Author Topic: supercap discharge demo (Read 7809 times)

willib · « **on:** February 06, 2007, 03:03:00 AM »

i thought of combining a supercap and boost converter , the boost is set low so the discharge lasts a while.

since the cap is 2.5 volts i ended up boosting into a 6 Volt battery

this is more of a supercap discharge demo instead of a boost converter demo.

Initially I charged the cap up to around 2.4V , and the current drain was 310mA

After three minutes the cap voltage was 2.19V the current drain is 110 mA .

After 10 minutes the cap voltage is 1.732 , still boosting , the current is now 70mA

the cap will put out as many amps as you can drain off of it by ohms law V=IR or I=V/R , with a high enough V and a very low R , I can be substantial indeed.

RP · « **Reply #1 on:** February 05, 2007, 08:33:48 PM »

When I saw the title I was expecting to see pictures of bright sparks and maybe a tear in the fabric of space-time. ;-)

Seriously though, was the current draw you mentioned on the output side into the battery? This seems like the makings of a boost convertor for VERY low winds.

TomW · « **Reply #2 on:** February 05, 2007, 08:49:37 PM »

Yeah, I expected possible retinal damage from a spark of Biblical proportions!

Interesting info.

Cheers.

tomw

commanda · « **Reply #3 on:** February 05, 2007, 10:22:10 PM »

You may find the equation

CV = IT

useful.

Amanda

willib · « **Reply #4 on:** February 05, 2007, 11:20:58 PM »

Initially the current into the 6.3 Volt battery was 90mA after three minutes it was 30mA and after 10 minutes it was 20mA

from left to right the meters are voltage , current ,voltage , current

the left two are voltage and current solely from the charged cap , the right two are the boosted voltage and boosted current.

input ::::::::::::: output

2.4V at 310mA and 6.3V at 90mA ; initial

2.19V at 120mA and 6.3V at 30mA ;after three minutes

1.73V at 70 mA and 6.3V at 20mA ; after ten minutes

the caps we are thinking of getting are the same voltage but are 350 Farads this one is just 110 Farads.

but it gives you an idea of what they are capable of, i hope.

capacitance in series add like resistors in parallel

two in series of the 350F variety can handle 5V and the total capacitance will be 175F

7 in series can safely handle 17.5 Volts and the capacitance will be 50 Farads , not too shabby

i know the caps can be damaged by overvoltage , thats what i hear .

on the Maxwell site they have a passive scheme , using resistors to balance the voltage on each cap in the string.

i dont think that i've ever had mine over 2.7 volts and it still seems to work fine,

My cap cost $31.20 less tax and shipping i'm not about to test how much overvoltage it will take before it doesn't work .

just a word of caution , i paid close attention to the cap voltage when charging it up.

i would spin the alt, while watching the voltmeter , stop it , see what it was up to , it would take several minutes and a lot of effort to charge by hand.

i've found that when i get close to 2.5V , i go over to say 2.6V stop and see where it ends at...

unlike a battery when you stop charging it, thats where it is , the voltage doesn't go down , without a load , on it.

tecker · « **Reply #5 on:** February 06, 2007, 06:49:40 AM »

O n page 4 is an equalization circuit for series ultacaps to max usage scale it up or down with matching componants.

http://www.otherpower.com/images/scimages/1431/SCSeminar_JMM_ME_.2.pdf

willib · « **Reply #6 on:** February 06, 2007, 01:54:55 PM »

good stuff

check this out , its their brand new module as of Nov 14 '06

http://www.maxwell.com/ultracapacitors/products/modules/bmod0063-125v.asp

tecker · « **Reply #7 on:** February 06, 2007, 04:41:45 PM »

Here's a 9 volt for your projects . I'm tring to blow it out to 19 for my Drill with a charge time of less than a minute I got to try it. It would make a dandy cell phone recharge with a a couple of solar cells. That's going to be the best use for it.

http://www.otherpower.com/images/scimages/1431/9v_capacitor_battery.pdf

windstuffnow · « **Reply #8 on:** February 06, 2007, 04:57:05 PM »

I drooled on my keyboard reading about that unit a bit ago... Pretty pricey right now though...

.

willib · « **Reply #9 on:** February 06, 2007, 10:02:04 PM »

thats a cool project.

i think i'm going to try something like that , because i'm allways running out of 9V batteries.

i use rechargeable NiMH 1.2V for my walkman , my razor , amd my rat shack vom meter , but the cost of rechargeable 9v batteries has prevented me from using them .

i gotta show yall my razor sometime.. you would get a kick out of it..

anyway i could use a rechargeable 9V battery for my other meters which all use 9V..

and two of the little 5V button caps could be charged to 9V , i wonder how long they would last,in a meter application

it depends on the load of course.

willib · « **Reply #10 on:** February 07, 2007, 12:43:55 AM »

well i've managed to turn a crappy working meter into a crappy non working one.

willib · « **Reply #11 on:** February 07, 2007, 12:58:52 PM »

Son of a B!$%^&*

i should have saved the pix i had stored on the HD BEFORE i wiped it out...

also lost all of my links in my favorites

damnit

sigh !!

jmk · « **Reply #12 on:** February 07, 2007, 03:03:56 PM »

So does this thing replace the battery or something? Looks to me like it stores power and can be discharged to 70%. I'm not to sure what I was looking at.

willib · « **Reply #13 on:** February 07, 2007, 05:28:19 PM »

The super cap doesnt replace the battery, i was showing how it could suppliment a system using one.

Here i demonstrated that the cap could store power after a lul in the wind and keep feeding a boost converter with that power.

the cap can be discharged to zero with no ill effects to it.

jmk · « **Reply #14 on:** February 07, 2007, 05:59:20 PM »

Willib, What about the control you gave a link to?

willib · « **Reply #15 on:** February 07, 2007, 08:31:53 PM »

could you rephrase that? i dont know what you mean?

windstuffnow · « **Reply #16 on:** February 07, 2007, 08:38:43 PM »

I think jmk is referring to the link for the 9v battery replacement link.

What/how are you driving your mosfet on your boost converter? Do you have a little circuit drawing for that? Remember my electronics skills are weak at best so add some explanations please...?

.

jmk · « **Reply #17 on:** February 07, 2007, 08:39:02 PM »

What does the control moduel do in your link that you posted that Ed was drooling over?

willib · « **Reply #18 on:** February 07, 2007, 08:55:31 PM »

oh that was a link to a module that probably cost a fortune , but was really cool , it was a bunch of caps hooked together to supply 125V dc for whatever application one could think of..

it has over one million charge discharge cycles

http://www.maxwell.com/img/content-design/products/bmod0063_125v.jpg

Here are some specs:

Max current [A] 750A (in 5 s discharge to half nominal voltage

Nominal Operating voltage [Vdc] 125V

Maximum Operating Voltage [Vdc] 135V

Surge voltage [Vdc] 142V

Nominal Capacitance [F] 63F

Tolerance Capacitance [%] +20% / -0%

DC Series resistance [mÙ] 17.0 RT

100 Hz Series resistance [mÙ]

willib · « **Reply #19 on:** February 07, 2007, 09:07:45 PM »

it may take a little while to get the whole circuit in one place ,i used the PIC microcontroller to drive the fet directly the fet is a "logic level" , what that means is it will turn on sufficiently with a 5 Volt logic signal (comming from the PIC)

i saw recently a PIC that can drive PWM up to 500kHZ( dont quote me on the frequency , but it was up there) , that is the one i need .

the one i am using can only go up to 19kHZ (PWM), and because of this i cant seem to optimize the inductor needed.

willib · « **Reply #20 on:** February 07, 2007, 09:18:57 PM »

sorry for the confusion the last two should read

dc series resistance 17 milli ohms

100hz series resistance 14 milli ohms

Nando · « **Reply #21 on:** February 07, 2007, 09:43:00 PM »

khz = 52.63 microseconds
4 to 6 volts is 6/2.4 = 2.5 ratio

Let's call it 3 as ratio

So the charging is set to 2/3 of 52.63 microseconds = 35 microseconds for ON time.

Choke value:

V=L di/ dt ; V= 2.4 volts ; dt = 35* e^-6 ; dI = ? let's make it 300 ma as per your info

L = V*dT/ dI = 2.4 * 35*e^-6/ 0.3 = 280 microhenries is what you need to make the unit to work .

use 270 or even 240 microhenries and everything will be ok, presuming that your PIC has the capability of doing PWM.

Nando

willib · « **Reply #22 on:** February 07, 2007, 10:50:12 PM »

that some nice figuring there nando

any idea of number of turns of # 17 wire and the resistance of the inductor to get me over 100Watts output?

elvin1949 · « **Reply #23 on:** February 08, 2007, 03:36:49 AM »

hahahahaha

willib

I thought i was the only one around here that did that.

later

elvin

Nando · « **Reply #24 on:** February 08, 2007, 08:34:10 AM »

100 watts under what conditions?.

Vin, Vout ?.

PWM frequency ?

Nando

willib · « **Reply #25 on:** February 08, 2007, 10:44:54 AM »

well output power would be nice

glad you asked about the pwm frequency

i just realized tht i can go up to 208kHZ PWM , the only drawback is the decreased resolution.

what that means is i would only have 97 different steps from full off ,to full on.

i can live with that.

The max available is 1024 steps at 19kHZ

this chart is from the 16F88 data sheet

Dont worry about the (timer prescaler & PR2 value) that has to do with programming the chip.

2 to the 10th power is 1024

2 to the 8th is 256

2^7 is 128 steps

and 2 to the 6.6 is about 97

heck even 156khz is a LOT better than 19khz..

i dont know why i never noticed this before

Nando · « **Reply #26 on:** February 08, 2007, 01:18:19 PM »

1024 steps @ 19 KHZ is OK.

That is less than 0.1 %/ step, which for your case the error sampling may represent a low error enough not to consider it.

So make your mind.

Nando

willib · « **Reply #27 on:** February 14, 2007, 07:42:20 AM »

i got the two new 1Farad caps yesterday, they are pretty massive, lots more testing to do..they are 8.75" tall by 3" dia..

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Author Topic: supercap discharge demo (Read 7809 times)