Tag Archives: Battery

Arduino Mini, using Micro Amounts of Current…

Last night, the weather was pretty rainy. I woke up a couple of times during the night (once, when my little cat friend Bailey decided to check my breathing and started head butting me around 4 AM) and heard a lot of rain falling on the roof. When I woke up, it was fairly wet outside. I made myself a cup of tea and settled into check messages and email…

And the power went out.

Sigh. I could have used my phone and the cell service, but instead, I just spent a few minutes thinking.

Like about my battery backed up temperature/pressure sensor I had running in the garage, which is battery backed up. And since it sends its data to the MQTT server at io.adafruit.com, it should wo…

Oh, except of course my network is down.

It got me thinking that perhaps logging data to a local SD card isn’t actually the worst idea. Maybe once a day or so, it could wake up and send all the backlogged data to the server, but continue to log data locally.

And while I could use a microcontroller like the ESP8266, those things take a lot of current. Maybe it was time to look into something else that could be efficiently powered down and then only power up the remote peripherals (like a radio) when needed. And instead of using any kind of fancy charging circuit, maybe I could make something that is just powered from either Alkaline batteries with a run time of maybe a year.

As it happens, last night I found a couple of Arduino Minis and a USB/serial connector, so it seemed to me that using one of those would be pretty reasonable. But I was pondering a couple of issues: just what is the standby current of an Arduino Mini when in deep sleep mode? How much current does the ubiquitous power LED consume?

So, during a break I dug around and found information about power consumption by the Arduino Mini.

The breakdown seems to be that if I use a 3.3V 8Mhz Arduino Mini which is unmodified, I could expect about a 4.74mA current running flat out, and about 0.9mA while sleeping. Most of the sleep current is actually the Power LED, which draws about 0.84mA. It isn’t had to get rid of that (just cut a trace and/or destroy the LED with some snips) and then you are down to just 0.054mA during sleep. Very nice.

You can further reduce the sleep current by getting rid of the voltage regular, which may or may not be feasible depending on the use case. I was curious about what voltage I could use as input if I got rid of the regulator, and it appears that the ATmega328P is good from about 2.7V to 5.5V, which is a very broad range. You can simply feed that into the VCC. Sleep current is down to around 4.5?A in power down mode. Really, really good.

But it might be worthwhile use a better regulator. The Microchip MCP1700 has a quiescent current down in the 1.6uA range, which might be worth looking into. There is a lot of information about the efficiency of these regulators on the page linked above. I’ll have to look into it some more.

I should note that some of my thinking about this today was probably nudged by the following video @JeremySCook


I thought there were a couple of cute ideas in here. He used the Arduino Nano instead of the Micro but the form factors are pretty similar. I liked his way of soldering down DIP switches to provide some inputs, and using some shrink wrap to make a nice tight little package. He also pointed out these cute little battery holders with built in power switches that I hadn’t seen before. But I was a bit concerned about the use of the Nano. The USB interface chip draws about 15mA, and the Nano is nominally a 5V chip, so I thought that supplying just 6v to such a system would result in very short life, as the CR2032 batteries are pretty low capacity already, and 6v is not really enough headroom above what the voltage regular needs to provide 6v. Still, definitely some good ideas.

I also think it’s probably a good idea to read some of the “low power” tagged items on JeeLabs, as well as some information like this on the Arduino forums.

Anyway, more to think about.

Pondering the 18650 Li-Ion Battery…

Back in October, I attended Pacificon, the local ham radio convention. While I was there I picked up a couple of wacky things that were super cheap on the vendor’s tables, and among them was a super inexpensive battery charger along with an 18650 3.7V Li-Ion battery.

If you’re like me, you are probably used to the common AA and AAA type batteries for most of your portable electronic needs. If you seek rechargeable batteries, these are often the NiMh or nickel metal hydride type. Typical ratings for such batteries is 1.2V and 2400 mAh, or about 2.88 watt hours of power per AA cell.

Recently though, lithium ion batteries in the 18650 format (18mm diameter, 65mm long) have become available and popular. They are a bit better than a AA (which are 14mm in diameter and 50mm long) but are pretty lightweight, and common types have a voltage of about 3.7V and capacity of maybe 2600 mAh for a total power of about 9.6 watt hours, or a little more than three times the power of a good high capacity AA.

Anyway, decided they might be interesting to play with, and the price was (suspiciously) cheap at the show, so I thought I’d give them a go. The combination was an “Ultrafire BRC18650”, along with a super cheap looking charger with the product identifier of “HZM888MA”. It’s hard to overstate how uninspiring the charger actually is. I admit that I buy a fair amount of dodgy Chinese electronics, but this seemed dodgier than most, and because of the energy density and the rumors of batteries bursting into flames has me paying rather more attention to it

My recollection is that when I bought the charger I did test it by charging up the battery and that it did its usual “red while charging, turn green when done” with its indicator LED. But when I found the charger and battery in my storage case, I decided to try it again. Now, my dodgy charger just blinks the red LED, which in the international language of devices should indicate that something bad has happened. Nothing appears to have caught fire though, the battery doesn’t get hot, so I am not sure what is going on. I decided to get a higher quality Tenergy model to test it, and the same thing happens: blinking red LED.

I have decided that ordering a higher quality charger is probably a good idea, especially one that can handle different battery types, so when that arrives I’ll give them both a try.

In the meantime I looked up the UltraFire BRC 18650, and found this article on YouTube, showing that their rated capacities are nowhere near realistic, and they often have less than one third of the total listed on the packaging.

I guess you get what you pay for.

Anyway, these might find their way into an IOT device that I’m working on, and it will be interesting to see how they perform. I may also tinker together a constant current load to test their capacity myself.

In the mean time, buyer beware.