Suggestions on mounting an 18650 pack on a pcb? - Page 1
Forum section: electronics / projects

author: fenclu
author_rank: Regular Contributor
timestamp: January 11, 2016, 08:45:21 pm
content: I'm working on a design that uses two 18650 li-ion batteries. For various reasons i decided to go with a paralell pack of two 18650s. I found a service provided by a polish company bto.pl of making up custom battery packs. I could have gone for two separate 18650s with classic PCB holders, but I heard that paralelling li-ion batteries requires some care and knowledge and since they claim to do it right and for basically no additional cost I decided to use their service.So we have a heat-shrunk pack made of two 18650 in paralell and I want to mount it rigidly on a PCB. Making connection isn't a big problem because for a small cost bto.pl can solder a cable with a classic connector. I found these holdersbut they don't seem to have a way of fixing to a pcb. I really don't want to go for zip ties, since this is supposed to be a commercial product in the future.

author: Maxlor
author_rank: Frequent Contributor
timestamp: January 11, 2016, 08:56:43 pm
content: I'd suggest mounting them to the enclosure, not the PCB. You'll avoid the mechanical stress, and save PCB space (if you can't find one: 3D print for now, injection mold later.) Or is there a reason why it has to be on the PCB? If it has to be on the PCB, I don't think cable ties are so bad really. Or you could get a stamped metal holder custom made (something likethis). Not realistic for one offs, but someone in china'll probably do it once you ask for a few hundred of them.

author: fenclu
author_rank: Regular Contributor
timestamp: January 11, 2016, 09:20:48 pm
content: As a last resort I could mount them to the case, just thought it would be nice and easy to take the PCB out without the extra step of unplugging the cable. Ideally I wanted to outsource assembling the PCB to someone and just put it into the case, but I guess your approach is realistic too.And how would suggest mounting them to the aluminium case without drilling? Hot glue, double sided tape?

author: nctnico
author_rank: Super Contributor
timestamp: January 12, 2016, 12:59:40 am
content: With Li-ion you need at least some protection circuitry like overcharge, over current and under voltage. I strongly suggest to look at pre-made battery packs also for legal reasons. Those packs are expensive for a reason!

author: station240
author_rank: Unknown
timestamp: January 12, 2016, 01:08:14 am
content: Double sided tape would do, so many products around which use that or glue to hold Li-Ion packs in place.

author: pmbrunelle
author_rank: Regular Contributor
timestamp: January 12, 2016, 05:30:09 am
content: Quote from: fenclu on January 11, 2016, 09:20:48 pmThis... you'll get lots of mechanical stress if someone tries to take out the PCB without unplugging the battery. Flying leads defeat the purpose of a PCB, which is to have the wiring on the board.What kind of crappy PCB wouldn't be able to support a small battery pack?I think zip ties could be a pretty clean and inexpensive solution. Make routed slots in the PCB for the zip ties.EDIT for idea #2:Get a thin flat (perhaps 1 mm thick) piece of material, perhaps laser-cut steel, aluminium, plastic, or even standard routed 1.6 mm FR-4 in the shape of the blue part in the attached drawing. Insert the blue part, THEN heat-shrink the cells to make the battery pack assembly with the mounting tabs.Now that you have mounting tabs, you can use screws (with nuts, and star washers as appropriate) to hold the assembly to the main PCB.For a really cool idea, if you do the flat mounting piece as a PCB, the cells can have their flying leads soldered only to the battery pack PCB, and then you make the electrical connections to the main PCB via the screw mounting holes. Make the mounting holes PTH with large enough pads for nice star washers or something.

author: Falcon69
author_rank: Super Contributor
timestamp: January 12, 2016, 06:33:27 am
content: you could make side posts (injection mold, 3dprint, or mill from aluminum) that attach to the side of these and lock in using the grooves, then have the understand of the mounts wuth a hole threaded, then have a hole in the pcb and please a screw from bottom side of pcb through hole and screw in side posts.If you don't understand, I can draw something up for you.There is also these too.http://www.digikey.com/en/product-highlight/k/keystone/pcb-plastic-18650-battery-holders

author: Julez
author_rank: Contributor
timestamp: January 12, 2016, 03:34:45 pm
content: First of all, paralleling LiIon cells is a piece of cake and nothing to worry about. Just make sure they are within 0.1V difference when connecting. After that, they will just behave like one bigger cell.Therefore, I would recommend using a battery holder as this:http://www.batteryholders.com/de/part.php?pn=BK-18650-PC4&original=Li-ion%2018650&override=Li-ion%2018650It can be soldered in without complication. If you worry about the cells falling out, shrink wrap before soldering.As a bonus, the cells are easy to swap if they wear out in a couple of years, I'd like that as a customer.

author: Siwastaja
author_rank: Super Contributor
timestamp: January 12, 2016, 06:11:49 pm
content: If you decide to use holders for user-changeable cells, add an SMD fuse for every cell so that it blows at maximum allowed charge current (typically much smaller than maximum discharge current!) in case the user connects cells in different state-of-charge and high current flows between the cells. The fuses will also blow if the cells are connected in different polarity.