SuperCapacitor Backup supply

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Steve001
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SuperCapacitor Backup supply

Post by Steve001 »

Evening all

i have been experimenting with the attached circuit for a data logging project

The circuit is based around the following ic's from Linear Technology

http://www.linear.com/product/LTC3225

The LTC3225 is a programmable supercapacitor charger designed to charge two supercapacitors in series to a selectable fixed output voltage

NEVER SHORT THE TERMINALS OF A CAPACITOR TO DISCHARGE THEM - USE A BLEAD RESISTOR


http://www.linear.com/product/LTC4413

The LTC4413 contains two internal ideal diodes, each capable of supplying up to 2.5 Amps from an input voltage between 2.5V and 5.5V. Each ideal diode uses a low resistance MOSFET that independently connects INA to OUTA and INB to OUTB with a status output pin

The circuit is going to be subject to supply failures, because i am using a vdrive 2 i didn't want corrupt data so a method of nicely closing everything down was required.

the circuit consists of a super capacitor charger this charges and balances 2 x 2.7V super capacitors and has a charge done flag at 94% charge
this is fed into input A of the "ideal diode" so that the status pin is high when running on the capacitor supply

test circuit

1 x ECIO 40P
1 x vdrive 2 (just powered up not reading / writing)
1 x 4 x 20 EVERBOUQUET-MC1604B-SBLW-LCDMODULE

initial tests using 2 x 1F super capacitors

http://uk.farnell.com/bussmann-by-eaton ... dp/2148482

after failing the supply the output only held up the test circuit for approximately 2 seconds
a test was done without the display and the circuit held up for longer, i know 2 seconds is probably ok and a eternity in computing terms but will feel better with a longer time.

I will order some larger capacitors and have another play

http://uk.farnell.com/bussmann-by-eaton ... dp/2148486

Please note these ic's are tiny

Hope this is of some use to someone

Steve
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Re: SuperCapacitor Backup supply

Post by Benj »

Thanks Steve,

Been meaning to play with super caps for a while, looks like a good opportunity. Many thanks for sharing.

Could you run the display off the power supply and then only run the micro off the super cap backup, this should give you more runtime when the supply fails?

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Re: SuperCapacitor Backup supply

Post by Steve001 »

Hi Ben,

I have played with that idea in a pervious project a while ago .I turned of the lcd back lighting after a few mins if no key was pressed with martins help :D

just a quick photo to show how small these ic's are

the device in comparison is a TL431 voltage reference in a TO92 package

Steve
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Re: SuperCapacitor Backup supply

Post by Steve001 »

Hi benj
Benj wrote: Been meaning to play with super caps for a while, looks like a good opportunity

Eaton do some very large super capacitors up to 3000 Farads and made up modules also


http://www.cooperindustries.com/content ... itors.html

Cooper Bussmann
Cooper (UK) Limited
Burton-on-the-Wolds
Leicestershire • LE12 5TH UK
Tel: +44 (0) 1509 882 737
Fax: +44 (0) 1509 882 786

Linear Tech do some good super cap chargers

http://www.linear.com/parametric/superc ... r_chargers

Steve
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Re: SuperCapacitor Backup supply

Post by Steve001 »

decided to dig out this little project again after martin jogged my memory :D

done some tests on autonomy with the capacitors

measured the current of a test pic form a unit a PIC16C710 this is monitoring a DC voltage and every 20 minutes turns on or off some transistors nothing too spectacular.this current was measured at 3.9mA with a fluke meter.

After some tests with a constant current generator it was found that 2 x 1F capacitors held the supply from 5.2 to 4 V DC for approx 18 - 20 seconds at this current level.

think i need to do some more tests with some other capacitors

steve
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Re: SuperCapacitor Backup supply

Post by Steve001 »

Afternoon All,

Dug this out again, and done some more tests with a Ecio and a 4x20 Backlit display 80mA all together

so using the following

1 x 20 farad capacitor - 2 mins 30 seconds
2 x 20 farad capacitor (40 farads total) - 4 mins 45 seconds

https://uk.farnell.com/vishay/mal223091 ... p/2930854?

this is only from 5.1 volts to 4.5 a further time extension could be gained by using a 3.3 - 5 volt dc-dc convertor to step the voltage back up to 5 volts

Steve
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Re: SuperCapacitor Backup supply

Post by Benj »

Hi Steve,

Wow that's a decent amount of time to keep the MCU running for. How long does it take the cap to charge back up when powered on again?

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Re: SuperCapacitor Backup supply

Post by Steve001 »

Hi Ben,

I didn't measure that to be honest, just switched the supply back on and went for some dinner :lol:

I will measure it and let you know

Steve
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Re: SuperCapacitor Backup supply

Post by medelec35 »

I think its a great idea!
Gives the hardware time to complete all routines to go into shutdown mode.
This could include displaying a message on an LCD stating: power failure,
Going to shout down in 10, 9 , 8 etc/

Thanks Steve
Martin

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Re: SuperCapacitor Backup supply

Post by Steve001 »

Hi Martin,

I am using it with the Vdrive you sorted out for me,
i use it because i am plotting voltage every 10 seconds of some batteries until the deep discharge protection operates then micro can shut down and close the txt file and not corrupt anything when the power goes.

The IC's are Tiny did struggle soldering them

Steve
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Re: SuperCapacitor Backup supply

Post by medelec35 »

Steve001 wrote:
Mon Jun 22, 2020 6:07 pm
I am using it with the Vdrive you sorted out for me
Great idea!
How is the Vdrive performing?
Wondering if worth having a Vdrive component?
Alternatively there is the FAT SD component.
The only difference for people that don't know about Vdrive.
It reads and writes to USB flash drive, instead of SD card.
Martin

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Re: SuperCapacitor Backup supply

Post by Steve001 »

Hi Martin

Vdrive working well - I did find they are a bit finakey with usb sticks though.
i didn't manage to get a .csv working with it though but works well sending to .txt I then copy and paste to excel so i can do my graphs.

do worry about long discharge times, and the amount of data going on the usb stick but not had an issue as yet .

V Drive Component - mm thats an idea :mrgreen:

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Re: SuperCapacitor Backup supply

Post by medelec35 »

When multiple files with different file numbers saved on the vdrive,
I used Auto hotkey to automatically merge all the files into one CSV file. at the click of a button.
Worked well for me as kept the files small so there was a fair few after 6 months, when I revisited the site Vdrive was installed on.
Martin

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Re: SuperCapacitor Backup supply

Post by Steve001 »

I used Auto hotkey to automatically merge all the files into one CSV file. at the click of a button.
Not heard of that will look into it sound a lot easier, than copy and paste each file ..... :oops: :lol:
Ben:

How long does it take the cap to charge back up when powered on again?
I did a quick test last night, current limit set at 150mA. I was only timing with the stopwatch on my phone and watching the current drawn on a meter the 20 Farad one, from completely discharged 40 seconds @ 150mA , then approx. 3 mins to reduce to 10mA.
Suppose this part of the charge curve to reduce to its minimum value will take a long time.

Steve
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