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How much power does the USB port provide?

Discussion in 'Gen 1 Prius Plug-in 2012-2015' started by Eug, Dec 4, 2023.

  1. Eug

    Eug Swollen Member

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    I’m curious. How much does the USB port (in the storage compartment) provide in the 2012-2015 Prius Plug-in?
     
    #1 Eug, Dec 4, 2023
  2. fuzzy1

    fuzzy1 Senior Member

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    I can only say that in my 2012 Liftback (not a plug-in), my phone doesn't seem to gain any significant charge from the USB port, but just either maintains charge or drops slower. A USB charger plugged in to the adjacent 12V socket does much better.

    My impression was that the USB port in that era was built to an old USB standard, either limited to 100 mA, or unable to handle the handshake signals necessary to permit my device to turn up to higher current. But I don't know the real story.

    Do note that all the high power USB charging standards were released after this model's hardware was designed or specified, so it just can't do much. So if you want any decent amount of USB power, your best option is to use a much younger 12V-to-USB converter labeled for the amount of power you need.
     
    #2 fuzzy1, Dec 4, 2023
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  3. Tideland Prius

    Tideland Prius Moderator of the North
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    My best educated guess is 2.1A.
     
    #3 Tideland Prius, Dec 5, 2023
  4. Eug

    Eug Swollen Member

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    I was testing this over the last couple of days and it will charge, but it's slow. However, if I have the phone on with the GPS app running, it mostly just maintains charge. I didn't test it long, but if it does charge, it's really, really slow. This is with the iPhone 12 Pro Max.

    I found my old USB 2 port monitor thingy and did a measurement. It's only 1 A.

    It's 5.17 V / 0.00 A when nothing is plugged in, and 4.87 V / 0.95 A with the iPhone plugged in. So basically it's just under 5 Watts, which is roughly the same as the old iPhone 5 Watt charger.

    Here is a test of the of the iPhone 12 Pro with various chargers:

    Apple iPhone 12/Pro 18W vs 20W vs 5W vs MagSafe adapter charging speeds - PhoneArena

    20 W adapter wired: 118 minutes
    20 W adapter MagSafe: 176 minutes
    5 W adapter wired: 187 minutes

    This didn't see right to me, as the MagSafe charging time was too close to the 5 W adapter. So here is another test of the iPhone 12 non-Pro:

    iPhone 12 chargers tested: 5W vs MagSafe vs 20W | Tom's Guide

    20 W adapter wired: 57% charged after 30 minutes
    20 W adapter MagSafe: 32% charged after 30 minutes
    5 W adapter wired: 21% after 30 minutes

    MagSafe did better here, but MagSafe at 15 Watts is still closer to the 5 W charger in charging speed. Lots of wasted energy there.
     
    #4 Eug, Dec 5, 2023
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  5. fuzzy1

    fuzzy1 Senior Member

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    When I went to work at a place making heavy use of USB in new product designs, the latest and greatest standard had just moved up from USB 1.1 to 2.0. See this convenient chart:

    USB - Wikipedia (#Connector_type_quick_reference)

    When the refreshed 2012 Prius was introduced, the latest and greatest standard was USB 3.0. According to this chart, it was defined or rated for only 0.9 A / 4.5 W (I don't have independent knowledge that this Prius was designed to 3.0, but Eug's measurement is consistent with this):

    USB - Wikipedia (#Power)

    If I'm interpreting this chart correctly, the USB Battery Charging standard at that time allowed up to 1.5 A / 7.5 W, but did not have data capability, whereas we know the Prius USB is meant to carry data:

    USB - Wikipedia (#Power-related_standards)

    The first USB Power Delivery standard was introduced in July 2012, too late for the last Gen3 Prius redesign which was already set and on the market. Any better performance in the Prius would have to wait until Gen4 (2016).

    Drivers can't easily upgrade the old car's built-in USB to modern higher power delivery standards. But they can easily buy a newer 12V-to-USB converter that does deliver higher power, and just plug it into the 12V socket.
     
    #5 fuzzy1, Dec 5, 2023
    Last edited: Dec 5, 2023
  6. Eug

    Eug Swollen Member

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    Maybe they just mirrored the common 5 V x 1 A that was used for numerous different USB-A phone chargers at the time. As you say, USB supported up to 1.5 A by then, and that did not require USB 3.

    The reason I was looking into this is because twice now while I was using my 12 V USB-C adapter with USB-C MagSafe charger, the "Check PCS System" warning came on. The first time that happened, nothing would fix it... until I unplugged the 12 V charging adapter.

    I drove a while without it and it ran fine for several days. and so then I plugged the MagSafe charger back in and it still worked fine... for several days and then the "Check PCS System" warning came back on again. So I unplugged it and warning stayed for a bit but finally disappeared, and hasn't come back since after many days, including when I plugged the phone into the USB port in the storage compartment.

    Sometimes this PCS warning (and the "Check Hybrid Battery" warning) may occur with a weak 12 V battery. In my case I had a recent collision that caused the hazards to stay on, draining the battery. The mechanic had to recharge it separately and it worked after that but the full drain and recharge cycle may have lessened its capacity.

    In the service menu the battery reads 11.8 V, but I tested the battery with a volt meter and it says 12.45 V, so at least the latter reading seems fine. Nonetheless, I wonder if my battery is sub-par now and is having problems with higher draw phone chargers. For the next little while I will continue to use just the 5 Watt USB port instead of a 20 Watt car adapter and see what happens.
     
    #6 Eug, Dec 5, 2023
    Last edited: Dec 5, 2023
  7. The Tramp

    The Tramp Italian Prius Expert

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    1A (5W). Just enough to keep the phone alive.
     
    #7 The Tramp, Dec 5, 2023
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  8. Eug

    Eug Swollen Member

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    Yep. Confirmed with my own measurement above.
     
    #8 Eug, Dec 5, 2023
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