obviously I'm not talking about running a compressor for more than twenty minutes, but some people use the 12V socket to charge their phone, power a radio etc.
     
    #6 Since2002, Nov 9, 2018
    Last edited: Nov 9, 2018
  7. Mendel Leisk

    Mendel Leisk Lapsed Cargo Cultist

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    Seems like the safest bet is to have the car completely on, aka "ready", to avoid running down 12 volt battery.
     
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  8. Since2002

    Since2002 Senior Lurker

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    Yes definitely when outdoors. I was referring to being in an enclosed garage. Although realistically I'm not in that situation very often. About the only time I need to turn on the car in the garage is to raise or lower the windows, maybe get a mileage reading, reset the oil change warning, etc. I have a battery powered tire compressor that I keep in the car, but in the garage I have an AC powered tire compressor that I use. If I was using the battery powered compressor in the garage I would open up the garage door and use READY mode. But for quick things things in the garage I generally use ON mode. And actually, if I'm outside and I just need to raise the windows or something I will probably use ON mode to avoid the gas engine coming on. Although in that scenario the engine would be on very briefly so it wouldn't make that much difference either way.
     
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  9. alanclarkeau

    alanclarkeau Senior Member

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    Yes, particularly with modern cars which have much cleaner exhausts than in the past.

    A European Parliament document states "... Since 1970, the level of pollutants, such as hydrocarbons, carbon monoxide, nitrogen oxide and particulate matter, produced from vehicles has been reduced by around 99%. ...".

    Safety first obviously, but the chances of the ICE firing up for the couple of minutes pumping tyres up are little, particularly if you turn the Climate Control OFF immediately you hit POWER. I generally find that I've opened the garage door if I'm working inside, mainly to give me better light.
     
  10. kithmo

    kithmo Couch Potato

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    Am I the only one who never needs to pump their tyres up ?
    Every time I check mine, cold, once a month, they are spot on.
    Could it be down to my low mileage, short journey, use ?
     
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  11. alanclarkeau

    alanclarkeau Senior Member

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    I checked mine last week or so - was at least a month or 2 since last time - they were fine. It's only after going to service that I need to adjust them, as they never seem as careful as I am.
     
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