Efficiency of Voltage Boosters

axillent

Looking forward to more test results. Don't forget to mention what brand / type of inductor and capacitors you go for in the circuits.
I'm currently doing tests with prototype of future MySensors board.
It is started today from a single AA battery.
The radio part is not yet soldered but will be soldered as soon as I will compile and test a correct bootloader

axillent

As for capacitors.
Do not mix different things.

old-style electrolitic and tantalum can be used to decouple radio module power.
this capacitor is needed to reduce drop of the voltage at a time of receiving and sending

as for step-ups/step-downs/LDO there is no ideal capacitor in general. You should always refer to the recommendations from the datasheet.
Most modern power chips are required multil-layers ceramic capacitors. Such capacitors they have stable characteristics and very low ESR (much lower than tantalum have). In most cases it is X7R or X5R (the difference between this two is temperature stability)
But for some power chips ceramic will be not recommended. Refer to the datasheet.

axillent

@marceltrapman for radio the capacitor is recommended always. For some good quality modules this capacitor is build on the board, but in most cases it is not. 220uf is too much. 10-47uf is sufficient, tantalum is better than electrolytic

Bandra

I've (perhaps naively) built my battery powered MySensors pcb's around the 3 pin configuration of the ebay cheapie. If many others have done the same then I can see some value in someone creating a drop-in replacement board based on the more efficient chips. I'd definitely buy the more efficient version if someone created it, whether pre-made or solder-it-yourself.

therik

Good to see new activity on this thread again.

@axillent Unless there is some EMI coupled into the power leads of a battery connected radio, or current draw from the battery can't keep up with demand, I don't see why a capacitor is needed. In fact, the product brief for the nRF24L01+ states that it is designed with an on-board voltage regulator and permits operation with a coin-cell battery. Is there something I'm missing?

Also, regarding capacitors, I think you mean 220 microF is 'overkill' or 'more-than-enough', rather than 'too-much'. Right?

Anyway, here is a comparison of aluminum polymer capacitors of different capacitance. Note how the 220 microF cap is cheaper and has lower ESR than either the 10 microF or the 47 microF, and is only slightly larger in physical size.

Tantalum on the other hand has a quite high ESR, on the order of ohms, not good for suppressing voltage ripple according to this document.

That being said, ceramics may be the way to go for sub-100 microF as they are lower cost, smaller, and very low ESR; above 100 microF ceramics get very expensive, ~$4 for a 220 microF.

therik

@Bandra Great, would you be able to share your run times so that we can get some real world data? That is, how long can you run a node before the battery is discharged?

I was thinking about making a board using one of the high efficiency boosters listed in the first post, if they prove their worth. I get my components in on Saturday, so sometime next week I should have preliminary results.

axillent

@therik

@axillent Unless there is some EMI coupled into the power leads of a battery connected radio, or current draw from the battery can't keep up with demand, I don't see why a capacitor is needed. In fact, the product brief for the nRF24L01+ states that it is designed with an on-board voltage regulator and permits operation with a coin-cell battery. Is there something I'm missing?

I'm not an EMI or decoupling freak but I knew from practice own and others that communication distance is very vary with and without capacitor soldered very close to the radio.
You can try yourself. My PA+LNA modules are having tantalum soldered near power pins while cheap $1 modules do not have a capacitor on board

therik

@axillent I totally agree with the radio being very sensitive to noise and voltage ripple on the power pins. I have had great improvements with running the radio on battery directly.

I know that the 4.7 microF electrolytic recommended on the MySensors store does very little to help.

When I powered the radio from the booster I was getting poor reception and many failed messages; I didn't have any tantalum capacitors on hand, so I tried to look at suppressing the voltage ripple of the power to the radio using the beastly 220 microF polymer capacitors and it worked well.

I think we have come to the same conclusion...voltage ripple to the radio is bad, suppress it any way you can and one will have better results.

Bandra

@therik

@therik said:

@Bandra Great, would you be able to share your run times so that we can get some real world data? That is, how long can you run a node before the battery is discharged?

I was thinking about making a board using one of the high efficiency boosters listed in the first post, if they prove their worth. I get my components in on Saturday, so sometime next week I should have preliminary results.

I only sent my pcb's off for production a couple of days ago. They have a 5cm x 3cm footprint which is designed to fit perfectly on top of a 2xAA battery holder. If the analysis of the chinese cheapie step up converters is right then it may be a couple of months before I run out of battery and have some real world results. However they have the battery level sensing circuit on them so I may have some results sooner once I tweak the algorithm for the 1.2 volt cells. Will let you know how I go.

a-lurker

On the cheap electrolytic capacitors: They tend to have a high leakage current, which is not good in battery powered scenarios.

a-lurker

(Note resurrected post) @therik I used to think that you could run the MySensor stuff just using two batteries connected directly to the processor but came to the conclusion that's a bad idea. First, to get the best out of some sensors running them off a fixed Voltage is preferable.

Secondly two alkaline AAs supply about 2.4V to 2.6V (during most of their operational life time) and the 3.3V CPUs have the brownout set to 2.7 V (typ). So if you use this method, you need to ensure the brown out detector (BOD) fuses are set to disable the brownout detection completely. Doing it in software is not sufficient, as the BOD is automatically re-enabled as soon as the CPU comes out of sleep.

The CPU spec shows the maximum Frequency vs. VCC line for between 1.8 V and 2.7 V. The line equation is Vmin = (F-k)/m, where from the spec k = -8 and m =6.6666 so for 8 MHz: Vmin = 2.4V Towards the end of their life two AAs will go below this Voltage. What happens then? With an inverter you can monitor the battery Voltage and trigger an alarm when it gets really, really low.

Also with the inverter you can squeeze every last ounce of juice out of them and everything will still work.

@axillent Totally agree about charging batteries - probably more hassle than it's worth. Depending on the application, just solar charging a super capacitor could work well. Imagine a temperature sensor reporting back every fifteen minutes and it consumes say 30ma at 3V3 for 0.5 seconds while it reports and we use one of these:

https://www.sparkfun.com/products/746

time roughly = (C/I)*(Vmax-Vmin)

so say we use say a Vmax of 2V and Vmin of 1V and use that to power an inverter to 3V3. Also assume we draw 100 mA at 1V, which is about 30 mA at 3V3 for the CPU and radio. We have a ten Farad cap but it's a bit out of tolerance, so it's actually only five Farads.

(5/0.1)*(2-1)= 50 seconds

That allows for one hundred 0.5 second samples to sent before the cap is "flat", which is 25 hours if sent every 15 minutes. So it looks like it could work OK. Should work for @HeK in Sweden where the shortest day is only about 7 hours long, with the main problem is keeping snow off the solar panel.

a-lurker

Just adding to the above. It does make sense to run the radio directly off the battery (1V9 to 3V6) but two problems remain: the CPU brownout detector and the minimum Voltage required to run the CPU, which is 2V4 at 8 MHz.. See also:

http://forum.micasaverde.com/index.php/topic,20078.msg164716.html#msg164716

The radio must have a supply Voltage of 2V7 to 3V3 if the input signals are greater than 3V6. you would encounter this when running a CPU at 5V, which hopefully you wouldn't be doing on a battery powered set up.

BSoft

@a-lurker If brownout detection is disabled we could power atmega328p with 1.9V minimum, but frequency of operation will decrease.
I know you get it right, i just want to standout that there is no problem of operation at low voltage if we know 2 thinks:

disable BOD (no soft)
we get lower frequency

Zeph

There are a few subjects in this valuable thread.

One is the best type of capacitor to use across the power and ground of the nRF24L01+ module. I'm very interested in that. My earliest tests were frustrating, I was busy trying to figure out what was wrong with the software (before I came here by the way), but it turned out to be power and/or too long SPI wires. A cap across the power at the module made a great difference. So I'm tending towards always doing that in the future, and I'd like to know what kind to stock up on.

I'm seeing some opinion that tantalum would be better, some that it has too high ESR. So a low ESR electrolytic (probable aluminum polymer) would be better. Or maybe a ceramic is better still, and cheap.

Are there any recommended caps below 50 cents in small quantities? Is there anything from eBay or Tayda or are those all junk for our purposes? If not, Digikey or Mouser is OK, tho the minimum shipping raises the effective cost per unit substantially for small quantities (and I may not have a large order to combine it with for months).

There is a variation of this question which is about caps for use with noisy boost converters. I am thinking that a good cap for that purpose would also be a good cap for use with the tranceiver in general - low ESR and with an appropriate value, with low leakage. (In another case the noise of a sensor or actuator might be what needs to be filtered out rather than a boost voltage converter).

marceltrapman

I changed the capacitor that I used for my radios from 4.7 mF into 220 mF and I can only say thank you for this discussion, it is really immediately much better :)

Damme

@marceltrapman mF as in milli or micro? :) µF I suppose..

axillent

@marceltrapman there is a convention to mark micro by µ if you have a special symbol or by u if you don't
this way 220 micro Farad should be market as 220 µF or 220 uF

@Damme it is a good point)

marceltrapman

@Damme @axillent Oh my, so much to learn :)
Thank you guys, I mean 220 uF...

Damme

@marceltrapman You're welcome :)

I tried 220µF myself now (EU keyoard can write µ with alt-gr+m or (ctrl+alt m if alt+gr is missing))

much better, I first used 33µF and then 100µF but 220µF is a winner.
The wierd thing is that I cant measure any difference with 33µF or 220µF with my oscilloscope. but with no cap at all my arduino nano 3.3v looks like this: (AC coupled)

And wit cap (33µF or 220µF makes no difference at all..) But it works much better..

Yveaux

@Damme strange, disturbance is around 50hz... Could it be caused by mains supply?

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