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Hobby Charger Charging Cradles Updated 2/18/17

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The manufacture of the MPD holders notified me that the holders are designed for Protected Button Top 18650 cells. In most cases these cells are about 70mm long. In some extreme cases some are 72mm long. An Unprotected Flat Top cell should fit in the holder with no problems. They are about 65mm long. To avoid fit up problems always carefully review the specifications of any 18650 cell or cell holder you are considering before purchasing.


I've learned that not all 18650 battery holders are suitable for building charging cradles. Poor QC and materials can lead to improper charging and/or damage to the cells. It is important that the material is not flammable and that the spring material doesn't induce a high resistance at the contact point. Quality holders will cost more but in the long term, I think they are a good value. When built I want my charging cradles to last a long time, not induce a high resistance at the contact point, produce a safe charge, and give consistent results.


I've found through my research that these cell holders are of good quality and work well.

Manufacture- MPD (Memory Protection Devices)

MPD holders from DigiKey are also made in China.


The MPD holders are clearly marked with the letters MPD with the part number while the ones linked to on EBAY are marked the letters BLM in the bottom and BLOSSOM on the back with a similar part number.

MPD 4 Cell Holder data sheet: Part Number BK-18650-PC8




BLM Holders from EBAY:



Be aware that Protected and Unprotected 18650 cells have different lengths so some holders may work well with Unprotected cells and may not be long enough for Protected cells.


As you can see there are several different configurations offered. I've decided to try the ones with the pins on the bottom for a PCB connection. These can be trimmed off and a good quality wire soldered onto the contact.

Look at the pics here for an example:




I'll use a 4 cell holder and wire it in series for connecting to the chargers.


Some people use magnets to attach charging wires to cells but I don't think that is practical in the long term but does work well for low numbers of cells.

These are good magnets to use:


If you don't want to have to solder wires on the magnets they also offer magnets with wires already attached. Very careful soldering is required because the heat demagnetizes the magnet so having wires already attached is a plus.


Here is some good information and one guy's DIY project.



I'll post my results with pictures when I complete the project.



Edited by ko4nrbs

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I've been using the BLM (Blossom) 18650 holders with excellent results. To ease getting the batteries out, put a piece of ribbon under them so you can gently pull them up and out of the holder. They are tight. I use Unprotected cells in them.


I used the PCB I had Far Circuits make for me and the connections show in this thread:


It connects the batteries in Series so I can Balance charge them



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