After fighting with the Smartthings Multipurpose (2015 models) batteries for a while, including several different units with various problems, reading all the threads on here, messing with the battery contact terminals, and replacing batteries several times with different brands of CR2450’s, I decided to give up on one of them and do some potentially destructive testing on it on my bench to figure out what’s going on with the dang thing. I’ll record my results here to help others, since I don’t see this info posted elsewhere.
CR2450 Batteries:
The MP2015 of course uses a coin cell CR2450. Physically, the coin cell contacts inside the MP2015 can be unreliable, exacerbated with certain brands of CR2450. I’ve had some luck bending the contacts slightly to make a tighter contact with the battery, but have had problems with the device going offline, only to come back online when the coin cell was twisted in it’s mount. One of the MP2015’s I used in a freezer, which worked for months with one battery type, but a new battery type (Energizer) does not seem to like the freezer.
Max/Min operational voltage of the MP2015:
The MP2015 hooked up to a lab power supply had the following characteristics:
Fully functional (temperature, accel., open/close) from ~1.8V to 6.1V DC with low current at all voltage levels. The Current generally dwells at some very low quiescent current (too low for my power supply current monitor to read, i.e. below 0.001 A). About once every few seconds, or seemingly when the open/close is triggered, the unit appears to transmit a status and draws some operational pulse current. It looked to be some times as high as 0.01 A, but its very possible the pulse is too quick to register properly on my power supply, and I’m not interested enough to put it on my O-scope and fiddle with it. In general, my point was to determine what voltages the thing operates and if it draws a lot of current at higher voltages, or gets hot (or just explodes). It didn’t. Interestingly, the battery % never went below 100% even when the device was operating at 1.8V, and the open/close sensor continued to work. Since my battery never measured while unloaded below 2.8V, but would not power the MP2015, it appears the software reported battery % must be measured during a transmit pulse based on peak current or low dips in battery voltage during the pulse. i.e., a beefy 1.8V is plenty to run the sensor, it would seem. Perhaps then, a simple capacitor in parallel with the battery could greatly extend the perceived CR2450 battery life.
My plan is to replace the MP2015’s CR2450 power source with various other sources, including an ultracapacitor connected to a small solar panel in two units (which will be used indoors with ambient light) and connected to a freezer’s internal wiring in another unit.
I can post some more info on the results if folks are interested.
-Gnosh