How to drop 9v to 3.7v to safely power a standalone mesh network?

xenon
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#1

Hi! First off I love this community section- I’ve solved a lot of issues just by reading around here so thank you!

I am trying to build a stand alone mesh network with an Argon and a few Xenons so I bought 9v rechargeable batteries to power each device individually. I didn’t realize until after I got them that the voltage of these batteries are way too high to safely power the devices. I am new to this circuitry world and don’t know what I should use to drop the voltage from the batteries to something acceptable and safe for the devices so I don’t fry them.

Can anyone provide any guidance on this? I would like to fix my mistake instead of just buying LiPo batteries.
Thank you in advance!

Edit: Found that a buck/step down/DCDC converter will do the trick. Not sure what the difference between those are.


#2

Buck- and Step down converters are the same type, just another name, they suit quite good for your usecase, just be sure it can handle the maximum current needed for you application. They are quite efficient devices.

Another type are linear regulators, they are meant for lower current applications so they are not suitable for your application since they burn all the unused voltage into heat (which is quite much for nearly 6V to drop that multiplied with the current that flows gives you the energy/heat dissipated by the regulator).


#3

@0xgaby, any reason you don’t use 3.7v LiPo batteries to start with? The Argons and Xenons are designed to use and even charge these (when USB power is connected). A dc-dc converter will work as @glx points out but their efficiency often drops when current consumption is low. Will be devices be sleeping or powered ON all the time?


#4

No real reason except my ignorance before purchasing and the fact that I already spent money on the li-ion batteries. I didn’t read enough before getting them but will probably use LiPo for the next project.


#5

@0xgaby, with the 9v batteries and the dc-dc regulator providing 3.7v to the Li+ pin (I assume), you will not be able to connect USB power as the onboard charger will attempt to charge the non-existing battery.


#6

Yea, just get some 3.7v lipo batteries with battery protection circuits built into them so your protected from short circuit and over charge and discharge situations. Then you can also recharge them via plugging in a USB cord to the USB input on the Gen3 devices.


#7

I am okay with unplugging the battery when I need to use usb, although that should not be often.
If I use a dc-dc regulator, would the + output wire go to the Li+ pin and the - output wire be unconnected to the device?


#8

@0xgaby, you would connect the + output to Li+ and the - output to GND on the device. You could also use a JST connector to “mimic” the battery, making it easier to disconnect when you use USB.


#9

I like buck converters, but agree with the others this is not a good application. I just received two 2500mAh LiPos from Adafruit for $14.95 each. Also like the JST PH2 extension cable with on/off switch for $2.95.


#10

It’s just for a short demo/proof of concept and won’t be running long at all. In fact, the pieces will likely be taken apart and used by someone else in my team once I am done. I ended up getting the buck converters and made sure I was getting the right voltage. It works well :smiley: !