Ok, I decided to share personal experience building the packs out of dewalt A123 cells. The goal is to have two 10s6p packs for my first e-bike conversion. I intend to later add a parallel / serial relay switch so I can run either as a 33V or 66V configuration.
I decided not to use original plastic cell endcaps to make parallel wiring of individual cells easier and packs a bit more compact. I plan to use sticky rubber strips to run along the pack edges before enclosing it in heat shrink.
For parallel buses I decided to use single strand bare tin-coated wire (McMaster is the only place I found that sells small pools) enclosed in sectioned high temperature sleeving between solder joints. This proved to be a right decision as soldering a pair of wires to the cell interconnect tab is more cumbersome than a section of continuous single strand wire. I ordered PTFE (teflon) sleeving for the wire (also from McMaster) which is fairly tough and high temperature resistant so you can solder right next to the sleeve (even touching it with soldering iron) without melting it. However if I would do that again - I'd go for a braided sleeving (coated fiberglass or kevlar), since the PTFE sleeve is relatively thin and can be punctured when the pack rattles on the bike. For now I'll probably add some reinforced tape pieces as protection between the cells and sleeved bus. I intentionally made a slight upward bend in each sleeved bus segment to add 1mm of separation from the cell.
The rest of this message are suggestions based on what I have learned in the process -
Building large packs resembles a production line - a lot of boring repetitive work. The key three things to survive it IMHO are (i) having proper tools, (ii) maintaining clean table with no metal bits and pieces to short the cells, (iii) being constantly alert (it is very easy to forget that you are working with charged cells and short something).
Cordless screwdriver, *temperature controlled* soldering iron are pretty much required for this work. Although I have a decent soldering station for precision work I got a Weller W100PG temperature controlled 100W iron specifically for working with massive wires. The other cheap department store non temperature controlled iron overheats and oxydises like mad.
Protection glasses are a must. Despite all the effort I did short the packs twice already
Both times trying to pull the original wire from output tabs - it sticks there sometimes and it is too easy to slip the iron and short something. The spark instantaneously evaporates away offending metal pieces and that can fly i your eyes. I also plan on buying fire extinguisher - just in case. Honestly working with packs that big and powerful scares me somewhat :? .
Some Dewalt packs come with pieces of yellow insulation tape. DO NOT throw this stuff away. It is a very nice heat resistant Kapton tape and is very usfull in insulating something next to the solder point as it does not melt at all. The white insulation tape on other packs is junk - it melts just seeing the iron.
A lot has been said in this forum about checking cells and balancing them prior to assembly - just a reminder.
If using bus interconnect tin-coat every welded tab prior assembling the pack and soldering buses. Clean the blue marker dots with alcohol and use rosin flux pen. The welded tabs are fairly easy to tin coat if (i) they are properly cleaned and prepped (ii) soldering iron is not overheated. On the picture you can see some intentional offset in coating where two buses run closely in parallel.
When doing final soldering use rubber mat to cover the remaining cells (this has been mentioned in the blog on car pack build that Doc posted recently). Maintain utmost attenion not to short things.
The pictures illustrates prepared dewalt pack (balanced, hot glued with tabs tinned). Notice extra isolation where the output tabs are located - in a pack these will overlap th other cell terminal. I used two layers of Kapton tape during assembly - one inserted under the output terminal sticky side up and another covering the overlapped cell top sticky side down. Make sure the tape completely overhangs the cell top. Later I plan to add some fiberglass tape in that area to avoid puncture.
As you can see there is no output bus yet on the pack - I am still waiting for 12AWG silicone wire to arrive.
One thing I have not decided upon yet as what to use as a fuse for the pack. I need something in the 150A range that is not too bulky. I may just use a very short section of AWG 16 wire wrapped in several layers of fiberglass outside the pack as a fuse
.
I decided not to use original plastic cell endcaps to make parallel wiring of individual cells easier and packs a bit more compact. I plan to use sticky rubber strips to run along the pack edges before enclosing it in heat shrink.
For parallel buses I decided to use single strand bare tin-coated wire (McMaster is the only place I found that sells small pools) enclosed in sectioned high temperature sleeving between solder joints. This proved to be a right decision as soldering a pair of wires to the cell interconnect tab is more cumbersome than a section of continuous single strand wire. I ordered PTFE (teflon) sleeving for the wire (also from McMaster) which is fairly tough and high temperature resistant so you can solder right next to the sleeve (even touching it with soldering iron) without melting it. However if I would do that again - I'd go for a braided sleeving (coated fiberglass or kevlar), since the PTFE sleeve is relatively thin and can be punctured when the pack rattles on the bike. For now I'll probably add some reinforced tape pieces as protection between the cells and sleeved bus. I intentionally made a slight upward bend in each sleeved bus segment to add 1mm of separation from the cell.
The rest of this message are suggestions based on what I have learned in the process -
Building large packs resembles a production line - a lot of boring repetitive work. The key three things to survive it IMHO are (i) having proper tools, (ii) maintaining clean table with no metal bits and pieces to short the cells, (iii) being constantly alert (it is very easy to forget that you are working with charged cells and short something).
Cordless screwdriver, *temperature controlled* soldering iron are pretty much required for this work. Although I have a decent soldering station for precision work I got a Weller W100PG temperature controlled 100W iron specifically for working with massive wires. The other cheap department store non temperature controlled iron overheats and oxydises like mad.
Protection glasses are a must. Despite all the effort I did short the packs twice already
Both times trying to pull the original wire from output tabs - it sticks there sometimes and it is too easy to slip the iron and short something. The spark instantaneously evaporates away offending metal pieces and that can fly i your eyes. I also plan on buying fire extinguisher - just in case. Honestly working with packs that big and powerful scares me somewhat :? .Some Dewalt packs come with pieces of yellow insulation tape. DO NOT throw this stuff away. It is a very nice heat resistant Kapton tape and is very usfull in insulating something next to the solder point as it does not melt at all. The white insulation tape on other packs is junk - it melts just seeing the iron.
A lot has been said in this forum about checking cells and balancing them prior to assembly - just a reminder.
If using bus interconnect tin-coat every welded tab prior assembling the pack and soldering buses. Clean the blue marker dots with alcohol and use rosin flux pen. The welded tabs are fairly easy to tin coat if (i) they are properly cleaned and prepped (ii) soldering iron is not overheated. On the picture you can see some intentional offset in coating where two buses run closely in parallel.
When doing final soldering use rubber mat to cover the remaining cells (this has been mentioned in the blog on car pack build that Doc posted recently). Maintain utmost attenion not to short things.
The pictures illustrates prepared dewalt pack (balanced, hot glued with tabs tinned). Notice extra isolation where the output tabs are located - in a pack these will overlap th other cell terminal. I used two layers of Kapton tape during assembly - one inserted under the output terminal sticky side up and another covering the overlapped cell top sticky side down. Make sure the tape completely overhangs the cell top. Later I plan to add some fiberglass tape in that area to avoid puncture.
As you can see there is no output bus yet on the pack - I am still waiting for 12AWG silicone wire to arrive.
One thing I have not decided upon yet as what to use as a fuse for the pack. I need something in the 150A range that is not too bulky. I may just use a very short section of AWG 16 wire wrapped in several layers of fiberglass outside the pack as a fuse
.
and a whopping 720A for 10 second "bursts". 
