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Air flow around Hybrid battery pack.

Discussion in 'Gen 3 Prius Technical Discussion' started by Old Wrench It, Apr 8, 2018.

  1. mjoo

    mjoo Senior Member

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    Hard to see where the tubing is going but very interesting!

    Pixel XL ?
     
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  2. Old Wrench It

    Old Wrench It Member

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    it's just a thumbnail jpg, click on it and it should expand, better on full screen pc. Thought I posted 2 or 3 more pics but not seeing them. Also if you have a model Prius with gas venting tubes it's apparent that Toyota determined they didn't accomplish anything. Probably they would work great as heat release by unplugging most of them and turning them with holes facing to side or upwards, the pressurized heat especially when fan blows will go to path of least resistance of pressure. The tube I installed goes through an extra hole bored out through soft plastic end piece, it is really easy to drill out. Hole goes in the corner and tubing exits open corner area where screw in end metal piece is open. My son came home last night and said that after install he hadn't added any gas but the indicator for how many miles left to drive went from 80 miles to 140...told him to track his actual mileage carefully. My mileage has improved some but have been driving more with an eye on voltage flow and battery health than seeking improved mileage. During process I only cleaned out EGR tube and need to go back in to do intake manifold clean as well as EGR valve and cooling valve( is that the right name- no, the cooling piece below egr valve.)
     
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  3. Old Wrench It

    Old Wrench It Member

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    PS WARNING: If you run a tube make sure to keep it high heat resistant, and all attempted operations are your own screw up fault if anything oges wrong! disclaim disclaim ;)
     
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  4. Raytheeagle

    Raytheeagle Senior Member

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    Egr cooler;).

    Once you pull it out you’ll see it looks like a radiator :).

    Or maybe not depending on the deposit level:eek:.

    Good luck with the maintenance (y).
     
  5. Old Wrench It

    Old Wrench It Member

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    Thinking of 3 new improvements, adding ductwork from original heat exit down to the low end flaps at rear drivers side, adding additional fan to my already added heat release tubing, and adding additional intake air vents under back seat that tie into existing vent which is so easily blocked on a long trip by tired passengers with pillows or a lot of fat. Still am amazed that Toyota chose to place exit vents for heat at low points in vehicle when it would naturally exit with higher located vents.
     
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  6. Old Wrench It

    Old Wrench It Member

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  7. 2k1Toaster

    2k1Toaster Brand New Prius Batteries

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    They did the higher vents thing in the Gen2. Worked great but also got blocked by people, things, and also now all the debris in the air, mostly people with hair shedding problems or those with dogs.
     
  8. Old Wrench It

    Old Wrench It Member

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    The exit vents were blocked or intake vents?
     
  9. Grit

    Grit Senior Member

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    My middle pack is usually 4-5 degrees F hotter than the 1st and 3rd packs also.

    One weird thing is that when I have the windows rolled down around 70F at night, the air intake temp climbs up. But when I close all windows and recirc w/no AC, the air intake temp goes down but it gets hotter in the prius also.
     
  10. Old Wrench It

    Old Wrench It Member

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    The air flow in the Prius needs cooler air to get the exit flow going unless windows are open. The exit vents are very low in the rear where the hybrid battery vents it's heat but not directly to vent. Since heat rises the only ways for it to flow out is to either make a direct connection to exit vent (s) or to get enough cool air flowing that the cool air sinks to the exit vents - cool air sinks, hot air rises- once there is a flow of cool air it will draw some of the hot air out. A very inefficient design by Toyota.

     
  11. Dxta

    Dxta Senior Member

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    Maybe they are not doing that, just to cut down costs.
     
  12. Buderim

    Buderim Junior Member

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    @ old wrench it , if you get a chance could you post the other pictures ? I have a 2010 and would like to do all I can to keep my traction battery healthy.
    Thanks
     
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  13. TMR-JWAP

    TMR-JWAP Senior Member

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    I'll preface this by mentioning I have a Gen2, not a Gen3. Wow, we are over complicating this. Probably 95% or more of the batteries get past 10 years. My personal opinion, if you're concerned about inadequate airflow, then why not just use an app that makes the fan run all the time? Why reinvent the wheel?

    A couple other things while it's on my mind and I'm feeling frisky and we need to keep this real.....

    (one)....Water cooled?....really? Dealers want 600 bucks to replace an inverter water pump that takes less than 30 minutes. Can't even begin to imagine the fees that would be involved with an HV water system. We recently did an upgrade at my plant to replace a few million bucks worth of water cooled variable frequency drives. I can't tell you how many times over the last 19 years we've had a drive go BOOM due to a small water leak. A water cooled high voltage system in a car. Just think about that for a few seconds. Guess how our new, upgraded multimillion dollar drive system is cooled? AIR cooled. Great big AC units. No more water leaks. A lot less BOOM.

    (two)....I'm not convinced a few degrees difference in battery temps will provide even a pinprick of measurable change in MPG, at least not measureable by any instruments any of us have at our disposal. NASA maybe, but not us.
     
    #33 TMR-JWAP, Jun 5, 2018
    Last edited: Jun 5, 2018
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  14. Old Wrench It

    Old Wrench It Member

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    will do a bit later this evening, have everything apart again chasing down low amps
     
  15. Old Wrench It

    Old Wrench It Member

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    10 years is probable if you're not using it as a taxi like some of us do. a fewdegrees is probably normal on fairly new or maybe under 150,000 mile battery but when you see consistent 10 to 15 degree difference and the high temp is often near 120 F I suggest either getting a new battery or so;vog some of the heat flow problems. My son's 'new' 2012 has about 40K miles on it, I installed an extra heat release tube and yes his mileage did go up a few miles per gallon immediately, from 51mpg to about 55 mpg.
     
  16. TMR-JWAP

    TMR-JWAP Senior Member

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    Obviously, we all have opinions, I stand by my assessment of not measurable. There may be another external influence causing your 8% mpg change, but it's not HV battery temperature.

    The gen 3 battery air flow path: The bottom plenum is pressurized by the cooling fan. These fans can move a very reasonable amount of air, especially when at full speed. The end of the supply plenum away from the fan is sealed. The bottom edges of the battery modules are sealed to the steel case by a foam gasket. Airflow has no option but to go vertical, up between the modules, with some very minor leakage going out the sides of the modules. But, the majority of it ends up in the top plenum. The air that flows out the sides of the modules(or leaks from the top plenum into the side area) escapes through the electronics section and some escapes out the end of the pack opposite the electronics end. The top plenum is sealed on the same side as the bottom plenum (driverside) and uses foam strips (just like on the bottom plenum) to seal against the modules . The exit duct is essentially the only possible flow path. It's directly above the inlet, and as you said, it's a short duct and the exit air flows into the spare tire area. With the fan running, there is zero chance that any air flow in the top plenum will recirc back to the bottom plenum, as the bottom plenum is always at a higher pressure. The path of least resistance is going out the exit duct.

    Notice that the large plastic storage tray has that corner cut at a 45 angle. If you do a bit of digging in your trunk, you'll notice this exit air will flow past the plastic tray and to some air vents on each side at the rear of the car. One is by the driver side storage cubby and the other is behind the 12v battery. Most of the exit air is directed toward the battery side vent, but some will also go the other way. So, believe it or not, the warm air from the battery has a designed exit path from the car. Gen 2 vehicles actually have a complete plastic duct that goes to the 12v battery side vent. The gen 3s just make use of what's already there.

    If the battery is having temperature issues: I would suggest making sure the fan is working and ensure the fan isn't packed full of crap. Then ensure there isn't excess dust/debris buildup on the bottom of the modules blocking the flowpath. Also, make sure there isn't a bunch of crap in the trunk/outside the plastic tray/blocking the designed flow path to the vents.

    If all that is good and I was still worried that it wasn't getting adequate cooling? Then I would just use an app to run the fan at a higher speed if desired. Forced airflow will always be better. Here's another question.....On a Gen 3, all three temperature sensors are located on the top of the battery. Is there any chance the tube vent is allowing a small amount of cool air to be "supplied" to the top of the battery while driving, causing a false low indication and possibly preventing the fan from operating as designed? Unlikely, I would think, but one never knows.

    Now that we're visualizing the design flowpath: to really add a "heat escape vent", why not just remove the upper plastic seal from the driverside top of the battery? (the one you drilled a hole in for the tube) Then you'll just have a wide open exit flow path for the 'warm' air side of the heat transfer equation. Air from that side of the battery will flow to the 'cubby hole' vent at the rear driver side (where your tube ends) and the short exit duct will flow to the 12v battery side vent. Much more vent area than the tube and easier to do. You can even leave the metal end plate off if desired. Then all that will be left to worry about is there will be less airflow through the electronics section for cooling, but probably not significant.
     
    #36 TMR-JWAP, Jun 10, 2018
    Last edited: Jun 10, 2018
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  17. Old Wrench It

    Old Wrench It Member

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    problem with your assessment and toyota's design, warm air has more pressure than cool air, warm air rises and cool air falls. Vents are at low point so warm air unless forced to go down by higher pressure or draw will rise back into vehicle. That's one reason why no one should just leave whole area of blocking off end of battery or remove casing itself = to extend the absurdity.
    Forced air will still seek path of least resistance, as soon as the air enters underneath the pack there is nothing to prevent it from rising immediately. As the upper temperature rises there is more pressure from the heated area but less pressure to immediately rise and enter exit area. Different temperatures create different pressures. That is part of why there are 3 temperature sensors in the pack instead of just one to determine fan usage. Yes, an app is great to force fan on and am using Dr. Hybrid which has recently upgraded so that you can choose at which temp you want the fan to come on at, their suggested temp is 86 F.
    I have for several months been learning to drive with an eye on voltages and emp rather than mpg. With older weaker batteries the voltages remain fairly even with good performance as long as the temps in pack remain well below 90 F. The higher the temps the less consistency in the pack with greater spikes. Don't know where you're getting the idea that temperatures do not affect batteries, do you have a link or resource paper?
    BU-502: Discharging at High and Low Temperatures – Battery University
     
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  18. TMR-JWAP

    TMR-JWAP Senior Member

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    Old Wrench,

    As hard to believe as it is, I have a decent understanding of thermodynamics, heat transfer, fluid flow, temperature-density relationships, natural circulation due to temperature/density differences, etc. If you believe any area in the plenum on the top of the battery where warm(er) air is located is at a higher pressure than the bottom of the battery where the fan is supplying cool(er) flow, I can't help you. This is a gross conceptual error.

    I don't recall saying temperature does not affect batteries. I stated a few degrees of temperature difference of the HV battery is not going to provide a measureable change in mpg unless you have NASA measuring equipment and that it is not the source of your 8% mpg improvement. If you really believe it is, I recommend you submit it to Toyota. They would probably cut a nut off to gain 8% mpg.

    I explained the design flow path for the cooling air. It is what it is, I didn't design it, Toyota did. I made a recommendation on how you can improve on your "heat escape vent" to get even more extra vent area. The question is, does it matter? Which is the actual restriction? The combined cross section area of the flow channels between the modules or the cross section area of the exit narrowest portion of the exit path? My bet is going to be the flow channels between the modules are the limiting factor for flow.

    And realistically, removing the top cover from a Gen 3 battery will have little to no impact on cooling (other than exposing the top to other air currents) since the fan supplies the bottom plenum. The bottom plenum is sealed on all sides to the module pack, forcing the cooling air to move upward between the modules. Once it passes between the modules, it doesn't matter where it goes. Now, physical damage to the battery pack with no cover installed is a whole different story.

    And, "Different temperatures create different pressures" In a closed, sealed system yes, temperature changes can drastically change pressures in a closed system due to density changes of the material enclosed in the system. In an open system like we're talking about, a density change is not going to cause a measureable pressure change. That would be like saying the hot air leaving the top of my chimney is raising air pressure on my roof.

    We obviously each have our opinions.
     
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  19. goku2

    goku2 Junior Member

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    It's actually pretty simple. You think a few degrees can't have a detrimental effect but you would be wrong. The prius charging control system is eager and willing to use the battery up until the point the battery either starts misbehaving or gets into temperatures that the computer decides is 'dangerous'. When the computer decides the pack is malfunctioning due to the heat or the pack is simply getting too hot, it will pare back usage of the pack and rely more on the gasoline motor. It goes without saying what happens when the car becomes more dependant on the gas motor.

    I have a techstream so I have been monitoring the pack voltages and temperatures on my Gen 2 prius pack very carefully after I got a red triangle on a 102F ambient temperature day and wasn't able to accelerate up a freeway ramp. Meanwhile, when the temperatures dropped, the check engine light and the triangle went away and all was well. On a 70F day, my pack has a tendency to be hanging out at 95f+ temperatures. On the day when the ambient temperatures were 102f, the pack temperature got upwards of 164f. I did not have my techstream with me while driving on that 102f day but I did monitor the pack when I got home and I pulled the freeze frame data to figure out what was going on. I tried running the A/C on that very day but the pack voltages got out of whack so the car wasn't able to charge the pack so it was losing charge faster than it could make it up so I was forced to keep the A/C off.


    I do plan on taking apart this pack in the future and seeing how much this issue is attributed to a cooling duct not properly secured, cleaning the fan or perhaps corroded electrical connections/sensing wires. But thus far, the car drives completely normally when the ambient temperatures are around 70F. Haven't tried again on a very hot day to find out but I am parking in the shade in the interim.
     
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  20. bisco

    bisco cookie crumbler

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    it is amazing to me that with all the engineers toyota employs, they don't know that warm air rises.(n)
     
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