Nice job! Some suggestions though: 1. Consider making the battery XT60 connector a female. As a general rule, sources of power should use female connectors because it’s too easy to accidentally short male pins together. 2. As already noted by others, is preferable to insulate the bodies of the 18650’s so the thin cell sleeves don’t wear through and short out. 3. I like to check the integrity of the spot welds as I complete each parallel “bus” connection, but BEFORE I spot weld the other side. You’re creating a “bus” for the 4 cells… check the voltage from the “bus” to each cell’s opposite end. If there is a bad spot weld on one cell, you won’t get a voltage reading for that cell, and you can fix it right away. Having one of the 4 parallel cells unknowingly disconnected will lead to an unbalancing of the 7 series sections. Yes, the bms will try to help offset this problem, but they really don’t do all that well honestly. 4. I’ve accidentally shorted out sections of the battery as I was progressing through the 7S sections. My advice is to add kapton tape over the sections as you go. Don’t wait until the end. If you accidentally drop on of your nickel strips and it touches the previously completed sections, it’s spark-tastic! 5. I usually solder on the XT60’s (or even better XT90’s) prior to soldering the lead to the BMS. That way you’re not trying solder to the XT60 with “live” wires. 6. You should mention that each of parallel sections in your 7S pack need to be capacity matched. If the four cells in S1 don’t match the capacity of the four cells in S2, S3, S4, S5, S6, and S7 you will quickly get an unbalanced battery. That leads to overcharging and undercharging of each of the 7 sections. Again, bms will try to help fix this, but they are far from adequate to effectively accomplish this. So much better to just match the capacity of each 4-cell parallel pack! Keep up the great work. Your videos are very helpful for many people!!!
Great tips. Never thought of putting the sheets between cells, although that’s how it was done in the 2 battery packs I salvaged and was wondering why that was. Will definitely do that with my next build. I did put another layer of heat shrink on each cell (the original Samsung cells have all the data printed on them so wanted to keep), so that does help a bit. Checking the cells after spot welding one side is a great idea as well. Chrs.
You are the best, I almost burned my pack using China shipped 7s3- box with bms , but they provided instructions for 12v 3p vs 29.4V intended. I looked up your video for battery orientation. Thank you!
Nice video. To make it safer, place heavy paper (rosin paper) plus capton tape between the series links to prevent wear and a series short. Thanks for the video.
The first pack I built was made with cell holders. But, it would not fit in the tube I have for my LED lights I make. When I put the next pack together without the cell holders I forgot to put barley paper between the cells. My bad.
hi i love your video! I was wondering if you could share your wooden system that holds your 18650 batteries. I have some old pallets of wood that are probably good for doing this. sorry for my english i am better in french
Here is a link to one similar. www.amazon.com/daier-Electric-Bicycle-Li-ion-Battery/dp/B07QPP7FHX/ref=sr_1_13?crid=3SFZN3OC5IYPG&keywords=7s+bms+18650&qid=1644703123&sprefix=7s+bms+18650%2Caps%2C70&sr=8-13
Nice job! Some suggestions though:
1. Consider making the battery XT60 connector a female.
As a general rule, sources of power should use female connectors because it’s too easy to accidentally short male pins together.
2. As already noted by others, is preferable to insulate the bodies of the 18650’s so the thin cell sleeves don’t wear through and short out.
3. I like to check the integrity of the spot welds as I complete each parallel “bus” connection, but BEFORE I spot weld the other side. You’re creating a “bus” for the 4 cells… check the voltage from the “bus” to each cell’s opposite end. If there is a bad spot weld on one cell, you won’t get a voltage reading for that cell, and you can fix it right away. Having one of the 4 parallel cells unknowingly disconnected will lead to an unbalancing of the 7 series sections. Yes, the bms will try to help offset this problem, but they really don’t do all that well honestly.
4. I’ve accidentally shorted out sections of the battery as I was progressing through the 7S sections. My advice is to add kapton tape over the sections as you go. Don’t wait until the end. If you accidentally drop on of your nickel strips and it touches the previously completed sections, it’s spark-tastic!
5. I usually solder on the XT60’s (or even better XT90’s) prior to soldering the lead to the BMS. That way you’re not trying solder to the XT60 with “live” wires.
6. You should mention that each of parallel sections in your 7S pack need to be capacity matched. If the four cells in S1 don’t match the capacity of the four cells in S2, S3, S4, S5, S6, and S7 you will quickly get an unbalanced battery. That leads to overcharging and undercharging of each of the 7 sections. Again, bms will try to help fix this, but they are far from adequate to effectively accomplish this. So much better to just match the capacity of each 4-cell parallel pack!
Keep up the great work. Your videos are very helpful for many people!!!
Thanks. I will remember your advice for future reference.
Great tips.
Never thought of putting the sheets between cells, although that’s how it was done in the 2 battery packs I salvaged and was wondering why that was. Will definitely do that with my next build. I did put another layer of heat shrink on each cell (the original Samsung cells have all the data printed on them so wanted to keep), so that does help a bit.
Checking the cells after spot welding one side is a great idea as well. Chrs.
You are the best, I almost burned my pack using China shipped 7s3- box with bms , but they provided instructions for 12v 3p vs 29.4V intended. I looked up your video for battery orientation. Thank you!
Nice video. To make it safer, place heavy paper (rosin paper) plus capton tape between the series links to prevent wear and a series short. Thanks for the video.
The first pack I built was made with cell holders. But, it would not fit in the tube I have for my LED lights I make. When I put the next pack together without the cell holders I forgot to put barley paper between the cells. My bad.
Nice Work
Thanks
Very well done, sir! :)
Thanks. Please subscribe so I can continue to make new videos.
hi i love your video! I was wondering if you could share your wooden system that holds your 18650 batteries. I have some old pallets of wood that are probably good for doing this. sorry for my english i am better in french
Hi
Please can you share the way you did this wood form, I mean the dimensions. Appreciate your help 🌹
Great video, what is the price of that bms?
If I remember correctly it was under $10. It's not the best BMS but a better one will not fit in the tube of the lights.
Here is a link to one similar. www.amazon.com/daier-Electric-Bicycle-Li-ion-Battery/dp/B07QPP7FHX/ref=sr_1_13?crid=3SFZN3OC5IYPG&keywords=7s+bms+18650&qid=1644703123&sprefix=7s+bms+18650%2Caps%2C70&sr=8-13
@@paulswoodshop395 tnx, for simple projects its great bms bcz of price :)
I've just started getting into this been searching TH-cam for 5 days and this is the best video so far.