Author Topic: Running moteino on 1 cell Liion vs 2 cell Liion  (Read 2308 times)

peter.

  • Newbie
  • *
  • Posts: 2
  • Country: hu
Running moteino on 1 cell Liion vs 2 cell Liion
« on: August 23, 2016, 03:58:42 AM »
Hey Guys!

First of all sorry for any stupid questions, I am primarily a SW engineer, I do electronics as a hobby ;)

I am planning to run my project on Liion cells. As i know moteduino has a low dropout linear regulator which is great, because it still outputs 3.3V with 3.3V battery voltage. However these Liion cells can discharge down to 2.9V without damaging the battery.
The question is, will the LDO output 3.0 volts if the battery can only supply 3.0? Both Atm328p and RFM69HW can work at that voltage.

Given the fact, that i am going to use 2 liion cells for a moteduino based node. Which configuration would be more energy and performance efficient:
- 2 cells in series
- 2 cells in parallel

If my knowledge of linear regulators are right, supplying any voltage higher than 3.3V will be burned to heat right?
So this way 2 cells in parallel would be more energy efficient even I can't use the batteries whole voltage range (2.9-4.1 vs 3.3-4.1)


Random fact for those interested:
I am creating an urban garage alarm with moteduinos. The difficulty is that it's an open garage on the -1 floor in a 10 story building. I need to create a reliable connection between -1 and 4th floor. There is a lot of electronics stuff, wifi, concrete and metal and like 100m horizontal distance between the transmitter and the receiver. So I might need to use a repeater node. However the transmitter and the relay needs to be run on battery power. The transmitter is not a big deal, because it can sleep a lot.
However the repeater can't sleep much, because it would lose signal from the transmitter while it is sleeping. I might end up running the repeater on like 20 liion cells wired in parallels (around ~30000mah i got a quite lot of them from used laptop batteries).

ChemE

  • Sr. Member
  • ****
  • Posts: 419
  • Country: us
Re: Running moteduino on 1 cell Liion vs 2 cell Liion
« Reply #1 on: August 23, 2016, 08:07:16 AM »
Would it be possible to use an empty Pringles can to make a waveguide for the radio in hopes of improving its range enough to do away with the repeater?  I know they work amazingly at wireless frequencies perhaps the same it not true with RF.

Felix

  • Administrator
  • Hero Member
  • *****
  • Posts: 6404
  • Country: us
    • LowPowerLab
Re: Running moteduino on 1 cell Liion vs 2 cell Liion
« Reply #2 on: August 23, 2016, 10:21:23 AM »
Peter,
Nice project!
The regulator will pass less than 3.3v but it will burn more power when it's below the dropout region (~3.55v), I think 30uA if I recall correctly. Not a whole lot but if you are looking for ultra low power (sub 10uA) I would look into removing the regulator, there are discussions in the forum about that. But sometimes depending on the overall load of your project that effort might not be worth it.

I find running a single cell works well and if the parts and MCU are properly slept, the power budget can be very low and last a very long time.
Yes the higher the input voltage the more heat will dissipate with any regulator. I haven't done measurements maybe others did. I guess I would try parallel rather than series. That way you have the same voltage as 1 cell but double the capacity.

emjay

  • Full Member
  • ***
  • Posts: 119
  • Country: nl
Re: Running moteduino on 1 cell Liion vs 2 cell Liion
« Reply #3 on: August 23, 2016, 11:57:01 AM »
Using a fully charged LiPo (can be as much as 4.3v when fresh from the charger) without the LDO in circuit is going to exceed the official RF Module Vdd absolute maximum.
A solution is to pull some charge out externally before connecting up (it drops back quite quickly) or use a permanent series diode to get rid of ~0.6v   The first method uses less of the stored charge.

Felix

  • Administrator
  • Hero Member
  • *****
  • Posts: 6404
  • Country: us
    • LowPowerLab
Re: Running moteduino on 1 cell Liion vs 2 cell Liion
« Reply #4 on: August 23, 2016, 12:17:24 PM »
emjay, good points!
I would also check this thread and see Tom's comments about running from 2xAA without removing the regulator.

TomWS

  • Hero Member
  • *****
  • Posts: 1925
Re: Running moteduino on 1 cell Liion vs 2 cell Liion
« Reply #5 on: August 23, 2016, 01:40:51 PM »
I guess I would try parallel rather than series. That way you have the same voltage as 1 cell but double the capacity.
I would not put two Batteries of any type, especially LiPo, in parallel without a blocking diode on each. 

Tom

peter.

  • Newbie
  • *
  • Posts: 2
  • Country: hu
Re: Running moteduino on 1 cell Liion vs 2 cell Liion
« Reply #6 on: August 28, 2016, 04:29:38 AM »
Would it be possible to use an empty Pringles can to make a waveguide for the radio in hopes of improving its range enough to do away with the repeater?  I know they work amazingly at wireless frequencies perhaps the same it not true with RF.

I have never though about making a tin-can antenna, but actually that is a good idea. Do i need that waveguide on both sender and receiver side?


Using a fully charged LiPo (can be as much as 4.3v when fresh from the charger) without the LDO in circuit is going to exceed the official RF Module Vdd absolute maximum.
A solution is to pull some charge out externally before connecting up (it drops back quite quickly) or use a permanent series diode to get rid of ~0.6v   The first method uses less of the stored charge.

The diode also burns that 0.6V so it's almost the same as the regulator in my understanding.


Peter,
Nice project!
The regulator will pass less than 3.3v but it will burn more power when it's below the dropout region (~3.55v), I think 30uA if I recall correctly. Not a whole lot but if you are looking for ultra low power (sub 10uA) I would look into removing the regulator, there are discussions in the forum about that. But sometimes depending on the overall load of your project that effort might not be worth it.

I find running a single cell works well and if the parts and MCU are properly slept, the power budget can be very low and last a very long time.
Yes the higher the input voltage the more heat will dissipate with any regulator. I haven't done measurements maybe others did. I guess I would try parallel rather than series. That way you have the same voltage as 1 cell but double the capacity.

Thanks!
I am going to use parallel batteries then. Parallel connections are also better in a way that they don't require cell balancing, they are self-balancing.
« Last Edit: August 28, 2016, 04:35:56 AM by peter. »

ChemE

  • Sr. Member
  • ****
  • Posts: 419
  • Country: us
Re: Running moteduino on 1 cell Liion vs 2 cell Liion
« Reply #7 on: August 28, 2016, 09:48:43 PM »
I have never though about making a tin-can antenna, but actually that is a good idea. Do i need that waveguide on both sender and receiver side?

If there is to be two-way comms then yes you would.  Any radio that needs to be heard a long distance away would benefit from speaking through a waveguide.  If your garage node will only be speaking and not listening then you would not need a waveguide on your gateway.

kobuki

  • Sr. Member
  • ****
  • Posts: 289
Re: Running moteduino on 1 cell Liion vs 2 cell Liion
« Reply #8 on: August 29, 2016, 07:05:05 AM »
@peter: have you thought about using a directional antenna, such as these, or any cheap chinese one? They might be a simpler solution than using a repeater. Plus, in fact you don't really need to have your Moteinos turned on all the time if you use listen mode in the proper configuration. Lots of info on the forum about these.

Also, instead of using LiPo/LiIon, have you thought about using LR20/D sized Alkaline batteries? Thet boast 12-18 Ah depending on model and load, 3 in series would be adequate for quite a long time even using the regulator.