Spontaneously aborted S4 glides at 26 MPH

Good evening, Jim!

Yes. It was sure was a scorcher out there today in that +104 F heat! I'm afraid I don't have any insight into your particular experience. However, here's what I observed over the last two days, which may lead you to some ideas.

I actually drove home from work this afternoon (at 5pm) with no AC and all windows down. Yeah, call me crazy. But you know what, it wasn't bad at all. Guess I'm pretty tolerant to extreme heat. My Prius had been parked in the sun all day (since 8am) and usually gets a little bit of shade (for about 1/2 hr) before I leave work. Anyway, I have no idea what the battery temp was during my drive home (don't have a scangauge or can-view, yet). However, at no point did I have any trouble gliding and my battery was charging as normal (got up to 6 bars a few times during the drive home). My mpg average actually climbed to 72.6 by the time I got home. For the most part, my speed varied from 25-41 mph. Yes, I've found an alternate route for my daily work commute, which has essentially eliminated any interstate driving.

Now, let's compare this to yesterday when the air temp in our area was "only" around 97 F. That day, I drove home with the AC on (lowest fan speed at lowest temp setting). During the entire drive, I had difficultly gliding and also could not get a decent charge on the battery (highest I saw was 4 bars). By the time I got home, my mpg had dropped from 71.6 to 68.9. Exact same route and pretty much the same speeds as today.

Here's my theory. This afternoon, even with the +104 F heat, I got more & stronger air flow to the vents in the rear seats (which lead to the battery pack) by having all the windows down. The better air flow (even if it's hotter air) actually did a better job of cooling the battery pack than running the AC at the lowest fan speed (in recirc mode) with very little air flow those rear battery vents.

What do you think? Does this theory make any logical sense to you?

 

I wonder if having just the right rear window down would do the same thing? The wind would be right on the vent for the battery wouldn't it? This may force air through the battery better than the fan?

 

The Cal-cars people have seen that at about 104F the Prius really protects the battery, especially if your SOC is below 6 bars. The battery fan doesn't kick in until about 120F. AC draws from the HV battery quite a bit, increasing ohmic heating inside the modules. The Prius was trying to protect the battery by running the ICE to run MG1 to provide the power to the AC and limit current in/out of the battery. I believe Doug Schaefer saw the battery temp go down 1F every 5 minutes of AC use, remember it has to be flow through, not recirc. Think Pete has the right, though uncomfortable, idea on how to drive.

My personal style is to open both front windows trying to create a high pressure area in the back seat which would vent through the battery vent. Really depends on your route, the outside conditions and what you can stand. When we had 97F going home the other day, I tried to keep the acceleration between 1200-1500RPM to limit ICE comsumption, keep under hood cool and limit MG1 current into the battery. Never had a unwanted ICE run and my ICE temp reached no higher than 194F, with an almost full grill block. SOC was almost always at 6 bars.

Wayne

 

Also remember the battery is a large block of metal, and it takes a long time to heat it up and a long time to cool it off once it's heated up. It isn't going to change temperature rapidly. It started at 100 F (ambient - and had all day to get there). You started using the battery, so it heated up a little more, but even if you blew 70 F air on it with a large fan it wouldn't cool off for at least an hour. The tiny fan the Prius uses is going to take a while to cool the battery. But at least it held the temp at 105 F while the car was using the battery.

We don't get those kinds of temps. here, but one day we were at +30 C and I noticed a lower SOC, poorer mileage, and more ICE operation. Yes, I had A/C on - set to 27 C - even 30 C is too hot for me!

Oh, and the Scangauge will not indicate traction battery temp or any other parameters. Those are "CAN" messages. The Scangauge only sees standard ODBII messages, such as coolant temp, 12V battery voltage, fuel use, etc.

 

<div class='quotetop'>QUOTE(JimboK @ Aug 9 2007, 07:34 AM) [snapback]492909[/snapback]</div>

Nice! I'll keep an eye out for that broadcast. If you do find out, please let me know exactly when the local NBC station will air that story.
I'll have to get your autograph the next time I see you :lol: (Prius meet in the fall?)



<div class='quotetop'>QUOTE(David Beale @ Aug 9 2007, 11:46 AM) [snapback]492992[/snapback]</div>

David, According to one of the techs I spoke to recently at scangauge, the ScanGauge II will soon have the ability to display battery temp as well as other additional readings (like CAN-view). Apparently, this will be possible via a firmware update. Feel free to contact scangauge to learn more.

 

I use a “Fan Mod†on my fan to get it to go full bore when the OEM battery temperature gets above 94 deg. I want to modify it further to run as normal and then at my will, push a button to force it to full bore. The fan itself makes no noise, but the sucking air sound through the plenum is loud enough to be annoying if the radio is not on.

Also, I have been looking into a direct tap modification to the AC/Heat vent to get the air into the battery compartment without mixing with the ambient passenger compartment air.

I believe the Toyota guys should look into improving battery temperature management for the next Prius. Right now in Houston, the passenger compartment can reach 130 degrees and why would you want to grab that air. On the other hand out side temperatures are reaching 100 deg F. here. They need a system that would grab air from the best possible place depending on the batteries needs, whether it be from the inside, outside, or if it has to start up the AC/Heater, on it's own and grab the air from there. That system would be fairly complex (no more so then the regular AC vent system) but I think it would be helpful in there plug in version if it ever makes it to market.

 

<div class='quotetop'>QUOTE(Cheap! @ Aug 9 2007, 12:49 PM) [snapback]493089[/snapback]</div>

Ford Escape Hybrid has those features.

Wayne

 

That's it! I'm trading in my Prius for an Escape Hybrid. :lol: Just kidding, of course!

 

The threshold of how much current you can draw probably went down,
so the whole system probably became much more sensitive to demand.
The other little wrinkle is that short period of engine-running when
the secondary cooling loop opens via the 3-way valve; the engine
tends to run long enough for the water pump to push stuff through
that piece of the loop [incl. the bottle] and make sure it's all
warm. That can yield a small period of frustration, but then it
sorts itself out again. Yup, it happens in stage 4 too.
.
_H*

 

I don't think this is too far off topic....
Where does the exhaust air from cooling the battery go? Is it vented outside the car or back into the passenger compartment?

If outside, where is the vent and how does blowing all that cool air outside affect the AC load? I know it is needed to cool the battery but just wondered about the additional load on the AC. Just sounds like driving a "regular" car AC with the windows down.

Bob

 

The only thing that comes to my mind is that 26 mph is around the speed where MG1 changes direction when the ICE is idling.

 

So, you'll post it tonight, right?