Ultracapacitor Energy Storage used for Off-grid Operation

Thread Starter

EDANN

Joined Oct 24, 2016
25
Hello,
I want to create a circuit that has a motor, and ultracapacitors. The power supply will come from the grid, and be converted to dc from some power adapter. From there the dc power will go to charge my capacitors, and run my small dc motor. When my ultracapacitors are fully charged, i want to unplug the grid power, and run my small dc motor for a little while.
Alight, so i am wondering if this idea is feasible firstly, can i run a motor of charged ultracapacitors? And, want parts i may be missing in my circuit, such as a controller that monitors the ultracapacitor,?
Any feedback or guidance that i can have would be great!
Thank you!
 

Sensacell

Joined Jun 19, 2012
2,720
In theory, yes.

But it all comes down to the numbers, what motor? for how long?

Parameters are necessary.

But be prepared to be terribly disappointed by the results, ultra caps have very low energy density, compared to a battery.
 

wayneh

Joined Sep 9, 2010
16,794
I think you're going to be disappointed. Figure out how much energy your motor needs to run for the time you want. Energy = volts x amps x seconds (or hours). Multiply that by two, to account for inefficiency losses. That's how much energy you need to store in your capacitor bank.

The amount of energy a capacitor can store is 1/2CV^2 where C is in Farads and V is volts across the capacitor. You can use this, combined with the voltage specification of the capacity, to figure out how many Farads you need.

My prediction is it will be more than you want to buy. Then you'll also need a controller to charge the caps and a DC-DC converter to feed the motor consistent voltage as the capacitors discharge. That won't allow going down to zero volts, but the factor of two fudge factor will hopefully include this loss also.

Why not use a battery? Cheaper and easier.
 

Thread Starter

EDANN

Joined Oct 24, 2016
25
Wow, thanks for the quick fast reply fellas!
Alright, lets say i want to run a 12V Gear motor (power rated at 18W) to operate a hoist pulley system. I will use use these 16V rated (leaves safety room), 58F ultracapacitors.
(http://www.digikey.ca/product-detai...es-inc/BMOD0058-E016-B02/1182-1027-ND/3079291)
(Note i have a very large budget, so any idea is noteworthy)

Therefore charging one capacitor to 100% (if possible) would give me E=1/2CV^2 = 4176 J.
Then i run my 18W motor (36W to assume bad efficiency) i could run my motor for 116 seconds (t=E/P).
Does this make sense so far?
I see it looks like i need some kind of controller, could an Arduino do this, what do you recommend?
Also i need a DC/DC converter, any you recommend?

I want to use ultracapacitors to complicate the project and to show a scaled down version of a real system.
Thanks alot so far guys!
 

ErnieM

Joined Apr 24, 2011
8,108
While you are correct in the energy held by the super cap you are ignoring the voltage dropping as you discharge it. So at minimum you need a boost converter to maintain a steady output voltage.

But this converter will have a minimum input voltage requirement, so you can't run the cap down to zero meaning you have stored energy you can't get to.

The next complication is the converter efficiency will drop as its input voltage also drops, so you waste more and more energy until you get to the point you can't take anymore.

Yes your idea is possible, but I might have just doubled your unlimited super capacitor budget.
 

wayneh

Joined Sep 9, 2010
16,794
For more clarification, i must show the usage of ultracapacitors.
It might be better, then, to choose an application where their advantages come into play. Supporting a very brief high current is their main advantage.
 
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Thread Starter

EDANN

Joined Oct 24, 2016
25
For a tradeshow model, the rest NDA.
Thank you ErnieM, now i know!
Ya so wayneh, my application would be to show the ultracaps can support my motor, when my main line fails (shut off in my case) (this would draw brief high current perhaps), and they can support it as long enough to safely shut off operations.
 

Thread Starter

EDANN

Joined Oct 24, 2016
25
Alright, perhaps i use batteries.
What would i need? Still the voltage booster from the battery output to the motor?
 

ErnieM

Joined Apr 24, 2011
8,108
Alright, perhaps i use batteries.
What would i need? Still the voltage booster from the battery output to the motor?
We haven't got a clue since you have not stated a battery voltage nor the motor voltage.

If A = B then you do not need a converter. If A <> B then you do.
 

Thread Starter

EDANN

Joined Oct 24, 2016
25
Yes sorry, i am not fully understanding electrical engineering circuits.
I will try to do some more research before i ask any more unanswerable questions.
I think the voltages will be different just because it might be hard for me to find a battery to fit a specific motor i want, i don't know yet.
Thanks for the response
 
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