Whether you’re in the market for an 18650 ebike battery pack or you’re thinking to build one from scratch one of the big decisions you’re going to have to make is whether you’re going to go for a pack that is glued together or one that uses plastic stencils to keep the batteries together. There are benefits and drawbacks to each and this article will help buyers & builders alike educate themselves on which setup is going to be best for them.
Hot Glued packs
For many years, almost every custom hand-built pack that was a non-standard shape was hot glued together. The idea is that you hot glue the cells together and the glue and batteries creates the structure of the battery itself. Doing this allowed builders to make batteries in almost any shape, but the problem was that the glue can trap heat in the center of the battery pack making it harder for the center cells to shed heat. Another big problem is that the packs really must be padded because when it bumps against the frame of the bike the cells themselves often take the beating.
- You can really make any shape you want
- The final volume of the pack is quite a bit smaller than a stenciled frame pack
- If you have a spot welder without a remotely attached welding tip you can build the pack up as you go
- Everyone is doing it
- The cells themselves make up the structural element of the battery
- Heat gets ‘trapped’ in the middle of the battery causing the center cells to be under more thermal stress
- You must pad the battery to protect it from damage against the frame or case
Hot glueing packs is the cheapest, simplest and most common way to get into pack building
Plastic Stenciled packs
Over the past year or two we’ve seen more and more packs come onto the market that use plastic cell holders to create a structure for the battery pack. These plastic stencils run about $5.50 shipped from China for enough stencils to hold 50 cells here. The quality of the plastic is pretty low and I have a hard time getting the stencils apart without breaking them. I’ve found that a good way to get the plastic stencils apart is to use 2 long blocks of wood, one on the top and the other offset on the bottom, and gently tap the top block with a hammer to get them apart. If you look carefully at the stencils you’ll see that they only go together and come apart one way. If you’re not taking them apart the right way and start beating on them with a hammer they are just going to break (trust me on this one). You also must put them together one dimension at a time or you can end up with the situation shown in this Bruno ‘Power’ Buccianti video where you can’t actually physically get the stencils together.
- Still pretty cheap at $5.50 per 50 cells or about $.11 a cell, but not as cheap as hot glue
- Adds a lot of structure to the packs
- The large air gaps between the cells means your pack will run much cooler and the temps will be more even throughout the pack, this is by FAR the biggest benefit
- Packs are about 15% bigger in volume than a hot glued pack with offset cells
- The plastic on the stencils is pretty low quality and can break under impact and are not easy to replace as the spot welded nickel strips will need to be cut and rewelded
- Padding your pack is still recommended as the stencils will not protect the edges of the pack which is where they are likely to contact the frame on a triangle pack
- Building a triangle pack means that it will not exactly be a real triangle but will have a jagged edge on the downtube
- If you are using a cheap spot welder without a remote welding tip wand you are only going to be able to get 2 cells deep with it, 3 if you bend the contact tips out a bit
So how do you find out if the packs you are buying are using plastic stencils or are glued together? Sometimes the description of the battery pack on the website will say, but often it will not. The only way to be sure is to ask. I’ve found that some packs I get, like every single soft pack from Lunacycle, has been plastic stenciled packs. The 48v shark packs (in the Hailong frame pack case) are all stenciled, but the 52v shark battery packs from Luna are not. When I asked Eric about that he said that there just was not enough room in the shark case for 52v worth of batteries and the BMS so they had to glue the cells together. When you buy a pack that is glued together it is important that you buy the right cells to go with the power load that you are going to use. You can get by with a 25 amp BBS02 with a 52v NCRb shark pack, but if you plan on using a BBSHD or another 30 amp motor then you should go with the PF or GA cells. My GA shark pack is currently my favorite battery and I’ve had zero issues with it after several months of hard
Just because a pack is glued together does not mean that you should avoid it. There are plenty of glued packs out there that work very well in the designed power range. The problems start to crop up when you are ‘pushing’ the cells to the limit of their discharge capability on a regular basis. If the pack is getting too hot after every ride then you need to consider getting a pack that can put out more power without generating quite as much heat. Certain battery chemistries like the NCRb and the GA cells tend to get warmer than other chemistries like the 25R which doesn’t seem to get hot no matter how hard you thrash on them. The best way to purchase batteries is to educate yourself about new cells and to try them before you buy, if you can.
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