Do Joule Thief's Work With Supercapacitors

[Puglife]

I have a supercapcitor to power some of my small projects. The only problem is that the voltage drops gradually, unlike a lithium ion battery, in which the voltage is mostly stable throughout. My boost converter that I am using to boost the voltage up to 5 volts, stops working with an input voltage below 1 volt, and it is a 2.5 volt super capacitor, so the power source dies almost twice as fast, because i can only use a little more than half the power in the cap.

My question was, How would I boost the voltage of my super capacitor up to the usable 1 volt, if it is lower than that? Can I use some sort of Joule Thief with my Super Capacitor? Is their some sort of other method I have not considered?

 

[mfb]

At 1 V, your supercap has only 1/6.25=16% of its original energy left. Do you need those 16% that urgently, or could a larger capacitor or something else be easier?

 

[Puglife]

At 1 V, your supercap has only 1/6.25=16% of its original energy left. Do you need those 16% that urgently, or could a larger capacitor or something else be easier?

My Apologize, I meant to say 2 volts not 1, I miss read the specs.

 

[mfb]

Okay, 25% then. Same question. It is certainly possible to get a bit more out of it, but not much (and certainly not the full 25%). I don't know your other constraints (space, money, weight, ...), but making something bigger is often easier than adding complexity.

 

[Puglife]

Okay, 25% then. Same question. It is certainly possible to get a bit more out of it, but not much (and certainly not the full 25%). I don't know your other constraints (space, money, weight, ...), but making something bigger is often easier than adding complexity.

so how would i go about getting more out of it, could i use a joule thief to boost the voltage to a constant 2.5 volts? or is their some other way, because i need as much capacity as possible, and for a small size

 

[mfb]

You can certainly do that, but the setup will need some space as well, especially for the coil. The transistor needs some minimal operating voltage, and will draw significant power. The resistor will also need some power.
This is very vague, but "a small size" is not very precise.

 

[Puglife]

You can certainly do that, but the setup will need some space as well, especially for the coil. The transistor needs some minimal operating voltage, and will draw significant power.
This is very vague, but "a small size" is not very precise.

so what kind of decrease in efficiency would i be seeing like 10% ?

 

[Puglife]

so what kind of decrease in efficiency would i be seeing like 10% ?

like overall capacity and storage

 

[mfb]

Depends on details of your setup.
If you have the Joule thief as intermediate step all the time, you have its efficiency loss for the whole discharge - you could even end up with less energy than before. If you want to use it only once the capacitor is below 1 V, you need additional logic for that. I would be surprised if it helps.

 

[Puglife]

Depends on details of your setup.
If you have the Joule thief as intermediate step all the time, you have its efficiency loss for the whole discharge - you could even end up with less energy than before. If you want to use it only once the capacitor is below 1 V, you need additional logic for that. I would be surprised if it helps.

so is their no other way to step up the voltage then, maybe using some other form of boost converter?

 

[meBigGuy]

There are low input boost converters. Google "low input boost converter" and other similar searches

http://www.ti.com/lit/ds/slvs776b/slvs776b.pdf
http://www.ti.com/lit/ds/symlink/tps61200.pdf

 

[Puglife]

There are low input boost converters. Google "low input boost converter" and other similar searches

http://www.ti.com/lit/ds/slvs776b/slvs776b.pdf
http://www.ti.com/lit/ds/symlink/tps61200.pdf

I have found none that are that good, the ones you sent were pretty good, but is the the max amount I can get out is having it cut off around .7 volts?

 

[meBigGuy]

There are a bunch of interesting parts at the bottom of this page
http://www.linear.com/product/LTC3108 This part won't switch 2.5V though.

http://www.linear.com/product/LTC3105 starts up at 250mV

 

[Puglife]

thanks for the help guys, it is much appreciated