Need 5v (battery) for servo

I’ve been working with a Electron asset tracker for remote sensing and alarm to meet a specific set of requirements.

With the help of many of you here in the forums as well as Particle’s technical support. I’ve got the communication working to send email and SMS messages. I’ve got the warning beacon working which is an adafruit digital LED ring.

I’ve also got a servo working when the USB cable is attached because it needs 5v. Since that’s not available when deployed in the field, I’m trying to figure out the best battery powered approach. I’ve got a 4x AA battery pack working, but AA batteries won’t last long enough and tend to corrode. I’m considering AA size Lithium Ion batteries, but don’t know if that’s really any better, or if that would be enough for the GPS shield.

I need extremely long lasting battery power in low power mode,1 year is the target but a few months at least. (the hazard we’re trying to alarm occurs rarely if ever, but can be deadly)

So I’m thinking 2 of these, one cell connected to the Electron, and both in series to the screw terminals of the shield. However 2 in series would be 7.4 volts, and the servo is only rated for 4.8-6v. I know a resistor would drop the voltage, but raise the current and drain the batteries.

I’m kind of at a loss for what the best setup would be?

For long term power, the self-discharge characteristics of the battery are probably your biggest concern. The 2200mAh battery you linked to will lose about 20% of its charge per month without anything connected to it. Perhaps you should consider an all external solution such as a 12v car battery. Then you choose a high efficiency, 5v power supply to feed the electron and servo.

From his posts, I know @RWB to have some advice in this area.

Unfortunately this is a compact device in a tight area, I’ve got 9v 10-year Lithium Ion smoke detector batteries, but am a little gun-shy about damaging something (already fried one tracker kit: post here )

I see. Well, you won’t be able to use anything but a 3.7 volt battery on the Electron batt connector. So if you need a higher voltage to power your device and peripherals, then it’s essentially the same as I suggested. Using an external higher voltage battery with a high efficiency power regulator. The nine volt battery is a good idea provided that you use it correctly. If the 9-volt battery can’t Supply the current Peaks needed by the electron, then you should probably use both batteries in conjunction; the 9 volt battery on Vin and the 3.7 volt battery on the battery connector.

The only other scenario I can think of is to use a step up converter to convert the 3.7 volts into 5 volts. I have no idea how efficient those converters are so it may or may not work on your application.

(2) Lithium Ion batteries can easily be 8.4V @ full charge.

Is Solar an option for you? Even a tiny 0.5 watt panel may be viable with such a low duty cycle.

Have you tried your servo with 4.2V ? I’m guessing it may still function but at a reduced max torque.

It won’t do anything with just the kit’s LiPo… I’m currently getting the servo to function with a 4-AA battery pack hooked up to to the shield’s screw terminals.

Solar is not an option, the unit is completely hidden from daylight during normal operation. (I know that isn’t much in the way of detail, I’m giving as much as I can but am bound under an NDA).

Since the 9v option won’t work, I’m considering replacing the regular AA batteries with lithium ion 10 year AA cells. The power works, I’m just concerned the life will suffer.

maybe a small buck converter between battery and each device. i realize using them burns off some power in the process however you would be able to use the same battery solution you decide on for both while dialing-in the voltage to each to conserve the most voltage.

The Energizer L91 (your amazon link) are the best primary AA batteries on the market that I’ve found.
There is a lot of data on the internet showing various discharge profiles.
You can expect 3,000 mAh minimum.

Be aware, you can see 1.8V per cell with no load.

Do you know your average current ?

No, I don’t know the current, with 2 batteriy sources, the LED strip, a piezo beeper, a one-time servo actuation, GPS, and cellular communication, I couldn’t guess how to measure it.

But when Idle mode, none of that will be active, I plan on figuring out how to shut everything off except the clock. It should wake weekly and send out a quick battery level report then go back to sleep. The hazard will make or break a switch then fire everything up and send frequent messages to dispatch until repairs can be made, at which time new batteries will be installed.

The servo shouldn’t matter much, because it will only function once, after which the whole thing is reset by maintenance and the batteries will be replaced.