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DC DC Converter/Transformer

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milvapp

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DC DC Converter/Transformer suggestion

I have a solar panel which has an output voltage of 4.5-7.5 V and average output current of 5mA .

I would to charge a set of supercapacitors at 5 V.

Could anyone recommend DC DC converter or a transformer which would fit my specs
and more important increase the output current a bit?

The problem so far is finding one becaue of the minimum input current specification.

Thank you in advance!
 
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Re: DC DC Converter/Transformer suggestion

milvapp said:
I have a solar panel which has an output voltage of 4.5-7.5 V and average output current of 5mA .

I would to charge a set of supercapacitors at 5 V.

Could anyone recommend DC DC converter or a transformer which would fit my specs
and more important increase the output current a bit?

Thank you in advance!
Click to expand...

What is link between that solar panel and supercapacitor ?

What is capacity of supercapacitor ?

For charging supercapacitor of several Farads you need at least several amperes.

If you whant to increase current of charging add more solar panels, I mean real solar panel. This of 5mA is for office calculator.
 

Re: DC DC Converter/Transformer suggestion

The DC DC converter will be the link ,I was thinking a Zener diode for not overcharging but it is not quite precise.
The supercapacitors have a total capacitance of 1.65 F.
This experiment is mobile devices purposes so the size of the PV should be kept as small as possible.
This is why the specific solar panel was chosen.
 

In terms of low cost and simple solution I would suggest a buck converter with output voltage set at 5 V.

However, the best solution would be implementing a buck-boost converter (so you can charge the capacitor on the whole solar panel voltage range even at very low light levels). The control however would be a bit tricky. If you want to extract as much energy as possible you have to operate the buck-boost in order to achieve the best efficiency point of the solar panel and provide the maximum output at the same time. Power tracking algorithms would be needed See: https://en.wikipedia.org/wiki/Power_optimizer . Of course you will need a MCU to control the charging process and definitively, depending on your system use and cost this is overkill.
 

emontllo said:
In terms of low cost and simple solution I would suggest a buck converter with output voltage set at 5 V.

However, the best solution would be implementing a buck-boost converter (so you can charge the capacitor on the whole solar panel voltage range even at very low light levels). The control however would be a bit tricky. If you want to extract as much energy as possible you have to operate the buck-boost in order to achieve the best efficiency point of the solar panel and provide the maximum output at the same time. Power tracking algorithms would be needed See: https://en.wikipedia.org/wiki/Power_optimizer . Of course you will need a MCU to control the charging process and definitively, depending on your system use and cost this is overkill.
Click to expand...


Panel have 5mA and we try to charge few farads. This 5mA will be losed just in wires which connect solar panel and capacitor.
 

Note that it is an energy harvesting application. With 5 mA you can charge the farad range capacitor with about 1000 seconds (17 min) which may be ok for this very specific application. Using low power IC's (nA current consumption) and a proper design I don't see why this is not possible. My main worry would be supercapacitor leakage currents but I guess they are < 1 mA.

milvapp: You can find similar applications like the one you are developing:
**broken link removed**
http://www.energyharvestingjournal....to-manage-your-power-00001921.asp?sessionid=1
**broken link removed**
 
emontllo said:
Note that it is an energy harvesting application. With 5 mA you can charge the farad range capacitor with about 1000 seconds (17 min) which may be ok for this very specific application. Using low power IC's (nA current consumption) and a proper design I don't see why this is not possible. My main worry would be supercapacitor leakage currents but I guess they are < 1 mA.

milvapp: You can find similar applications like the one you are developing:
**broken link removed**
http://www.energyharvestingjournal....to-manage-your-power-00001921.asp?sessionid=1
**broken link removed**
Click to expand...


I dont think that 5mA can charger few farad in 17min, I will be gratefull if you can show me calc for that. Maybe you forgot to multiply that value with 10000. :smile:

We speaks here about Farads not micro Farads.


Use thise calc and tell me how many days (should I say month/years) charging will finish charging. Also exclude night without lights and include selfdischarge of supercapacitor parameter :

**broken link removed**
 
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I think you are making a mistake in your calculations..
As far as charging time is concerned which is approx 5 times t=R*C ,R=5V/5mA=1000 Ohm and C=1.65 F t=2.3 hours :D
 

"Ideal calculation"
capacitor.jpg

C = 1 F
i(t) = 0.005 A
Vc(0) = 0 V --> discharged
Vc(1000 s) = 5 V --> charged

1000 s = 16.66 min

Ok its is not exactly 17 min ;-)
 

Thank you emontlo.I have already considered buck boost converter but it would be quite complicated and costly for the specific application.
I have already come across your links ,especially the first one in quite helpful,thnx anyway!
 

It is not a RC charge... is a constant current charge (deppending on your system of course).
The energy stored in a 1 F capacitor at 5 V is 12.5 Joules (not that much). With a 0.005 A, 5 V panel you have a 0.025 W power source...
Considering a poor chargin process (50%) energy is lost --> 12 / (0.025*0.5) = 960 s.
Conclusion: with full light it won't take hours to charge the capacitor. Only some minutes... :)
 

The current is not constant.5mA is considered as the average value I get.
Sounds very ambitious to me..I will test and tell you :)
 

The current is not constant.5mA is considered as the average value I get.
Sounds very ambitious to me..I will test and tell you :)
Click to expand...

Conclusion: with full light it won't take hours to charge the capacitor. Only some minutes...
Click to expand...


Dont worry my friend emontllo calc shows that you can do this in from 17minutes to one hours.


You should try, and announce us about famous results.

Milvapp should try charging and see this practical best learning from practice.
 
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