Questions about battery cooling.....

[Rotarypower]

Ok, so driving my roadster to work on Friday, parked the car and 8 hours later start the drive home. The car was hot, no shade in the parking lot and we dont have chargers at work, so I assume the battery was pretty hot. It was mid 90's *F and the car temp measured over 100*F . While driving home I hear a clunk in the passenger compartment (really loud) and notice the a/c gets really uncomfortable, so assume that the battery is demanding cooling. This has happened several times since I've had the car and was never bothered by it assuming it was doing its thing. So I get curious and go into the service menus and check out the HVAC diagnostics and notice that the battery is 40*C and demanding cooling but I never see the battery max T go down. Also notice the coolant temp never goes down either. So it appears the system runs for a set time (maybe 1-2 minutes) then clunk, I hear the same sound, and notice the cabin air is now cooling, but the battery temp never went down. I am very concerned that my battery isn't getting any cooling while driving. So when I get home I go and do a range charge in an attempt to force cooling. By this time battery temp is around 36-37*C and this time the coolant temp goes down, and I see the battery temp go down. However, as always, this cooling demand only lasts for 1-2 minutes, then shuts off, and cooling stays off until the coolant temp matches the battery temp, then maybe 3 mins later the system will cycle on again. Is this normal behavior? Why would battery cooling while driving not respond in a similar manner to a cool down while charging? I've never seen battery temps less than upper 30*C's while driving. While driving I don't see coolant temp drop when it is demanded while driving. At this point I don't want to drive the car until I am confident I'm not killing the battery, it's been hot in NC and I am already seeing my CAC and ideal miles drop just in the past month+ I've owned the car. A few questions....

1. Is there a detailed system operation guide, schematic, or description out there that could be shared, I want to understand the cooling system mechanical and software design so I am not in the dark on what should vs is going on with the car, especially in the terribly hot summer months.
2. What are the battery cooling demand set point while driving. When should ESS cooling kick in? What is the programmed logic for time in this mode, is it based on delta T or simply a timing algorithm?
3. Why would the system not appear to work while driving, but seem to work while charging?
4. I have never seen pump demand go to zero. It appears my coolant pump is running 24/7? Shurely this isn't normal?

Sorry for the wordy post, but I am getting a bad feeling that this might have been going on for awhile at the expense of battery health. Any recommendations to further asses the issue and troubleshoot it would be appreciated.

 

[ML Auto]

That sounds normal except for the loud clunk. The valve for the battery cooling is near the passenger footwell, but doesn't make a loud noise when activated. The compressor make a clunk when is first turns on, but if you already were using the A/C it would be on already. Cycle the A/C on and off to see if your clunk is the compressor coming on. You can put the A/C system into service mode to operate the valves individually and see if that is your noise as well. The battery cooling comes on around 41C and goes off around 38C, so if your battery was at 37C (down from 40C) when you got home, the system was working. While charging the cooling cycles on and off to slowly bring the temps down, ending in the mid to upper 20s (depending on the charge mode) when the charge is fully completed. The coolant pump seems to run 24/7 if the battery is in the low to mid 30s.

 

[hcsharp]

The A/C generally starts cooling the battery while driving if it gets above 40C. At that point it cools it down to about 38 to 40C. I don't know why you didn't see the coolant temp go down because it obviously did in order to cool your battery or it would have gone well over 40C in those conditions. Maybe you didn't watch it long enough or were on the wrong screen. Sometimes it takes a long time to cool it down after you finish your drive.

While charging the target temp is much lower than 40C and depends on several factors but generally in std mode it will cool it to 25C if it gets a chance. The circulator pump will run whenever the battery is above 30C to keep all the cells at the same temp which helps prevent thermal runaway of any individual rogue cells, which is unlikely. It also provides a small amount of cooling.

It sounds to me like your car is behaving normally. I strongly recommend that you perform a cool-down charge any time you get somewhere and the battery temp is above 30C. Don't just park and wait until your normal charging time.

edit: I see MLAUTO beat me to it providing most of this info already.

 

[Roadster]

+1 to both @MLAUTO and @hcsharp's comments above.

FWIW, in case you were wondering what the various color bar indicator thresholds were on the VDS temp readout, below is an oft shared matrix @scott451 put together back in 2011. Our understanding is the values listed for v.3.5.17 are still valid so this should give you an idea of the safe zones the car is happiest in:

I've seen my PEM and ESS temps go briefly into the first yellow bar while driving in this summer's SoCal heat but they normally move back down to the fourth blue bar a few minutes after the HVAC reroutes the cold air to the rear. I haven't seen the Motor get into the yellow yet but I can imagine if it's 90°+ outside and you're doing a steep climb up a mountain that could easily happen as evidenced by what @ecarfan and @doug experienced recently. I've learned to just keep my VDS set to the temp bar display to help inform if I'm posing any potential damage to my vital components.

That clunk on the other hand...

If your ESS temps don't continue to rise while you're driving, I'd take that as a sign that the system's working; albeit perhaps not as efficiently as it should due to whatever's causing that sound. Do you know if the PO you bought the car from ran the A/C often? Perhaps the compressor's clutch is a bit stuck from lack of use?

 

[hcsharp]

I've seen my PEM and ESS temps go briefly into the first yellow bar while driving in this summer's SoCal heat but they normally move back down to the fourth blue bar a few minutes after the HVAC reroutes the cold air to the rear.

That's true for the ESS but the HVAC system has no effect on the PEM thermal management. The PEM is entirely air cooled from its own fan in the back of the car. The A/C system will reroute the refrigerant to the chiller in the rear of the car that chills the battery coolant, but it doesn't reroute any air.

Perhaps the compressor's clutch is a bit stuck from lack of use?

Does the compressor have a clutch? Isn't that a relic of ICE powered cars that have a belt constantly spinning the A/C compressor pulley?

 

[Roadster]

Thx for the corrections, Henry. I'll leave further diagnosis to the experts. I've clearly got ICE on the brain still, LOL.

 

[Rotarypower]

Everyone thanks for your input. I do feel better and I think tomorrow I will run the car and take some data to alleviate my fears (or confirm them, hopefully not). The clunking noise while driving is odd and from the feedback I'm getting does not sound normal. As for the a/c system service mode, can that be run while the car is being driven? I think I would like to run some tests both while parked and while driving, just not sure you can do that. I'll give it a try and report back. I have also discovered some good reference info on set points that I'll clean up and share out.

It sounds to me like your car is behaving normally. I strongly recommend that you perform a cool-down charge any time you get somewhere and the battery temp is above 30C. Don't just park and wait until your normal charging time.

@hcsharp so this is what I'm puzzled about. Few destinations (esp. in NC) have charging, certainly not my work. Is there a way to force cool down without being on a charger? Can OVMS do this? My understanding is no to both Q's, but correct me if I'm wrong? If not, why not? As long as you have the charge margin, seems this should be an option. Could it be that going into the a/c service mode this could be done manually where you can control the solenoids and compressor manually? Wonder if OVMS could do this? Car might need to be on however.

 

[ML Auto]

Service mode only controls the valve activation, unfortunately you can't force the compressor to run. It is designed to open the entire system when you evacuate the refrigerant.

 

[Rotarypower]

So any idea how to get into service mode on a 2.5? Instructions I have dont seem to work!

 

[gregd]

So while contemplating this puzzle, I have a related one which may have an answer for both questions...

Should the activation of the A/C for battery cooling also cool the cabin, even if the cabin's A/C is off? That would seem wrong, yet that's what happened to me.

I took a trip down the hill yesterday. 67 miles of freeway each way. Started the early morning outbound leg with a fresh range-mode charge, low-70's F ambient temp. The car sat all day, in the sun, no charging available. Because it was a down-hill run, I arrived with some 145 miles of Range-mode range, and a battery that was somewhere in the middle of its temperature range. The return trip had a 1,200 ft elevation gain, and a mid-80's ambient temp. The cabin A/C was never turned on (but the fan was). After about 40 miles on the way home, as I was hitting the main climb, I noticed that the battery was right at the top of the blue zone (as were the PEM and motor), and sure enough, the A/C kicked in with its usual "click" (barely audible over the road noise, not a clunk) to cool it down. A few minutes later, the battery was down one block from the top blue.

I know the cabin was getting some of it, because there was an odor change in the air, consistent with the moisture collecting on the evaporator (normal for my car). The cooling effect for the cabin wasn't very strong, but it was definitely there.

So, why would the cabin be getting some of the cooling? Do I perhaps have a stuck valve somewhere, so both sides get cooling, or is this normal? I know that when the cabin A/C is on, and the battery needs cooling, most of the cooling gets switched to the battery and the cabin warms up for a few minutes as a result. But if the cabin A/C isn't on, why would some of the cooling still go there? Is there not a separate valve for the cabin evaporator loop?

 

[ML Auto]

So any idea how to get into service mode on a 2.5? Instructions I have dont seem to work!

key off
push and hold both the a/c and recirculation buttons
key on
continue holding down both buttons for 10 sec or until the red heat light comes on

So, why would the cabin be getting some of the cooling? Do I perhaps have a stuck valve somewhere, so both sides get cooling, or is this normal? I know that when the cabin A/C is on, and the battery needs cooling, most of the cooling gets switched to the battery and the cabin warms up for a few minutes as a result. But if the cabin A/C isn't on, why would some of the cooling still go there? Is there not a separate valve for the cabin evaporator loop?

I would assume both valves operate when battery cooling is requested. The battery heat exchanger is very small and I doubt there is enough flow or heat removed by it to allow the compressor to run at 100%.

 

[Rotarypower]

key off
push and hold both the a/c and recirculation buttons
key on
continue holding down both buttons for 10 sec or until the red heat light comes on




I would assume both valves operate when battery cooling is requested. The battery heat exchanger is very small and I doubt there is enough flow or heat removed by it to allow the compressor to run at 100%.

Yep, those are the instructions I had too. Just don't seem to work, tried multiple times, with several variations (key in every position, hold for longer, shorter). Weird.

So, the other thing is looking thru some of the reference material I have collected over the past months, I did find a decent reference to the roadster "cooling strategy" which does shed some light on my question. It also invites additional questions.

My question is when driving max range, is the HVAC compressor really turned on at 17*C? And is the battery cooling loop solenoid activated at that point?

 

[hcsharp]

That chart is very confusing. Several of the entries contradict other entries. At first I thought maybe one side was for charging and the other for driving but that doesn't even make sense.

Most Roadster drivers know from experience that thermal control is different for each mode depending on whether you're charging or driving. For example charging in Range mode attempts to cool the pack to 15 - 17 C at the end of the charge. Driving in range mode it allows the pack to reach 40C without any attempt at cooling before then.

 

[gregd]

That chart is very confusing. Several of the entries contradict other entries. At first I thought maybe one side was for charging and the other for driving but that doesn't even make sense.

I think the idea is that you go down the left-hand side as things heat up, then over to the right (starting at wherever you are, temperature-wise) as they cool down. Temperatures listed are the thresholds that one crosses to take the listed action. Seems to make sense that way.

But, you're right, that Range vs Standard mode throws another wrinkle into the picture that doesn't seem to be fully accounted for. There does seem to be some criteria in each for when that threshold applies.

 

[hcsharp]

I wonder what the car does to warn the driver before it hits 54C and shuts everything down. For example "Pull over safely" at 52C.

 

[Msjulie]

One day a month or so back, my car tossed up an error about power train and the car literally stopped in place.. I knew it was heat though because it was blazing outside and I had the AC on for like the first time ever ..

 

[DanielFriederich]

maybe I have some info on that - hope its useful

 

[gregd]

View attachment 240833 One day a month or so back, my car tossed up an error about power train and the car literally stopped in place.. I knew it was heat though because it was blazing outside and I had the AC on for like the first time ever ..

Mmmm, 972 isn't listed specifically as an overtemp fault. See Roadster VDS Messages Says "DMC FW: Accelerator Erorr fault" (sic)

Might be something that's overly sensitive to heat (accelerator pedal sensor?), or something else indirectly related to it. You might ask next time you're at the service center what else it might be, so you don't have it happen again at an inopportune time.

 

[Curt]

View attachment 240833 One day a month or so back, my car tossed up an error about power train and the car literally stopped in place.. I knew it was heat though because it was blazing outside and I had the AC on for like the first time ever ..

Keep an eye on this. I started getting this error at the beginning of June, and once it started, it repeated every few miles. I also feel this was heat related.

My local Service Center ended up replacing the Accelerator Pedal, the PEM, and the VMS. Fortunately, since I had just done the "3.0" Battery Upgrade in March, they decided it was covered under warranty and didn't charge for anything but the Pedal.

See the thread here.