Main Traction Battery Upgrade i-MiEV

[Jiminy]

I think these press fit nuts might be a better option since we could reduce the thickness of the bus bars to 1.6mm from 3.2mm. Cost for 66 pieces of Bus B goes from $436.26 USD for 3.2mm Cu down to $231.66 for 1.6mm. I think they could be installed with a vise or arbor press, worst case. Cell height would have to be adjusted downwards by 1.5mm to accommodate the thickness of the nut. OR, maybe they can be installed in the underside of the bus bar.

 

[Jiminy]

I think Kiev is right about aluminum. The terminal blocks are aluminum so why make the bus bars copper? If we can use the pem nuts for the 3mm thread then we can get the price for 77x pieces even in 2.0mm aluminum down to a more palatable level. SCS want's $1.23 each for the press fit (pem) nuts installed. Unfortunately, their minimum part size for debur is 5 inches so we would have to knock off any interfering hard edges with a file before installing them.




Tapped 2.3mm thick aluminum:

 

[Jiminy]

Y'all will have to pardon me. I'm on a roll today.

From: https://help.leonardo-energy.org/hc...-area-of-conductor-cables-Copper-vs-aluminium

"One of the major differences between copper and aluminium is that copper has a significantly lower electrical volume resistivity than aluminium. This property quantifies how strongly a given material opposes the flow of electric current. A low value indicates a material that readily allows the movement of electric charge. On a relative scale the differences are significant: copper has a volume resistivity of 1.72e-6 Ohm-cm, compared to 2.82e-6 Ohm-cm for aluminium.

This difference is particularly relevant when designing and installing electrical networks and related components. To attribute to an aluminium conductor the same resistance as a copper conductor, the cross-sectional area of the aluminium conductor must become larger to compensate for aluminium’s higher electrical resistivity. In fact, the aluminum conductor will have a cross-sectional area 64% larger than copper for the same current-carrying capability. This leads to a number of serious drawbacks."

I think we would need to use 3.2mm thick aluminum and make it 20mm wide to replace the 18mm wide 2.0mm copper bus bar. That is roughly 64% 78% greater cross sectional area if my rusty math is correct. 36 millimeters squared vs 64. There is no material between 2.5mm and 3.2mm and 2.5mm is too thin. I hope someone checks that for me.

Jim

 

[kiev]

During my search for cells to replace the LEV50, i bought a module of SDI 94 A-hr cells used in a BMW, too bad they were just a little bit too big to fit in the box.

But the buss bars were al-u-mini-um strips 1.8 mm thick x 30mm wide that were welded to the aluminum terminal blocks. i used a little hack saw blade to cut the bars to separate the cells.

 

[Jiminy]

I have two 8S 67Ah Samsung SDI packs here that I use to power both my stereo amplifier and TV of all things and they started my enquiry into repowering the I-MiEV. Cells are sadly too large, I agree.

The i3 bus bar at 30mm x 1.8mm equals 54 millimeters squared which is 50% more area than the copper bus bars in the Mitsubishi. And that car has 137kW motor output which is almost three times the Mitsubishi's published 49kW. Interestingly, my son and I saw 159A at 345VDC (sag) from my car though in full acceleration tests so 54kW indicated. Guess I got a hot one.

Needless to say, bus bars with more cross sectional area than the BMW i3 should be sufficient. Only thing to confuse the issue is aluminum oxidation at the terminal's contact point and it's effect on conductivity. I thought of hitting the bus bar with a buffing wheel and quickly applying dielectric grease at the contact points. Way overthinking it, I know.

 

[MickeyS70]

, maybe they can be installed in the underside of the bus bar.

One of the functions of these tabs is to transfer the “heat” of the cell to the tiny temp sensors on the CMUs. Therefore best to have these (if you’re still running with this) on the underside but as some are used ‘mirrored’ you need to introduce type “C” again

 

[Jiminy]

I am leaning toward the design below in 3.2mm 6061 aluminum, 22mm wide. Hand tapped and inexpensive. Will need pair of A busses for ends of modules.

 

[mradtke]

Hi Mike,

I drew this if you wanna use it:
View attachment 1267
The 54mm measurement in your drawing would not work in Cad based on your other numbers. If you see a mistake here please let me know and I'll correct it.

Jim

Jim,

Nice drawing.

You said: "The 54mm measurement in your drawing would not work in CAD based on your other numbers." You dimensioned things a bit differently than I did, so I can't spot the error. I show a bus bar length of 74 mm which agrees with 54 mm jumper length and 20 mm washer (spacer) length. Your drawing shows a 51 mm jumper length.

I see from subsequent posts that you are probably going to use aluminum U's or L's combined with I's for combined cell bus bars and jumpers. So perhaps my drawing is only of interest to those who wish to cut their own jumpers from bus bars.

 

[mradtke]

Very cool. Thank you. May I ask what the CTC distance is on the cells you used? Based on what you have here your cell's terminals have different centers than Piev's.

Jim

Jim,

If you are asking about the CTC distance on the same cell:

It is a valid concern that piev's may be different than mine as they were purchased from different vendors at different times. That certainly could affect mass producing jumpers. However, I don't see a discrepancy between piev's measurements and mine if you consider he was using M6 terminals and measuring from the terminal slot edge.

 

[MickeyS70]

However, I don't see a discrepancy between piev's measurements and mine if you consider he was using M6 terminals and measuring from the terminal slot edge.

If one is to use ‘combined’ bus bars then there is no need to upgrade the NMC cells to M8 terminals either…

 

[Jiminy]

Jim,

Nice drawing.

You said: "The 54mm measurement in your drawing would not work in CAD based on your other numbers." You dimensioned things a bit differently than I did, so I can't spot the error. I show a bus bar length of 74 mm which agrees with 54 mm jumper length and 20 mm washer (spacer) length. Your drawing shows a 51 mm jumper length.

I see from subsequent posts that you are probably going to use aluminum U's or L's combined with I's for combined cell bus bars and jumpers. So perhaps my drawing is only of interest to those who wish to cut their own jumpers from bus bars.

Hi Mike,

I made that drawing to assist you with your super helpful guide if you chose to use it. It was unsolicited help and I don't mean to step on your toes. I think I made a logical error in my first attempt to recreate your drawing. I think I fixed it but I think the saw kerf between the two parts breaks my brain. The drawing adheres mostly to your drawing but the small spacer on the right has it's 8.5mm obround hole off-center. If you want to use the drawing and see where I missed something just let me know and I'll fix it. If you don't then you don't have to do anything.

 

[Jiminy]

If anyone needs to make bus bars for their new battery cells I only need to know the cell's terminal to terminal distance and terminal diameter as well as what material thickness you want (though thickness doesn't really matter for quoting as you can specify different thicknesses and materials on the SCS site.). I can create the model and send you a link to the .step file on the Prusa Printables website for you to download and get quoted at Send Cut Send or wherever you want. The model below shows only two different bus designs, straight and L-shaped. You can flip the L shaped ones over.

https://www.printables.com/model/1036239-l-shape-bus-bar-for-1233mm-ctc-battery-cell
https://www.printables.com/model/1036252-i-shape-bus-bar-for-1233mm-ctc-battery-cell-for-mi

 

[kiev]

Thank you for sharing, that is an elegant and simple solution with flipping the "L's"--i really like it.

 

[piev]

If anyone needs to make bus bars for their new battery cells I only need to know the cell's terminal to terminal distance and terminal diameter as well as what material thickness you want (though thickness doesn't really matter for quoting as you can specify different thicknesses and materials on the SCS site.). I can create the model and send you a link to the .step file on the Prusa Printables website for you to download and get quoted at Send Cut Send or wherever you want. The model below shows only two different bus designs, straight and L-shaped. You can flip the L shaped ones over.
View attachment 1280
https://www.printables.com/model/1036239-l-shape-bus-bar-for-1233mm-ctc-battery-cell
https://www.printables.com/model/1036252-i-shape-bus-bar-for-1233mm-ctc-battery-cell-for-mi

I sent you a PM on this..... but I left off the singles which I believe will be needed as shown in your drawing above.

 

[mradtke]

If one is to use ‘combined’ bus bars then there is no need to upgrade the NMC cells to M8 terminals either…

We chose to make the change to M8 terminals, I think that it was $1 per cell, because we thought if Mitsubishi thought M8's were correct, we'd go with the flow. Piev had some thoughts on this as well.

The M8's allow for higher terminal nut torque. I lived through lead acid ICE conversion days with lots of issues with bad battery terminal connections. My feeling if I were to do another car, I'd probably do M8's again to be on the safe side.

Mike

 

[mradtke]

Hi Mike,

I made that drawing to assist you with your super helpful guide if you chose to use it. It was unsolicited help and I don't mean to step on your toes. I think I made a logical error in my first attempt to recreate your drawing. I think I fixed it but I think the saw kerf between the two parts breaks my brain. The drawing adheres mostly to your drawing but the small spacer on the right has it's 8.5mm obround hole off-center. If you want to use the drawing and see where I missed something just let me know and I'll fix it. If you don't then you don't have to do anything.
View attachment 1277

Jim, you are certainly not "stepping on toes." I appreciate the work that you have done. I think that either drawing would do for the document.

I don't know what the folks who follow will choose for the terminal jumpers. The "L" and "I" combined jumper and bus bar is a good approach but I found it too expensive for me when I considered it. So, I chose the less expensive but labor intensive solution of modifying "off the shelf" bus bars.

Mike

 

[mradtke]

I sent you a PM on this..... but I left off the singles which I believe will be needed as shown in your drawing above.

Piev,

As you know there is another Phoenix IMiEV owner here in Phoenix who is considering rebuilding his car's pack. He may very well wish to use the "L" and "I" combined jumper solution. So, if you get a quote on these jumpers, would you please post it to this list?

By the way, using the combined jumper solution will affect the way the modules are assembled, It's not a big deal but it will require a little more care.

It has already been mentioned that the battery height may have to be shimmed differently than explained in our document because the vertical offset of the jumper will be different. It may also require some additional plastic removal.

Mike

 

[Jiminy]

I just spoke with Piev and he's gonna provide me with some important dimensions from his new cells so I can make an accurate pair of jumper designs. But here is a quote below for two jumpers that are very close to correct. These are 3.2mm thick 6061 aluminum without tapped holes. SendCutSend will not tap the small "I" jumpers since they don't meet their minimum part size for tapping. This means you will need to hand tap 24x bus bars with a 3mm tap in a vise with a cordless drill (easy). And if you are gonna do that then might as well do the L shaped bus bars as well as the tapping by SCS costs as much as the parts themselves. Tapping 76x of the L shaped parts cost $133.26 extra at SCS.

 

[piev]

I just spoke with Piev and he's gonna provide me with some important dimensions from his new cells so I can make an accurate pair of jumper designs. But here is a quote below for two jumpers that are very close to correct. These are 3.2mm thick 6061 aluminum without tapped holes. SendCutSend will not tap the small "I" jumpers since they don't meet their minimum part size for tapping. This means you will need to hand tap 24x bus bars with a 3mm tap in a vise with a cordless drill (easy). And if you are gonna do that then might as well do the L shaped bus bars as well as the tapping by SCS costs as much as the parts themselves. Tapping 76x of the L shaped parts cost $133.26 extra at SCS.

View attachment 1285

.

The dual cell bus bar above won't work with the stock plastic covers because the bus bar is mounted on top of the plastic cover. The cover has ridges or separators if you will that keep the original Yuasa cells from moving around, this feature prevents the cover from closing because these ridges hit the bus bar. In addition, the board will no longer connect to the CMU board because it is lower than the bus bar (even if you cut out the battery divider ridges. Looks like for this to work a new lid would need to be designed. The single CMU board connectors above look like they will work. Then just use stock bus bars to connect cells.

 

[kiev]

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