3D printed enclosure + modern battery retrofit question/advice

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benguild
 
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3D printed enclosure + modern battery retrofit question/advice

Post by benguild »

Hi all, I'm trying to retrofit a rechargeable battery into a 3D printed enclosure for a MiniDisc player, which of course is no longer in production nor are its accessories.

The batteries for all of these units are 10+ years old and generally even a new one (if you can find it) is "new old" stock, so folks have been experimenting with 3D printing an enclosure for a 3.7V 350mAh battery as a substitute: https://www.hallaminventions.com/projec ... -obsession or https://www.head-fi.org/threads/diy-lip ... ld.960086/

It looks like a pretty easy build (literally just soldering contacts onto trimmed wires, then gluing the contacts into place), and Adafruit sells a similar battery that I think may fit: https://www.adafruit.com/product/2750 (But, it looks like it's maybe ~1mm thicker?)

Would appreciate advice here, as I could order the battery and try if this all seems fine, but a few questions:
  • Is the Adafruit battery mentioned here essentially (potentially?) to the same spec as the eBay equivalent of the build's battery and likely approximately the same physical dimensions, and is the aforementioned larger dimension on the Adafruit page potentially more of a "worst case" in this instance? Its auction lists a ~40mm height, and fit really does matter here since it's a small device. I may not know the answer to this without actually measuring the batteries themselves, though.
  • The main thing I'm concerned about is charging compatibility ... luckily the original batteries for this MD player (which are charged by the player themselves) were indeed Lithium-Ion. This substitute battery has a protection circuit, so is this likely totally OK for use and charging? (Some other players of this generation used NiMH batteries, but luckily this was not one of those.)
... The original linked article talked about fabricating brass contacts from larger strips, but there were concerns about conductivity.... If anyone has any suggestion for a better idea for fabricating contacts with less leftover material, would be awesome to hear. Someone had used silver strips instead, for example, but still the strips are larger than what's needed.

Thanks for any thoughts!
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adafruit_support_bill
 
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Re: 3D printed enclosure + modern battery retrofit question/advice

Post by adafruit_support_bill »

The listed dimensions for the cell we carry are pretty accurate. The one I have here measures 5.1mm at the thickest part.

If the charge circuit in the player was designed for 3.7v LiPo/LiIon chemistry, then any 3.7v LiPo/LiIon cell should be electrically compatible.

On a scale that small, the difference in bulk conductivity between brass, copper or silver is going to be negligible. What is more of a concern is surface oxidation and contact resistance. And silver is probably the worst of the three in that regard.

The original cell probably has gold-plated copper or brass contacts. If you could scavenge those it would be ideal. Other than that, I'd probably go with brass and just be sure to keep them clean. Products like 'DeOxit" can clean as well as protect against further oxidation.

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benguild
 
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Re: 3D printed enclosure + modern battery retrofit question/advice

Post by benguild »

adafruit_support_bill wrote: Tue Dec 06, 2022 8:14 am The listed dimensions for the cell we carry are pretty accurate. The one I have here measures 5.1mm at the thickest part.

If the charge circuit in the player was designed for 3.7v LiPo/LiIon chemistry, then any 3.7v LiPo/LiIon cell should be electrically compatible.

On a scale that small, the difference in bulk conductivity between brass, copper or silver is going to be negligible. What is more of a concern is surface oxidation and contact resistance. And silver is probably the worst of the three in that regard.

The original cell probably has gold-plated copper or brass contacts. If you could scavenge those it would be ideal. Other than that, I'd probably go with brass and just be sure to keep them clean. Products like 'DeOxit" can clean as well as protect against further oxidation.
Thanks Bill! Great thoughts and recommendations. 🙌🏻
I actually found one of these 3.7V batteries here attached to another project and indeed, it'll be too thick.

So, back to the drawing board. I might try to source one of the thinner ones (the original for the player is very thin!) and see if that works, but we shall see.

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