It’s no real secret that battery packs for power tools aren’t the foremost when it comes to user serviceability, so if said battery pack suddenly stops charging outside of warranty, you generally just e-waste it. That’s what [The Repair Forge] could have done for the Makita battery pack in question, but instead it was opened up for a diagnosis and fix.
Rather than the charger throwing up an error with this specific battery, it would flash its red LED and run its fan, but never actually start the charging process. Apparently the charger seems to think that the battery is either too hot or cold to be charged, which already gives a big hint as to what might be wrong.
Using the open source PocketOBI tool it’s possible to query the battery, which showed that one of the internal thermistors reported the battery being at a chilly -30°C while the other a more reasonable 28°C. After popping open the pack and measuring the thermistors, the faulty one registered as infinite resistance thus confirming that it had failed.
By putting in a temporary resistor this diagnosis was confirmed, thus the next step will be to replace said thermistor. This same procedure was then used with a second battery, whose thermistor read a wild 64°C.
Overall it’s a pretty easy fix, using a 20 cent part, with the entirety of diagnosis to repair taking maybe ten minutes when using a tool like PocketOBI, itself based on the great Open Battery Information project that originally reverse-engineered the Makita battery protocol.
Okay, just so its said. Treat these batteries with the same care and cuation you would a Jerry can of gas.
Depending on the industry, that’s a pretty broad range of care levels…
Ok. But how much is the pocket obi tool? And where do we find this 20 cent part at? But otherwise thank you for you article. I much rather fix something then throw it out anyday!
TME
I did not quite understand the nature of your question, so I took it literally.
https://github.com/mnh-jansson/open-battery-information
I understand, searching is hard. I hope you find what you’re looking for.
Check out duckduckgo.com, you’re gonna lose your mind when you realize all the things you can look up.
/s
oh man. search engines are broken. type in two words. it will show all pages with one of the two words, and maybe pages with both of them. why?? putting in quotes sometimes helps, but not often.
They always assume OR nowadays, instead of AND like they should.
You can make one with an arduino, 2 resistors and a makita yellow clip thingy – truly fantastic bit of opensource magic that has saved me many a battery!
I’d be tempted to cheat and just leave the “temporary” resistor in place. Save myself 19 cents.
Sure, what could possibly go wrong…
So glad to see this article, I can’t wait to build and use the pocket obi on my batteries. Despite trying a recent web search for a Makita BMS diagnostic tool yealded nothing.
But how can a passive thermistor fail? And both of them?
Usually cells fail in these batteries and the controller locks up. The situation with thermistors is a made up one.
What if you combine
thermistor that read a chilly -30°C
thermistor that read a wild 64°C
on the second battery ?
64-30 = 34. Should be fine :)
Does every single hack require a yt video? Does HaD have stock in YT? Tired of this. HaD is becoming more and more annoying.