Joule Thief

[DreamThinkBuild]

Hi Freepow, All

A cap will only charge to the level of voltage supplied. Think of a 10v cap and you have 5v it will only charge to 5v.

Another analogy is like having a 10 gallon bucket and you fill it with a 5 gallon bucket it will still be 5 gallons of water. Current filling a 5 gallon bucket to the 10gallon bucket would be considered a hose, have a small hose it will take longer(low current). A large pipe will fill it quicker(high current). Just don't get too caught up in using the water analogy as it's pretty frowned at by electronic engineers.

I recently built a solar cap charger. There are 6 panels at .5v wired in series 3volts out and the open current is 1.60 amps so around 4.8watts. There is a blocking diode which drops around .35 volts so the output average is around 2.65v +/- .5 if in direct sun or cloudy. In maximum sun it will go over the 2.7 limit but since I don't use any kind of sun tracking it does this for only about 1/2 hour. The reverse diode keeps it from going down when clouds go over. There is no regulator since it will charge to that maximum supplied. It usually takes a full day to charge a 1500F cap to around 2.56v-2.69v with the current setup depends on cloudiness. If I increase the amps with another row of six I could get it charging faster.

[Pirate88179]

DTB:

Nice solar panel there.  Wow, you have a 1500 F boost cap?  Mine is only 650.  Can I ask where you bought it from and how much?  One of those is on my wish list.

Thanks,

Bil

[freepow]

  Thanks everyone for your answers.

  @ BILL...  How long does it take to fill your 650 Farad 2.7v CAP to full capacity with your EB ?
     How many available mA's do you have in your fully charged CAP to use for projects ?

     Also if you had a solar panel with diode with output of 2.7v at 10 Amps, would that fill your Cap
     to full capacity in say 1/2 hour or so ??

     Or would a EB  fill it quicker ?
     Thanks.

[Pirate88179]

Good questions all.  I can only answer some of them.

The last time I filled my big cap it took about 4 hours, give or take.

The mA's available in a cap like that depends.  The 650 F cap has, according to the literature, available 3,000 amps.  Now, it can only do that for a very short time but, it will melt large wires if shorted and it can hurt or kill you.  The thing I like about these and other supercaps is that they only deliver the mA's needed and do not dump everything they have all at once.  So, you can use it like a battery which is what I have been doing with all of my supercaps.

As far as the solar with a diode, I have no idea but, with that much power I would guess it would not take that long.  My EB puts out about 19 mA's give or take generally speaking so, your solar panels have much more power.

Funny thing is, I have never used a diode in my EB charging system.  To be honest,  I didn't know I needed one.  The thing that saves me is that my EB, with the large spikes, must have more input flowing to the cap than the other way around.  The DMM shows my EB as putting out about 1.9-2.0 volts but the spikes will charge it up to the full 2.7.  It must be higher than the 2.7 volts or I would need the diode to keep it from reversing.

I hope this helps.

Bill       PS  I just got a line on a boost cap of 1,600 F for like $50 US.  If I can find the money, I want one.

Bill

[DreamThinkBuild]

Hi Freepow, All

In order to calculate the charging time you would need to figure out the RC time constant.

T=R*C

Using my solar charger as an example I would need to calculate the resistance from the maximum amps which is 1.6a.
2.65v is from solar panel at ideal conditions after diode.

R = V/I = (2.65v/1.6a) = 1.6ohms

Now we can calculate the time constant.

T = (1.6*1500F) = 2400 seconds

Charging to full power will take 5 time constants:

(5T*2400)=12000 seconds= 200 minutes = 3.33 hours in a ideal world with constant sun and optimum angle. More like 4+ in the real world with clouds.

@10 amps it would be:
R= (2.65v/10amps) = 0.265ohms
T= (0.265*1500F) = 397.5 seconds
Charge time = (5T*397.5)=1987.5 seconds = 33.12 minutes

I just got a line on a boost cap of 1,600 F for like $50 US.  If I can find the money, I want one.