I have a slew of Makita 18v Tool batteries and was considering other ways in which they might be repurposed. I know the Makita range of BL18XXB batteries from teardowns on the internet uses internal circuitry for balancing, temperature sensing, over-discharge etc but they also sell two adapters that I decided might be a better method of accessing the power rather than just using a 'dumb' contact plate.

One adapter provides two USB ports, another (126655-4 Battery Holder) designed to run a cooling jacket, converts to a barrel jack that I assumed output something around the 12v the fans would need.

I ordered one but after hooking it up to the multimeter, and then a PC fan, can't get it to work, it blinks the power led but doesn't stay on. Doing my own teardown I'm surprised by the amount of internal circuitry for what I might have expected was a glorified voltage divider. The same can be said of the internal circuitry of the other adapter.

Does anyone have any idea what these adapters might be doing? I always understood the smarts of Makita's battery protection systems were in the batteries and not the tools so I was trying to work out what might be preventing the adapter from staying on. I didn't think there could be a DC 'protocol' over the barrel jack coming from the jacket to confirm the adapter was plugged in to a legitimate accessory so I wondered if it might be some sort of load/resistance detection? Does that sound feasible and without access to the jacket are there any suggestions for how I might test for that, or get around it?

Thanks in advance for any help.

Edit: Have added a picture as requested. Hadn't taken it apart in a while, and I'm new to electronics, so it does have less IC's than I remember. enter image description hereenter image description here

It does have a USB (shown) and the wiring you see leads to daughter board with buttons and leds. You can cycle three fan speeds which I assume are output voltages not PWM. Label says 14.4V/18V followed by a solid over dashed line, which I gather indicates an output DC range.

Found an instructable (https://www.instructables.com/Making-a-Over-Discharge-Protection-for-Makita-Batt/) that indicates the battery doesn't internally have over-discharge protection and communicates instead via a third pin with the tool to prevent over discharge. This pin is present on the power tools I own but neither of the adapters (nor the work light I have) use it.

  • \$\begingroup\$ The cooling jacket apparently draws about 300mA. What happens if you connect the adapter to a load that draws about this much current? Can you show us a photo of the internal circuitry? Does the adapter have a USB port? (I can't find any information on '126655-4 Battery Holder'). \$\endgroup\$ Jun 26, 2021 at 21:55
  • \$\begingroup\$ Wow, thanks, have edited post with pictures and more information. Any suggestions as to what types of loads I might use for a trial 14-18V, 300mA load without buying/building a resistive load tester? \$\endgroup\$
    – John S.
    Jun 26, 2021 at 22:44
  • \$\begingroup\$ I will take a guess, I think it shuts down because the battery voltage is too low as to protect the user etc. \$\endgroup\$
    – Gil
    Jun 26, 2021 at 23:24
  • \$\begingroup\$ The battery is fully charged and I have tested multiple, do you mean the draw/load I'm applying is too low? I have referenced over-discharging in my update to the post. \$\endgroup\$
    – John S.
    Jun 26, 2021 at 23:37
  • \$\begingroup\$ Your images are a bit too dark and grainy to identify all the components, but the fan output appears to be fed from a switching regulator so you are probably right about putting out a DC voltage. It does appear to have current sensing, so perhaps it does require a load to start up (I bet the USB port is the same, as this is commonly done on 'power banks' to reduce standby current drain). If the fans run on 12V then a 40 ohm resistor would draw 300mA (and dissipate 3.6W). One 12V PC case fan might be enough (these typically draw 100~300mA). \$\endgroup\$ Jun 27, 2021 at 7:31


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