4S3P Battery Pack

[The Chairman]

I will be documenting this here and on Thingiverse: https://www.thingiverse.com/thing:5386125

We've all heard it before, you can't fly with that many connected 18650 batteries. That makes a lot of our can lights a no-no, especially on international flights. My first foray into 3D printing was to design a battery pack that any of us can print out that will hold 12 18650 batteries in a 4S3P configuration. For those who don't know the shorthand, that means 3 sets of 4 serial batteries wired in parallel. I started this design in January of 2018 (2019?), but I had no luck or confidence in my printer. She's doing great now since I finished the upgrade I chronicled. There are five printed parts; base upper, base lower, connector, and two Star Wars looking battery clips.

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I first printed it in PLA but the clips were too brittle. I've heard a lot of good about PETG, so I'm going to go ahead and print this puppy in that. It's supposed to be stronger, yet springier. I already have limiters and springs somewhere around the shop, and I won't mind designing and printing a PCB if needed. But to get started, I need it in my hand and popping batteries in and out to stress test it. I've got the bases and connectors printing already and they are looking good. In fact, I'm about 2 hours into a ten-hour print.

Please, give me feedback on this, especially as it finishes printing. Share any thoughts, pics or files as you see fit.

 

[The Chairman]

Can you spell warp? I need these to be straight and accurate. The clips, not so much. I'll see if sanding helps.

 

[letterboy]

Can you spell warp? I need these to be straight and accurate. The clips, not so much. I'll see if sanding helps.

View attachment 722907

View attachment 722908​

Is that petg?

In my experience it prints like candy... It look beautiful but it's gummy and stringy.

I used it to print some compass parts for a project that was going to me exposed to seawater...

If I remember I got it to print well using an enclosure (cardboard box over the whole thing) and slowing it down, more than reasonable...

Are you using fans? I can't remember, precoffee, if faster or slower cooling was better for petg to bond better. I think slower so no fans.

 

[Bobby]

FYI, any cells packaged together form a pack. All LiION battery packs must be UN/DOT 38.3 certified for commercial air travel. The limit for carry on is 160wh. IMHO, taking home brew packs on an aircraft is not a good idea.

 

[The Chairman]

All the batteries pop out and will be transported and charged individually. This is just a battery holder, not a pack per se. Rather than having to have a dedicated battery pack I have to charge, I can pop in 12 fresh batteries and go dive

Fans are all off for printing. Warping is more optical than actual. A bit of sanding and it appears we're good to go.

I'm thinking of printing the retaining clips in TPU. It might be too soft'but I won't know till I print it.

 

[emoreira]

Is that petg?

In my experience it prints like candy... It look beautiful but it's gummy and stringy.

I used it to print some compass parts for a project that was going to me exposed to seawater...

If I remember I got it to print well using an enclosure (cardboard box over the whole thing) and slowing it down, more than reasonable...

Are you using fans? I can't remember, precoffee, if faster or slower cooling was better for petg to bond better. I think slower so no fans.

I print many things with PETG and, for me, it has the benefits of easy printing of PLA and the strength of ABS, but with a bonus, a better interlayer adhesion (Z axis).
One thing that benefits the strength is narrowing the distance between extruded lines. Most slicers use a default interline distance of 0,48 mm for the 0,4 mm nozzle. This is too much and sometimes the lines are not bonded together. I set that parameter manually to 0,42 (Simplify3D) and the print is much more uniform. This is even better if the printed part is going to be submerged, as there are less void spaces inside the printed part that can ingest water.

 

[ScubaBunga]

Can you spell warp? I need these to be straight and accurate. The clips, not so much. I'll see if sanding helps.

Can you spell warp? I need these to be straight and accurate. The clips, not so much. I'll see if sanding helps.

I only used PLA for mine and it's worked great. It's a 3p3s setup - fits nicely in my 3" battery case. If needed I could pack two of these in there - but one pack has a 6 hour life so I never had a need to pack two in there. I "think" these (links below) are the final ones I ended up with - These were plain and I had to glue on the battery ends/springs (my next update will have connector links like you have), but it was very easy to pop out the batteries for travel, I do have a iMax charger and wired up the connectors so I could charge them in the pack (with bms connector for the 3s). Even with the 9 holders and being thin, once I got it all symmetrical I did not have any breakage issues with PLA. Simple PVC glue worked great as well to make it a solid single part.

3D design Final-Base v8 | Tinkercad

3D design Final-Base v8 created by thebrian with Tinkercad

www.tinkercad.com

3D design Final-Holder v8 | Tinkercad

3D design Final-Holder v8 created by thebrian with Tinkercad

www.tinkercad.com

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[The Chairman]

Thanks for the insights! This TPU sure prints purdy! I'm about a quarter way through the print.

 

[The Chairman]

8 hours later and they look great, albeit a bit stringy. This direct drive head is awesome! However, I'll have to adjust the design or go to a different filament. The PLA just cracked after a few inserts, but they do have carbon-reinforced PLA out there. Or, I could fill in a bit of the empty space between the battery holders. I think that's my best option. Tomorrow, I'll get out to the shop and fit everything together.

 

[emoreira]

8 hours later and they look great, albeit a bit stringy. This direct drive head is awesome! However, I'll have to adjust the design or go to a different filament. The PLA just cracked after a few inserts, but they do have carbon-reinforced PLA out there. Or, I could fill in a bit of the empty space between the battery holders. I think that's my best option. Tomorrow, I'll get out to the shop and fit everything together.

View attachment 723008

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Perhaps you should try with flex filament.