Thermal performance of gen 2 Prius HV battery

Nice charts and analysis. Let me share something from my testing, the effect of a forced charge. Charging our NHW11 batteries is exothermic:
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I found a 7-9C increase in battery temperature doing a forced charge. If the battery is already warm from the ambient temperature, this would be a bad thing.

Although harder to quantify because grade, altitude, and speed are needed, I am sure that rapid driving over hilly country can and does 'heat pump' the traction battery to a higher temperature. What happens is at high speed, climbing a hill at or over 65 mph, leads to traction battery energy 'borrowing.' On the reverse slope, the battery gets a charge proportional to the climb deficit. But ohmic heating on the next hill climb keeps the temperature up.

Bob Wilson

 

2009Prius,
A question and a comment

1, I wonder if the battery fan turned on.

I am interested in battery cooling when the AC is set to recirc vs circ. Any data ?

 

Interesting... Makes me wonder why Toyota doesn't just put an A/C vent that runs directly into the HV cooling system? I mean this whole internal air intake concept seems flawed... I mean telling people to keep the rear intake vent unobstructed? Come on! Glad the GenIII, V and C... have eliminated that air intake problem. But why not just run an A/C system direct to the Battery Pack? If well designed it seems it could offer a significant boost in gas mileage?

 

Cooling the battery just means the thermal effects are minimized. I've found in my charging/discharging experiments that if the battery is getting warm from the exothermic charging, it is also generating internal gas. If left alone for 12-24 hours, the gas recombines as the module cools. But I don't see this improving mileage but minimizing traction battery stress and aging effects, especially in the older NWH11. The other models have much improved batteries.

Avoiding heating is the best course so:

• avoid forced charge in warm weather
• climb hills without borrowing energy from traction battery (55 mph works great up an 8% grade.)

GOOD LUCK!
Bob Wilson

 

Well summer is here in N Texas. Few trees and little shade . We are hitting the triple digit temps too. Daytime high's will easily find 103-107 range in July-Sept. Today hit 103 and my hv cooling fan has come on. Question about MFD and color codes Green(full charge cell) Blue(partial charge) Red(scary color) . What are leading signals of HV battery/cell failure.............................

 

Based upon NHW11s:

• uneven temperatures
• uneven voltages in the module pairs, above 0.3 V difference can throw a code
• other battery codes

You'll notice my temperature increase was a little larger due to:

• the internal heat takes a minute or two to reach the surface and show up in the external temperature probe
• my goal was to measure traction battery capacity so I did not wait for temperatures to plateau but started backing up the hill, the altitude change would be proportional to the traction battery energy capacity

Bob Wilson

 

Is it normal for the battery to reach 48 °C, I have tracked the values with Torque app and on a steep downhill when SOC was 79% it reached very high temperatures. Ambient temperature was 18°C in car temp wasn't more than 25°C. Here is the data:

Welcome to Google Docs

 

According to Seilerts' posts, that is about the upper limit of the acceptable range. I use B mode extensively to avoid these high SOC downhill situations. Turning up the A/C also helps. Roll down the windows for more drag.

Interesting data.

 

Once the battery is fully charged the car takes care of not overcharging/overheating, so you don't have to worry about that. (unless you live at the bottom of a steep hill and always turn the car off before it can fully cool the battery). Point being, once the battery is fully charged on a long downhill there is value in putting the car in neutral and getting some extra distance with as little friction on the wheels as possible... Then once it's time to brake or accelerate again don't forget to put car back in drive!

 

Isn't there an issue with Gen2 in neutral above a certain speed?

 

There's lots of threads on here about using neutral at speed... Nothing definitive though... Long ago you could run into problems with a car in neutral at speed, they even past laws against it. But those problems are no longer likely. One dude on PriusChat claims to be using his Prius as a guinea pig for doing neutral coasting as often as possible, he's yet to notice any problems... You might want to find and follow that thread to see what happens!

 

^^ The same volunteer is asked to set the car rolling, and watch from the top of the hill. We want to check the steering.

 

Another data from Gen 3 Prius:
Welcome to Google Docs

I started on a hill pass on 1350 m (4.400 feet) car was parked for 2 hours on the sun outside temperature around 20° C (68° F). I started A/C to cool down the car, when I started driving SOC was at 34 %, I was using B mode. It took only 5 min of steep downhill driving and 211 m (656 feet) of elevation drop to fill the SOC to 80% (600 Wh in 5 min?). I took a 3 min pause in the middle (white line on the graph phone was off for 2 min), with car on and A/C running on very low setting (400 W). Notice how the temperature was still rising, I think there is 5 min delay of actual battery temperature and temperature sensor (sensor 2). After the pause the battery was filled again from 70% to 80% and temperature was going even higher to 47°C (116 °F).


The most aggressive regen charging was 78 A at 266 V (20 kW).
My previous data (couple posts above) was similar, with a little higher temperature but it included driving up the hill, the interesting part is that my wife didn't use B mode down that hill, and max regen charging was 72 A at 252 V (18 kW) and when the SOC was 80% regen stopped and engine would spin just like in B mode. This suggests that there is very small difference between D and B mode, of course B mode brakes more by default.

Edit: There is difference between D and B mode, B mode will spin the engine even when the soc is bellow 80% while in D mode engine starts spinning when it reaches 80%. From B mode I would expect even more engine braking (when SOC < 80%) and not that aggressive regen.

 

I have a 2005 with 134000 miles. Battery pack replaced last year - first pack lasted 15 years!
I learned a lot about batteries after my pack failure and every battery whacker agrees that heat and time are the real enemies of battery life/performance.
I monitor the battery temperature sensors. I have found that middle sensor temperatures can easily reach 130 degrees F on a warm Georgia day in stop and go traffic. Any appreciable regen causes the temperature to climb. The fan, at speed 1 or 2 seems to have little affect on the temperature rise in stop and go traffic. I have seen the pack temperature at 125 F before even driving if it has been parked in the sun for a hour or two. 20 minutes of heavy regen and battery draw got me to almost 140 F before getting home.
The fan is clean. I didn't rebuild the battery pack when it was replaced so I'm not certain all the air dams were properly installed when the Toyota tech rebuilt the pack but the fan does drop the temperature when driving at a steady speed until it reaches 90 F. Fan then stops and temps return to slow climb. Fan is more effective in the winter months of after it rains.
I have searched and searched but no one seems to be able to quantify an acceptable operating temperature range for the battery pack. What are others finding to be the typical or normal range?

Tom