Radio Draw on the Drive Battery

Discussion in 'Clarity' started by CIvan, Apr 30, 2021.

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  1. MrFixit

    MrFixit Well-Known Member

    So, I had to google "Reserve Capacity"....
    It looks like that is how long a fully charged battery can run a 25A load before it drops below 10.5V.

    So, for a fresh battery, the Clarity should be able to operate a 5 Amp load (Accessory) for 5 * 85 = 425 minutes (~7 hours).

    OK, not forever... Use "Ready" if you want to be safe. And carry a jump pack to be double-safe (don't forget to charge it occasionally) !
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  3. Keep in mind that deep cycling a starting battery is a great way to murder it. While our 12V battery doesn’t start an engine, the battery is designed to provide a quick burst of power and then be quickly recharged and kept fully charged.

    If one chooses to run 12V accessories in Accessory or On mode, I’d advise to either put the car in Ready mode or plug the car in to charge afterwards, to ensure the 12V battery gets fully recharged.
  4. Earl

    Earl Active Member

    I'll hypothesize that the GOM that the OP used is probably not the best way to estimate battery power. Remember that it measures WH/mi. If you aren't driving "mi" = zero, thus throwing that figure of merit estimation off.
    However, while I'm sure the radio doesn't draw more than maybe 5 watts (~2800 hours of operation or ~4 months with a 14 kWh battery), there are likely other computers and systems that may be on when the radio is on that could draw a lot more power. You might only be able to run the radio for one month without having to take action :)
  5. MrFixit

    MrFixit Well-Known Member

    As identified in Post #17, we seem to be stuck with ~250 Watts when the vehicle is in "Ready" mode (the only way to operate accessories from the HV battery). As such, the 14 kWh battery would only last 56 hours. Of course, the ICE will kick in and prevent complete depletion.

    Yes, the radio is undoubtedly a few watts at best, but you have to burn 250 W just to get it turned on, and operating from the HV battery system !
  6. 665B8D1A-030C-48D1-99AC-84350027D586.png The audio system is specified as 180W of mind blowing, acoustical magic. Surely none of us could withstand such power and live to share the experience with others. Even at idle, turning on the audio system on a modern car turns on much more than the AM/FM radio in a 1972 Chevelle. We could listen to Paul Harvey and Casey Kasem for hours with that Sears Die Hard under the hood.

    In Ready mode, everything is powered, including the DC/DC converter, so a couple hundred watts makes sense.
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  8. MrFixit

    MrFixit Well-Known Member

    Audio spec's have been bizarrely overstated for decades.
    If the infotainment center really could produce 180 watts, I'm sure all the speakers would instantly burn up.
    People don't appreciate that several watts can be uncomfortably loud.
  9. Well, there’s 180w at 12V and then there’s 18w at 120V. Same same.
  10. MrFixit

    MrFixit Well-Known Member

    Audio ratings are always the output power (to the speakers). 180W is 180W regardless of whether the prime input is 12V or 120V.

    You are somehow conflating watts and amps. 180W @ 12V requires 15 Amps. 180W @ 120V requires 1.5 amps.
  11. No conflating. Just basic electricity.

    The system can consume 180W at 12V, presumably at full volume, hence the 15A fuse. You would be mistaken to believe that output would be the same from a 180W home system operating on 120V.
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  13. MrFixit

    MrFixit Well-Known Member

    No -
    A 180W Audio system is rated for an output power of 180W, not input power. It will deliver 180W to the speaker. If it is for a car, then it will run on 12V @ 15A. If it is a home setup, then it will run on 120V @ 1.5A. In both cases, 180W is drawn from the source and delivered to the speakers.

    (ignoring inefficiencies)
    Last edited: May 1, 2021
  14. petteyg359

    petteyg359 Well-Known Member

    Only if the volume is all the way up at maximum, and I very seriously doubt anybody ever does that.

    The "dial" goes up to 40. I usually find 10 is the loudest comfortable volume. Assuming the scale is linear, and that it really can produce 180 watts, then that's only 45 watts. Perhaps less, if 180 is an inflated measure, or a lot less if the scale is logarithmic.

    Then what you're listening to comes in. Is it people talking on NPR? Then there's a lot of cumulative silence between words, so the average output goes down. Is it classical music? Then the volume probably varies a lot throughout the piece. Only bad pop "music" tends to be a constant static volume level.
    Last edited: May 4, 2021
  15. PHEVDave

    PHEVDave Active Member

    The 180 watts is likely a peak rating and the system likely has that capacity. The speakers would not be able to dissipate all of that wattage continuously, for sure. But, for very brief periods they can handle it. The real benefit of a peak rating that is that high is that your system has plenty of headroom to reproduce instantaneous peaks thus preventing excessive distortion in the audio (clipping).
  16. PHEVDave

    PHEVDave Active Member

    Except that generally speaking you cannot drive a typical 8-ohm speaker with 180 watts of power at 12 volts. A DC load of 8 ohms across 12 volts only draws 18 watts. It’s true that with AC signals (audio) it’s more about the impedance than it is the resistance but, still, it’s pretty much impossible to dissipate 180 watts from a speaker driven with no more than 12 volts.
  17. PHEVDave

    PHEVDave Active Member

    And the audio level control is definitely not linear. It is logarithmic. For every 3dB increase in audio level, twice as much power is needed to reproduce it. So, for instance, if it takes 1 watt of audio power to reproduce the sound of a car honking in traffic (80 dB) then it would take 1,024 watts to reproduce the sound of a concert or loud sporting event (110 dB). This gives you an idea of why headroom is so important in audio systems in order to correctly reproduce sound.
  18. quiet-cheese

    quiet-cheese New Member

    That's pretty similar to my case. If I read the HV battery power output from the OBD2 port, ~220 watts seems to be the range with all lights off and fan off. audio system probably just a tiny portion of that ~220 watts because i don't see any watts drop when the screen or the audio system is off. (which make sense, the audio system seems pretty much just an Android table. maybe drawing ~10-20 watts at most)
  19. quiet-cheese

    quiet-cheese New Member

    Here's some data I have over the 12v battery voltage measured by a multimeter.

    12.43 V - car off, no plug
    14.51 V- car ON, READY to drive, HV battery charging the 12V battery
    13.27 V - car off, but plugged in, maybe 12V is also being charged in this mode, but just not as fast as when the car is in ready mode
    13.30 V - car ON, plugged in (not in READY because the plug is connected, no AC/heater/electric power steering), very similar to "car off, plug in", so i am assuming it is still charing the 12V battery.

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