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For my LTO conversion I’m still in a quandary about what to do about battery-pack cooling. From what I’ve read maybe cooling is only necessary in the SW??

I’m trying to utilize the existing fan or maybe something with a little more air flow and my considerations are noise and air flow. I’ve posted several times in Natalya's LTO Conversion trying to get a feel for the topic and since I’ve only heard from two people I’m not convinced as to a location, or even if it’s necessary.

My current plan is to have a new air duct modeled for the DC-DC exhaust to the existing exit hole. I’ve read that the DC-DC fan doesn’t turn-on very frequently so I thought about not installing this exhaust duct and let the end remain open with the terminal metal grate in-place and installing the existing fan at that location, on the inside, on top of the grate. Does water come in during a heavy rain? The fan would be connected so it would turn-on when the battery required it, if at all, to get air moving and keep things cooler. But when the car sits in sunshine and heats the interior and the battery soaks I could connect a Bluetooth gadget to not only turn-on the fan but have it reversed so it would draw cooler air from beneath the car into the passenger compartment. If that were possible, what are anyone’s thoughts?
My concerns:
  • Leaving the DC-DC hole open, albeit with the metal grate and putting the fan in that location
  • Is battery cooling necessary and will this ‘little bit’ suffice?
  • Is there any concern about leaving the DC-DC exhaust duct?
My other thought is about installing a fan for the battery pack while there is a DC-DC exhaust duct. Real cooling may not be necessary except in the SW. I was thinking of two fan locations: one beneath the ‘cheese grader’ plate above the spare tire and the other on the vertical surface of the aluminum battery cover, directly behind the pack so the air has a more direct path from the intake duct behind the passenger seat. Is one preferential to the other?

Am I overthinking all of this battery cooling stuff?
 

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The LTO have a reasonable surface area and coupled with low IR won't heat much themselves during use.
Ambient temp or heating due to extreme sun etc is likely your main concern.
The blocks have a big thermal mass so will take a while to heat up and cool down even on very hot days.

The cooling fan/blower for the MDM is important, as the IGBT and DC-DC do get hot under heavy load.
You should certainly ensure any fan replacement is at least as capable as the stock blower and is controlled by the OEM systems (MCM).

In OEM config it sucks air in from under the car over the petrol tank, and exhausts it in that right hand corner.
In my A123 conversion I blocked the outlet hole in the floor, removed the outlet pipe from the fan,
and just let it exhaust the warm air into the IPU.

The extra warmth was useful to keep battery temperature nearer normal.
The average yearly temp where I live is ~10C. See what your area average is.

In the temperate UK I won't be bothering with any fancy heating or cooling provision..

.............................................................................................................................................

In your shoes I would probably first of all get a cheap $2 e/bay digital temp gauge with 2m lead and put the sensor in the IPU somewhere above the batteries to try and capture the air temperature inside the case.

If the temp readings warranted it and I wanted to keep extreme daytime sun heat out of the IPU I might get a sheet of 30mm Kingspan and using the rear carpet as a pattern cut a piece to fit under the rear carpet.
Heat inside the car would then be much less able to penetrate into the IPU through that insulation It's available in various thicknesses. From 20mm upwards..

Or if you want to splash out for high efficiency and thin insulation, you could get one of those vacuum insulated sheets that I think Ian experimented with a while back.

Or cheapo foil bubble wrap style insulation cut to size under carpet.

The world's your oyster..
 

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The cooling fan/blower for the MDM is important, as the IGBT and DC-DC do get hot under heavy load.
You should certainly ensure any fan replacement is at least as capable as the stock blower and is controlled by the OEM systems (MCM).
Yes, I agree. I did find a way to use the MDM & dc-dc duct for bringing in outside under car air to help prevent heat buildup in the IPU. Once you remove the duct work, you are left with the output tube of the MDM farn itself. It is about 3" in ID and has a nice tapered lip. You can buy a cheap 3" computer fan off ebay and easily custom fit it to the round MDM outlet tube. (A 3/16" to 1/4" adapter block in the middle helps.) A generous amount of epoxy all around will seal the fan and keep it in place. Since the MDM fan is sealed, you can safely assume that you are effectively sucking outside under car air into your IPU and batteries. Since you only use this when parked for long periods, there is no danger of water being sucked in.

I haven't tried mine in summer so this is currently an unproven idea, but I think it works. As Peter says, we in the U.S. are going to need to make measurements.

Last summer, I just used a silvered car cover and that was very effective. That is a bit inconvenient, but I only park mine long term at home.

I did fit 4 small fans, side-by-side, into the cabin duct work just in case I later need to get A/C air to the batteries. I also sealed the duct nicely. It is an easy mode and the OEM power source can be controlled directly by the OBDII C&C.

The world IS our oyster ;)
 

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Hope that isn't directed at me. I certainly agree with you. I put my fan on the outlet round fitting of the MPI fan itself. It can suck air through the MPI fan and the MPI/dc-dc duct work with very little resistance.

This fan for the "heat soak" problem only,:)
 

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Here is some photos of how I rigged several small fans to bring air into the LTO pack from the cabin, once the weather starts to get hot (not finished yet). These were in process pictures - sorry don't have a final final pix. Fans are 12V and will be powered by the "standard" fan 12V, so fans will be under control of OCBDII C&C. I'll be installing temperature sensors as Peter suggests.

A foam strip will be used to seal the fan/duct to the IPU case outer surface.

In final installation, the fans will be used only as necessary.
 

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Here are pictures of the fan arrangement I hope will prevent "heat soak" or heat buildup in to LTO pack if the can must be parked for long periods, without cover, on hot sunny days. Since this fan is only used while parked, there is not danger of sucking water into the compartment. The fan assembly is epoxied and sealed to the MDI fan, which itself is sealed. Pulling air through the MDI fan squirrel cage will not be an issue. The fan is fairly low volume, but should help prevent heat buildup.

The brown piece is a piece of 3/16 Bakelite which is used to adapt the taper of the MDI fan and to space the fan so that the blades do not rub on the fan housing. Again, this is incomplete at the moment. Sealant is used between the fan and the adapter.

I plan to use 12V power from the left rear corner, which powers the hatch latch. A switch will be installed in a convenient location.
 

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Has anyone baselined the temperatures of the IMA battery/fan output, IGBT module/heat sink/fan output, and ambient IMA compartment temperature (perhaps vs outside and interior air temperature), over a variety of operating currents?

I would like to characterize this to see if I need to factor it into my build, and avoid duplicating these tests if I can.

If the data exists, I would definitely attempt to duplicate at least a subset of it to confirm that the data is reliable/repeatable.

I plan to drive in parts of the country that can get very hot and at high altitudes where the cooling efficiency drops because of fewer molecules to carry away heat. I suspect I will need to include temperature protection in my build and want to get an idea as to how extensive those protections must be, particularly if operating the motor at higher currents.

I'm also concerned about the additional heat load on the IGBT at elevated current and temperature. It might not be an issue, and actual numbers from test data would show that conclusively.
 

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Has anyone baselined the temperatures of the IMA battery/fan output, IGBT module/heat sink/fan output, and ambient IMA compartment temperature (perhaps vs outside and interior air temperature), over a variety of operating currents?
Nope.

The IGBT/MDM cooling is pretty good. The MDM fan is a leaf blower detuned by some nearby series resistors.
Your could probably easily take one or more resistors out of play and see how much more air it shifts v current consumed. The IGBT mdm/dc-dc will protect themselves anyway as they have temp sensing built in.

The motor is a completely different kettle of fish, running in enclosed area with no temp sensing or active cooling.
However IMA motors are cheap and plentiful so if you overheat/kill one in testing you will know where the limit is.

I presume you have seen the old pdf outlining some accord IMA motor testing years ago done by researchers.
It's on here somewhere and Google will find it.
 
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