Main Traction Battery Upgrade i-MiEV

[Jiminy]

The bus bar issue was figured out. Single CMU taps were made to go underneath the stock Mitsubishi bus bars. Where there was no CMU connection a simple, laser cut rectangular washer was used instead as a spacer.

 

[Jiminy]

would you be willing to contribute these files to the repo? https://github.com/imiev-battery-upgrade/imiev-battery-upgrade

It is my opinion that sharing the specific part files I made for the last set of Piev's cells would be of little use as it seems that the cell dimensions and terminal details change from batch to batch. The first set he used was very different from the second. -Jim

 

[program5628]

Thanks for the context I'll remove this recommendation.

 

[VoironIon]

I feel like we need a bigger warning about freezing temps until we figure out a solution for that.

I do live in the mountains (French Alps). Freezing temperatures are a winter concern down here. Actually it is snowing, BTW.

The way heating unit is designed in this car is not ideal. 5KW power, warm air is directed to cells. Best option would be to have heat closest to batteries.

My idea is to add some heating pads within the battery, by using the lost space at the bottom (newer cells are shorter in height).

I use Lifepo4 batteries as main power in my home, and need to warm them a bit, because they are installed in cold storage. It really works. Everything is managed by the BMS, that switch heat depending on various conditions.

We could do the same, by reading cells temperature value from within the CAN bus, and then switching off/on heating.
System will only be triggered only when car is ON or charging.
The same Arduino for capacity cheating can be used for this.


Heating element could be either heating pads (see AliExpress for heating pad batterie) or resistive wire,...
Standard solid state relay (SSR) should be able to switch the load. Concern is to find a DC variant or having multiples SSR in serie to minimize electric arc (same as DC switch load in photovoltaic applications). I can explain if someone wants.

I think that a 300-500 watt heating power should be sufficient from my guess.

Hope it helps!

 

[MickeyS70]

The way heating unit is designed in this car is not ideal. 5KW power, warm air is directed to cells.

There simply is no battery heating function as stock LEV50x cells don’t have a ‘do not charge below freezing’ limitation

 

[Jiminy]

I deleted both the simple and the L-shaped bus bar files on Printables so the links to Printable files on Post #286 for bus bars do not work and should be deleted in the post. The L-shaped bus bar I designed does not and cannot work. The simple bus bar also does not work as I found out during the iteration process with Piev. I corrected it for Piev but posting it is pointless as I believe his last set was a one-off set. Let's hope so, at least.

Purchasing cells from a vendor in China should be done with maximum care. Terminal design is of utmost importance. And the terminal studs Do Not Need to be 8mm as I have had hands on a few different battery packs from other manufacturers that use either 5mm or 6mm terminals. These are used for far greater power levels than the 66hp Mitsubishi motor. The packs I am working with now come from a very large and well-known OE and they use 5mm studs and bus bars connections. In fact, the bus bars themselves are just 1mm thick and 12.15mm wide at the narrowest part. The system fuse is 250A, roughly equivalent to the 260A Mitsubishi system fuse. The horsepower of the drive motor is 102hp. We don't need 8mm studs. Yes, they are more convenient since Mitsubishi uses 8mm but it is more important to get the correct detailing of the terminals.

Piev's last set of cells were modified by the vendor to have 8mm studs. This was specified by Piev to reduce the chance of breaking a terminal off during the torqueing of the 8mm nuts during assembly. According to Piev, he broke off a few 6mm studs during his first conversion so he wanted to reduce that chance by specifying 8mm studs on the second set of cells. But during the second conversion he broke off a couple of 8mm studs as well since they are just welded to the actual aluminum cell terminals. A weld is a weld and in my very experienced opinion if you ask a vendor to change something from what is standard you might not get what you expect to get.

In my opinion, the second set of cells that Piev received with 8mm studs were severely deficient. The studs rose out of two different steps welded onto the cell terminal. This required us to design and manufacture a set of intermediate spacer washers to allow a nice flat surface for the CMU bus bars to sit. The cells really needed to be like his previous set where the 6mm studs rose out of a flat terminal face with no surrounding steps. He and I never discussed this since we had to work with what he received but I can tell you there were a lot of brain cells and US dollars killed by the orientation of those 8mm studs. Here they are:



I am willing to participate in the design process of conversion parts for a cell swap. I would need 8 cells sent to me in Texas. I have a shipping system where four cells are put in a 7" cubic double walled box and then into an 8" cubic double walled box. Trying to get measurements right from afar is no bueno. With the cells present I can design the cell spacers and bus bars and send back the cells.

When you purchase cells you must buy cells with a simple terminal structure like the stock Mitsubishi LEV50 cells. There should be no steps or ridges surrounding the studs. Perfectly flat and ready to accept a bus bar, no weld ridges whatsoever:
I would be happy to evaluate cells for you prior to purchase. I could even perform capacity testing for you if you bought a small amount to ensure they meet specs. I would need to know from the manufacturer what discharge Amp rate and upper and lower voltages were used to determine rated capacity.

 

[mradtke]

I deleted both the simple and the L-shaped bus bar files on Printables so the links to Printable files on Post #286 for bus bars do not work and should be deleted in the post. The L-shaped bus bar I designed does not and cannot work. The simple bus bar also does not work as I found out during the iteration process with Piev. I corrected it for Piev but posting it is pointless as I believe his last set was a one-off set. Let's hope so, at least.

Purchasing cells from a vendor in China should be done with maximum care. Terminal design is of utmost importance. And the terminal studs Do Not Need to be 8mm as I have had hands on a few different battery packs from other manufacturers that use either 5mm or 6mm terminals. These are used for far greater power levels than the 66hp Mitsubishi motor. The packs I am working with now come from a very large and well-known OE and they use 5mm studs and bus bars connections. In fact, the bus bars themselves are just 1mm thick and 12.15mm wide at the narrowest part. The system fuse is 250A, roughly equivalent to the 260A Mitsubishi system fuse. The horsepower of the drive motor is 102hp. We don't need 8mm studs. Yes, they are more convenient since Mitsubishi uses 8mm but it is more important to get the correct detailing of the terminals.

Piev's last set of cells were modified by the vendor to have 8mm studs. This was specified by Piev to reduce the chance of breaking a terminal off during the torqueing of the 8mm nuts during assembly. According to Piev, he broke off a few 6mm studs during his first conversion so he wanted to reduce that chance by specifying 8mm studs on the second set of cells. But during the second conversion he broke off a couple of 8mm studs as well since they are just welded to the actual aluminum cell terminals. A weld is a weld and in my very experienced opinion if you ask a vendor to change something from what is standard you might not get what you expect to get.

In my opinion, the second set of cells that Piev received with 8mm studs were severely deficient. The studs rose out of two different steps welded onto the cell terminal. This required us to design and manufacture a set of intermediate spacer washers to allow a nice flat surface for the CMU bus bars to sit. The cells really needed to be like his previous set where the 6mm studs rose out of a flat terminal face with no surrounding steps. He and I never discussed this since we had to work with what he received but I can tell you there were a lot of brain cells and US dollars killed by the orientation of those 8mm studs. Here they are:

View attachment 1662

I am willing to participate in the design process of conversion parts for a cell swap. I would need 8 cells sent to me in Texas. I have a shipping system where four cells are put in a 7" cubic double walled box and then into an 8" cubic double walled box. Trying to get measurements right from afar is no bueno. With the cells present I can design the cell spacers and bus bars and send back the cells.

When you purchase cells you must buy cells with a simple terminal structure like the stock Mitsubishi LEV50 cells. There should be no steps or ridges surrounding the studs. Perfectly flat and ready to accept a bus bar, no weld ridges whatsoever:View attachment 1663
I would be happy to evaluate cells for you prior to purchase. I could even perform capacity testing for you if you bought a small amount to ensure they meet specs. I would need to know from the manufacturer what discharge Amp rate and upper and lower voltages were used to determine rated capacity.

When Piev ordered his cells, I was surprised at his choice of terminal design, but not the 8mm size. I think that he called them "circular." Photos of the cells that we used may be found at:

https://5by9.net/prune_batteries/module_rebuild.html

The M8 terminals were an option on our cells, not a "special." We had no terminal failures.

Jiminy, could you please expand on why the L and simple links didn't work? Is it only because of the cell terminal type chosen?

The documentation that my son produced (url above) is of a pack upgrade that is reliably in service.

Thanks,
Michael