How to use a lithium battery for a 3.3V low-consumption circuit?

Go To Last Post
25 posts / 0 new
Author
Message
#1
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Hello,

 

I have decided to create temperature sensors in my house.

 

I use an Arduino Pro mini, with NRF24L01+ radio and a DS18B20 temperature sensor.

 

Everything works on 3.3V with a 18650 Li-ion battery, that I want to last for about a year on a single charge.

 

Basically, each sensor reads the temperature, transmits data to a receiver, and sleeps for a minute, then repeats the process.

 

The first problem is that the battery delivers a voltage that depends on the remaining capacity and can go up to 4.2 V. How do I down-regulate it to 3.3V?

 

Here are my questions, in the descending order of importance:

 

1) I heared about “Buck-Boost” voltage regulators (example) and low-dropout linear regulators (example). But do they consume any current if my sensor is in sleep mode most of the time and consumes only a few µA? So, what solution do I have that will only consume about a few µA in stand-by mode?

2) How can I detect a low battery condition? I'd like to be able to send a "low battery" signal to my receiver.

3) Can I power everything off after a grace period when I detect that battery is low?

 

I think that I need some kind of voltage regulation, because I already tried without, and the NRF24L01+ module isn't working properly with a fully-charged Li-Ion battery that delivers 4.2V (well-above the required 3.3V).

 

Thank you for your suggestions!

 

Temperature Sensor with NRF24L01P radio

Attachment(s): 

Last Edited: Wed. Jan 11, 2017 - 11:43 AM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Li Ion is not the best choice for long term power. It has significant self discharge characteristics. Other lithium chemistries are used for long term, low current applications. These are usually 3 or 3.6V and are not rechargeable. Or use standard alkaline primary cells.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

When I google "constant 3.3v from lithium cell" the top hit is:

 

http://electronics.stackexchange...

 

Seems to have lots of useful answers.

 

While I'm just a bit mangler I thought it was a buck/boost regulator you would need as you actually face two issues: it's true that at the start of the discharge the lithium will start at 4.2V but it's going to end at 2.7V (as long as you are careful) so you face both a period where the supply is above the 3.3V you require and then a period when it is below the 3.3V. Hence buck/boost.

 

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

I too would use 2x alkaline cells for this app, and no regulator would be needed.

As for the how to detect low batt, see this:

 

https://code.google.com/archive/...

 

Although written for arduino, the concept can be used in C .....

 

Edit: Do you expect your temperature to change in a minute?  perhaps every 5 or 15 minutes would be be enough and will extend battery life.

 

Jim

 

 

 

Last Edited: Wed. Jan 11, 2017 - 01:54 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

I don't think a Li-Ion battery will last a year. They usually have rather high self-discharge. Also, this type of battery doesn't like to rest at high or low charges. So I'd recommend to look out for other options.

 

Buck-Boost regulators have usually a high power consumption. So your battery will be empty within days. So I'd go for a linear regulator with low quiescent consumption and low dropout voltage.

 

I currently power my remote sensors (xmegaE5,  si7020 and nrf24l01+) from 3 AAA batteries and use MPC1703 as voltage regulators. This setup is running since the end of November and if the voltage keeps dropping at the current pace I won't have to replace the batteries for the next few months and I could still decrease the average current consumption.

 

Edit: Typo and bracket removed

"Some people die at 25 and aren't buried until 75." -Benjamin Franklin

 

What is life's greatest illusion?"  "Innocence, my brother." -Skyrim

 

Last Edited: Wed. Jan 11, 2017 - 02:15 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

ki0bk wrote:
I too would use 2x alkaline cells for this app, and no regulator would be needed.
Or two nickel-zinc (NiZn) cells and no regulator.

If there's a charger for the NiZn battery then the 3.8V charged battery will exceed the nRF24L01+ max VDD of 3.6V; otherwise, the charged NiZn battery will be about 3.2V to 2.6V discharged (nRF24L01+ min VDD is 1.9V)

NiZn is not low self discharge (LSD); two LSD NiMH (3.0V down to 2.0V) would be within nRF24L01+ VDD range (3.6V down to 1.9V)


Nickel-zinc batteries, the alternative to conventional batteries from Conrad Electronic UK

http://www.conrad-electronic.co.uk/ce/en/content/ti_rechargable_batteries/Nickel-Zink-Akkus-die-neue-Alternative-zu-den-herkoemmlichen-Batterien

eneloop, environmentally friendly and energy saving batteries

http://main.panasonic-eneloop.eu/

http://www.nordicsemi.com/eng/Products/2.4GHz-RF/nRF24L01P

 

"Dare to be naïve." - Buckminster Fuller

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Thanks for the replies.

 

So, I think I throw the buck-boost regulators away. First I need very low power consumption, and second, I think that scaling the voltage up is not really needed, or only when the battery is already almost empty anyways.

 

MPC1703 looks really interesting, looks like it consumes only 2 µA when not in use: http://ww1.microchip.com/downloa...

 

By the way, I realize that Arduino Pro Mini already has a regulator, MIC5205: http://ww1.microchip.com/downloa...

 

One thing that doesn't seem very clear is what is the ground current they talk about? I looked at this article and it seems like removing the regulator might not be worth the gain:

 

https://andreasrohner.at/posts/E...

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

alexpirine wrote:
I think that I need some kind of voltage regulation, because I already tried without, and the NRF24L01+ module isn't working properly with a fully-charged Li-Ion battery that delivers 4.2V (well-above the required 3.3V).
NRF24L01+ can run on a coin cell :

http://www.nordicsemi.com/eng/Products/2.4GHz-RF/nRF24L01P

...

With peak RX/TX currents lower than 14mA, a sub μA power down mode, advanced power management, and a 1.9 to 3.6V supply range, the nRF24L01+ provides a true ULP solution enabling months to years of battery life from coin cell or AA/AAA batteries.

...

 

"Dare to be naïve." - Buckminster Fuller

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

alexpirine wrote:
One thing that doesn't seem very clear is what is the ground current they talk about?
MIC5205 has significant ground pin current :

http://ww1.microchip.com/downloads/en/DeviceDoc/mic5205.pdf

(page 3)

(idles at about 80microA typical)

The MIC5205 has a PNP pass transistor and therefore will have some ground current.

There are a plethora of LDO voltage regulators with PMOS pass transistors that reduce the ground current by an order of magnitude or two.

 

"Dare to be naïve." - Buckminster Fuller

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

gchapman wrote:
Or two nickel-zinc (NiZn) cells and no regulator. If there's a charger for the NiZn battery then the 3.8V charged battery will exceed the nRF24L01+ max VDD of 3.6V; otherwise, the charged NiZn battery will be about 3.2V to 2.6V discharged (nRF24L01+ min VDD is 1.9V) NiZn is not low self discharge (LSD); two LSD NiMH (3.0V down to 2.0V) would be within nRF24L01+ VDD range (3.6V down to 1.9V)
Interesting!

 

OK, for the nRF24L01+ module. And what about the ATmega328P chipset? At 8 MHz, it seems like it should be go below 2.7V: http://www.atmel.com/Images/Atme...

 

Also, the temperature sensor is said to operate at at least 3.0V: http://datasheets.maximintegrate...

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

alexpirine wrote:
One thing that doesn't seem very clear is what is the ground current they talk about?

 

The ground current is the regulators own current consumption which usually varies with output current. So the total consumption is this current plus whatever your circuit draws. That means you want it to be as low as possible.

 

The regulator on the Arduino is not ideal but not that bad either. The MCP1703 is far better in terms of power consumption though. The problem is that it doesn't fit on the Arduino, so you will have make a second board for it. Or you design everything to run on a wide enough supply voltage and omit the regulator entirely.

-Patrick

"Some people die at 25 and aren't buried until 75." -Benjamin Franklin

 

What is life's greatest illusion?"  "Innocence, my brother." -Skyrim

 

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

gchapman wrote:

alexpirine wrote:
One thing that doesn't seem very clear is what is the ground current they talk about?
MIC5205 has significant ground pin current :

http://ww1.microchip.com/downloads/en/DeviceDoc/mic5205.pdf

(page 3)

(idles at about 80microA typical)

The MIC5205 has a PNP pass transistor and therefore will have some ground current.

There are a plethora of LDO voltage regulators with PMOS pass transistors that reduce the ground current by an order of magnitude or two.

 

So, 80 µA, or let's say 100 µA, for a 2000 mAh battery, it's 2 years of lifespan. Doesn't seem like a limiting factor, so I might go with the onboard MIC5205 regulator, even if it's sub-optimal.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

pawi777 wrote:

alexpirine wrote:
One thing that doesn't seem very clear is what is the ground current they talk about?

 

The ground current is the regulators own current consumption which usually varies with output current. So the total consumption is this current plus whatever your circuit draws. That means you want it to be as low as possible.

 

The regulator on the Arduino is not ideal but not that bad either. The MCP1703 is far better in terms of power consumption though. The problem is that it doesn't fit on the Arduino, so you will have make a second board for it. Or you design everything to run on a wide enough supply voltage and omit the regulator entirely.

-Patrick

Yes, it doesn't seem that awful. I am designing my own board, so the space is not a problem:

 

PCB for temperature sensor with nRF24L01+ radio

 

I'm not really convinced about the without regulator solution since it seems that if I combine various components, my voltage range is 3.0-3.6V.

 

3 AA batteries seem to take quite a lot of space. What do you think about a 9V battery?

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Thanks for the DS18B20 datasheet; its VDD range is 3.0V .. 5.5V with an excellent standby current (1microA max)

Buck-boost SMPS looks good for the common range is 3.0V .. 3.6V given Li-poly of 3.0V .. 4.2V.

mega328P at 8MHz per your statement.

IIRC, there are PMIC (power management IC) that will charge a Li-poly and do the under-volt cut-off; will do a look through what I'm aware of.

 

Couldn't recall a complete PMIC.

The following is a buck-boost that has a precise low battery comparator with a summed quiescent current that may be low enough :

http://ams.com/eng/Products/Power-Management/DC-DC-Buck-Boost-Converters/AS1331

 

Edit : AS1331

 

 

"Dare to be naïve." - Buckminster Fuller

Last Edited: Wed. Jan 11, 2017 - 06:57 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

alexpirine wrote:
3 AA batteries seem to take quite a lot of space. What do you think about a 9V battery?

 

There are hardly any worse choices than a 9V battery. Their capacity is very low for their price and the increased voltage doesn't make it last longer. On the contrary even. Also, you waste nearly two thirds of their energy.

You could consider three AAAA(four As, no typo here) batteries. They were very rare, but since many computer manufacturers including Microsoft use them in their touchscreen pens, they became easier to find.

Things change however if you decide to use a switching regulator since they don't waste the excess voltage. Then a 9V block seems reasonable.

-Patrick

"Some people die at 25 and aren't buried until 75." -Benjamin Franklin

 

What is life's greatest illusion?"  "Innocence, my brother." -Skyrim

 

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Oh and by the way: To measure the battery voltage, you can decrease the voltage by a constant factor using a resistive voltage divider and then feed it into any of the ADC pins of the atmega.

Because you need a very high resistance in order to keep the current low, I suggest to buffer the output with a ceramic capacitor. Otherwise you might get noisy measurements. The capacity is unimportant, but I'd use something in the range of 100nF to 1uF.

 

Writing this reminded me of something: You should also place capacitors on the supply lines of the radio module, as close as reasonably possible. These modules are known to be unreliable on noisy or unstable power supplies. I speak from experience here. Again, anything around 100nF to 1uF is fine. Use ceramic or tantalum types because they offer low ESR and low inductance.

-Patrick

"Some people die at 25 and aren't buried until 75." -Benjamin Franklin

 

What is life's greatest illusion?"  "Innocence, my brother." -Skyrim

 

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

pawi777 wrote:

Oh and by the way: To measure the battery voltage, you can decrease the voltage by a constant factor using a resistive voltage divider and then feed it into any of the ADC pins of the atmega.

Because you need a very high resistance in order to keep the current low, I suggest to buffer the output with a ceramic capacitor. Otherwise you might get noisy measurements. The capacity is unimportant, but I'd use something in the range of 100nF to 1uF.

Hello Patrick,

 

At some point I was even thinking about adding a voltage divider, but then I came across this article and thought that this should be enough and avoid me another 3 µA current draw (from the resistive voltage divider): http://provideyourown.com/2012/s...

 

But could you please elaborate on buffering the output with a ceramic capacitor? Does it mean just connecting a capacitor between the analog pin and the ground to smooth out the signal?

 

pawi777 wrote:
Writing this reminded me of something: You should also place capacitors on the supply lines of the radio module, as close as reasonably possible. These modules are known to be unreliable on noisy or unstable power supplies. I speak from experience here. Again, anything around 100nF to 1uF is fine. Use ceramic or tantalum types because they offer low ESR and low inductance

 

I think I will do this, at least. Seems like a good idea.

Last Edited: Thu. Jan 12, 2017 - 08:34 AM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

pawi777 wrote:

alexpirine wrote:
3 AA batteries seem to take quite a lot of space. What do you think about a 9V battery?

 

There are hardly any worse choices than a 9V battery. Their capacity is very low for their price and the increased voltage doesn't make it last longer. On the contrary even. Also, you waste nearly two thirds of their energy.

You could consider three AAAA(four As, no typo here) batteries. They were very rare, but since many computer manufacturers including Microsoft use them in their touchscreen pens, they became easier to find.

Things change however if you decide to use a switching regulator since they don't waste the excess voltage. Then a 9V block seems reasonable.

-Patrick

Do you know if there are 3xAAAA battery holders? I can only find 3xAA and 3xAAA holders.

 

I'd like to put all my sensors in a plastic box that I will design, so it's quite important to have solid battery holders that I will be able to glue or to screw.

 

I am beginning to think that maybe a 3xAA battery holder with nickel-zinc accumulators wouldn't be a bad idea.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

alexpirine wrote:
At some point I was even thinking about adding a voltage divider, but then I came across this article and thought that this should be enough and avoid me another 3 µA current draw (from the resistive voltage divider): http://provideyourown.com/2012/s...

 

This only works as long as you don't use a voltage regulator between your batteries and the atmega. The voltage divider is absolutely necessary if you want to measure voltages higher than Vcc, which is the case here. And yes, the capacitor goes between the ADC pin and ground. Sorry for not making that clearer the first time.

 

alexpirine wrote:
I'd like to put all my sensors in a plastic box that I will design, so it's quite important to have solid battery holders that I will be able to glue or to screw.

What do you mean by design? If you're going to 3D-print something, you could incorporate the battery holder into the design. The contacts could be salvaged from some cheap battery holders.

 

alexpirine wrote:
I am beginning to think that maybe a 3xAA battery holder with nickel-zinc accumulators wouldn't be a bad idea.

I suggest to read the Wikipedia article. There are limitations to this battery technology, but I think it's reasonable if done correctly. For example, you should use brand new cells as used cell have higher self discharge rates.

 

-Patrick

 

"Some people die at 25 and aren't buried until 75." -Benjamin Franklin

 

What is life's greatest illusion?"  "Innocence, my brother." -Skyrim

 

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

alexpirine wrote:
Do you know if there are 3xAAAA battery holders?
Have 2xAAAA :

http://www.batteryholders.com/search.php?cat=Battery+Holder&num=&type=AAAA&term=

alexpirine wrote:
I'd like to put all my sensors in a plastic box that I will design, so it's quite important to have solid battery holders that I will be able to glue or to screw.
http://www.memoryprotectiondevices.com/documents/attaching-and-fastening-battery-holders.pdf

via

http://batteryholders.com/documents.php?type=Tips

alexpirine wrote:
... nickel-zinc accumulators ...
NiZn have self discharge similar to original design NiMH; NiZn is more for a cycle duration of daily to monthly and for high discharge (EV, hybrid vehicle starter battery, e-bike, intersection signal backup battery)

Li-Po is a better fit for your application because it'll be approximate to room temperature (above freezing), you may want it to be relatively small given a capacity, and these can be built to the required volume.


PowerStream Power supplies, battery chargers, batteries and packs, dc/dc converters, injection molding

The world's first round lithium polymer battery from PowerStream

http://www.powerstream.com/round-li-polymer.htm

December 7, 2016

...

Now we have developed a technology to make round or even free-form shapped batteries.

...

4. Self-discharge is less than 1% per month

...

(350mAH, 490mAH)

...

"Dare to be naïve." - Buckminster Fuller

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Why would you need boost if your battery is empty @3V7?

Lots of Buck converters have too high quitescent current for this. Some Lineair regulators have very low quitescent currents.

But preferaby, make you circuit so it can be powerd from you battery without a regulator (Maybe add a good old 1N4007 to drop the voltage a bit?)

 

Also research "jeelabs" "jeenode". He has blogged extensively about battery powered sensor gadgets.

Paul van der Hoeven.
Bunch of old projects with AVR's:
http://www.hoevendesign.com

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0
  • Power just the CPU with a coin cell
  • GPIO pin drives P-Channel Mosfet to switch power to the transmitter and sensor (regulator is optional)
  • read the sensor
  • send out data
  • switch off The RF module and sensor
  • CPU goes back to sleep

while(!solution) {patience--;}

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Dunno if you've seen this yet: https://provideyourown.com/2012/...   <-- measure the arduino's voltage against its internal 1.1V reference.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Many times.... including here (see post #17 above).

 

Ross McKenzie ValuSoft Melbourne Australia

Last Edited: Fri. May 26, 2017 - 12:15 AM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

pawi777 wrote:
Buck-Boost regulators have usually a high power consumption.

No, that is not necessarily the case - there are plenty of buck/boost converters specifically designed for low-power applications like this.

 

See: http://www.avrfreaks.net/comment...

 

And: http://www.avrfreaks.net/comment...

Jim wrote:
 I like the TPS63051 buck/boost switcher - 3.3V out with Vin from 5.5V down to 2.5V. It has VERY low quiescent current and when the load current is low, its operating current is very low

Last Edited: Fri. May 26, 2017 - 07:51 AM