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Better battery cooling.

18437 Views 90 Replies 32 Participants Last post by  Sigma Projects
Ok, Arizona summer's here and it's reaking havoc on my poor batteries. I've been keeping the car as cool as I can stand to keep it, but while it's sitting there it get hot again. A windshield cover and car cover have helped some, but still haven't prevented the car in to going in to thermal cut back several times already. So I've had a few ideas which might help some. The question is does anyone know the specifics on the battery cooling fan? I looked at it once and noticed it was a panaflo fan, but can't remember if it was a 120 mm size fan or what and also is it the low or high rpm model. If it is the quiet one I'm thinking replacing it with the faster one would help some potentially.

Any thoughts?
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I guess I need to pull my lid off one day and install a temperature probe like you have. Lately it's been so hot I just gave up and set the air to full auto. If the car's been sitting in the sun and I use econ the pack will get hot enough where it will only allow 4 bars of regen shortly after starting out, and I can feel it isn't much at all.

Did you ever get those numbers off of the battery cooling fan? If it's the low speed one I was thinking I could put the higher speed one in it's place. They use the same Panaflo fan that I use to cool my computers so they're easy to get.
Mike wrote:

The regular display showe the normal 4 bars of background charging, but the actual charge rate is less than 12A. The same 4 bars with cool batteries and a low battery charge can be nearly 20A, so the regen bargraph is not true amps.
We see this same inconsistency with reality bar graph display in the coolant temp(another thread). Seems our dashboard indicators are somewhat of a dog_and _pony show. Thank you Mike for giving us an accurate indication of charge/discharge activity via MIMA :D
I was watching the battery temp on my test run yesterday. The cabin temps were in the high80's. The battery got to 115 F. Even at temperatures of less than 100 on the battery, if the batterys are charged heavily for several minutes straight (long downhill full regen) the charge will get limited to 12-25 amps. A few minutes of non use and full regen returns. The limit is not MIMA related, as the regen with brake activation in normal IMA mode is limited the same way. I think it is nearly time to open my pack, check all connections for tightness, install a temp circuit on all of the subpack and then compare the temps under heavy use conditions to see if a subpack is getting hotter than the others. I can design a separate temp monitoring micro based system that watches all the pack temps, and sends the average to the MIMA processor, or possibily does the temp control for the fans and opens up the MIMA pins now used for temp and fan control for other functions. Engine rpm(NEP),and the brake switch, are the first signals on my wish list. :wink:
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Mike Dabrowski 2000 said:
You pose a good point, is it better to look at total outlet air temp, or measure one subpack. Each has pros and cons.
If you had the 'fancy' temp gauge for outside and inside temps.. couldn't you stick both sensors in the battery pack... one to measure the cell temp directly and the other to measure the average air temp? Might be interesting to have both of those numbers in concert to do analysis.
Some other ideas I had.

Idea #1
Using a Liquid Cooling system of some sort (that they use in computers). I have no knowledge on how effective this would be. The other aspect of this is that they normally plug into 110v AC, but the fans/pumps work on 12v ?.
for example.. one of the cheaper units

If you had to put these metal things in direct contact on each battery cell... that would add up in cost quickly and make this prohibitive. If you could just string this tubing all around and suck up the heat... that would be a lot cheaper and easier to install. Added Ok, these metal things are heat sinks 1) you need them and 2) they need to be in nearly perfect contact with the object to be cooled. In addition, I've read that only 4 of the battery packs can be accessed easily so only 4 of ? could actually be cooled. This is looking like an expensive dead end.

Idea #2
Redirecting the passenger AC output directly into the Battery Area. Whether this is partial and/or full depends on what is set up. I figure you intercept the 'tubing' with a 'T' (45 degree angle?) under the dash and run it back there. The question is whether you are adding excess moisture at all (condensation would be a very bad thing I would expect).

Idea #3
Rigging up a mini cooler (the cooling part obviously) which uses the Peltier Process and cooling the battery compartment. It would plug right into the DC power plug. The question is whether you are adding excess moisture at all (condensation would be a very bad thing I would expect).

The cheap $100 coolers don't freeze anything and in Arizona your humidity is almost nothing. So I'd be surprised if condensation is a problem there. New England or during a rainstorm (high humidity) is a different scenario! This table (in blue) gives you an idea what to expect for creating a condensation problem. Another issue is this is basically a heat transfer, the inside get colder and the outside gets hotter so the interior of the car is going to get hotter while the batteries get cooler. That's a potential problem for the driver and perhaps would require the vent behind the passenger seat to be blocked off? That wouldn't be a big deal if you operated this when not driving (just keeping the batteries cool). Also... this little appliance will suck your battery dry (it will keep on working in the Insight after you turn the power off; however it doesn't do this in the Pilot.. check other threads on battery usage for details on this phenomenon), but you can buy an attachment that 'cuts out' when it reaches a certain point to mitigate that. This battery sucking thing may make this whole thing a moot point!

Whether condensation occurs, depends on the temperature of the cooled object, on the ambient temperature, and on the air humidity. Here is a table that will give you an indication whether you are risking condensation problems:

Air humidity . /
Air temperature 30% 35% 40% 45% 50% 55% 60% 65% 70% 75% 80% 85% 90% 95%
30 C° 10,5 12,9 14,9 16,8 18,4 20,0 21,4 22,7 23,9 25,1 26,2 27,2 28,2 29,1
29 C° 9,7 12,0 14,0 15,9 17,5 19,0 20,4 21,7 23,0 24,1 25,2 26,2 27,2 28,1
28 C° 8,8 11,1 13,1 15,0 16,6 18,1 19,5 20,8 22,0 23,2 24,2 25,2 26,2 27,1
27 C° 8,0 10,2 12,2 14,1 15,7 17,2 18,6 19,9 21,1 22,2 23,3 24,3 25,2 26,1
26 C° 7,1 9,4 11,4 13,2 14,8 16,3 17,6 18,9 20,1 21,2 22,3 23,3 24,2 25,1
25 C° 6,2 8,5 10,5 12,2 13,9 15,3 16,7 18,0 19,1 20,3 21,3 22,3 23,2 24,1
24 C° 5,4 7,6 9,6 11,3 12,9 14,4 15,8 17,0 18,2 19,3 20,3 21,3 22,3 23,1
23 C° 4,5 6,7 8,7 10,4 12,0 13,5 14,8 16,1 17,2 18,3 19,4 20,3 21,3 22,2
22 C° 3,6 5,9 7,8 9,5 11,1 12,5 13,9 15,1 16,3 17,4 18,4 19,4 20,3 21,2
21 C° 2,8 5,0 6,9 8,6 10,2 11,6 12,9 14,2 15,3 16,4 17,4 18,4 19,3 20,2
20 C° 1,9 4,1 6,0 7,7 9,3 10,7 12,0 13,2 14,4 15,4 16,4 17,4 18,3 19,2
19 C° 1,0 3,2 5,1 6,8 8,3 9,8 11,1 12,3 13,4 14,5 15,5 16,4 17,3 18,2
18 C° 0,2 2,3 4,2 5,9 7,4 8,8 10,1 11,3 12,5 13,5 14,5 15,4 16,3 17,2
17 C° -0,6 1,4 3,3 5,0 6,5 7,9 9,2 10,4 11,5 12,5 13,5 14,5 15,3 16,2
16 C° -1,4 0,5 2,4 4,1 5,6 7,0 8,2 9,4 10,5 11,6 12,6 13,5 14,4 15,2
15 C° -2,2 -0,3 1,5 3,2 4,7 6,1 7,3 8,5 9,6 10,6 11,6 12,5 13,4 14,2
14 C° -2,9 -1,0 0,6 2,3 3,7 5,1 6,4 7,5 8,6 9,6 10,6 11,5 12,4 13,2
13 C° -3,7 -1,9 -0,1 1,3 2,8 4,2 5,5 6,6 7,7 8,7 9,6 10,5 11,4 12,2
12 C° -4,5 -2,6 -1,0 0,4 1,9 3,2 4,5 5,7 6,7 7,7 8,7 9,6 10,4 11,2
11 C° -5,2 -3,4 -1,8 -0,4 1,0 2,3 3,5 4,7 5,8 6,7 7,7 8,6 9,4 10,2
10 C° -6,0 -4,2 -2,6 -1,2 0,1 1,4 2,6 3,7 4,8 5,8 6,7 7,6 8,4 9,2

All values are in °C.
Example for using this table: Ambient temperature=20°C, air humidity=65%. Result: Condensation will occur at a surface temperature (CPU, Peltier cooler) of 13.2°C

This table is copied from this website: Page 4 In fact there might be a lot of other interesting things (beyond Peltier) about cooling there as well. Perhaps the same idea that doesn't use the Pelier process would work better. I'm going to check it out and will post again if i find something.
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Here is something from that same site (site for cooling computer/electronics The key thing for cooling is having the temperature sensor on the object you want to be kept cold.. not the air temperature. Sort of makes sense.. who cares how hot it is if you are cool (and have a beer in your hand?).

Adding a temperature control to a fan would only add a few cents to the manufacturing cost of the fan. But most fans still come without temperature control. A temperature control integrated into the fan isn't always the best solution, for the following reasons:

On inexpensive temperature-controlled fans, the temperature sensor is integrated in the fan case, so that it measures air temperature - not the temperature of the device to be cooled. Better and more expensive temperature-controlled fans have the sensor on a separate wire, so that it can be placed directly on the device to be cooled.
The MIMA temp sensors are located one right on one of the subpacks with thermal grease to improve conduction, and one in a depression in the magnesium heat sink of the MPI DC/Dc converter. Both out of the air flow.

If either gets above 95 degrees, both fans turn on full, and stay on even when in autostop. The batteries still get to 110 or more if you do not have the AC on and it is above the cabin.
Sorry I did not look back at the earlier post, all of your suggestions are good.
The cooling rate increases if the air flow increases, and also increrases as the inlet air temperature difference is greater. it takes less energy to run a small booster fan than to run the AC, so the non AC solution I like is to just blow more air.
If the AC is going to be on, the best cooling we can get would be a direct shot from the passenger AC outlet,to the battery inlet vent I bet with the booster fan effect of the built in blower, we would have a turbo cooler. Condensation should not be a problem, since the air will be heated when it goes into the hot battery, and be exhausted before cooling. Maybe a shaped aluminum 3" flex duct could be made to tuck into the gap between the seat and the door on the passenger side.
Highwater and the guys with temp probes already installed should try it out and compare temperatures with and without.
Mike Dabrowski 2000 said:
Maybe a shaped aluminum 3" flex duct could be made to tuck into the gap between the seat and the door on the passenger side.
Yeah, I was thinking that was one of the three decent routes for running something and probably the best one except I think 3" wouldn't fit... more like 1".

The other would be thru the center transmission hump/rib... I have no idea how much room is in there (if any) or if that would involve cutting thru something. If that has a lot of room... your 3" becomes reality.

Another would be underneath the carpeting along the door edge... but I think that could look pretty strange/cruddy if it wasn't done right.
Highwater and the guys with temp probes already installed should try it out and compare temperatures with and without
I have on hand some high volume/low amp 12v case cooling fans for a figgy style solar vent mod. I can try mounting them directly to the vent behind the pass seat and plug them into the dash power for now, shouldnt take too much effort or time.

I got the fans mounted to the plastic vent grill behind the passenger seat. All thats left is to get a male aux. power plug from auto parts house, which I will do today. I will begin collecting data on the commute tonight. What I will get is the difference between cabin temps and BAT/MPI temps with the new vent fan running. We already have data without the fan, as that is the data I had previously collected. I have a temp probe (per Mike) on both the BAT and MPI locations.

I removed the plastic vent from the carpet, and cut out the grill portion in the middle of it. I will take this opportunity to say that the little grill is ONE_OVER_ENGINNERED_PIECE_OF_HARDWARE. Unless its part of the SRS :D :D. I mounted two (2) 80 MM case cooling fans to the face of the modified grill frame, and ran the wires under the carpet up the center console to the front. I'll hardwire them in later with a switch.

It might be that a blower of some configuration...squirrel cage or centrifigal, etc........could provide a greater volume of air movement. Finding the right one to go behind the seat will be the limiter.

These fans add about 3/4 of an inch (20MM) of height to the vent grill. If there is a passenger onboard they will need to keep the seat clear of the fans.

The original grill is made with an angle to the openings. This angle is canted toward the inside of the cabin (the back of the passengers seat), instead of toward the passengers door. It is made to fit the carpet only one way. Looks like it would have been better to point the angled grills toward the door, as it is real easy to restrict the airflow to this vent in the stock configuration. Have you got anything in that pouch on the back of the seat :eek: . Maybe it was thought that the air near the window would be to hot :?:

Took plenty of pics, if it will help anyone send me a PM. (Until I get hooked up with a hosting page) :oops:
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In a subterainian garage at approx. 70 deg. F, I noticed that the battery pack temperature increased by about 3 deg. F in about a 2 hour period. This is with all power off, and with the car windows open.

This observation would suggest a large thermal inertia of the Insight battery pack.

While in some parts of the world, the ambient temperature of the Insight interior in a parking lot in the summer, despite the best radiation-deflective efforts, can reach the upper limits of optimal perfomance and longevity for the battery pack, modifications to the sub-optimal stock cooling system, like those in the MIMA_C system and Highwater's previous message would seem to be worthwhile investments.

For those who may not have followed the details of this and other related threads, the Insight battery pack cooling fan doesn't remain on during auto-stop, possibly to maintain the "silence" of the situation.

From my observations and that of other MIMA modification users, the auto-stop condition is often where forced convective battery pack cooling is most necessary and effective.
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There's already defroster air in the doors for the little vents at the front of the door. Perhaps a tube could be run from there down to the lower back corner of the door, with a vent blowing out towards the battery air intake...
Just a quick observation from the first 1-way trip with the fans running behind the passengers seat.......
This is the first time I have seen the indicated battery temps DECREASE.
They stayed right in line with the cabin temps, dropping 3.1 compared to the cabin dropping 3.3 over the trip. The best previous data was an increase of only .3 on the bat with a decrease in cabin of 8.5 degrees (F).
More later :lol:
Just a thought for you guys looking at plumbing some cooler air toward this vent behind the seat, How about a flat inflatable tube under the carpet between the passengers feet and under the seat. There could be an auxillry blower up under the dash perhaps, tied into the dash air, that would push air thru this tube :?:
Got to get over that hump in front of the seat tho :evil:
That is good news. I have a slew of 12V fans(MIT swap meet), and will try the same thing on my car. The differential between cabin temp and battery temp is a good indicator, but Nemystic's point about thermal mass is a real factor. As I recal you do most of your driving at night, so your heating of the batteries is only from current draw and charging, and your cabin probably stays fairley cool. A hot cabin will be a more extreme test . I like the idea of tapping into the passenger AC vent (which could blow air with the AC off as well), and ducting it to the rear battery inlet. There is no question that the batterys will live longer and be happier if they are better cooled in cars with or without MIMA. Maybe we could have MIMA control the AC, and switch it on during down hill sections of road as the battery temps start getting high, and of course switch it off going up hills to save gas.(MAP control)
That would be "Cool" in several ways. :wink:
Mike is right about my commute, and I certainly want to make sure folks understand that my given conditions are most likely quite different than most. I drive at 11PM and return at 9AM, never seeing much intense direct sunlight, as I park in the garage at home.

I have also observed that thermal inertia with the 144 volt pack.

For a qiuck summary of what I am seeing with this vent fan behind the seat, the battery temps are staying within a couple of degrees(F) of the cabin temps, and also quite often end up less than the beginning of the trip. Prior data indicates battery temps as much as 12.0 more than cabin and only once was the battery temp less at the end of trip and that occured when the cabin temp had dropped about 10 degrees. I use some assist on quite a few hills and get all the regen I can on deceleration, so the battery sees a little activity. I intend on working the battery more when I get MIMA.
I will put a couple more trips on tonight and post some actual figures tomorrow.
I would think that those units seeing daylight might benefit more than my data indicates, but it certainly looks like putting more_GOOD_air into that little vent is a_GOOD_thing. The MPI temp is also realizing some good out of this.

My fans are the 80mm size, so there might be some smaller fans that would fit inside the vent frame after the grill is cut out, providing a lower, flush profile, just a thought............
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I took some aluminum duct tape, some reflectrix attic insulation, (bubble wrap with aluminum on each side)and made a duct that goes from the AC exhaust on the passenger side, across the bottom of the dash, takes a corner, goes down on the passenger door pillar, then fits between the seat and door jam, then finally expands and is stuck to the plastic battery inlet vent. All out of the way so the seat can slide back and forth. All the way back still bumps it , but it is flexable so that don't matter.I made a 100 mile round trip, with lots of mima use. The battery emp got to 113 at the max. with the cabin temp at 77. The AC being on, dropped the inlet air to 55 degrees, and was making the car too cold as I had the blower on full. I turned off the AC and tried just the blower. The result was that the battery did respond by staying at the 113 temp, and cooled down when no assist or regen was happening, but not as fast as I would have expected with so much air flow(I could hear the rear fan speed up when the blower was turned on)and at such a large differential in temp. 55 to 113 is a lot.
Conclusion! the battery pack cooling is a joke. I should have been able to cool that mass much faster than It was able to, especially with the cold air, and the booster blower.
I wish I had a prius pack configured so I could just drop it in, and set up a good cooling system. I am sure I could do better than the poor Insight pack. The circumfrence of the duct was 8 inches.
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Well sounds like we might be barking up the wrong tree here, since the thermal inertia is significant with the MIMA usage, that is if your going to do MIMA, but I will post the afformentioned temp data for whatever good it may be. The temps are in (F) and are the differencial from cabin temps.

Perhaps in the winter we would want the battery cabinet vented into the passenger compartment or pushed back through the secondary duct into the defroster :?:

11PM 36.3 11.8
9AM 20.9 2.7
11PM 36.6 7.6
9AM 16.1 2.1
11PM 36.7 10.2
9AM 17.0 1.0
11PM 45.1 8.2
9AM 13.1 -7.4
11PM 40.3 10.8
9AM 14.9 -0.2
11PM 47.5 10.2
9AM 13.7 -3.6
11PM 45.9 12.2
9AM 16.2 -0.9

11PM 39.0 1.6
9AM 23.5 -0.6
11PM 35.5 2.4
9AM 16.9 -1.9
11PM 33.8 3.2
9AM 23.2 0.3
11PM 40.3 2.3

Noticable improvement under my current driving conditions, is the lesser values of the battery temps on the 11PM drive. Used to be an increase of 10 degrees, now along the line of 2 degrees(F).
Sorry about the tight fit, I couldn't get the data to paste in like i wanted.
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Reset :oops:
Faulty experiment!
I just did another run with the A/c duct into the battery inlet, and was heating up pretty good. I stopped and looked at the duct, and found that my wife Sue had kicked it off the duct the last time, and I did not realize it.
I reconnected the duct, The temp was at 115 when I reconnected, ten minutes later the battery temp it was down to 108. It does work, I just did not realize she had knocked out the duct.
I can post some photos of the setup if any one else wants to try it.
I will leave it connected and see what else I can learn.
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