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.
Main Traction Battery Upgrade i-MiEV
- Thread starter piev
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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
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Thanks for the context I'll remove this recommendation.
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!
There simply is no battery heating function as stock LEV50x cells don’t have a ‘do not charge below freezing’ limitation
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.
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.
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- Nov 6, 2013
- Messages
- 33
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
Hi Michael,
The L-shaped bus bars as shown in Post #267 cannot work since they interfere with the upper plastic CMU holder. There is a plastic partition between cells and the L-shaped bus bars would have to pass through the partition or you'd have to remove plastic to make it work. That is not a good solution. The simple CMU taps did not work due to the specific design of Piev's second set of cells. The ID of the hole had to be changed to match one of the steps in his terminals.
I designed those parts with no real hands on experience with these modules. Just designed what I thought would work without having the parts in front of me. There is an L-shaped bus bar that can work but the CMU tap would come out of the main rectangular cell-to-cell section at a 90 degree angle from an 8mm cell tap hole. No sweeping curves, however pleasing to the eye. Just boring right angles like this (from post #261):
BUT, as I have no experience in installing these Chinese cells As you do I cannot say with 100% surety that they would be easy to use. I do have experience with a set of different, much smaller cells and I can say that without question that the "tuning" process of getting the 3mm holes lined up with the holes in the CMU before torqueing down the nuts holding the bus bars is very tedious. When you torque the nuts the whole assembly rotates unless you very carefully hold the bus bar to keep it from moving. Super unfun. It was my least favorite part of the conversion.
What is needed (it just occurred to me) is a fixture made of the stiffest, non-conductive material that has the hole pattern of the CMU so that you can torque down the bus bars while holding the 3mm holes in perfect alignment with the CMU hole pattern. The problem is that it cannot be metallic or carbon fiber as they conduct and the other problem is that there is a good sized tolerance in the hole pattern from CMU to CMU as they have already been mounted before and the floating contacts have already moved a little like they were designed to do. The fixture would have to be designed around the "ideal" brand new CMU and all used CMUs would have to be tweaked slightly to mate with the hole pattern created by setting bus bars to the ideal fixture.
I look forward to refining this process. I really need a set of at least four cells to fully flesh this out. I have all of the rest of the parts needed.
The L-shaped bus bars as shown in Post #267 cannot work since they interfere with the upper plastic CMU holder. There is a plastic partition between cells and the L-shaped bus bars would have to pass through the partition or you'd have to remove plastic to make it work. That is not a good solution. The simple CMU taps did not work due to the specific design of Piev's second set of cells. The ID of the hole had to be changed to match one of the steps in his terminals.
I designed those parts with no real hands on experience with these modules. Just designed what I thought would work without having the parts in front of me. There is an L-shaped bus bar that can work but the CMU tap would come out of the main rectangular cell-to-cell section at a 90 degree angle from an 8mm cell tap hole. No sweeping curves, however pleasing to the eye. Just boring right angles like this (from post #261):
BUT, as I have no experience in installing these Chinese cells As you do I cannot say with 100% surety that they would be easy to use. I do have experience with a set of different, much smaller cells and I can say that without question that the "tuning" process of getting the 3mm holes lined up with the holes in the CMU before torqueing down the nuts holding the bus bars is very tedious. When you torque the nuts the whole assembly rotates unless you very carefully hold the bus bar to keep it from moving. Super unfun. It was my least favorite part of the conversion.
What is needed (it just occurred to me) is a fixture made of the stiffest, non-conductive material that has the hole pattern of the CMU so that you can torque down the bus bars while holding the 3mm holes in perfect alignment with the CMU hole pattern. The problem is that it cannot be metallic or carbon fiber as they conduct and the other problem is that there is a good sized tolerance in the hole pattern from CMU to CMU as they have already been mounted before and the floating contacts have already moved a little like they were designed to do. The fixture would have to be designed around the "ideal" brand new CMU and all used CMUs would have to be tweaked slightly to mate with the hole pattern created by setting bus bars to the ideal fixture.
I look forward to refining this process. I really need a set of at least four cells to fully flesh this out. I have all of the rest of the parts needed.
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I think you’re overthinking this, have look at the picture in post #280. You can screw the CMU to the ‘tabs’ before you torque the bus bars?
You cannot do this as the torqueing process will rip the CMU's floating contacts apart when the bus bars rotate. The bus bars must be fully torqued before attaching the CMUs. I saw movement of up to a millimeter when torqueing down the bus bars.
The cells in Piev's/MRadtke's setup are located by hand milling out the plastic cell holders to allow the longer cells to fit. The cells are imperfectly centered front to back and so the CMU taps/bus bars need extra tolerance around the 8mm terminal holes to account for this. That extra tolerance requires extra care in aligning CMU taps after the torqueing process. Those guys might beg to differ but they need to make their own comments on the CMU alignment process.
I did this process within the last couple of days on 88 cells with 5mm studs. The terminal holes in the laser cut L-shaped bus bars were cut to 6mm and I needed all of the extra wiggle room to make it work and that was with 3D printed cell holders which are much more exact than hand-worked cell holders. Getting everything to line up and torqued took about 20-25 minutes per module. My brain hurt afterwards.
The cells in Piev's/MRadtke's setup are located by hand milling out the plastic cell holders to allow the longer cells to fit. The cells are imperfectly centered front to back and so the CMU taps/bus bars need extra tolerance around the 8mm terminal holes to account for this. That extra tolerance requires extra care in aligning CMU taps after the torqueing process. Those guys might beg to differ but they need to make their own comments on the CMU alignment process.
I did this process within the last couple of days on 88 cells with 5mm studs. The terminal holes in the laser cut L-shaped bus bars were cut to 6mm and I needed all of the extra wiggle room to make it work and that was with 3D printed cell holders which are much more exact than hand-worked cell holders. Getting everything to line up and torqued took about 20-25 minutes per module. My brain hurt afterwards.
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IMHO, if the tabs are under the bus bars then torquing shouldn’t affect them as there isn’t much movement on the 8mm stock bars when in situ?
That has not been my experience but I am not using stock anything other than CMUs. Those guys need to chime in but based on my experience, there will be a lot of movement in the relative positions of the 3mm threaded holes when torqueing down the bus bars regardless of what non-OE cell you are using.
