A new journey with my 2005 Prius

Discussion in 'General' started by Ophbalance, Jan 18, 2017.

  1. S Keith

    S Keith Well-Known Member

    I repeated the above and left them connected for 22 hours.

    Both settled at 7.93V at the time of disconnect, i.e., resting voltages for BOTH modules was 7.93V.

    2013 module: 1161mAh (17.9% SoC)
    2007 module: 2468mAh (38.0% SoC)

    The 2013 module was EMPTY - no usable capacity left - 0% SoC
    The 2007 module was charged to about 61.5% SoC - right where the Prius tends to keep them.

    After 22 hours there is still a 20% SoC different between those two modules. That is terrible. Given that there was essentially no change between 2 hours and 22 hours, it's hard to imagine that leaving these connected for even a week would do anything more.

    Now imagine paralleling an entire packs worth of modules with not 4000mAh of difference between them, but maybe 1000mAh or more or less. I expect LITTLE transfer would occur between modules.

    I'll try one more experiment to test that. I've charged 2013 with 1340mAh (20% SoC) and 2007 with as much as I can before it starts swelling (4250mAh). 2013: 8.13V, 2007:8.41V

    Strapped together and we'll see what happens in 22 hours or so.

    I'll admit I'm a little tickled by this. I've always told people this was a waste of time. Now I have the data to prove it. :)
     
    Last edited: Jan 21, 2017
  2. Ophbalance

    Ophbalance Administrator Staff Member

    Does the Turnigy also measure mAh?
     
  3. S Keith

    S Keith Well-Known Member

    Yes. Charge input and discharge output (capacity) are reported as mAh. Most chargers/dischargers developed for RC hobby batteries do the same.
     
  4. S Keith

    S Keith Well-Known Member

    And after 23 hours, the verdict is:

    Starting voltage for both modules: 8.03V
    2013 capacity: 1783 mAh (27% SoC)
    2007 capacity: 3225 mAh (50% SoC)

    The closer they are in state of charge, the less they transfer to one another. Current transferred between modules with similar voltages and relatively large SoC differences will NOT become "balanced" by putting them in parallel.

    About 16 hours into it, I briefly disconnected them and put an ammeter in series. I'm not sure I interpreted it correctly, but on the 200uA scale, it read... 6

    As in 6 micro Amps. 0.000006A of current was flowing between them. That's not going to transfer squat. All transfer occurs very quickly before the voltage stabilizes between the two modules, and then current flow is clamped to near nothing.

    Conclusion: paralleling modules to equalize voltage only yields a placebo effect. While the voltage may remain very similar at rest, the moment they are used in charging or discharging, their differences in SoC will obliterate any illusion of a similar voltage.

    The practice is a complete and total waste of time.

    Steve
     
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  5. Jay

    Jay Well-Known Member

    I don't understand the need for charging and discharging and charge-balancing a new cell. Your traction battery pack should have charge-balancing circuitry for each cell. No?
     
  6. S Keith

    S Keith Well-Known Member

    Prius packs are NiMH, not Lithium.
     
  7. Ophbalance

    Ophbalance Administrator Staff Member

    Nothing but waiting for equipment for the present. The Turnigy will be here Weds. The power supply may be here by Friday, but I've not yet seen a ship notification. Luckily the rain stayed away on the commute today. I might end up picking up something neoprene based to make sure the work laptop remains dry in all situations.
     
  8. Ophbalance

    Ophbalance Administrator Staff Member

    Well the Turnigy decided to come in today. Still waiting on the PSU.
     
  9. S Keith

    S Keith Well-Known Member

    Heh... It's crazy how fast they ship from Hong Kong. I'll get the leads in the mail tomorrow. USPS is cheap, and they should be there by Thur/Fri.

    Steve
     
  10. Ophbalance

    Ophbalance Administrator Staff Member

    Sweet! In this case it came from Ohio. But it is brand new.
     
  11. Ophbalance

    Ophbalance Administrator Staff Member

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  12. Carcus

    Carcus Well-Known Member

    While your back there... I'd be curious to know how dirty the cooling fan is.. (i.e. is there a lot of buildup on the blades, reducing efficient airflow?)

    Reading through priuschat,.. seems like there are just a handful of reasons why the battery might fail "early"...
    - excessive heat (i.e phoenix, south texas)
    - hilly terrain (excessive cycling)
    - cooling fan capacity reduced (i.e. dirty fan (pets?)
    - infrequent use of car (sits for weeks/months)
     
    Last edited: Feb 9, 2017
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  13. S Keith

    S Keith Well-Known Member

    You've called it on the causes. All of those factors contribute to failure, but "early" is subjective.

    The single biggest factor is the design - you have 168 individual cells that all respond slightly differently to current flow. Eventually, the state of charge of cells starts to diverge with cells at significantly different states of charge. The prismatic module design helps to minimize this as it makes them behave a little more like 28 individual cells instead of 168, but they're not perfect. What eventually happens is a SINGLE cell is repeatedly driven in reverse polarity at high current until the cell fails and can no longer carry significant charge/discharge current or retain a charge.

    The sitting for extended periods, even though the owner's manual says it can sit for "several months," is a major factor. The extended self-discharge period does the same thing... all 168 cells self-discharge at slightly different rates. This is NOT addressed or minimized in the design. It's probably the single biggest contributor to individual cell failure as even for cars that are driven daily, they are still sitting for 22 out of every 24 hours - this is why periodic maintenance with grid chargers can greatly extend the life of the battery.

    The claimed design life of the battery is 180K miles. I'm aware of failures between 90K and 190K. The most common are in the 140-160K. Of course, that's in Phoenix, so I would expect the average to be on the low side of the design life.

    I have yet to see a build-up of dust/dirt that substantially affects cooling air flow, and I've blown out some massive chunks. The fan has 7 speed settings, 0-6. 0 is off and 6 is hurricane. Fan speed is predicated on pack temperature, so the only time the battery is actually overheating is when you hear that battery fan howling full blast in the back. It is almost silent even on 5.

    HOWEVER, pet hair is absolutely, positively the worst. The hairs essentially lay transversely over the fan vanes and severely restrict their ability to "bite" the air.

    EXTREMELY dusty environments that coat the battery in dirt has a notable impact as it inhibits effective heat transfer in an already challenging application.
     
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  14. Carcus

    Carcus Well-Known Member

    Thanks for the info.

    Related to your last point. ....
    As we move (maybe?) into an EV future, I have a hard time seeing how they will engineer an EV pickup. It seems like designing a battery pack that could sustain daily dust and rugged road environment (i.e. farm, oil field) would be a huge engineering hurdle -- and/or the maintenance and regular cleaning costs would be significant.

    Unless maybe somebody can engineer a better "leaf" type battery that can survive in a totally sealed,non-cooled environment.
     
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  15. RedylC94

    RedylC94 Well-Known Member

    Too much reliance on EV mode (whether by using the button or by creeping slowly) might be another. Relatedly, spending a lot of time stuck at stoplights or in slow traffic with air-conditioning on.

    I'm fighting most of the threats you listed, living in a hilly area, having to park in full sun most of the time, and not using the car much in winter. I try to deal with the terrain by approaching hills that have stop signs or red lights at the bottom slowly.
     
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  16. S Keith

    S Keith Well-Known Member

    There's never a good reason to push the EV button. It's a placebo thing. In almost every circumstance, it's worse for the battery, and the net effect on efficiency is a drop in mpg.

    Indeed. Stop and go is also hard on it - basically anything that increases the depth of charge/discharge of the battery.

    Regardless, heat is the biggest killer. Tips:

    Use a sun shade in the front windscreen
    park facing the sun during the hottest part of the day so the sun shade blocks it.
    Crack all 4 windows 1/2 inch
    For cars so equipped, use the cargo cover to provide a dead air space over the battery where the top surface of the battery is not heated by direct sun.


    IMHO, the EV pickup system will be pretty straightforward. The Ford Escape Hybrid has an exceptional system. It uses an air filter and automatically selects between exterior air or interior air drawn through a chilled evaporator. Ford Escape Hybrid batteries have exceptional life due to their robust cooling system. I recently inspected one with 64K miles of AZ driving on it, and there wasn't a spec of dust inside the battery pack.

    Liquid cooled batteries are also an option.
     
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  17. BillLin

    BillLin MASS: 2018 Bolt EV and 2017 Prime

    I can only think of air pollution reasons for pushing the EV button. If you, the driver, think or know that the gas engine will not run long enough to let the catalytic converter do its thing on a cold start, e.g. moving the car very short distances for parking reasons. IIRC, though, someone said the gen3 Prius EV button does not necessarily allow for engine-off running in certain circumstances, so my example above regarding parking may not actually work. I don't recall from when I had a 2010.

    Any idea what's bad for larger batteries intended for EV use, as in plug-in hybrids and BEVs?
     
  18. EdwinTheMagnificent

    EdwinTheMagnificent Legend In His Mind

    I would use the EV button to back the car out of the garage , so I can get out and manually close the garage door. I've never been able to actually DO it. But I can usually get the car out of the garage , into Park , and turn off before the engine lights. When it's super-cold , you may only have 1.5-2.0 seconds before that happens.

    I will have to check that again , when I'm not in the garage , just to see if I can get into EV mode before engine starts.
     
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  19. RedylC94

    RedylC94 Well-Known Member

    I believe the one good reason to push the EV button (assuming of course ample battery state of charge) is in order to move the car a few feet, when that would avoid running the engine for a few seconds. Stupidly, Toyota doesn't allow that in USA , except in warm weather.

    Parking facing the sun doesn't work so well when the parking orientation in not negotiable, and the sun moves through a large angle during hot parts of the day in summer.

    Cracking all 4 windows doesn't work so well in places subject to sudden thunderstorms every other summer afternoon.

    I can keep the state-of-charge display at 6 (of the 8) segments most of the time. The most frequent exceptions are large (or successive moderate) downhills that require braking, and slow traffic.
     
    Last edited: Feb 10, 2017
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  20. S Keith

    S Keith Well-Known Member

    We're discussing "minimal use" issues with the EV button. These are minor in nature and very specialized, so I'll back off my stance a bit because the scenarios described are at least a reasonable argument. Generally speaking the EV button should be avoided unless there is a clear and specific advantage for its use.

    Not all options are possible, but they are still best practices. One can get some stick-on rain guards from Amazon for all 4 windows for less than $30, or you can drop $100 on the WeatherTech brand. I have WeatherTechs on the front that came with my car, and those work well enough (fronts only are better than none). I don't really like them because they interfere slightly with the window when it's all the way up (they fit into the groove). My wife has stick-ons all the way around her '07 Prius, and they work exceptionally well even here in AZ heat.

    One thing the rain guards STINK on is dust... we don't get a ton of rain here in AZ (but when we do, it's violent), but we get a lot of dust storms. The rain guards act as a scoop for getting about 3X the dust into the vehicle than it would without the rain guards.
     
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