Help me tweak my 2x 18650 waterproof holder
I've been making a bunch of these 2x18650 waterproof holders for headlamps and they work really nicely. The downside is that they were really hard, time-consuming, and expensive to make (something like $50 per case).
So I'm looking into getting some more professionally made in a bulk batch (more like $20 per case). Before I drop the money, I thought I should tweak the design so that it can be easily mounted on a bike frame.
As you can see, it's made up of two parts:
1. A piston carrying the cells, contacts, and sealing oring,
2. An oval-shaped box with mounting lugs.
On the headlamp, the mounting lugs are screwed to a head-shaped bracket (through which the elastic is fed).
At first I thought I could replace the head-shaped bracket with two C-shaped clamps which would bind to a bike's frame. Then I thought that it probably shouldn't be held too rigidly because the impacts will eventually crack the plastic.
So now I'm leaning towards:
- a single C-shaped mount (to match the round tube of the bike's frame),
- rigidly screwed to the box,
- possibly rubber-lined on the frame-side,
- and then wrap some double-sided Velcro (One-Wrap) around everything
- (holding the box and the bike frame together).
Velcro is already used to hold the piston in the box, so it's no hassle to just wrap an extra piece around a bike frame. I initially chose Velcro because I wanted a design that:
- had very few parts to break when bashed around the bush,
- was easy to use with heavily gloved hands (no screws or fiddly latches),
- was very lightweight,
- and was easy to manufacture.
Any thoughts? Is there a better way to safely attach a small box (approx 100 x 45 x 25mm) to a bike frame?
Something like this maybe. This would be the main part of the container with the cover of the same shape and two screws holding both parts together. Velcro loop strap through the openings on the sides of the fatter bottom part of the holder in this view. All made out of plastic so no seals would be needed if the screws are tightened with a little bit more force.
Don't forget the segment of the market that wants to mount this on the helmet.
A shape that can accommodate helmet and frame mounting would be excellent.
Can we see the other side of the outer case please.
not many bikers would want to clip a C type clamp to their painted frame specially when it gets covered in gritty mud
and also the differing tube diameters
a simple velcro strap and some cushioning IMHO and it would fit a helmet too
I think typically people who will buy these will be having setups that consume a lot of current. On a frame mount, 4 cell versus 2 cell is insignificant to me. Since I don't have it on my helmet or jersey bouncing around.
I think the 2 cell holder as is would appeal to helmet and jersey people for headlight lamps. But a 4 cell would be more attractive for handlebar use.
Will the holder fit protected cells? Or unprotected? Does the holder have built in protection board for the cells?
Toaster, your suggestion is similar to what I'm imagining. It'll be very easy to attach a bracket to the box that makes it look like what you've drawn. I'm going to leave the sealing design in place, since they get used underwater a lot (mainly kayaking, but I went surfing once - and only once!).
Attaching it to a helmet is already very easy. The box attaches to a headband bracket which can be zip-tied or velcro-ed to a helmet. Some people have pestered me to make a clip-on system so that the headlight can go on and off the helmet during a multisport event. So that's next on the todo list.
On the left is the box that you see in the photo above. The right is a more recent version.
I agree that a 4-cell would be better in many situations, but right now I want to get the 2-cell into production. I have some ideas in mind for both 4 and 8 cell designs. I need at least 4 cells to power one of my headlights and I want to use individual 18650s instead of custom packs.
The present design takes 18700 cells. I wanted to be able to fit in the bigger XTAR 3100 (Panasonic) cells since I like them and they're the biggest cells I've come across.
There's enough room in the piston's head to drill a 12mm hole and fit a small momentary switch, though this requires a thinner (say 12mm) velcro strap to hold it closed. A very small driver (eg, 4xAMC7135) could be squeezed into the head, but it'd be fiddly work and there would be no thermal transfer for it.
What are you using for the cable gland? Are they planning to come prewired or as a kit for DIY assembly? Since you said they can fit bigger XTAR 3100 (Panasonic) cells, I'm assuming you have no PCB for cell protection in the design?
Initially I used a brass cable gland with M8 thread, but now I just flood the inside of the piston's head with a low viscosity glue. It's extremely strong and water tight. A large radius fillet (bell-mouth style) prevents the cable from bending sharply at the exit.
It doesn't have a protection circuit, but one could be installed in the piston's head before flooding it with glue.
I don't have any specific plans for selling them. The high cost and effort previously made it unfeasible, but they might get cheaper now. Kit or assembled will both be possible if I end up selling them.
I don't have anything very useful to add, but this looks awesome!
I'd definitely be interested in some if you get these made.
When and if you do a mass produced double then I will have a few off you .
Sadly, 'mass produce' is probably a bit ambitious at this stage. Making a hundred is all I can consider if I'm funding it myself.
In my dreams, I get more than 5000 made at once. Then I set up an aluminium extrusion to make the oval shape of the outer case as well as the inner cell holder, and cast a black plastic plugs for the ends.
Total cost for the whole thing would easily be under $5, and it would be both beautiful (annodised) and strong. It also opens up opportunities for using the body to conduct current, and they could be made to any length (though 2 or 4-cell are probably all that would be useful). ... Anyway, I have heaps of dreams...
I'm loosely planning out a kickstarter or indiegogo campaign just to see if enough others want something like this too, but for now I just want to play with the design more and get it perfect.
I was just going to suggest you set up a kickstarter project!
The oval shape would be nice for carrying the battery in your pocket, but for mounting on the bike or helmet I would prefer it to be more square-ish or something like in Toaster's design.
How about making the end caps out of some rubber-like material? That would provide some impact protection and would be easy to glue to the aluminum shell with Sika flex or something similar.
I'd definitely go for the lightest weight you can as weight on the helmet can be quite noticeable. For shape I'd stick with something that is slightly concave on at least one side so that it sits on a frame tube easily, but without any stickyout bits that would snag on a jersey pocket or make mounting to a helmet difficult.
Some way of retaining a single velcro strap would be useful - could be something as simple as a screw + washer that would thread through the strap into the middle of the case.
A supplied stickysided rubber pad(s) would be useful too, for the frame mounters.
Can this be wired up 2S1P and 1S2P? Both set ups would be very useful.
Does it need the velcro strap to keep it closed? If there are matching grooves for the o-rings in the housing then 2 o-rings should provide enough force to keep it together.
I like the idea of there being space for a PCB in the head of the holder. Would there be enough space to tuck a balance wire in there too? I know I can take the cells out to charge, but it would be nice to have the option, especially if you offer a 4 cell pack.
If this is set up for protected cells up to 70mm long, are the springs long enough to make good + reliable (ie. no bump disconnects) contact with unprotected cells?
I'd seriously consider one of these holders, even up to ~$30, just for the ease of assembly :)
Lots to respond to...
Lightweight is definitely essential. I've struggled with this because it's very easy to make the case with thick walls, but I wanted thin to save another 20g on the head. Doesn't sound like much, but it all adds up.
I also would love to have a concave side, but it adds other problems. A minor problem is that the cell-holder (or piston) can only have one leg (or none if you take toaster's design). The bigger problem is that orings nolonger work well on the inside. So the seal becomes some sort of gasket (I tested with some custom silicone ones) that presses on the end profile. This works fine if you keep up the pressure. So you need a reliable and strong latch (eg over-centre). I much prefer the Velcro because (in normal use) it is 'unbreakable'. It also only takes a tiny force is to keep the piston inside the case. Even if the piston and box move a few mm wrt each other, the seal is maintained.
** An interesting idea, is to get an oval extrusion, and with a multi-part mandrel, crush the tube so as to get a concave part and still hold the oval at the ends (where the seals are).
As it is now, 1S2P and 2S1P are both possible.
A balance plug would be tricky without a design change.
with a 70mm cell it's very tight, so it still holds a 65mm cell.
The Velcro is needed because the chamber gets a slight positive pressure and tries to push the piston out. It's only slight. It's very satisfying to know that the seal is working!
Nice design. How about making some silicone molds molds from your prototype and then casting. I've found that the expense is making the pattern, the casting resin per part is pretty reasonable, and durable. I've used several different suppliers and have been satisfied with my results, there are many choices, here's a couple;
Molds OOMOO® 25 and OOMOO® 30 Silicone Product Information | Smooth-On
Pourable Black Plastic Casting and Finishing Smooth-Cast® ONYX® Deep Black Resin
Great idea! In fact I've been doing that for a while now.
I've been through more than 10 different polyurethane formulas (including the S-on Onyx which I found too brittle) and eventually settled on S-on 310 for a variety of reasons.
The custom plastic parts in these headlights were all made by this method.
For most parts it works excellently, but the battery case turned out to be a real challenge. After several masters and many moulds, I found I could have any two of 'consistent', 'quick and easy' or 'good quality'.
With an aluminium extrusion, the plugs and cell carriers will be really easy to cast.
NB: For those interesting in making custom plastic parts this way, I have a few bits of advice:
1. Invest in a pressure chamber
2. Invest in a vacuum degassing chamber
3. Since you've done the above two steps, skip the OOMOO silicones and go straight to the Mold-Max or Platinum cure ones. They perform better and last longer.
4. Get excellent masters. The polished nylon parts from Shapeways are great, but machined masters are better.
5. Spend a lot of time getting your moulds right (do not rush this stage).
6. Don't skimp on the Silicone. Use heaps more than your wallet wants you too.
7. Use a slow-cure polyurethane (eg S-on 310)
8. Work in a low-humidity environment
I started out trying to save money and time ... and got what I paid for. When I eventually invested about $500 in all the better gear, I started getting great results.
That's a slick looking headlamp; I'd be interested to know more about that one!
I can imagine the thinner-wall large volume castings are a PITA, agree it would be easier to go with an extrusion with plugin caps. Nice work!
That headlight is designed more for walking. It's not so good as a bike light (though I do use it).
Anyway, back to design options for the battery case:
The 4-mounting-posts design I showed earlier is ideal for some applications (like my headlight), but I'm wondering if a dovetail rail might be more universal. As bonuses; it spreads the mounting forces more evenly along the length of the case and is extrudable (for later on).
Here are some quick sketches of possible cross sections of the case + matching rails-mounts.
The mounts could be made from a cast plastic, or a silicone/rubber. With a good friction fit they probably wouldn't slide, but could always be secured with a single lateral screw halfway along their length.
Along the top row (numbered from left to right):
Numbers one and three, if made from a rubber, could be flexed to allow mounting without actually sliding it along from the end. By contrast, number two can only be mounted by sliding axially, but the final mount would be more secure.
The fourth represents a simple tube which requires much bigger mounts to surround the whole thing. In that case you'd probably only use a couple of 10mm thick mounts, rather than a whole rail.
On the bottom row, I just demonstrated a way to combine two back-to-back and compared it to how a real 4-cell case might look. Obviously it ends up about 20% bigger in one dimension.
Some other concepts that I considered:
A T-slot design or a ribbed-slot design (to accept machine screws or a strip of similarly ribbed rubber/plastic).
I think I still prefer the dovetail style. It can always be drilled and tapped if a screw-mount is desired.
Well, this is an interesting proposition.
I think that a similar design was made by Magicshine in their crazy LCD battery pack. For a bike I suggest to make an aluminium extrusion with machined eyelets for Velcro straps and plastic end caps with sealing gaskets. And 4 cells is the bare minimum.
I think that we can cooperate on this project. PM me if interested.
Yeah, what's the headlamp? I want to find something for my wife to run with.
Originally Posted by ahorton
For the price, the Magicshine case is great. Yet another reason not to build a 4-cell section in my mind. Though I do think that a double-length 2-cell section (4 cell total) could be nice and practical.
Another reason against a 4-cell section is that a 50x1.6mm or 50x2mm aluminium tube is fairly easy and cheap to buy and fits 4 cells nicely enough for the diy guy.
One thing that put me off the Magicshine style, is that I want it to be quick and easy to swap in fresh 18650 cells. Even if I modified a Magicshine case to have a 4-cell holder with spring contacts, the seals require screwing it together.
This to me is the nicest 4cell 18650 case. It's so nice, I convinced Kevin on candlepower forums to just sell me the case with the holder and cable gland. Would fit perfectly in the back pocket of a cycling jersey because it is a flat 4 cell config instead of a round config.