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Better battery cooling.

18443 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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A good ideal

I think I've found a good way to cool the whole car during the summer. A 12v solar powered fan placed in the rear bumper above the license plate.

The solar powered fan is on ebay. The solar panel could be placed anywhere. You would need the two peice system.

The fan would be placed in the rear bumper. There is a nice huge opening above the license plate that would be perfect for the air exhaust. Ideally you would need to cut a small vent in rear storage bin. The lid would also need to be left open. Though I'm sure air would still be sucked out if the lid was closed because there is plenty of gaps around the battery compartment.

Second ideal for fan would be to insert the fan into the cars vent system. This would allow use of the cars vent just below the windsheild.

Several different sizes of 12v fans can be purchased.
My 2 cents:
The need to monitor the battery temp with heavy MIMA use has led me to install a cheap indoor/outdoor thermometer in the battery pack. Brian has also installed one on his MIMA equipped Insight. It is easy to install once you get the covers off the IMA box. Warning! The screws holding the fan to the metal clips on the plastic shroud can be real tight, and the metal clips will twist and rip out of the plactic , so be sure to hold on to them with some vise grips while removing them. Once the fan is removed, you can reach in and tuck the outdoor temperature probe into the space between the side of one of the subpacks and the plactic holder for the batteries. Some white thermal transfer grease to improve the thermal transfer, and you will know how hot the batteries are. The temperature probe wires can be routed next to the reinstalled fan, and be careful routing them into the front of the car.
The battery fan shuts off when the car is in Auto stop for some strange reason, even when real warm, so that does not help the situation. I also noticed that there was a fair sized gap on the sides of the fan, and since the fan is blowing out of the box, the gaps will allow air to get sucked in near the fan, which reduces the air flow through the pack. I taped the gaps with black tape, and it showed a little better air flow. I am looking at placing a smaller fan blowing into the duct behind the passenger seat, to force more air through the pack.
The fan also does not seem to run continously, even when the pack is hot, so on the MIMA_C, I am tapping into the fan control relays, and I am putting the fan on at high speed whenever I sense the temperature rising to the 100 degree point. I have seen 117 deg on the batteries when the ambient was at 75. :wink:
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It sounds like you're on track with one solution to several ways to make the Insight/IMA system MUCH better!!!
Well, since this thread lives once again. It's going to be 110 here on sunday so this should be interesting. What you just said about the fan not running in auto stop (my god) somehow makes a lot of sense as to why I get insane thermal issues from time to time. So that gives me some incentive now. If I have issues with mine agian this summer I'll do the same and put a manual tap in to the fan control relays.

Also, I noticed that the fan used is a panasonic panaflo. If you happen to still have your box opened up could you write down the model number on that fan. I think they used the quiet one. If so I was thinking replacing it with their higher flow model should help also.

Knocking on wood... It's been in the low 100's the last couple of days and I haven't had anything happen yet...
Just happens I am starting to work on a temp monitoring project (while patiently waiting for release of MIMA_C dot1) for my insight this weekend using the indoor/outdoor thermometers. After doing some research on the meters it appears that most all of these type digital display / battery powered units have the same specs and sensing ranges :roll: so I deducted they must all be using pretty much the same circutry and soforth. I found an online source that had Oregon Scientific #EM899 brand on sale for 10 bucks each. These display both indoor and outdoor at the same time which IMHO are the ones to use since we don't need another switch to be having to flip back and forth. I bought several as I wanted to monitor intake air at the cat and also at the air cleaner: ambient and cabin temps: and in prep for MIMA I was thinking about the bat box as well. Am also considering a location in the tailpipe just prior to the back bumper, for kicks and grins. ( has been in the 90's here this week and after arriving home after my return commute of 40 miles I can grab the tail pipe bare handed, its body temp :shock: ) Anyway, Long story shortened you can take the thermistor that is attached to the pcboard desoder it and add length of wire to put it in another location like the outdoor probe. Now you have 2 remote location points per unit. I have also purchased a dc/dc converter to supply the 1.5 volts for these units so I don't have to do the battery thing and they can be powered by a switch or thru the onboard fuse box. Down side to this is the displays are large so as to be read across the room and I dont think they are backlit. What did I expect for poorboy style. I will take lots of pics and start (perhaps) another thread. I havent done a search on IC for this project, so sorry if I stepped on someones thread. :oops:
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A member from Phoenix did a improved IMA battery cooling mod last fall. Cheap, easy and confirmed results: ... php?t=2020


Looks like Dennis's how to pic's are still available here:

HTH! :)
In contrast to the sub-optimal Insight design, IMO, the Prius battery pack has an elegant cooling configuration.
And, in contrast to the Arizona climate, the weather here in New England so far this year has been unseasonably cool. However, I did notice one day last week, that despite having the windows cracked, the interior temperature of the car was in the high 90's. The battery pack temperature showed only 71 degrees, suggesting effective thermal isolation.
Unfortunately, if it stays hot through the night, there isn't much that can be done to keep the batteries cool. Like Mike, I would recommend monitoring battery temperature, so at least you can know what's going on. My car has no A/C.

The themal mass characteristics of the Insight battery pack seem to enable a gradual increase in temperature, particularly with heavy use. As Mike mentioned, the fan isn't active during auto-stop or when the engine is turned off. Perhaps if you could force the fan on for about 5 or 10 minutes before solar radiational heating and heavy battery use it might help somewhat.

With regard to digital temperature indicators with remote sensors, I'm using an older Springfield model to monitor battery pack temp. The best feature of that unit is a temporary backlight that comes on for a few seconds at the touch of a button, enabling visibility at night.
Being a frugal yankee, I went for the $7 Oregon Scientific instrument for the engine air intake temperature monitoring, and I plan to replace it with a better one, as it's quite large, has no backlighting, and displays time and remote temperature alternately, which in this case is a nuisance.
The instrument I'd suggest is about $15 at Radio Shack, quite compact, with a dual simultaneous display of interior and remote temps.
The AAA batteries seem to last for years, and are easy to replace.

Stay cool!
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Thanks John
I missed that one. That is exactly what I was going to try when I was finished withthe MIMA_C board testing. I asked Highwater to include the MPI temp monitoring in his test, so the best setpoint for MIMA to activate the fanscan be determined. Any additional fans needed (within reason)can be tied to the fan control power transistor in the MIMA circuit, using diodes to isolate the individual fans so the normal stock fan controlls will work if MIMA is turned off.
It turns out that the MIT electronics swap meet always has hundreds of those small fans available for cheap. I have a fair assortment in my fan drawer, but next month I will go there and buy up some nice ones that fit well in the ducts, and can include them with the MIMA kits.
Would still be great if we can get data on what temp the fans come on at, how quickly the battery temp can be brought down with the standard fan on high speed, and how much faster the pack cools with the booster fans.
Nemystic is all set up to also test the cooling characteristics, and may want to add some small fans on his car.
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Since installing the battery temp. monitor, I haven't seen pack temperatures over 100 deg. F. Then again, here in New England, spring has been postponed. :? Today's high temperature is approximately 55 deg. F.
Next week, more of the same weather is predicted, so it looks as though we'll need to wait until summer to get more meaningful hot weather battery temp data from Sputnik.

Yesterday, while travelling well over 100 miles round trip, over nothing but large hills, the batteries had quite a workout. However, the pack temperature never exceeded 97 deg. F.

With compassion for the battery pack, and an unexpired IMA warranty, I've tried to limit assist to 50 amps, and regen to 30 amps. However, with the MIMA_L modification, it is possible to assist up to 100 amps, and to regen to 50 amps.
I've been thinking of replacing the stock insight battery cooling fan with a pair of Vantec tornado's they are a little noisy but the car is a little noisy inside also and they move huge volumes of air, maybe someone could engineer a controller that controls their speed based on battery temps.

Also I've seen these window vents that are solar powered, you put them in the window and raise the glass to hold them in place while parked. The sun powers it, blows ambient outside air into the car. That should be the ticket. I would think.
I got the MIMA_C fan control to work , and did a 100 mile high speed trip while testing it. With the fans on stock control, the pack got to 120 deg, with heavy MIMA use (80-90 MPH highwa, full 100A assist up hills, full 50A regen down .) I used the forced fan control on the return trip, about the same speeds, and the pack only got to 107. The ambient in the car was about 80.
The blower that cools the power electronics would not run on my car even with the MPI case temperature was at 130, No codes were set, but if the temp sensor were bad, it would not run the fans and not know the temp to set a code.
Highwater has been running some temperature test, and found that his MPI fan turned on at somewhere over 120, It would seem that the blower should come on at more like 110 or less, to keep things cool. The control signal for the relays is generated in the MCM.
It may be a good idea to check your fans operation. A simple resistor and led accross the fan run to the dash will let you know if it is running.
I have set the on threshold for the MPI and Battery fans to turn on at 95. With this mod, the battery fan will continue to run in autostop.
I would suspect that because of the stock battery fan design that many other fans would work better, and would be interested in any test results.
One interesting thing that I have been noticing, is that the regen function is limited until the battery has a chance to warm up and stabilize.
I have seen this regen limiting effect quite often, almost always just after the car is started for the first time. After a few minutes, I can always get full regen.
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Wal-Mart also sells a $10 indoor-outdoor digital thermometer (in the car accessory department) that seems like it might be useful for monitoring the battery temperature. It's a cheap plastic thing that uses a AAA battery.

It has a wire about 12 feet long; now I just have to figure out how to get it down into the battery pack...
For the MIMA temp probe, and the indoor/outdoor thermometer that I have on my car, I removed the battery fan, and using some thermal grease, was able to slide the temp probes right into the gap between the battery and the plastic case. The wires wee run out of the battery box between the fan and the outer plastic. Getting the wires into the front of the car is a little tricky, but on my car, I just used the two extra wires in the MIMA rear harness to carry the temp probe signals.

If you want to see photos, send me a PM and I can send some to you.
Where does the battery cooling air come out? Maybe it would be easier to put the sensor there?
AFAI remember ist ducted to a point above the fuel tank. The only "easy" way to access it is from the top with the IMA cover off.

HTH! :)
Dougie wrote:

Where does the battery cooling air come out? Maybe it would be easier to put the sensor there?
It has a wire about 12 feet long; now I just have to figure out how to get it down into the battery pack...
To do anything along the lines of monitoring any of the IMA BATTERY or MPI temps, you are going to have to do as Trekker suggests and remove the IMA control box cover. Once removed everything is right there handy.
Take Mike up on his offer of sending a pic, I did :lol: I routed the temp probe lead up thru the bottom of the IMA box as there are plenty of vent holes there, then around the right side to a place where I could get it out from under the carpet, and just put the display in the passengers seat for now. You'd be amazed at how quickly 12 ft. of lead will disappear :evil:

For what its worth I sealed up the extra gaps around the BATT fan housing with some black electrical tape.

We are all concerned with adverse temp conditions of the BATT, and justly so. But also of interest, I am seeing MPI temps of 128F before the MPI cooling fans come on (LED"s wired in for monitors). I also see higher MPI temps at night (midnight commute) than during the 9am drive back home. Since my MPI temp probe is on top of the case joining the MPI and the DC/DC converter, I would say the latter is working overtime for the headlights
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What I was wondering about was whether it's more useful to put the probe somewhere in the airflow as it leaves the battery compartment, instead of on one cell. Maybe the airflow value would be more valid because it encapsulates all of the cell readings into one average?
You pose a good point, is it better to look at total outlet air temp, or measure one subpack. Each has pros and cons.
The air temp solution while providing an average of all batterys temp, will be influenced as much by the cabin air temp as by the batteries.
The subpack temp solution will show the actual subpack temp with out much influence of cabin air temp, and will be faster to respond to a rapid temp rise, but would not show if one of the subpacks is getting hotter than the rest.
The best way to do it would be to put a sensor on each subpack, and have a dedicated battery management computer that looks at all of them much as the stock system does. I originally looked at tapping into the existing sensors, but had the same noise issues as I had with the MAP and TPS signals, and felt it was better to just add my own sensor, since the cost of the opto isolation circuits for one sensor could pay for 4 or more temp boards which do not need isolation.
Four of the subpacks are accessable if the cooling fan is removed as Highwater pointed out. So the last 4 of the subpacks could be independantly monitored to see any differences between them, but since I have used all the I/O of the proicessor, I cannot use more than 2.
My MIMA solution of just turning on all the fans to full, when the temp of either the MPI or battery exceeds 95 F. will cool at the maximum rate, so that is all we can do with the stock fans. I have not looked further into the good suggestion of mounting 1 or 2 small fans in the inlet duct. That should at least double the airflow, and further keep the temps down, and the fans could be directly added to the MIMA control system, as it is currently configured.
Mike :wink:
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Also presumably running the HVAC fans at top speed maximizes the cabin pressure, which helps the battery cooling airflow. Probably not much of an effect, though.
Running the AC and reducing the cabin temp has a huge effect on the cooling rate of the battery pack, as the differential between the cooling air and the battery temp is maximized. It is much harder to cool a 110 degree battery with 85 degree air than with 70 degree air.
The major issue with hot batteries is that the BCM limits the regen amps. It is 90 today, and my batteries were at 105, and I am seeing some limiting of charge current. 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. The MIMA regen is also limited in the same way, so the BCM has the last word on how much charge or assist is allowed.
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