Creating a home office in my car

Discussion in 'Gen 2 Prius Technical Discussion' started by Kent Hinson, May 28, 2019.

  1. PriusV17

    PriusV17 Active Member

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    I use Dr. Prius app to check the HV status using a bluetooth ODB2 reader. It can be checked in Ready mode or in 12v mode (where you just press the Power twice w/o stepping on the brake). The 12v mode can drain the 12v battery fast. I had to jump my car a few times because of that. To get the watt usage I multiply amp times voltage. In the screen shot, just sitting still in Ready mode consumed about 211 watts. When the AC is on the amp jumps to 3 to 4 amps (600-700 watts). I think Torque Pro app can provide same info. Dr Prius is free.

    I don't plan to charge my v on a regular basis. I want to be able to have a charger available in case I need it. Like if the HV pack drains for any reason and I need to bring it back up. For now I've been running tests.


    Screenshot_2018-07-19-16-11-03.png
     
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  2. Kent Hinson

    Kent Hinson New Member

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    Thanks for the info! I ordered a obd 2 adapter yesterday but was unsure what app to use. I'll check that one out :)
     
  3. Kent Hinson

    Kent Hinson New Member

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    Got my OBD2 adapter today. Looks like my car pulls 4.95a if I set the AC to full blast (LO instead of a set temp and full fan).

    I found a 250v 4a power supply for $180 on ebay. :)
     

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  4. Kent Hinson

    Kent Hinson New Member

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    That's great! Sorry somehow I missed this message.
     
  5. kevin.c

    kevin.c Member

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    Not sure this is a good idea. Rather than constant voltage, I think you need a constant current mode (where the power supply output voltage tracks the battery voltage, like a charger).

    To give a real world example, Gen 3 priuses simply attached the aux battery to a 14V constant voltage power supply when the car was running. Those batteries’ lifetimes were shorter than expected given the easy loads. The gen 4 aux DC/DC is fancier which improves the longevity.
     
  6. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    Hey, I don't know if it's a good idea either. I do know that we'll never find out unless somebody takes the risk to experiment a bit.
     
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  7. Landon51

    Landon51 Member

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  8. landspeed

    landspeed Active Member

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    My ongoing exploration of the BMS explains this:
    The BMS remembers what the state of charge of the battery is; it uses 'coulumb counting' to do so. My traction battery is quite worn, and has perhaps 50-75% the capacity of new (haven't checked it properly). The BMS calculates the 'state of charge' and reports this to the rest of the car. The state of charge displayed on the screen is based upon the state of charge that the BMS reports.

    On my car, if I use 'EV' mode until the battery is drained (I don't recommend doing this regularly, but is useful for exploring the BMS with realtime diagnostics running), I end up in a situation where the battery is charging, but the state of charge is dropping. The same happens if I really drain the battery and then go down a big hill - I can end up with a situation where the battery is 'discharging' (putting out power), but the state of charge is still rising.

    I don't have the code from the BMS yet, but essentially, the BMS has something like this, somewhere in the code:

    loop:
    (calculate the actual SoC) - this can change suddenly to 'low, 1-2 bars' if one cell drops voltage and is in danger of reverse charging a cell.
    (shift the *reported* state of charge to the *actual* state of charge) - do this at a rate of maybe 1%/second (approximately).

    Basically, on your car, 2 bars is anywhere from maybe 36-45%; when you charge it, it might end up at 80% (full battery). It would seem to 'slowly' top up once the BMS goes online and finds all the cells at a higher voltage.

    The code is more complicated; for example, when my BMS is deciding to 'lower' the reported SoC, I have found that it likes to leave it unchanged, but then drop at the 'max' rate when I am driving on electric - including if I am using only 200 watts of power through MG2, for example. This is likely to make the display less confusing to the user.

    This also explains why the SoC goes through periods of 'charging' even when the engine is off, and discharging for no reason, when there are battery problems; the BMS decides the SoC is 40% all of a sudden, when it thought it was 60%. This would go from 'full blue bars' to '1 bar', but rather than an instant switch, it lowers the reported SoC gradually.
     
  9. PriusV17

    PriusV17 Active Member

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    After running some test. My conclusion is. DO NOT charge the Prius HV battery on a regular basis. Why?

    1. The hybrid system (at least for my v) will not recognize the new packs charged voltage and will keep charging it for some reason. Even to FULL and it still will not show up as full on the bars. The bars can literally stay at 2 while the pack is completely full. So there is something out of sync and this can be unhealthy to the battery if keep overcharging. I have charged it to 228v. Then let the system handle itself and find that it goes to 240v which is considered full but only 2 bars still show up.

    2. This out of sync stuff will only create uncertainly as to what is happening. And it can stress the battery long term. Because it is dropped low and then pushed back up high. Which can reduce long term hv battery life.

    So my conclusion is not to charge the pack and just let the hybrid system do it's own thing. The hybrid system will try to keep the pack optimal at about 60-80 charge.

    My hunch is that there are really 3 main batteries. The 12v, the hv (200v) and then there is the inverter battery. The inverter batteries not being in sync w/ the hv pack battery may explain why the bars don't match up. So the hybrid system is trying to charge the inverter battery pack(capacitors) and at the same time the hv pack. Until the bars are matched. Which can lead to the hv pack being overcharged.

    inverter.jpg

    Also the 250v charger that was found on ebay is on the dangerous side and is considered VERY overcharged should the pack go there. You want to keep it within 60-80 for longer lifespan of the hv pack.
     
  10. bisco

    bisco cookie crumbler

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    there is no inverter battery. there are fob batteries though.

    if you are running the a/c, and charging the battery, and the car is also running the engine to charge the battery, it could be catastrophic.

    i would check my life and home insurance
     
  11. Skibob

    Skibob Senior Member

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    My opinion is you need a 5 amp supply if you can use up to 4.95 amps. Although the 4 amp would work it would draw the battery down during high drain situations then recharge it when the drain is less. You would be cycling the battery. If you go with a constant voltage set just below what you normally park at the power supply will just be a second faucet, a supply to replace the battery and the computers would be none the wiser. Just like having a super big battery.
     
  12. Kenny94945

    Kenny94945 Active Member

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    Wow, what a story.
    I guess the OP is saying not a home office, but a spot for his laptop work.
    Using their Prius for the seat, air conditioning and maybe sound proofing/ isolation.

    Rear seat of a Maybach, Rolls or Bentley might be more roomy and those cars include foot rests and massaging seats. haha.

    Home office to me means copier, fax, computer, printer, calculator, coffee maker, executive secretary (haha) and etc.
    Plus heat, cooling, running water, toilet.

    In for the result !

    FWIW I'd think a portable shed/ tent with an AC power generator and air conditioning etc would be a better idea than the interior of a Prius, yet what do I know, OP may be onto something.
     
  13. landspeed

    landspeed Active Member

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    Thinking about it, the safest ‘home office in a Prius’ would be to get a mains portable air conditioner and use that to lower the temperature, since you will be near the mains anyway. A small fan can circulate the air when air con isn’t needed, and you can use the portable air con wherever else you need it, too!
     
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