Welcome to Laser Pointer Forums - discuss green laser pointers, blue laser pointers, and all types of lasers



5V Super Cap Bank Quesiton

TheDukeAnumber1

Well-known member
Joined
Jun 7, 2012
Messages
2,064
Points
63
I'm at a circuits-I level and am tired of learning non-intuitive lessons the hard way so I figured I'd ask.

If just for funsies I bought a dozen of these - https://www.ebay.com/itm/1PC-Farad-Capacitor-2-7V-500F-35-60MM-Super-Capacitor-NEWCSUS/232574155576?hash=item36267ffb38:g:HXkAAOSwB09YQFTk

And also bought one of these - https://www.adafruit.com/product/2465

Then wired a 5.2V cap bank in place of the Lipo, any way to tell if the chip could handle charging/discharging the caps without issues?

Thanks again...
 
Last edited:

WizardG

Well-known member
LPF Site Supporter
Joined
May 9, 2011
Messages
678
Points
63
I'm thinking that this will kinda work, but not very well. That circuit is made for dealing with a battery that must never go outside of a voltage range of ~3 volts to 4.2 volts. You won't be able to use all the charge in the super cap's as the circuit will shut down below 3 volts and will never charge them up to more than 4.2 volts.
 

paul1598419

Well-known member
Joined
Sep 20, 2013
Messages
14,776
Points
113
With two caps in series you should have a max voltage of 5.4 volts. The boost charger may try to charge these higher than that voltage as they are capacitors, not batteries. If you try to use them in place of batteries, they may work for a short while, but I wouldn't waste my time.
 

Cyparagon

Well-known member
Joined
Sep 12, 2007
Messages
9,607
Points
113
1 won't work, because 2.7V is lower than the cutoff voltage for the IC you bought.

Two in series would work for a few cycles before they became imbalanced and self-destructed from overvoltage.

With a random chinese supercap, I've found their actual capacity is 2/3 the rating. Two in series is half of that, so you get only 160F or so at 5.4V. The energy in a capacitor is given by the equation E=CV²/2. Since the charging circuitry will keep the "battery" voltage between 3.2 and 4.2V, you are only able to use the charge between these two points.

E1 - E2
160 * 4.2²/2 - 160 * 3.2²/2 = 592 joules

If we compare to what a lithium cell would get, 3.6V at 1A for 164 seconds is also 592 joules. Therefore, you have a 164As lithium cell, or in terms more readable, a 45mAh cell. That is pretty terrible considering how large those caps are.

You could add a balancer circuit so they are in the proper voltage range, and you could add a bunch of pairs in parallel, but why would you want to? You'd need about a hundred of them to rival that of your average ultrafire cell.
 
Last edited:

TheDukeAnumber1

Well-known member
Joined
Jun 7, 2012
Messages
2,064
Points
63
@ All
Glad I asked, thanks all for the input.

but why would you want to?
It's as simple as I haven't had time to do any fun electrical projects in a while and I wanted to work with super caps. I realized that the capacity would be small and it would be more of a novelty project, but I didn't know that the IC wouldn't charge from 0V and would probably break the Caps anyways.
 
Last edited:

CynicalBrad

Active member
Joined
Sep 4, 2016
Messages
538
Points
43
Just hook them up to a voltage regulated source at a few amps. I use one of these to drive a PT-54 led but it should work for this. 5A-Lithium-Charger-CV-CC-buck-Step-down-Power-Supply-Module-LED-Driver
You will need a voltage/current meter to set it and there is not much info from the seller. One of the trimpots sets voltage, the other sets current. There is however a resistor on the bottom on the output side that gets quite hot with how hard I am pushing mine.
 

Cyparagon

Well-known member
Joined
Sep 12, 2007
Messages
9,607
Points
113
I haven't had time to do any fun electrical projects in a while and I wanted to work with super caps.
In that case, I'd recommend just switching to a different charge controller. There are several that specialize in supercaps.
 
  • Like
Reactions: GSS




Top