Step 2 – Series Connect: With the initial top balance out of the way, it's on to step 2. The first part of this process is going to be to address the threading issues and install grub screws (I've been using the supplied bolts to this point). I'm using a
M6x1.0 bottom tap to chase the existing threads and in most cases, complete the threading to the bottom of the hole. In the first picture below, you'll see just how incomplete some of the holes are. In that example, I could only get the grub screw in about 3mm. With re-threading, I'm able to all the screws in at least 6 mm.
I'm not using any cutting oil, so the threading is a bit 'crunchy' at times. I'm about half way through the threading at this point, and haven't botched any of the holes yet. Fingers crossed my luck continues.
One new issue that has come to light now that i'm installing grub screws is that several of the holes are not tapped straight (ie, not vertical). The positive terminal in the pic on the right is one of the worst examples I've found so far. I haven't tried to measure it, but it looks to be at least 5 degrees off vertical. I'm worried that this is going to seriously compromise the quality the bus-bar/terminal contact. I'm wondering if I should include a copper crush washer under the flange bolts to even out the compression force. Other thoughts/ideas on this?
Once i'm done with the re-threading and grub screw installation, I'll series connect the pack and wire up the BMS and inverter for an initial capacity test.
Edit: In case anyone's interested, I'm using
20 mm M6x1.0 grub screws. I've seen that others have been recommending 25mm, but that seems to be a bit longer than I need. After re-threading, I've got about 13 mm of screw to work with. 3.2 mm for my 1/8" bus-bars leaves 10 mm for a
flange nut and washer.
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