Note that this is a 4S6P whith means that you need to connect 4 banks in series to get to the required voltage (3.7V*4=14.8) and each bank has 6 batteries in parallel to get the required mAh. (3000mAh * 6 = 18000mAh)
After building this first battery, I found that the shrink wrap we got was a bit too wide, I would recommend a smaller diameter to do a nicer finish.
Note that the fitting inside the 3inch enclosure is tight so you have to keep everything as low profile as possible.
If it’s of any interest, I can put a link of the final procedure and job safety analysis. Let me know.
In conclusion, it would take 3 batteries for us to break even. I would still recommend BR’s battery if you can get it shipped. There are considerable risks involved in making this. Make sure you know what you are doing, never solder directly on the batteries and protect the contacts with electrical tape when you are doing your manipulations.
The rest of the material come in bulk and cost me about 140USD
The welding machine cost me about 85USD
So 375USD all in with shipping and enough material to make about 10 batteries (except for the silicone wire)
So lets say 175USD per additional battery
I also bought a 400W charger which is why I mentioned I would break even with 3 batteries. I won’t post the link to this charger as it would compete with BR’s charger which would be a d**k move.
I just thought I’d share my experience with the battery packs I made.
The LG Choco turned out to be a very bad choice. Multiple failures if you go over 50% gain.
I am now using Enook 3200mAh batteries which works very well. I have clocked 4 hours with 25% lights on all the time and 25% thrust. Continuously on depth hold or stabilize.
Thanks for sharing this. In my day job we have been producing batteries in a very similar fashion to your technique and, after a couple of fires and a refusal to ship from a major shipping company, we had a major review meeting today to discuss our ongoing battery strategy. I’ll sum it up as follows:
We will no longer build battery packs in-house.
We will lay out a specific set of designs and outsource to pro battery manufacturers.
They will produce the batteries and provide the necessary QA/QC documents along with a Safety Data Sheet (SDS).
From our experience, it is worth noting that if you get a failed cell it can drop its internal resistance and then overload all the other cells in the circuit, this results in a minor fire which gets progressively worse. I can’t share the ugly photos but we were very lucky that nobody was injured.
Furthermore, there are now cells which have internal protection like this one. We are going to be testing them but it’s worth noting that all these cells have guarantees and SDS’s but all those assurances disappear once you start packing them in combined battery packs.
This is where we get into the everlasting argument between Li-Ion and LiPo. I’ve been flying drones with LiPo’s for 8 years and the charger will tell you when it’s time to retire a battery but Li-Ions can get very scary without any warning - just take a look at the e-cigarette videos on Youtube.
After all my research, I am happy to continue with LiPo. This isn’t an empirical decision - it’s just a gut feeling from previous experience.
It would increase your cost but for a little bit of added security and redundancy you can get a protection board to regulate your batteries and improve their life. For aerial operations where weight is huge factor I could see skipping it, but for dive batteries or any ‘really big juice’ packs I wouldn’t go without… My dive batteries see a lot of abuse and the protection boards have saved me from some very nasty accidents. They’re solid state and can be potted right into your battery unit if your solder connections are good.
edit: Also as others have stated, you want avoid cheap vape or offbrand batteries at all costs, although I get it may be hard to find good batteries in some parts of the world. Cheap Li-Ion batteries are not made to the same standards and are more prone to catastrophic failure. There is a fair bit research on this; NASA did failure tests on a handful of manufacturers, and they send 18650’s into space incidentally. I use Panasonic for 18650.
When building batteries in-house, there are a couple things you can do to prevent fires and accidents, charge and balance correctly, and make a safer battery in general.
Design your battery with fusible links ( Tesla-Style ) and solid metal bus bars rather than using welded nickel strips. If the internal resistance of a battery gets very high, or the capacity of the battery falls far below the others, using a glass fuse or a piece of 1/4 W resistor wire metal will break and drop it out of the cell.
Always use a BMS in your pack to charge and monitor it. I use a variety of BMS’es for LiCobalt chemistry batteries such as this 4S controller : http://a.co/d/2UIscbm
When building packs, don’t trust the cell manufacturer! Test each cell and get the actual mAh rating for each one, and match cells as closely as possible in each parallel line and if possible in the series for maximum capacity. The investment in time to do this is well worth it for reliability down the road.
Invest in a non-contact IR thermometer, and if you can afford it – a FLIR module. Charge and discharge the packs after you build them and see if any cells or bus bars are getting hotter than they should.