Author Topic: Battery Operated Device Power supply  (Read 7080 times)

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Offline paulcaTopic starter

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Re: Battery Operated Device Power supply
« Reply #25 on: February 18, 2018, 09:54:09 am »
It has a 3 pin + tab with marking

L5  (might be E5)
OP

Which I assume is the boost IC.

A large 2 pin device marked

SS14

Which I assume is a diode.

An inductor marked 220 which I assume is a 220nH inductor.

An LED with a 222 SMD resistor and a few caps.
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Offline paulcaTopic starter

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Re: Battery Operated Device Power supply
« Reply #26 on: February 18, 2018, 09:56:13 am »
E5OP would make it a TP8350 boost IC.
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Online Ian.M

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Re: Battery Operated Device Power supply
« Reply #27 on: February 18, 2018, 10:36:49 am »
For maximum battery life, you'd probably do a lot better with a nominally 3.3V 8MHz Arduino, board, (or better a bare Atmega328P so you don't have any extra power drain)  and a low quiescent current buck converter down to 3.0V.    Even bucking to 3.3V then letting the output voltage follow the input as the 18650 cell drops below about 3.4V  would be a vast improvement.   

As you are building a clock, you *may* be relying on the CPU clock for accurate timing.  Rather than running a 8MHz crystal primary oscillator all the time, you'll save power by providing a 32.768KHz crystal for the Timer/Counter 2 Oscillator, and use the 8MHz calibrated internal osciillator as the primary clock, sleeping as much as possible with wakeup by timer 2.   See http://kineticsandelectronics.com/sleep.html
 

Offline paulcaTopic starter

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Re: Battery Operated Device Power supply
« Reply #28 on: February 18, 2018, 10:43:13 am »
I'm using a DS1302 RTC with NiMH battery backup.
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Offline soubitos

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Re: Battery Operated Device Power supply
« Reply #29 on: February 18, 2018, 11:11:57 am »
It has a 3 pin + tab with marking

L5  (might be E5)
OP

Which I assume is the boost IC.

A large 2 pin device marked

SS14

Which I assume is a diode.

An inductor marked 220 which I assume is a 220nH inductor.

An LED with a 222 SMD resistor and a few caps.

I am no expert to calculate how the changes from manufacturer recommended values vs installed values affect efficiency in this module but....

L1 is 47uH (resistance <0.1 ohm)
a 47uF cap is in the input and a 100uF cap or a 20uF with a 0.05 ohm resistor in series are in the output

With these, they claim 80% efficiency when 3.2V<Vin<4.2V. Vout is 5V and Iout is 150mA<Iout<500mA

I think with a very small load the efficiency of this chip is going way down. Same for Vin bellow 3.2V with 5V output
 

Offline paulcaTopic starter

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Re: Battery Operated Device Power supply
« Reply #30 on: February 18, 2018, 11:15:20 am »
With these, they claim 80% efficiency when 3.2V<Vin<4.2V. Vout is 5V and Iout is 150mA<Iout<500mA

I think with a very small load the efficiency of this chip is going way down. Same for Vin bellow 3.2V with 5V output

Yep.  Sounds fair.  My prototype is probably only pulling at most 20mA.

I know I promised current measurements, but I'm trying to fix a PC OS issue that came up which has broken a number of things on me.
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Offline soubitos

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Re: Battery Operated Device Power supply
« Reply #31 on: February 18, 2018, 11:24:00 am »
Actually, its mentioned in the datasheet
4) The customer can reduce the inductance (about 22uH) if it drives large current load (more than 150mA) and the ripple requirement is not high. Customers who drive small current loads (less than 50mA) and want low ripple output voltages can increase their inductance

If you have an inductor around 47uH with Isat over 1A try to replace the 22uH inductor with it... also i would try replacing the output capacitor with an electrolytic 100uF in parallel with a 100nf ceramic
 

Offline Kalvin

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Re: Battery Operated Device Power supply
« Reply #32 on: February 18, 2018, 12:02:58 pm »
If I have understood correctly you want to run Nano and the LEDs from the re-chargeable Li-Ion battery, and you want to keep the LED intensity constant. As the battery voltage drops the LEDs will be getting dimmer, you want to run device from +5V power supply.

About the Li-Ion battery: The battery is almost dead when it reaches 3.3 so the voltage range you effectively get is 4.2V down to 3.3V, and you have used more than 90% - 95% of the battery capacity when the battery voltage is 3.3V.

You may want to run Nano directly off the battery voltage 4.2V ... 3.3V as the Atmega328 runs fine between +1.8V ... +5.5V.

The 74HC595 is specified for 2V ... 6V operating voltages, so you can run it directly from the battery as well.

About the LEDs: The LEDs will consume few milliamps each, and a low-power linear regulator will consume around 100 uA maximum. So, one option might be to use a low-power low-drop voltage regulator to power the LEDs in order to keep the brightness constant without affecting the power consumption too much. There will be some losses due to the nature of a linear regulator, but you are using the current limiting resistors with the LEDs anyway, so there won't be any extra loss compared to running the LEDs directly from the battery with current limiting resistors.
 

Offline paulcaTopic starter

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Re: Battery Operated Device Power supply
« Reply #33 on: February 18, 2018, 12:42:08 pm »
Interesting, as I was going to be using the TLC59282 LED Constant current Driver that allows me to set the current for all LEDs with 1 resistor.  It sinks the current from the LEDs ... so I can run them off a 3V rail.  (I'll have to check the IC doesn't mind).

Actually, I added an I2C header on the board for an optional oLed.  When I start talking about oLeds and potentially a dozen LEDs on at a time, a battery solution that will run for a few weeks it probably going to be looking at multiple 18650s in parallel, even if I do get it to be efficient.

I'll have to test the oLED, but 10mA sounds fair. 

If I consider a ball park duty cycle of 50% of the LEDs on at a time, that's 8 LEDs (8.5 if you count the AM/PM light).

10mA oLED screen
32mA 4mA*8 LEDs
uC 10mA
neglibilbe RTC

That's 52mA, call it 60mA.  2600mAh battery, even if it gave it's full capacity range, would last 43 hours.  More likely 36, one and a half days.

To get a week I would need 4 18650s in parallel.

It's starting to sound like a USB powered device.
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Offline Peabody

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Re: Battery Operated Device Power supply
« Reply #34 on: February 18, 2018, 07:56:37 pm »
My guess is that the efficiency of your converter is not good at the current you're drawing.  I just finished converting my scope to lipo power using an MT3608 boost converter module, and it seems to work fine going from a single cell lipo to 8.2V.  It's more expensive, but runs at 1.2 MHz, and from the datasheet it looks like you'd be at over 90% efficiency even at low current.

But you have several things working against you as far as battery life is concerned when using the boost converter versus powering directly from the battery:

Your circuit probably uses less current when run at 3.5V than at 5V.

Even with 100% efficiency, converter power in must at least equal power out.  So if you need 25ma at 5V for your circuit, you'll need 36ma at 3.5V coming out of the battery.  Powered directly from the battery, you might only need 20ma at 3.5V.

No converter is 100% efficient, and may require tweaking for the current you will be drawing.

Drawing more current out of the battery drops its instantaneous voltage a bit more, which makes it hit the protection low-voltage disconnect earlier.  So you're actually using a lower percentage of the battery's capacity.

For all these reasons, it wouldn't be at all surprising if battery life was cut in half using the converter, even with a very efficient converter.  But you're off by 6 to 1, and unless you just got a bad copy of the converter, I suspect it just isn't at its best at low current.

The current measurements should tell you a lot about what's going on.
 

Offline paulcaTopic starter

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Re: Battery Operated Device Power supply
« Reply #35 on: February 18, 2018, 08:10:16 pm »
Well I sent the board for manufacturer, so I'm commited now.

Of course the board does not include the PSU :)  It just +5V and GND headers.

I think what this will end up is a USB desktop powered device that has a battery backup that will run it for a few days.
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Offline paulcaTopic starter

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Re: Battery Operated Device Power supply
« Reply #36 on: February 24, 2018, 03:17:55 pm »
On the prototype power situation...

It's still running on the same charge since my last post on removing the boost module.  Cell voltage is 3.2V, Nano and LEDs all seem happy though a little dimmer of course.

I wonder how long it will go for.  Anyone wanna place bets?  I recon it will make it until Tuesday.
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Offline paulcaTopic starter

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Re: Battery Operated Device Power supply
« Reply #37 on: February 24, 2018, 09:47:22 pm »
Nope.  It just died.  Nano locked up first, LEDs dimmed quite rapidly and the TP4056 cut out.
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Offline soubitos

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Re: Battery Operated Device Power supply
« Reply #38 on: February 24, 2018, 11:37:53 pm »
there is something wrong about this...
 

Offline soubitos

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Re: Battery Operated Device Power supply
« Reply #39 on: February 24, 2018, 11:46:06 pm »
If i remember correctly, you mentioned you use a brand new cell...
1. have you done any capacity test on it?
2. have you measured the current draw before and after the booster?
3. In ideal conditions a 2600mAh cell directly powering a 100mA load should last... 26hrs if i am not wrong?
With a booster working at 80% efficiency this would drop to near 20hrs... so, its either you expect it to keep going for much longer than it can, the battery is of much lower real capacity or the current draw is much higher than you estimate or a combination of the above... plus the fact that MT3608 at low loads is NOT efficient at all
 

Offline Peabody

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Re: Battery Operated Device Power supply
« Reply #40 on: February 25, 2018, 02:55:02 am »
And he should look at the circuit's current draw at the booster's 5V output vs when powered directly by the lipo at, say, 3.6V.  The circuit will likely draw more current at 5V.

Also remember that even if the converter is 100% efficient, when going from 3.6V to 5V, the current drawn from the battery will be 139 ma to provide 100 ma at 5V.  Power in must equal power out.  Then for 90% efficiency, that would change to  154 ma out of the battery.

About the MT3608, the graphs in the datasheet show the efficiency to be quite good, especially at low currents, down to about 40 ma.


 

Offline viperidae

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Re: Battery Operated Device Power supply
« Reply #41 on: February 25, 2018, 03:11:30 am »
Your boost converter could be chewing 2mA quiescent current.
Your leds will be using a lot more current at 5v too. That extra volt is going to end up across the current limiting resistor with a corresponding increase in current flow.
 

Offline paulcaTopic starter

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Re: Battery Operated Device Power supply
« Reply #42 on: February 25, 2018, 09:14:55 am »
Sorry, I think I've confused everyone.

The final circuit will run 16 LEDs and an oLED constantly with an estimated average 8 LEDs on at a time.  It uses a constant current LED driver IC, no current limit resistors, I have guesstimated 100mA total for that.  So yes, a fully charged 2600mAh 18650 should get me at least 24 hours.  Making it more of a UPS style thing rather than a battery operated device.

The prototype on the breadboard only has 6 LEDs with current limiting resistors (470R).  Without the boost converter the board ran for over a week!  With the boost converter it lasts less than 24 hours.

I'll try testing the boost converter current now.  BRB.
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Offline paulcaTopic starter

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Re: Battery Operated Device Power supply
« Reply #43 on: February 25, 2018, 09:27:20 am »
So, test circuit:

4 x White LEDs --> 470R current limiters.  Common Anode.
Input voltage: 4.0V


With boost converter:  0.029A  Output voltage: 5.0V
Without boost converter: 0.006A Voltage: 4.0V
Without boost converter: 0.011A Voltage: 5.0V

An efficiency of 20% or 37% depending on how you look at it.

Also, it randomly squeals quite loudly when unloaded.

I don't have anything to hand right now to test it under a more decent load.  But for the project in question it is not going to work.
« Last Edit: February 25, 2018, 09:33:04 am by paulca »
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Online Ian.M

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Re: Battery Operated Device Power supply
« Reply #44 on: February 25, 2018, 10:06:43 am »
I said back in reply #27 you need to *BUCK*, not boost.   If you buck to the lowest voltage your design can tolerate, you'll save most of the power being dissipated in those resistors or constant current LED drivers.

Also, add a photosensor so you can auto-adjust the LED intensity to track ambient light levels.  The LEDs only need to be bright in full daylight, so there are considerable power savings to be made overnight.
 
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Offline Peabody

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Re: Battery Operated Device Power supply
« Reply #45 on: February 25, 2018, 06:43:15 pm »
I'm not sure a load that small tells you much.  But it may well be that your boost converter just isn't that good.  That doesn't mean you couldn't find one that works much better.
 

Offline soubitos

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Re: Battery Operated Device Power supply
« Reply #46 on: February 25, 2018, 07:10:46 pm »
hold on.. the booster in this case is NOT MT3608 but TP8350.
And its not as efficient at low current draw.. not at all..
https://datasheet.lcsc.com/szlcsc/TP8350-5-0_C21998.pdf

Plus, the module is not following datasheet suggested values either in inductor or capacitors..

In the datasheet is also mentioned:
4) ????????????? 150mA??????????????????22uH ????
Which means, you can use a 22uH inductor IF your current draw is over 150mA and you dont care much about ripple.
Its normal spec is for a 47uH coil and in the module is a 22uH yet the current draw is well bellow 150mA and the capacitors are definitely not as recommended... This speaks in Chinese "I am not a good module for your application, take an MT3608 or better" LOL
 

Offline soubitos

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Re: Battery Operated Device Power supply
« Reply #47 on: February 25, 2018, 07:14:04 pm »
HAHA Chinese didnt go through.. anyway. it would be VERY interesting to see how this little module would operate with a 47uH coil and a 100uF//100nF caps in its output
 

Offline paulcaTopic starter

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Re: Battery Operated Device Power supply
« Reply #48 on: February 25, 2018, 07:24:18 pm »
HAHA Chinese didnt go through.. anyway. it would be VERY interesting to see how this little module would operate with a 47uH coil and a 100uF//100nF caps in its output

Well unless I have a project for it that pulls circa 500mA it's a superfluous device.  Meaning, I now have no other purpose for it and can modify it.

When my hot air gun arrives I will try and replace a few things and see how it goes.

Can you post the links to datasheets?
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Offline soubitos

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