ElectroClassic EV
Classic Cars Reborn into the Electric Future

Connect the Cells

The connecting straps that originally came with the CALB batteries presented an unexpected glitch. The CALB 180AH cell terminal distance is shorter when the cells are placed side-by-side, than when they are end-to-end. The shorter dimension is 2 13/16″ (71.4mm) and the longer is  3″ (76.2mm).  Calib had supplied me with 36 of the shorter copper bus bars, but most of my connections will be end-to-end and require longer ones. They told me a new order would take several weeks to ship from China, sending me back to the interwebs to scout alternatives. As it happens, copper bus bars are scarce online, explaining why some EV builders fabricate their own from layered copper sheet. An excellent alternative is tin-plated, braided straps. They are tinned to resist oxidation, flexible to transfer less shock and vibration between battery terminals, and offer greater conductivity because they are stranded. There’s a useful discussion of the advantages of braided connecting straps on the EVTV blog. Like copper bus bars, they were also hard to find, and they were pricey. The least expensive retailer I found was EV Works in Australia. In spite of the exchange rate and shipping, I still saved more than a buck per strap over the best US price. Shown above are the original copper bus bars with the shorter and longer braided straps.

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Because EVs use substantial amperage, loose battery terminal connections can cause loss of power, resistance heating, or even severe cell damage. Once the connecting straps are tightened down, it’s very important they stay that way. While researching this issue, I discovered a crucial innovation to the humble lock-washer. A Swedish company called Nord-Lock carries a two-piece washer that incorporates wedge-like cammed surfaces that face each other. A normal lock-washer is designed solely to prevent backward rotation of the bolt, while the Nord-Lock washer slightly tightens if the bolt tries to unscrew itself. Here’s a video link that shows what that means. There have been very good reports online, so I bought a few boxes from Page Auto Supply’s Amazon site. Above is the assembly line of all 72 terminal bolts with Nord-Lock washers, ready to install.

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All of the cells were numbered and labelled according to their exact fit and order in the connection scheme. Starting with cell #1, the blue masking tape was peeled back and a braided strap was bolted in place. This proceeded in sequence from cell to cell, positive to negative, creating a serial daisy-chain of lithium batteries. The BMS will need to be installed before any serious juice flows through this system, so I left the terminal bolts only slightly tight. You may also notice that the braided straps have each been given a heat shrink sleeve for added protection against acts of God and careless humans.

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The above shots show the braided straps completely installed in the fuel bay and front trunk. The front and rear battery packs have also been cabled together, but the main lines that run to the contactor and controller will not be connected until all of the other EV electrical components are in place. In fact, for safety reasons all of these cell terminals will be taped over until the BMS is ready to install.

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An EV drive circuit includes both expensive power transistors and a bank of lithium cells, so a meltdown here is a very pricey proposition. Although the Curtis controller has built-in protection against external overload, its own catastrophic failure would put the entire battery pack at risk. The obvious solution is a fuse, but a regular thermal fuse would not react quickly enough to protect all of this sensitive gear, although a semiconductor fuse will. Instead of a thermal melt, this kind of fuse uses electronics to break the circuit immediately if the current suffers an unexpected spike, saving the circuitry and batteries from frying. Two Ferraz-Shawmut semiconductor fuses were purchased from EV Source for this purpose, and placed in series between the 3 battery packs. The white object above is one of them, bolted and heat-shrunk into the 2/0 welding cable connecting the front and rear driver side pack, and clamped to the firewall below the engine cooling deck.

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2 Responses to “Connect the Cells”

  1. This is amazing. Better than the couch.


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