Introduction: Replacing a UPS Battery With Super-Capacitors

Picture of Replacing a UPS Battery With Super-Capacitors

Got tired of replacing the lead-acid battery in a UPS (Uninterruptible Power Supply), so put together a super-capacitor array to go in its place.

Such units are now commercially available

Step 1: Super-Capacitor Array

Picture of Super-Capacitor Array

Started with six used 2600F 2.5V Maxwell super-capacitors that I found for $70 with postage and cross-bars included (from, but they no longer stock them). The six are wired in series to allow for the voltages seen by a 12V battery; fortunately the array was found to be so well balanced by itself, that no extra circuitry was needed to ensure that no capacitor experienced an over-voltage. A UPS that trickle charges its battery will overcharge such an array, so a protective Zener diode would need to be added; the UPS I used it with did not have this problem, so there was no need for any extra components.

Step 2: Carrier Design

Picture of Carrier Design

Designed a wood carrier that would take the place of the lead-acid battery. Tried to keep the design simple, and got it down to two dowels and two end-plates that needed holes drilled. The carrier is glued together permanently for strength, but still allows the capacitors to be removed and replaced. The two central dowels hold things together and stop the capacitors moving around; added a final cross-bar of wood across the output for physical strength.

Step 3: Possible Alternative Configuration

Picture of Possible Alternative Configuration

Considered the possibility of reconfiguring the array if the space available was narrower but higher; in my case the original design fitted well and was preferred for the support the inner dowels gave. In both designs the bolt heads reside part way into the end-plates, ensuring that the array cannot unfold.

Step 4: Final Product

Picture of Final Product

Made the carrier of oak; a tough wood to work with, and not cheap (the ends were made from a plank sold for stair steps). The array is equivalent to a 1Ah 12V battery, and can hold up an average computer for a couple of minutes, more than enough to carry it through short glitches, and should endure a lot longer than the lead-acid battery it replaced. One can see here how the capacitor bolts are accessed through holes in the carrier end-plates (for assembly and dis-assembly). The rear plate is taller than the front to match the original battery mounts.

Super-capacitors can hold a lot of charge, so a disclaimer is necessary, and one must proceed at ones own risk.

Step 5: In Situ

Picture of In Situ

Fortunately there was enough room inside my UPS to house the capacitor array.


cesarm001 (author)2017-01-03

Just a note here ..... Cars use the batteries to start the car that's it then the battery gets recharge by the alternator.

If you turn the radio on while the car is not running a discharce will occur at your batteries and if use capacitors will discharge quicly so a combination of Capacitors and small Lithium battery (Hibrid) will be great and very powerful

wiggyss (author)cesarm0012017-02-14

I just finished a project like that. I ended up with a small lead acid battery though.

cesarm001 (author)cesarm0012017-01-03

Adding to my comment ..... have a look this video ...

ashiekh (author)cesarm0012017-01-03

"An error occurred."

cesarm001 (author)ashiekh2017-01-03

Sorry the only way will work is in a picture you may have to type this sites into your browsers I am sure you will like this ones

ashiekh (author)cesarm0012017-01-03

Yes, but the lithium battery might not like charge scheme for lead acid batteries.

ashiekh (author)cesarm0012017-01-03

The UPS is designed to charge a lead acid battery, so will not be suited to charging a lithium battery; and the capacitors will no longer serve a purpose (just use the lithium battery). The other problem is the lithium battery may not be happy being discharged so quickly.

cesarm001 (author)ashiekh2017-01-03

Yes UR correct but the lithium battery and the capacitors could replace the car battery complete there are a few videos on this subject.

Anyway the Caps are great to support batteries cranking power and will help the battery life on the long run.

I have a solar design using 10 x 2.5 volts connected in series giving me a total of 24 Volts and 35 Farads they are connected to my battery pack of 4 x 12 Volts batteries and 100 Watts each (2 x 2 in Series then in parallel) to obtain a total of 24 volts and 400 watts more than sufficient for my home run at the moment but I am ready to increase the power this year.

I only use the Caps to assist in the initial crank of my Fridge and some power tools that I use from time to time.

All this is connected with a 2 x 200 watts panels 12 each in series = 24 Volts and 400 Watts then to a MPPT 30 amp Power controller also use a Pure sine 3000 watts inverted and a few breakers along the way

All this works very well ... I check the Caps and Batteries when I crank my grinder and other power tools and the Caps discharged and charge in seconds ..... so my batteries are relax he he he

I am preparing a 18650 power wall as backup support for my solar installation as back up and have a petrol generator for emergencies (I have average 5 to 6 Hr sunshine every day all year) - similar as telsa wall pack ..... will see how I go

Thanks for your input

ashiekh (author)2017-01-03

Yes, for a car application the hybrid makes sense; but not for the UPS application being discussed here.

How does your fridge run at night?

cesarm001 (author)ashiekh2017-01-03

No problems I have a reserve of 3 days on Battery power so is ok I check every morning to be sure the batteries are fully charge and the Caps as well.

All running Ok I have the new Samsung fridge that takes low power so is Ok

Keep in touch

ashiekh (author)cesarm0012017-01-03

3 days is most impressive; I just hate how lead acid batteries don't last long.

cesarm001 (author)ashiekh2017-01-03

Yes 3 days because in this type of emergencies I have another set as backup and the fridge is the new technology inverter technology so is no much compsuption also at nights is all off Only fridge no freezer needed.
We use gas for cooking no need heaters and I do not like or need aircon ... so is perfect for low comsuption solar energy also use small petrol generator and a battery alarm if the power is offo so I can fixed on the spot.
Almost all angles are cover I hope .... in the near fufure I will also install a small wind generator so I may get extra power at night ...they are very cheap to buy and install

FreddieN3 (author)2017-01-03

hi ashiekh, could you please update this excellent instructable? thks

Wonder if this capacitors can do the job..

ashiekh (author)FreddieN32017-01-03

No, these are only 10 Farad, despite the picture showing 3000 F

ashiekh (author)2015-09-16

Much appreciated, but they don't hold much energy, so chemical batteries might suit your application better.

ddavis662 (author)2015-09-16

I added a link to your Instructable in my comment section about this same idea that was told to me..

ddavis662 (author)2015-09-16

Intersting information!

I'm giving the super capacitors some serious thought for my solar and wind generators!

Anwar_Shiekh (author)2015-01-09

The energy in a capacitor is 0.5 C V^2, but I use half this as the UPS turns off before reaching zero volts; from this the Ah can be calculated. I picked capacitors that would physical fit. 30-60 amps should be easy for the units I used.

krafty.rhino (author)2015-01-09

How did you figure the Ah equivalent and choose the CAPS? could something like this in a smaller package push 30-60 amps for a few seconds B4 having to be topped off?

dbonggon (author)2014-09-16

sir i have a question where can i find that kind of capacitor i am here in philippines

ashiekh (author)dbonggon2014-09-16

ebay; search for boostcap

sam522 (author)2014-03-18

hello guys;

i have sun tracker
project, i wanted anyone can help me to know the specifications of my
supercapacitors ( my dc source voltage is 20 volt ) i need to have 12 volt and 1.2 amp from my supercapacitor


ashiekh (author)2013-08-26

Easily many KW if one wants; each capacitor is 2600F so the bank of 6 in series is 433 F

ndege (author)ashiekh2013-11-29

if they are hooked in series, you still get 2600F.

gene99 (author)ndege2014-01-13

No, you don't get 2600F. Check your physics textbook, or just listen to ashiekh, he really does know what he is talking about.

bigjeff5 (author)gene992014-01-18

Give him a break, it's really counter intuitive.

The capacitance for series-connected capacitors is 1/Ctotal = 1/C1 + 1/C2 + 1/C3..., while the voltage goes Vtotal = V1 + V2 + V3...

The confusing part is that 1/C, to get the final capacitance you still have to invert it, so the final capacitance of the array is 2600 divided by 6.

Capacitance is not a direct measure of energy storage, it's a measure of the ability to store a charge. To get the total energy stored, you need to do a bit more math. C = joules / voltage squared, so a 2v capacitor at 2600 farads holds 5200 joules of energy, while a 12v capacitor at 433.3~ farads holds 31200 joules of energy, or 6 times the amount.

ashiekh (author)bigjeff52014-01-18

It gets even tougher when one connects a source of voltage V to a discharged capacitor and only half the energy gets to the capacitor no matter how low is the resistance connecting the two.

bigjeff5 (author)bigjeff52014-01-18

Er, C = 2 * joules / voltage squared

I got the calculation right though! :P

ashiekh (author)ndege2013-11-29

Actually not so; but they do carry 6 time the energy

One way to see this is the energy is 0.5 C V^2, and 6 in series carry 6 time the voltage, that is one way to see that the overall capacitance is now 1/6 th

wbond1 (author)2012-06-20

Please forgive my stupid comment, but when you say UPS, I am thinking United Postal Service. What does UPS mean hear?

wbond1 (author)wbond12012-06-20

I figured it out, Uninterupted Power supply, my bad.

ashiekh (author)wbond12013-12-01

I have modified the document to clarify this; I hate acronyms.

apirzada1 (author)2013-08-26

how much power do they provide? and capacitance?.:D

ashiekh (author)apirzada12013-12-01

In principle many kW is possible, but the UPS I use is only 500W; each capacitor is 2600F, so the series array is 433F

mashayekhi (author)2012-04-24

This is very nice idea. I am interest to negotiate with you about this idea, if it is possible please send me an email (

ashiekh (author)mashayekhi2012-11-11

Such UPS units are now commercially available

carlos66ba (author)2012-01-25

This is a wonderful idea, but have you tested how long it lasts in operation (how many minutes)? The reason is that the discharge curve of a battery and a capacitor are very different, so the UPS may shut down the discharge assuming that the "battery" is nearly dead when in fact the capacitors still hold plenty of juice. (Batteries have a long "flat" region in the voltage vs. discharge charge, whereas capacitors V declines linearly with the discharge Q.)

ashiekh (author)carlos66ba2012-01-25

About 2 mins (as mentioned at the end); strictly the capacitor bank has 2Ah, but because the UPS shuts off early, it is only equivalent to 1Ah. I only intended it to carry across glitches, so 2 mins is more than I need; it would actually be closer to 3 mins but the UPS itself consumes about 75W

The real issue is when the UPS tests the 'battery' and in my case the capacitor array is seen to test as good, unless the UPS tests when I have a high load connected and then the UPS feels the voltage is falling faster than expected.

sunwukong1947 (author)ashiekh2012-11-10

Can you elaborate how you charge this device? What kind of circuit you use? Im interested in something like this for home use.

ashiekh (author)sunwukong19472012-11-11

The super capacitor array goes inside a UPS, so the UPS itself does the charging; I was fortunate enough to have a UPS with a lot of space inside.

ashiekh (author)2012-08-27

It has been in service for over a year now holding up one computer and all the networking gear; as a result I have been able to retire all the other UPS units and don't so purchase anymore batteries.
Still, there are now lead acid batteries of claimed 12 year life but hopefully the capacitors will live even longer than this.
Then again, one anticipates a new generation of UPSs based on lithium technology.

rcisneros (author)2012-08-27

great idea. Most power outages I've had last just a few seconds or cycle 2 or 3 times in just a few seconds. This would be perfect.

ooda55 (author)2012-06-22

Nice concept :)

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More by ashiekh:Desulfation in Lead-acid Batteries; a Novel (resistive) ApproachReplacing a UPS battery with Super-Capacitors
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