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supercapacitors

Former Member

Hi guys

 

I am looking at alternative/additional electrical storage for when I go bush and the only other devices currently available are the super capacitors. 
Unfortunately my knowledge of such devices is very limited.  Are you able to assist in providing technical support regarding the number, size, connection,
and buffering/distribution circuits that might be required to maintain 12 volt devices (mainly an Engel and Primus fridge)?  The system I have at the moment
incorporates a 120W solar panel, charger, and lead acid battery that is fine during the day, but I am finding the size of the fridge drains the battery
overnight so was looking at incorporating a capacitor storage system that will compliment the battery by providing additional charge overnight.

 

From what I understand of the supercapacitors they can be set up in either parallel or series but there are issue with current leakage that can cause
issues for individual capacitors.  I would imagine that if the configuration is similar to a battery, then setting up several 12 v capacitors in parallel would
provide the current reserve needed to maintain a steady discharge overnight (current consumption is 4-6 amps depending on settings), but have no idea on
what additional circuitry or chargers etc are required, if any, to maintain the system.  At this stage I have two separate systems, one on my vehicle and one on
the trailer so need to fit additional support circuits etc for both.

 

I am looking at latent or ambient energy too and have looked into some of the tesla circuits and collectors but have only managed the breadboard stage yet.

 

Any advice you can offer would be most welcome.

 

Regards

Phil

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  • 0

    Hi Philip, Your solar panel, at 120 watts may not have enough capacity to provide energy for a refrigerator even if you had the additional storage capacity. I am not an expert on solar energy but I would be surprised if you can get more than 10 hours a day of good sunlight. Ten hours times 120 watts, assuming 100% storage efficiency leaves 1.2 kilowatt hours of power. This means that you have to average less than 0.05 kwh per hour throughout the day. This is equivalent to a 50 watt bulb on all the time or about 4 amps at 12 volts. To answer you question about the super capacitors they are unlikely to be an economical  alternative to just getting an additional lead acid battery. A one Farad capacitor can theoretically supply one Amp for one second at one volt. If we extend this process (12) 1 F caps can provide one amp for one second at 12 volts. If we need 4 amps for the refrigerator we will need 4 times as many or 48 super 1 F capacitors. Finally we need to multiply the 48 by how many seconds there are in the day or 4,147,200 1 Farad capacitors to give youthe capacity to provide 12 volts at 4 amps for 24 hours. The other downside to super capacitors when considering their use for high current applications is that they has a high efective series resistance. This means that a lot of your stored energy is lost to heat. The only place where the super capacitors curently make sense is in low current applications. I know that this doesn't solve your problem but there are a lot of really smart people working to solve the energy storage problem and who knows when something new will crop up.

    John

  • 0 in reply to jw0752

    Although I agree with John that supercapcitors won't help you to power your fridge I have to point out that not all supercaps have high internal resitance - there are supercap packs designed for starting engines which can deliver 100s or 1000s of amps. The problem is that the energy density of supercaps is quite low compared with lead acid cells. The best energy density in reasonable devices is in Lithium Ion batteries but big power packs are very expensive.

     

    Super Capacitor 12V bank - (6 x 3000 Farad Ultra Capacitors)

    (NB this part won't help with a fridge !!!)

     

    I suspect that the answer to your problem might lie in doubling up (or more) on the lead acid batteries and (if possible) insulating the fridge more (but don't insulate the radiator on the back !!).

     

    MK

  • 0 in reply to michaelkellett

    Thanks both John and Michael.  I made the mistake of buying a fridge/freezer combo not thinking how much would be needed to keep the freezer going, and of course the Primus runs a fan all the time to cool the electronics (mind you this is the third one under warranty so it still could be the fridge), but the last time I went bush I had two batteries connected in parallel during the day and the solar panel charged both batteries within 4 hours (max output is 18 V, level of volts being directed by the charger).  The first time I left it hooked up and just connected the Primus to the front battery and of course it was dead by morning, despite the fridge supposedly shutting itself off at 10.5 V.  I then put a switch in the circuit with a couple of more leads to isolate them from the solar charger  so that the fridge had the reserve of both and it worked quite well until I ran out of sun (and my generator died too).  So what I thought was using the capacitors as a trickle feed back into the batteries overnight or on cloudy days as a means of maintaining level of charge, rather than running any loads directly from them.  I imagine I would need some kind of control circuit to do that, and of course could be way off beam with the concept in the first place.  Or it may be that the battery would act to limit the discharge from the caps, based on it's state of charge.  I guess I can't see the difference between inputting energy from the solar panel as being any different to inputting energy from the caps, but again that may mean I misunderstand their rate of discharge.  It may be I will still have to use two batteries, and buy a better generator, but just looking at alternatives (ie F&P/LG direct drive washing machine motors acting as generators using wind etc, ambient energy multiplied many times to provide a decent level of power etc etc).

     

    Not sure if that has added to the problem or made it a bit clearer, but again if there is anymore you can add that would be great.

    Phil

  • 0 in reply to michaelkellett

    Hi Michael - I took a look at your link for the supercaps with low ESR. The technology just keeps getting better. Thanks for your input and correcting me on the blanket categorization of super caps as having high ESR.

    John

  • 0 in reply to Former Member

    Hi Phil  - There is energy lost every time a transfer is made. Going directly from your solar panel to the battery is better than first charging the caps and then trying to charge the battery from the caps. Also the caps will not maintain a voltage unless you get a regulator involved. As soon as the caps start to discharge their voltage will begin to drop. If you had a load that had high current, short time period demands, such as100 amps for 1 second then hooking one of the super caps that Michael mentioned would be a benefit to the battery as it would protect it from having to suddenly ramp up a chemical reaction to accommodate such a high load. It doesn't sound like the caps are going to be much help for your use at this time.  I always thought that a good situation would be to find a big lake on a hill and then run a water line down hill to a small turbine generator. Of course is we get too much technology involved I suppose we negate the reason for going to the bush in the first place.

    John

  • 0 in reply to jw0752

    Ta John

    Looks like I will have to settle for the traditional methods for the time being until someone comes up with the concept of a generator without the need to consume petrol that will act as an auxiliary to the batteries etc but still be able to be portable.  Might have to invest in more Redarc devices for now.

    Cheers

    Phil

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