I just got this assembled last weekend.
printables, complete with F3D file.
This is a battery adapter that will allow you to insert D cell batteries into a LiitoKala Engineer Lii-500. I included the Fusion 360 file, so you can customize it to fit other applications, but odds are it will fit most 4+ 18650 based chargers that are also compatible with Ni-MH.
It prints in two halves that I simply hot glued together around their perimeter. It’s not like this part is going to see very high loads… The parts are designed to print without supports. My copies are 20% infill (you could easily go with less) and 3 walls for an overall wall thickness of 1.16. Wall thickness is something I wouldn’t change, at least for the battery side so the battery terminals don’t eventual fail. The batteries are a very slight interference fit to ensure a robust electrical connection.
For terminals, I used 8mm wide nickle strip. I’m sure you could use something else, but I had some on hand and it seemed like an obvious application. Connections between the two halves were made via wires and solder.
There’s supposed to be a heat sensor on the positive contact that you are rendering useless. That said, given the lack of longevity of every nickel battery I’ve tried on the past couple of decades, I don’t think the charger manufacturers take this guideline seriously.
This is true, but at the default 500 mAh charge rate it seems unlikely that much heat will be generated? Worst case of 100% of input voltage getting converted to heat would be 700mW or so of energy needing to get dissipated per cell.
Yeah, the big cells can handle that just fine. The charger would overheat first unless a cell is shorted, which only possible with NiMH/NiCd if the charger malfunctions or the battery is physically damaged.
given the lack of longevity of every nickel battery I’ve tried on the past couple of decades
Early Ni-CADs and NIMHs I agree with that assessment. However for low duty cycle applications the 3rd and 4th gen Eneloop type technology NIMHs perform very well for me. I’ve got about 20 operational cells I purchased in 2011 from an original batch of 30.
This isn’t my data, but my anecdotal experience matches this:
If you have issues with longevity you should focus on getting a new charger. Many chargeres over charge the batteries and completely ruins them. Do it once and they are ruined forever and they wont hold charge anymore. Take a look at lygte-info.dk (don’t worry the site is in English) where he reviews chargers. I can recommend many of the xtar chargeres.
Direct link for comparison of chargeres. https://lygte-info.dk/info/roundCellChargerIndex UK.html
What do you D batteries for?
I hadn’t used them in many years but then my gf got me the hot wheels set I asked for at Christmas 30 years ago and never got and it uses D batteries. I’m planning to make a wall adapter for it.
The hot wheels set is Criss Cross Crash and it’s probably the best toy ever made. They haven’t changed it in the last 30 years.
Amusingly, this is almost exactly the reason why we have D sized batteries. The batteries are for a Criss Cross Crash, which I also never owned for a kid. But we got it for our kids (one of the perks of being a parent - you can buy the toys you wanted as a kid but didn’t get).
I initially purchased a pair of these chargers to charge 18650s for… high power flashlights. Yes, that’s a thing, go check out !flashlight@lemmy.world. Then I started tearing down older laptop batteries to harvest 18650s for a DIY electric scooter. Then we had kids and now these chargers see a lot of use for Mi-MH
Def not UL Listed
This is true, but the risk is very low. Amusingly, the chargers themselves are not UL rated despite being fairly highly regarded. Maybe I’ve got bigger problems.
You really don’t know the risks unless you open it and minimally reverse engineer it. The charger shouldn’t be very complicated and it’s not directly connected to mains so that is nice. Charging chips are super simple and there are not too many ways to screw those up, unless they do.
If anything at all is shady, it’ll be the power brick or the way the USB plug is powered. If the brick is crap and somehow starts passing mains, I am willing to bet that the USB plug will pass the bulk of the current through you or whatever is connected to it. It’s something to check, anyway.
Reverse engineering to determine safety is what UL does. If anything here, the charger needs to account for fucked batteries with fail-safes but as long as the batteries are fine, it shouldn’t be a problem
I love the idea of being able to fit 4 big D’s
I love the idea of being able to fit 4 big D’s
I’m more interested in knowing whether the charger actually supports that type of usage.
Bold move!
Not really bold, just a cool hack. There is pretty much nothing to go wrong.
