[kakheath]

Cell testing is progressing. I just pulled #258 off the bench. I thought I would update my car pack design ideas to hopefully get some feedback from the group.

Each 4s5p module would have 10 pieces of aluminum flashing cut to approximately 7" by 7" square and placed in between every other cell. So that every cell has one side contacting a piece of flashing. This is to provide about 0.25" fins on each cell edge for wicking away heat from the pack. Below is a top view of the design. The electrical connections on top would be made of 1/4" by 2" angle to provide a solid terminal for each module. To minimize the outer dimensions on the clamp side, I plan to weld one end of the all-thread to one end of the clamp and use a lock washer and lock nut on the other to hold the clamp in place. I will torque this lock nut several times between cycles to ensure that there's no thermal expansion problems.

Then I plan to construct a trunk pack out of 12 of these 4s5p modules in a design that minimizes the connection lengths on top - see attached top view. In addition, I will arrange the modules such that perforated air tubes can deliver air from the floor of the battery box. See the green line depicted below. The air inlets will be routed to a safe location to draw clean fresh air. A fan will be installed in the lid of the box to pull air across all the battery fins.

[kerrymann]

Originally Posted by kakheath

Cell testing is progressing. I just pulled #258 off the bench. I thought I would update my car pack design ideas to hopefully get some feedback from the group.

Each 4s5p module would have 10 pieces of aluminum flashing cut to approximately 7" by 7" square and placed in between every other cell. So that every cell has one side contacting a piece of flashing. This is to provide about 0.25" fins on each cell edge for wicking away heat from the pack. Below is a top view of the design. The electrical connections on top would be made of 1/4" by 2" angle to provide a solid terminal for each module. To minimize the outer dimensions on the clamp side, I plan to weld one end of the all-thread to one end of the clamp and use a lock washer and lock nut on the other to hold the clamp in place. I will torque this lock nut several times between cycles to ensure that there's no thermal expansion problems.

Then I plan to construct a trunk pack out of 12 of these 4s5p modules in a design that minimizes the connection lengths on top - see attached top view. In addition, I will arrange the modules such that perforated air tubes can deliver air from the floor of the battery box. See the green line depicted below. The air inlets will be routed to a safe location to draw clean fresh air. A fan will be installed in the lid of the box to pull air across all the battery fins.

I am contemplating the same but do you think you will need the cooling? From bench testing these cells at 2C continuous for 30 minutes I only get a rise of 10°F. And if I do another cycle with little to now cool down, I get a lower IR and a percent or two higher capacity. After 1.5 hours at 2C of charging and discharging, it was only at 98°.

[kakheath]

Originally Posted by kerrymann

I am contemplating the same but do you think you will need the cooling? From bench testing these cells at 2C continuous for 30 minutes I only get a rise of 10°F. And if I do another cycle with little to now cool down, I get a lower IR and a percent or two higher capacity. After 1.5 hours at 2C of charging and discharging, it was only at 98°.

I think it all depends on how many amps you plan to draw at use. What controller and number of cells in parallel do you plan to have?

I had planned my conversion for performance and thought I would get a Z2K, but have decided to go with a Soliton 1 instead. This will limit me to 1000 Amps, but should be more versatile for everyday driving. Since I don't really plan to drag race the car, I thought it would be the best choice for me. I do however, plan to add a second motor to take advantage of the full controller voltage (~350V). I don't know if I will really need the cooling, but it doesn't add much cost to build it into the design at this point. In fact, I may find that heating the cells will be as important as cooling them. The air flow and fins will allow me both options if I install some kind of inline heater for the inlet air flow. Depending on how well it can control the temperature, it may be feasible to install some sort of thermostat control depending on what the ideal temperature should be. Remember this is my first conversion. I don't claim to know anything about this subject. So I'm way over-thinking everything, but that's part of the enjoyment for me.

[kerrymann]

Originally Posted by kakheath

I think it all depends on how many amps you plan to draw at use. What controller and number of cells in parallel do you plan to have?

I had planned my conversion for performance and thought I would get a Z2K, but have decided to go with a Soliton 1 instead. This will limit me to 1000 Amps, but should be more versatile for everyday driving. Since I don't really plan to drag race the car, I thought it would be the best choice for me. I do however, plan to add a second motor to take advantage of the full controller voltage (~350V). I don't know if I will really need the cooling, but it doesn't add much cost to build it into the design at this point. In fact, I may find that heating the cells will be as important as cooling them. The air flow and fins will allow me both options if I install some kind of inline heater for the inlet air flow. Depending on how well it can control the temperature, it may be feasible to install some sort of thermostat control depending on what the ideal temperature should be. Remember this is my first conversion. I don't claim to know anything about this subject. So I'm way over-thinking everything, but that's part of the enjoyment for me.

Yep I wasn't trying to talk you about of it. This is my first time using these cells too. I had been going back and forth on it and ultimately decided to put in the fins. Everything I have seen and read shows that keeping the cells at a comfortable temperature is key to cycle life. Especially at high C rates. I have been thinking the same thing on my motor situation and going to dual later to replace by ADC. For the heating are you going to insulate your boxes?

BTW, you conversion is looking nice. Sorry to hear you had the same problems I had with Electric Car Company and it's adapter and hub but glad it didn't set you back too much.

[EVPowers]

A friend of mine is posting data points from his testing of cells from a group buy of 500 cells we did earlier this month.

He recently bought an infrared camera so he can measure the thermal qualities when charging/discharging. Without any cooling, he did a 103 amp discharge and saw a max temp of 105 degrees Fahrenheit.

[kakheath]

Originally Posted by EVPowers

A friend of mine is posting data points from his testing of cells from a group buy of 500 cells we did earlier this month.

He recently bought an infrared camera so he can measure the thermal qualities when charging/discharging. Without any cooling, he did a 103 amp discharge and saw a max temp of 105 degrees Fahrenheit.

That's great. How many cells in parallel was he using when he discharged at 103 amps and for how long was he discharging the cell?

[marc02228]

I took another way to assemble the cells.
The attached image is a PCB for a 9s3p module.
You put the tabs of three cells in parallel through one slot, fold them to the soldering pad and fasten them with two screws to the next three cells in series.
It will be a 3.2mm thick PCB, that should be solid enough.
Each terminal has a trace to the BMS connector.

I am still waiting for the produced PCB's. Actually it should take 10 working days. But I am waiting since 11th of June, now.

I will get double the number of PCB's I need, because it was almost the same price.

[kerrymann]

Originally Posted by EVPowers

A friend of mine is posting data points from his testing of cells from a group buy of 500 cells we did earlier this month.

He recently bought an infrared camera so he can measure the thermal qualities when charging/discharging. Without any cooling, he did a 103 amp discharge and saw a max temp of 105 degrees Fahrenheit.

Interesting. One question is did you insulate the sides of the cell? When I tested mine I had similar results on single cells (just using a thermocouple) when I didn't cover them. But when you stack the cells into a module the heat can no longer escape the large flat sides of the pouch because it's covered by another cell. If you insulate both sides of the cells with some low density foam you'll get a much higher temperature.

Kerry

[EVPowers]

Originally Posted by kakheath

That's great. How many cells in parallel was he using when he discharged at 103 amps and for how long was he discharging the cell?

He was simply bench testing two cells.

He has done testing with and without insulation.

Here is a link to his testing page.
http://99mpg.com/workshops/designingandbuildi/