Power Supply for Remote Devices

Any have experience with remote devices. The g120 for example requires a 5volts supply but alot of peripherals need 12volt, do people usually use a 12V lead battery or maybe a LIPo with DC-DC converter.

Lipo do not come in 12volts nor do i see other batteries in 12volts? If i series lipos to get 14v then, what method do i use to charge them?

Hoping someone can shed some light on this?

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A sealed lead acid (SLA) battery is a common source. But remember, it’s only a nominal 12V, it’ll range from 14.4v at max charge down to under 12V, and you need to handle the varying power.

I have a remote sensor in the garden, it has a 12V SLA (6AH) and a solar panel and a cheap solar charger unit to keep it topped up. I then have a reasonably cheap variable output power supply connected to the nom 12V output from the solar charger (it has discharge protection to I can’t drain the battery excessively) and this generates 5v (for the few 5v things I need) and I power the uC with a linear regulator on a small PCB taking the 5v down to 3v3.

How much current do you need at 12V?

I use a boost converter to step up 3.3V or 5V to 24V at around 500mA for powering 4-20mA sensors and this works fine for the max 4 sensors I need to support.

Remember that the current at 12V will mean this is 2.4 times at 5V so make sure your lower voltage supply can handle the current.

You can also use those handy little DC-DC modules from the likes of Murata or Traco and are ideal if you want isolated too but connecting the grounds so the reference is the same works just as well.

So a DC-DC convert from 3.7v LiPO for example would be enough to power some relays and low power 12volts devices?

I’m thinking of using a LiPo(due to efficiency,weight and longevity)…basically want to use a battery technology that will last longest in the field without maintenance(i will have the ability to add a solar panel of course).

Thanks Guys in advance :slight_smile:

Hi Anthony,

Remember that a LiPo will go from about 3.4 to 4.2V during operation so you need to either find an off the self DC-DC that covers that input range or design your own with the many BOOST switched mode IC’s that are on the market. The LM3224 is one such device and the very one I have used myself. Can generate up to 2.4A

Because you will have some form of charger, this IC can handle up to 7V input so makes it ideal.

have you figured how much power you need ?

mm…i have never cared about Power for some reason…just out of curiosity, what type of power usage would a device use. Yes…i know its a broad question?

Eg

G120 board with 4relaysand gsm module? What sort of power usage would you estimate?

G120 board with GSM module, xbee module and ethernet? What sort of power usage would you estimate?

I tyhink i need to do some power measurements for my boards…not something i think about until you go remote!

Hi Anthony,

The best way to do this is to use a good bench power supply that you can read out the current drawn on a nice digital display. They are also great too because if something goes wrong, they have excellent current protection. I have the GW-INSTEK GPS-3303 here and this has a nice feature that you can switch on the output after you configure the voltage and current. No need to unplug the device first.

As you most likely have a multimeter in you test box, this too can be used to measure the total power drawn.

By plugging in each part you can measure the current. For example I have on my desk a G400 with a 24V input and 3.3V regulator on the main board. The 24V is drawing 125mA according to the power supply so by simple maths, the 3.3V is drawing approx 900mA and its switching regulator is good for 1.5A

@ Dave McLaughlin - Nice power supply. But i do have fluke MM :slight_smile:

relays = active coils = more power drain. Are you use you need them? As @ Dave says, start measuring to get broad brush ideas

Picking a battery really needs to be based on figuring out how much demand you have and how much time you need to run, and for solar how much sun you get. Then, depending on the battery chemistry, you don’t want to deplete it too far otherwise other bad things happen; so you increase the size.

for your implementation… What else happens if you run out of power - for example, it’d be really bad if the garage door you had locked electronically became unlocked; but if a snow monitoring alert didn’t send an SMS after a couple of days of bad weather, that may not be an issue.