Well, yesterday was a whirl of activity. I started populating a battery rack, mainly to try out our idea of giant cable ties for clamping the cells:
You can see a pair of old, analogue style BMU boards installed; at least they are the right size. Also, I installed a few Sky Energy links upside down, noting that they do fit. It's probably not a great idea, as there is almost no room at all for the links to give, at least not without distorting, which would put a lot of load on the cell terminals. We were considering upside down links at one stage when we thought we might connect boards along the side with a sort of loop of PCB material. However, we're well past that now.
All of the links from one particular plastic sealable bag were really shiny and bright; you could use them as shaving mirrors. These links would be a year old now, and all the others are quite tarnished. So if you know that you won't be needing your links for some time, consider storing them in plastic sealable bags, and possibly make an effort to exclude most of the air.
Perhaps we should have done the same with the cells themselves; some of the terminals were tarnished rather badly; a few of them had copper terminals that were completely black. I touched them up with fine sandpaper as best I could.
The cable ties (which were quite expensive, about $2 each I think for a bag of 25) didn't work out well. They fit, and you can put a bit of tension on them, but nowhere near enough. Nylon is 6 times stretchier than steel, as technical guitar aficionados (like Weber) will know.
At the moment, we're back to "what was so bad about the threaded rod again?". Weber has shown that they can be welded (they're supposed to be stainless) to make the appropriate lengths, so that's something. It's just going to be quite tricky getting cells in and out of battery boxes.
Meanwhile, Weber and Newton were attempting to mount one of the recently made battery boxes, so we can paint it before it rusts. (Even our motor's rotor is rusting... definitely need to get to that.) Alas, it failed the "fitness test", as in, "it fiddn' dit!"
It was decided to "move" the corners of the protusion with 6 cells in it, 16 mm at one end, and 30 mm at the other, losing 46 mm overall (1 cell width). Unfortunately, "moving" corners like that is almost as much work as building a new box, but it was done by late evening. So now we're back to where we thought we were at the start of EV day. I guess these things are to be expected.
Weber was 95% finished with panellising the BMU boards for production; we've decided that $400 is too much to pay for an artwork modification, and we don't have time for another Batch PCB prototype, and quick prototypes are also expensive. So we're going to make 250 boards, order parts for 250 boards, and make them work. The "squiggle joins" (or should I capitalise the "s" now?
) are completely untested, but we have the fallback of guillotining them off and just using wires. After lunch, he decided to finish the panellisation, so the order could be sent off. The BMU artwork has been taking up most of our time for a while, so it will be good to have the order sent. I showed Weber some pointers for quicker deleting of tracks (Tools Unroute Connection on Protel), and I learned some tips from him as well.
A half hour after I left him to finish that job, I was called upstairs. "There's all this green!". Green on Protel indicates a design rule violation, such as a short circuit, track too close to a via, etc. It's good to fix these, as some manufacturers will refuse to make the board if there are such violations, and also of course, it might mean an actual error in the design. It took a bit of detective work to establish that the problem was some text "uTXD+" on the bottom layer. Sadly, we don't have such text on the board. Although we did, a hundred revisions ago, back in the analogue days. Back then, we used the "comment" field of a component as actual text in the copper, back before we were paying extra for a second silk screen overlay. We had changed this text to appear on the bottom layer and mirrored. When we didn't want that any more, we clicked the "hidden" box, so it doesn't appear on final artwork. It seems that the Protel design rule checking didn't respect the hidden checkbox, and the text, now floating off to one side of the board, caused no problem until panellisation, when there is now another board there, and the clearance check failed.
The solution was to change that text to be on the bottom overlay, but that meant 34 changes. Protel does have a global change facility, but when I tried it, it asked "you are about to make 1620 changes; ok or cancel?". With a bit of fiddling, I worked out how to only change the texts that were on the same layer, i.e. the bottom layer, to the bottom overlay layer. This time, 32 objects were changed (I know I had done one by hand, and must have done another). Anyway, the violations were gone, so by about 4pm, we had the order off to BEC Manufacturing.
Next on the list was ordering the charger; we've decided to get a 2 kW Elcon charger that should be able to charge helf the pack. It might end up being our primary charger, depending on how things go with controller charging. As others have mentioned, Elcon also sell DC/DC converters, and some of those are high voltage and isolated. Alas, only the "800 W" models (600 W continuous, 800 W peak) will take 420 V, which isn't quite enough. Still, we could turn off the DC/DC while charging, and the Elcons may be quite economical. Indeed, all their DC/DC models are under US$100 (before shipping), except the 800 W models, which are over US$350. We'd eventually need two of these for 730 V working, and two of them would be huge. So we just ordered the charger. It will "go into production" as soon as Weber wires over the money. It came to US$649, including US$165 (
) for shipping. We've ordered the CAN version, even though others have pointed out that the RS232 option may be available in the non-CAN version, and is more convenient for us to use. But we can't be sure about that, and getting technical information like that from a Chinese company... well, I guess most of us know how likely that is. The CAN option is US$44, so it's not a deal breaker.
Edit: added two more images.