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Old 12th Jun 2016, 6:18 pm   #1
ekcopyephilips
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Default Capacitor to replace battery?

Hi All

Hope i have this in the correct section. Is it possible to replace a 1.2v 6600mAh AAA battery with a capacitor of some value? If so what calculations do i need to use.
Its just for some outdoor solar powered LED string lights, the batteries were never any good and water has got in and rotted the terminals, it was just something i wanted to play with and see if i could get going again with what i had laying around.

Any ideas?

Cheers

Mike
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Old 12th Jun 2016, 7:19 pm   #2
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Default Re: Capacitor to replace battery?

A big cap would cost a lot more than a brand new set of garden lights. I like fixing things but if it costs a lot more than a new one pragmatism has to reign.
 
Old 12th Jun 2016, 7:19 pm   #3
paulsherwin
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Default Re: Capacitor to replace battery?

What is the current drawn by the lights? What you suggest is possible, but would require some pretty man sized capacitors and would cost a lot more than rechargeables for the same performance.

I would wire up an AA holder and use an off the shelf NiMH.

Are you sure the power rating is correct? That's an awful lot of capacity for a single AAA cell.
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Old 12th Jun 2016, 7:31 pm   #4
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Default Re: Capacitor to replace battery?

One problem is the discharge characteristic of a capacitor, the voltage would gradually fall as the charge decreases. With a NiCad the voltage remains fairly constant as the battery is discharged.

Dave
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Old 12th Jun 2016, 9:32 pm   #5
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Default Re: Capacitor to replace battery?

Is there also any other issue that should be considered like internal resistance?
Thinking that a battery if accidentally shorted wouldn't deliver sufficient current to do any substantial damage, but a capacitor would try and discharge fully as quickly as possible? Or have I got my theory all mixed up?
Places like maplins sell "Supercapacitors" in farad values, I think they are often used in certain automotive backup duties? But I agree with Paul S etc, why not just get a battery holder and wire it up to the existing supply?

A.
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Old 12th Jun 2016, 10:19 pm   #6
ekcopyephilips
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Default Re: Capacitor to replace battery?

Hi all

Thanks for the replys. I'll get a couple of rechargeable batts with tags from maplin. I was just thinking aloud about the capacitor.

Cheers

Mike
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Old 20th Jun 2016, 4:06 pm   #7
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Default Re: Capacitor to replace battery?

Is it about 10KF ?
(assuming 1.2V initial, 1.0V final - after delivering 600mAH)

Or, a fair bit less if you don't mind sucking all the charge out down to 0V !

dc
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Old 20th Jun 2016, 6:17 pm   #8
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Default Re: Capacitor to replace battery?

An array of ultracaps to supply that ma/hr would be big and expensive!
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Old 20th Jun 2016, 7:48 pm   #9
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Default Re: Capacitor to replace battery?



mAH. Not mA/H or ma/hr.
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Old 20th Jun 2016, 9:43 pm   #10
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Default Re: Capacitor to replace battery?

Quote:
Originally Posted by ekcopyephilips View Post
Thanks for the replys. I'll get a couple of rechargeable batts with tags from maplin. I was just thinking aloud about the capacitor.
I don't know how naming other places stands, but hopefully it's allowed. If so, then it might be worth looking at the £ shops-Pound land/world or Pound stretcher. I've resorted to using AAA & AA rechargeables from this sort of place in our TV /Other remotes and even in one Digital camera that eats even Alkaline cells.
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