Using batteries?

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turboscrew
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Joined: Fri Mar 10, 2017 7:36 pm

Using batteries?

Post by turboscrew » Mon Mar 13, 2017 11:23 am

Hi.
Does anyone have a good idea how to make a blue pill + DHT-22 run on batteries?
I was thinking of using 3 rechargeable AA batteries, but I wonder if the blue pill can take
the voltage from 3 fully charged NiMHs? I understand that the voltage of a fully recharged NiMH
is around 1.4V without load. Then again DHT-22 may not work with 3.0V.

Or maybe someone has a better idea?
The voltage converters seem to have quite high current consumption.

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Pito
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Re: Using batteries?

Post by Pito » Mon Mar 13, 2017 1:13 pm

3x 1.4 = 4.2 - 0.7 = 3.5V in case you use an Si diode in series.
1.4V is fully charged, it usually drops fast to 1.2V, when empty 0.9V.
There are DC-DC converters with 1.5uA quiescent current and 80-90% efficiency.
For example from a 0.8-4.2V cell input to fixed 3.3 or 5V output: https://www.maximintegrated.com/en/prod ... X1724.html I used to use in past..

Or, do use a lion, lipo, life cell with low drop lin volt reg.
There are low drop, low quiescent current linear regulators, ie. 3V one, work from 3.2+ input.
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turboscrew
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Re: Using batteries?

Post by turboscrew » Mon Mar 13, 2017 2:49 pm

Thanks.
At the moment the diode sounds like a good trick.
The regulator option is hard, because I'm probably need several of them. Maybe 10 - 20.
And I remember that the chip can draw 150 mA max (STM32F103C8T6).
I'm not sure if 100 mA is enough. Have to check...

I've been trying to search DC-DC converter modules, but almost all (at that range) are AMS1117 based
(quiescent qurrent 5 to 10 mA) and most others the no-load current is not given.

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Pito
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Re: Using batteries?

Post by Pito » Mon Mar 13, 2017 5:33 pm

And I remember that the chip can draw 150 mA max (STM32F103C8T6).
OMG, are you going to use the stm32 as the heater in your toaster :) ?
The chip itself draws 15mA max.
AMS1117 is not a DC-DC converter but a linear voltage regulator.
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turboscrew
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Re: Using batteries?

Post by turboscrew » Tue Mar 14, 2017 10:51 am

Well, according to the data sheet, max. 25 mA sink/source per I/O pin and max 150 mA through Vdd/Vdda power lines.

There seems to be lot of all kinds of converter chips, but not so many (almost) ready-to-use modules.
I wonder if there were modules better than this?
http://www.ebay.com/itm/mini-1-8V-3V-3- ... 1612513907
Voltage Input Range: 1.8~5V
Long time maximum output current 100mA
Short time maximum output current 150mA
working frequency 1.2MHz.
Short-Circuit Protection
No load input current : 0.65mA
2.54mm pin pitch, Arduino Breadboard MCU Development Board friendly
Oh, and I didn't mention that there's also a RFM96-module attached, and it can take 130 mA.
I didn't mention that before, because it's not a problem from the voltage point of view, but it seems to be
a problem from the current point of view.

The idea is that the board is in standby (or stop) mode and wakes up every now and then for a couple of seconds.
Last edited by turboscrew on Tue Mar 14, 2017 12:55 pm, edited 2 times in total.

zmemw16
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Location: St Annes, Lancs,UK

Re: Using batteries?

Post by zmemw16 » Tue Mar 14, 2017 12:29 pm

what does a nrf24 or esp8266 take on transmit ?
now where did i put those 22-47uf caps ? :)

stephen

turboscrew
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Re: Using batteries?

Post by turboscrew » Tue Mar 14, 2017 1:17 pm

Hmm, this looks a bit better:
http://www.ebay.com/itm/DC-DC-Input-0-8 ... 2a7296201b

And it's mentioned about the 5V version here that:
"With nothing connected to the 5V CE012’s output the battery was sourcing 0.5mA."
https://dzrmo.wordpress.com/2017/01/26/ ... converter/

Any thoughts?

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