How to boost voltages below 0.6V ?

Other Hardware General Electronics
1

I have very strange custom made 1V capacitors that have very large capacities - 800-2500F
However they hold 1V very short and basically go down and are super stable at 0.6-07V.
My friend asked me if there is a way to boost such small voltage and how.
They don't want to connect them in series because of large shape so they want to use one.
Output would be 9-12V

What would be the best way?

2

At first blush a boost converter would seem to be the answer but I don't know of any that will work at such a low voltage. The normal use is to series wire them to add their voltages to a useable level but you say they are too large. Sounds like a real conumdrum.

3

There are IC boost converters, that support input voltage below 0.6V.

Try "energy harvesting" as google search pattern, there could be some modules on chine i-net market.

4

Those are "supercapacitors". A quick ebay search turned up a 500F 2.7v supercap for $8 shipped. These might be better, since they give you a more reasonable voltage to work with.

There's another problem with putting them in series - the self-discharge rate is not identical between individual caps, so the voltage would not end up being split equally, leading to one of them getting an excessive voltage applied while charging.

5

In general you shouldn't put capacitors in series, and if you do the total applied (DC) voltage shouldn't exceed to voltage rating of any one capacitor (because you cannot guarantee that the voltage will distribute equally).

There may be some AC applications (including RF applications) where capacitors are wired in series, and the AC will distribute according to the capacitive reactance, but I'd still say "be careful" and use capacitors that can handle the full voltage in case something goes wrong..

If you are trying to use them as "batteries" it would be OK to charge them individually (or in parallel) and discharge them in series. But, that's not very practical.

And in case you don't know this (and in case you care) capacitance in series combines like resistors in parallel. For example, two 10uF capacitors in series is 5uF. (Of course you can look-up the formula if you wish.) Two 10uF caps in parallel makes 20uF.

6

I suspect boost convertors aren't very efficient at those low input voltages - that's a 15:1 stepup required.

And why would they have a stable plateau at about 0.7V ? - surely a capacitors storage is governed by

J = 1/2 C x V^2....

I'd find another way.

Allan

7

Thanks. Like I mentioned - I know wiring in series is not great solution.
They are trying to make commercial prototypes but going above 1V brings significant extra costs.
Seems like popular silicon ICs cannot handle well lower voltages....
Harvesting circuits make sense here. I will look into it however I am looking for really low cost solution

8

I am looking for really low cost solution

Your approach is wrong, then. You are NOT going to get 9-12V out of a <1 V supercap with a decent amount of current.