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Daduck748

Ultimately Most Compact Mini-ITX Case

by Daduck748 Nov 16, 2016
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Guys, Why LIPO ??? Take the 18650 elements(LiIo) and make whatever capcaity 4S you need !
Suggest to use LG HG2 or Samsung 26F Elements as the ones that are able to provide high currents !!
Personally I would be very much interested how it will go :-)

Hi !
Thank you for your work ! You make me save lot of hours for my project with a Jetson TX1 !
I will use a LiPo as you do, but 3S and i'm looking for a protection and charge circuit. Did you found a reference ??
Thanks !

I'm glad this design helped you. I wish I had more time to work on this case, and I hope I will soon.

As far as a charging circuit, I have not found a single IC solution to take care of anything more than 1S batteries. However, I did find a circuit online with a transistor array switching circuit that cycled through each battery and repeated the following process per cell:

  • sample voltage on the current circuit
  • if below upper threshold, trickle charge for x ms, else skip charge on current circuit
  • advance to next battery circuit and repeat loop

Don't ask me for the link. I don't remember it, nor did I add it to my favorites. I do remember the method and it was quite simple as outlined above.

Protection is basically just periodically checking to make sure each cell isn't being over charged. If you've got a microcontroller charging your battery pack, it's already performing half of the protection/monitoring tasks already so why add another IC? Check the datasheets for any LiPo battery charger IC. I think the upper limit is around 4.2v and lower limit is like 3.2v or something like that. Undercharge protection is just basically making sure each battery doesn't drop below a certain voltage or it will be be permanently degraded or damaged. If you are to build your own microcontroller Li-Po protection and charging system, you might as well build it as a trickle charger, always topping off the LiPo, so it's always kept fully charged.

I think what most people won't tell you is that in a multi-cell LiPo battery, each cell must be serviced individually... like it's a secret or something. That's why on a LiPo back, there is your main power connector, + and -. Then you usually have another cable with 4 wires (for a 3S battery back). If you measure the voltage between adjacent wires, they will give you around 3.5V each. If you measure from end-to-end on the connector, you will see roughly 11V, because the batteries are connected in series. So in order to service each battery separately, you have to tap in between cells/wire-pairs. That's the trick.

Most people will tell you "there's a chip for that". Well, yes, but not for multi-cell battery packs, as far as I know. If anyone knows of any, please let me know.

Obviously, the design I came across was based on a microcontroller (of your choice), and well within the capabilities of any Arduino. I'm surprised there aren't as any (AFAIK) Arduino multi-cell LiPo chargers/examples/libraries out there.

I hope that helps or gives you a direction on a protection and charge circuit. I have not designed or built one myself yet, but the theory and method is quite simple. You just need to make sure your circuit operates within the tolerances of the LiPo technology and you should be fine.

My background is Electrical/Mechanical Engineer and I have worked on power supplies up to 1000A so this type of thing doesn't phase me. I have caught work-spaces on fire on several occasions while testing (in controlled environments) so the work that I do is deemed "safe". I make PCB for everything with proper solder masks so my connections aren't "dodgy" and safe from short circuits. Your mileage may vary.

My disclaimer, because I like to be helpful, but I wouldn't want anyone getting hurt or dinging me for someone using this information in a poor manner:
This information is for educational purposes only and I hold no responsibilities for any action you decide to take on. LiPo batteries are the most unstable battery technology and anything can go wrong and of course, your hardware, property, or self can get hurt or worse and I will not be held liable for anything if something were go wrong.

What weight was printed by the 3d printer?

The weight depends on your settings. The one I printed was a working prototype, and I printed it in a hurry, but I usually print with these settings for prototyping:

Width: 0.4mm
Resolution: 0.25
TopL: 3
BottomL: 2
Shells: 2
Infill: 10

The weight is calculated at about 144gr for the case.
The weight is calculated at about 84gr for the lid.

I don't have a precise scale so I can't weight the actual part. The final weight will depend on several other factors like bottom layer height and width (not a huge difference, but if you want an extremely accurate number), extrution ratio and whether or not you have solid infill layers. In this vase, it's not really necessary, since everything is so thin.

My recommendations for final print are the following:
Width: 0.4mm
Resolution: 0.15 (to print the ventilation holes with more details)
TopL: 3 (I find 2 layers still show artifacts )
BottomL: 3
Shells: 3-4 (since this part is designed to use screws instead of inserts. More shells also give you the possibility to drill out the holes to install threaded inserts for a cleaner product.) It will also solidify the final product.
Infill: 15-20
Material: CF-PLA or ABS (Counter-intuitively, my CF-PLA parts feel heavier than standard PLA, so this is also a factor in weight)

Once again, I haven't had time to make enhancements. I still want to add features like TPU bumpers, internal battery (maybe LiPo or 18650. The peripheral shell will be up to you guys since everyone will have a different motherboard.

Thank you very much for the attention, I intend to make one as well, however I want to use it with orange pi and HD, so I will have to increase some measures to fit everything including ventilation. If I do put a photo here.

Work has me really pinned down so I haven't had any time to make any changes to this model. I'll have to mark this part "work in progress".

Does the io-shield fit into the open back?

Sorry for the delayed response. No, this case was designed to be super compact. As in my description, I had to desolder the audio block to get it to the maximum smallness I could. When looking from the rear profile, the audio block stood about 2-3mm taller than the next tallest component. Granted, every motherboard will have a different shield, but don't think any of them will fit.

Coming this far, we should all be able to 3D print our own custom shields fairly quickly. I remember the days before 3D printing, I had to measure up everything the best I could, model it, and cut out of 1/8" aluminum plate. That was really what I had to work with back then.

It's been busy for me here, so no real movement on further modifications to this case. However, in the last few weeks, I've discovered Carbon Fiber PLA, and it would be an excellent filament material for this case. I've already started reprinting a bunch of my everyday parts with the CF filament and the difference is amazing. Imagine the strength of ABS with a "glass-filled" polymer look and feel, yet just as easy to print as PLA. When I have a chance, I'll reprint my case with this material.

I have also noticed that if you choose the right size DIMM, you might be able to fit 2-4 18650 batteries behind the heatsinks, or where ever. Every motherboard will have some space to shove these batteries in there.

I just uploaded an updated lid, v1.3. It has the following features:

  • Moved the exhaust port to better match the CPU fan
  • Recessed the area above the picoPSU area
  • Bulked up the CPU fan area to reinforce the lid
  • Added bosses above the heat sinks also to reinforce the lid
  • Added 4mm high perimeter to add stiffness to the entire case

Also, I uploaded a vanilla .STP file so you can make your own lids to suit your Mini-ITX board.

I apologize to anyone who already downloaded and started printing the bottom already. I just realized it was an early model without the back removed. I've uploaded the STL with the open back, so please redownload the updated files.

Comments deleted.

Where is the PSU going to go???

If you look closely, the PSU is shown in the photos. It uses a tiny PSU called a picoPSU. It's basically a DC-to-DC converter, takes a 12VDC input. The PSU plugs right into the ATX connector.