12v A2D circut with minimal power consumption

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What circuit and technique should I use for a lest power consuming design for 8 bit AVR measuring the charge of a 12V battery bank?

 

* Post your questions in the appropriate forum. The "AVR Freaks Projects" forum is for questions about existing, fully completed submissions in the "Projects" area. Moderator. *

Last Edited: Thu. Nov 22, 2018 - 01:07 AM
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One approach is to put a FET switch between the battery and the resistor voltage

divider that feeds the ADC input.  Switching it on to measure, then off, keeps current

consumption low. 

 

Here is a diagram for measuring a 9V battery:

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another example that's for a 4S Li-ion battery :

AVR1300: Using the AVR XMEGA ADC

(page 21)

via AN2535 AVR1300: Using the XMEGA ADC | Application Notes | Microchip Technology Inc. 

Adjust the source resistance as XMEGA can have a larger source resistance than megaAVR at a given sample rate.

 

Edit: source R

 

"Dare to be naïve." - Buckminster Fuller

Last Edited: Fri. Nov 23, 2018 - 07:16 PM
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I never posted a thank you for these circuits, Thank You! I have a related problem. I need a minimal power consumption AVR solution for 13.5-11V DC. Can I somehow beat the voltage divider method of powering this AVR? I want it to mostly sleep. 

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capnkeith wrote:
I need a minimal power consumption AVR solution for 13.5-11V DC.

Do you mean you need a voltage regulator for your project? 

One linear regulator I have used on past for a battery powered project was the TI LP2985, the quiescent current is only 95uA.

You may have even better results using a switching buck regulator, other freaks may be able to offer examples of these.

 

Good luck with the project.

 

Jim

 

 

(Possum Lodge oath) Quando omni flunkus, moritati.

"I thought growing old would take longer"

 

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Thanks Jim! 95uA seems great. Can anyone do better? What about without a regulator just a voltage divider are there some combinations of resisters and uC that can beat this for total power consumption? Source is 12V marine battery bank...

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Go to Digikey and use their selector for  Product Index > Integrated Circuits (ICs) > PMIC - Voltage Regulators - Linear

 

Click on "More Filters" where you can select quiescent current along with maximum voltage input, voltage output and much more.

 

With selection of
Stock Status:          In Stock
Number of Regulators:  1
Max input Voltage:     18-60V
Quiescent current:     < 10 uA
Output Voltage:        5V
Dropout Voltage:       < 1V

 

I get 170 items.

 

Beware, if this is for an automotive application it will be quite nasty, start with the 60V max input.

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capnkeith wrote:
Source is 12V marine battery bank...

do you really need to worry about current drain with these, what is the amp/hour rating of your bank?

Jim

 

 

(Possum Lodge oath) Quando omni flunkus, moritati.

"I thought growing old would take longer"

 

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There are a number of low drop out regulators of up to 0.2A or so with very low standing currents: the MCP1702 is 2uA.

 

Neil

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How big is this battery?  If you had a 50uA draw, in one month that is only 0.036 Ah total for the month, or 0.43 Wh.  Is that significant for a marine battery?  Doesn't seem likely (even the smallest marine battery seem to be rated for 100Ah).  The self-discharge rate should be looked at too...how much loss do you get with nothing at all connected?  If it self-discharges 5% per month on a 100Ah battery, that would be 5 Ah. 

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

Last Edited: Thu. Oct 24, 2019 - 07:41 AM