This battery was excited to see me


I have a small area on my desk for batteries of various sizes, including these 9-volt batteries. I came home one day last week to see one of them popped its lid… I’m not sure why. There was nothing across the terminals or nearby that would short it out. I’m not sure if it slowly rose out of its casing like a growing flower but I’m glad that if it was violent at all that it wasn’t harmful to anything around it.

I had to share because it’s not something you see every day!


Eye on the power

I added in the battery level code from into my ESP8266 program and it works like a charm. The code uses a reference voltage in the Atmega328p microcontroller to get a reading of Vcc going into the ATmega328p. For the ESP8266 project, that would be the 5v output of the AMS1117 board. In my testing with the dead-ish battery yesterday, I found that the system started to fall apart once it dropped below 5v. The LCD backlight would start flickering and the sending of data seemed to fail more often.

I already have the system sending me emails if it gets bad values from the DHT22 sensor or the ESP8266 fails at sending to both ThingSpeak and my webhost in the same cycle. It was easy enough to add a little more code so it would send me emails at certain voltage levels. I’ve got it sending emails to me when it drops to 5, 4.8, 4.6, and 4.4 volts.

Screenshot_2015-01-24-00-02-03I got this email when I retried the battery for the third time after bringing it in from outside in yesterdays outdoor trial. If I give the battery a rest, it’ll be able to power up the system again but it’ll die after a short period. The lowest threshold email I got was for 4.6v before the battery died again.

I don’t expect this project to go battery powered again but this is definitely something I’m glad I found and I hope it finds a place in other projects.

At this point, I feel like the project is over. It’s been a great learning experience working with two programming languages, my custom PCBs, and seeing the community that has gathered around the ESP8266. It doesn’t have to be over though… Solar power, anyone? Perhaps in the future.

Like I mentioned a couple posts ago, I have other projects coming up, including some experiments with some RF transmitter and receivers, and my custom shift register PCBs that should come in next week if the postal service is consistent with the last two times I ordered from Dirty PCBs.

 Thanks for reading!

The doctor is in

The USB Charger Doctor, that is.IMG_20141028_152728I went on a small eBay shopping spree, though it was mostly restocking some components like resistors, capacitors, and some RGB LEDs. The only interesting item in the mix was this USB Charger Doctor which reads out the voltage and current through a USB connection. I bought it because I’ve always been curious to see exactly how much current my devices were drawing. I tested the stock charger for my Nexus 7 (2012), the stock charger for my Samsung Galaxy S2 Skyrocket, and that battery pack I got from China. The results are all over the place, and I like that.
IMG_20141028_152420The voltage regulation of the two chargers and battery are not bad. It seems as though all three test subjects can sway +/-200mV with or without a load.

A bonus test was with my Powerocks 2600mAh battery. It’s of much better quality than the China battery pack in build quality, and as gives a very nice regulated 5V compared to the 5.08V (no load) output of the China battery pack.
IMG_20141028_152600 The current tests were what I was really interested in. I got some pretty fascinating notes out of it.

The picture above is my Skyrocket (phone) being charged. When I was doing this test, it would actually pull that 910mA only when the screen was on. It would drop down to around 400mA when I turned the screen off. I suspect it’s a current limit for the battery when it’s already charged to >90% which is what it was during that test. As I test it now with my phone around 70%, it draws a consistent 960mA regardless of whether the screen is on or not. The Samsung charger for my phone is rated at 1A so the charger is perfect.

As for the Nexus 7 charge test, it was pulling 910mA. I find that curious since the included charger is rated for 2A. Perhaps it’s a software limitation, or a change in the Nexus 7 hardware after the charger was already designed?

The current test for my China battery pack was the one I was most interested in because I wanted to know how much current it draws so I could use an appropriate charger to charge it. There’s no label for the input current, unlike the Powerocks battery, but it’s not like I’d put much trust in it if it was labeled anyway. Using the Doctor, I see it pulls a constant 700mA so any one of my 1A chargers would suffice.IMG_20141028_185028It was pretty neat to see what was going in with the batteries and chargers I’ve been using for years. I’ll still have to play around with it more as my tests have been pretty quick and not very practical. I would totally recommend one of these USB Charger Doctors if you’re interested in seeing what your devices are drawing. Thanks for reading!