Air flow around Hybrid battery pack.

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

Pixel XL ?

 

Egr cooler.

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

Or maybe not depending on the deposit level.

Good luck with the maintenance .

 

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.

 

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.

 

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

 

@ 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

 

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.

 

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.

 

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.

 

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.

 

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