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Topic: How can One Turn 2.5V from Capacitor into 12V @ 1A DC Motor (Read 2 times) previous topic - next topic

fungus



This is all assuming the ESR of the caps is low enough to flow the current required.
...


Well, the engineer who knows theory always wins. This analysis really paints a full picture. When one now calculates a typical super-cap cost and weight, it becomes too uneconomical. Back to batteries.


I didn't bother doing that part because I know the ESR of cheap supercaps isn't low enough.

No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

afremont




This is all assuming the ESR of the caps is low enough to flow the current required.
...


Well, the engineer who knows theory always wins. This analysis really paints a full picture. When one now calculates a typical super-cap cost and weight, it becomes too uneconomical. Back to batteries.


I didn't bother doing that part because I know the ESR of cheap supercaps isn't low enough.




What about those gigantic 1F caps that car stereo freaks use next to their KW amplifiers.  They can surely flow some current or they are worthless; that's the whole point they even exist.  I'm not saying they work, I'm just saying that high ESR surely wouldn't do with those.
Experience, it's what you get when you were expecting something else.

fungus


What about those gigantic 1F caps that car stereo freaks use next to their KW amplifiers.  They can surely flow some current or they are worthless; that's the whole point they even exist.  I'm not saying they work, I'm just saying that high ESR surely wouldn't do with those.


Those people don't mind spending money on low ESR caps.

Not all caps have high ESR, only the ones that are cheap enough to replace batteries. :)

No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

Retroplayer

So what about simply trickle charging a battery with the solar instead? Unless the demand for the motor is very high, that may be an option.

And is a 12V/1A motor really necessary for your application? Is it speed or torque that you need from the motor?

DROBNJAK


So what about simply trickle charging a battery with the solar instead? Unless the demand for the motor is very high, that may be an option.

And is a 12V/1A motor really necessary for your application? Is it speed or torque that you need from the motor?


Oh, most likely I do not need that much. I was asking more for the sake of self education. I watched recently some YouTube videos about energy harvesting, so I though that was an interesting angle for many new projects.

On the end of the day, the old Mars Rover, was using solar panels to store power in a battery, not capacitors.

Retroplayer

Yep, caps in general are designed to store and release a charge quickly. The main difference in a supercap is that it charges quickly but discharges slowly and not capable of high currents due to internal resistance.

Things like motors, relays, solenoids require lots of current at startup, and relatively high currents throughout operation. So, a cap is well suited for help starting it up (hence why they are often used on motors) but not well suited for trying to power them long term.

You could experiment with PWM to prolong the use, but you have to start with a voltage higher than your motor requires. So, say 24V for your 12V motor. Then PWM max of 50% and you theoretically get twice the life out of a battery or whatever. A 12V or 24V solar panel will be fairly large though.

Your original question was how to turn the 2.5v from a supercap into 12V. You would use a voltage booster circuit (a special type of switching power supply) but it isn't that simple as you generally get less current capability out than you put in.

MarkT


Lets say one has this big super capacitor with 2.5V and 200-400F of charge. And you want to run 12V / 1A DC motor off that super cap. How is it done?


Charge is in coulombs, capacitance in farads (F).  2.5V and 400F would mean 1000C.

A boost converter is needed, and one which maintains the output voltage as the input voltage drops.
A capacitor stores energy equal to 0.5 C V^2, so 2.5V and 400F holds 1.25kJ, enough to supply 1A
at 12V for 100s assuming very efficient boost converter

A 400F supercap designed for high loads will probably handle 100A or more.  Indeed a search
locates a WIMA SuperCapR 400F that handles 80A continuous, 600A pulse.  Internal resistance
4 milliohms.
[ I won't respond to messages, use the forum please ]

retrolefty

Quote
The main difference in a supercap is that it charges quickly but discharges slowly and not capable of high currents due to internal resistance.


Funny, I would think that it's internal resistance is reciprocal, in that if it can only discharge slowly then it should only be able to charge slowly as it's internal resistance dictates?

Or do you have other information available?

Lefty

afremont

#23
Mar 08, 2013, 08:38 pm Last Edit: Mar 08, 2013, 08:41 pm by afremont Reason: 1


Lets say one has this big super capacitor with 2.5V and 200-400F of charge. And you want to run 12V / 1A DC motor off that super cap. How is it done?


Charge is in coulombs, capacitance in farads (F).  2.5V and 400F would mean 1000C.

A boost converter is needed, and one which maintains the output voltage as the input voltage drops.
A capacitor stores energy equal to 0.5 C V^2, so 2.5V and 400F holds 1.25kJ, enough to supply 1A
at 12V for 100s assuming very efficient boost converter


As someone once told me right here, "wish I'd thought of that". jk  ;)  Very efficient here meaning 100%.  But I saw a 100% efficient solid state HF linear amplifier.  The designer showed it to a crowd of hams and sure enough when powered by a car battery, it put out 600W @ just under 50A input.  Nobody seemed to think a thing about it.  :/

Quote

A 400F supercap designed for high loads will probably handle 100A or more.  Indeed a search
locates a WIMA SuperCapR 400F that handles 80A continuous, 600A pulse.  Internal resistance
4 milliohms.


Man they go all the way up to 3000F in the line with a 3000A discharge rate.  I'd like to have a few of those.  Wonder if they're regulated by an gov agency like DHS. ;)
Experience, it's what you get when you were expecting something else.

Nick Gammon

According to the video those ultra capacitors had an ESR of 0.7 milli-ohms.

I thought they had been pulled from electric cars, so presumably using them to drive motors isn't that ridiculous.
http://www.gammon.com.au/electronics

Nick Gammon

#25
Mar 08, 2013, 11:40 pm Last Edit: Nov 26, 2013, 02:43 am by Nick Gammon Reason: 1
The ultra capacitor discharges fairly slowly. I have a demo here of running an Arduino from two of them together (giving just under 5V) and it ran for hours, doing a "lots of LEDs" demo which would have consumed a fair amount of current:

http://vimeo.com/80330992

7 hours later it was a bit dodgy, but with a suitable step-up converter you could probably extract those last joules:

http://vimeo.com/80331335
http://www.gammon.com.au/electronics

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