Bus Leads Question

[jackp98]

I am using 18650 cell brackets for my 12s10p pack and would like to use bus leads. I would like to place the bus leads in between strings of + and - cells (see attached for example) but what are the best ways for attaching the copper bus leads to the cell brackets? zip-ties perhaps? i really don't want to solder onto the cell brackets for obvious reason, please help

 

[OffGridInTheCity]

There are many approaches and most of them are just fine.

In my case, I use hot-glue + wires from cell to cell across the bus-bar + zip-ties and I get a stable / hardy unit.

On the 7s7p (red one on the left) I add a protection cover on each side + tape on the corners before adding zip-ties to protect against shorts since I slide it in/out of an APC UPS and it can rub on the sides etc. The long (green one) doesn't need short protections like that because its a 1s and the mechanics of its placement in the powerwall.

Each battery/pack is solid to handle but I don't care what they look like

 

[jackp98]

There are many approaches and most of them are just fine.

In my case, I use hot-glue + wires from cell to cell across the bus-bar + zip-ties and I get a stable / hardy unit.

On the 7s7p (red one on the left) I add a protection cover on each side + tape on the corners before adding zip-ties to protect against shorts since I slide it in/out of an APC UPS and it can rub on the sides etc. The long (green one) doesn't need short protections like that because its a 1s and the mechanics of its placement in the powerwall.
View attachment 24203
Each battery/pack is solid to handle but I don't care what they look like

Hot glue is a good idea. I must use that and zip ties as well it looks good! Don't worry those battery units look neat and tidy especially the balance cables! Definitely better than most I have seen on YouTube Thank you this helps a lot and incredible work! I hope my one turns out just as good haha

Is it okay if I connect the balance leads of the BMS directly to the bus-bars since it is connects the two strings in series? Or does it have to connect to the positive strings of the cell as shown in BMS wirings (like you did on the left battery pack)?

 

[OffGridInTheCity]

>Is it okay if I connect the balance leads of the BMS directly to the bus-bars
Yes, the busbar that connects to + of the cells in parallel instead of just 1 cell is preferred. The way I did it in the picture - if that cell's fuse wire blows it would disable the voltage reading of the entire group of parallel cells and the BMS would not like that.

I think I soldered it to a cell so I wouldn't melt the hot-glue by heating up the busbar - e.g. took a shortcut as the battery in the picture isn't very important

 

[jackp98]

>Is it okay if I connect the balance leads of the BMS directly to the bus-bars
Yes, the busbar that connects to + of the cells in parallel instead of just 1 cell is preferred. The way I did it in the picture - if that cell's fuse wire blows it would disable the voltage reading of the entire group of parallel cells and the BMS would not like that.

I think I soldered it to a cell so I wouldn't melt the hot-glue by heating up the busbar - e.g. took a shortcut as the battery in the picture isn't very important

Perfect thank you! Since I will use fuse wires and busbars for my battery, is it ideal to wrap it around kapton tape or heat shrink? I also want to integrate cooling fans to the housing case so heat shrink may be a bad idea though, not too sure about this. Perhaps I will use kapton take to insulate the fuse wires and busbars on both sides and leave the sides exposed for the air to circulate around and through the pack since I am using cell spacers

 

[OffGridInTheCity]

When I first started, I worried about heat - but I've discovered that.... 1) my powerwall is .3a-.6a/cell and it doesn't have any noticeable heat and 2) my APC batteries can go up to 2a/cell sometimes (7s7p) but at most they might get 'a little warm' but don't need any cooling and these are typical low-amp laptop cells (that get hotter than high amp ebike cells would at 2a).

How much current / cell are you planning to pull from your battery continuously and peak ?

 

[jackp98]

When I first started, I worried about heat - but I've discovered that.... 1) my powerwall is .3a-.6a/cell and it doesn't have any noticeable heat and 2) my APC batteries can go up to 2a/cell sometimes (7s7p) but at most they might get 'a little warm' but don't need any cooling and these are typical low-amp laptop cells (that get hotter than high amp ebike cells would at 2a).

How much current / cell are you planning to pull from your battery continuously and peak ?

ah that explains it. yes my pack is bigger so i need to accommodate the heating aspects

the controller will draw 300A from the battery and the rating of the battery is 360A. I was thinking maybe I should add more cells in parallel to up the amperage so it's not overworked when the load pulls 360A

 

[OffGridInTheCity]

the controller will draw 300A from the battery and the rating of the battery is 360A. I was thinking maybe I should add more cells in parallel to up the amperage so it's not overworked when the load pulls 360A

In the 1st post - you show 12s10p... e.g. 44v nominal. 300a * 44v = 13,200watts and at 10p that's 300a/10cells = 30a per cell. 30a per cell is pretty hefty and I would expect the voltage to drop instantly below anything useful - the battery wouldn't have a chance to get hot, it just wouldn't work

What kind/specs of the 18650(s) are you're using?

Don't mean this as being critical / against your plans - its just that I'm not understanding how this would work at all from what you presented so far and want to make sure you get good advice

 

[jackp98]

In the 1st post - you show 12s10p... e.g. 44v nominal. 300a * 44v = 13,200watts and 300a/10p = 30a per cell. That's pretty hefty for any 18650 cell I've ever heard of - not sure that will work as the voltage would just drop instantly below anything useful as soon as you connected a 300a load. Heat/cooling will not be the issue

I'm still on the planning and design stage i still have a lot to learn before doing the practical work hence my questions

i saw some youtubers use a sony vtc6a rated at 30A (linked below) although one youtuber said they must be kept below 80 degrees celsius to discharge 30A else it all discharge up tp 20A. I should really use 13s to be frank as most high current controllers are rated at 48V so I think I will go with 13s10p

I designed a case on cad that uses multiple cooling fans to keep the temperature regulated. Although I am still researching the different methods of cooling

Sony/ Murata VTC6A - 21700 Battery - 4000mAh - 30A

4000mAh - 30A Continuous Discharge - Flat Top/Button Top/TabsOrder by 3pm (Monday to Friday) for same day dispatch!Brand: Sony/MurataModel: VTC6ASize: 21700Chemistry: IMRNominal Capacity: 4000mAhNominal Voltage: 3.6VDischarge: 30A Max ContinuousPositive: Flat/Button Top/Tabs (please select)...

www.18650.uk

 

[floydR]

The cells linked aren't 18650's if the designs use 18650 dimensions, this might cause a problem with your cad designs.

later floyd

 

[daromer]

Go 14s instead if you plan going normal 48V appliances. They suit the best.