0
\$\begingroup\$

I am looking for some advice on how to improve my current system. In brief, I live off grid but am a keen drone enthusiast. As such, I am constantly having to charge these 0.9 amp, 7.4 volt, 2 cell Lithium Potassium batteries.

A friend helped me to rig up a little system with a 45 watt solar panel and a supercap bank featuring 6x 2.7 volt, 500 F units.

This system is excellent, being very much offgrid, and allows me to charge the batteries very easily. However, there is one catch. I have to be careful to unplug the solar panel so that the voltage coming through does not exceed 16.2 volts (and blow up). This means that I am constantly having to march back and forth to check & plug/unplug the system. Also means that I can never leave the house and go to work to come home to fully charged batteries.

I have included photos of the set up below.

My question:

I would like to put in some sort of resistance between the supercaps and the solar panel so as to limit the voltage coming in from the solar panel to 16.2 volts. But as am not a very tech-lingual, I have no idea what the part I need is called. So can someone advise me on the component I would need? I gather it would be either some sort of DC voltage stabilizer but I am not really sure...

Help!! :D

edit: could not post all the photos as have 0 rep being a new user. Posted the ones I felt were most useful.

the 'super' caps

the batteries & charger

\$\endgroup\$
  • \$\begingroup\$ A big enough zener diode would be one of the easiest solutions I can think of. Can you cool away almost all of that 45 W during full sun but full battery bank? \$\endgroup\$ – winny May 28 '17 at 20:12
  • \$\begingroup\$ Sorry, I don't understand the second sentence... can you please explain in layman's terms? \$\endgroup\$ – Tristan Trevissick May 29 '17 at 16:05
  • \$\begingroup\$ How much space do you have available to put a large heatsink, either on your solar panels, on or near your regulator? If you have palm-sized space available and free air, you can put a quick and dirty zener regulator there. \$\endgroup\$ – winny May 29 '17 at 16:13
  • \$\begingroup\$ space is not an issue... mm... will look into this. Thanks! \$\endgroup\$ – Tristan Trevissick Jun 5 '17 at 8:16
  • \$\begingroup\$ You're welcome. Also, "Li-Po" is not Lithium Potassium, it's Lithium-polymer. \$\endgroup\$ – winny Jun 5 '17 at 9:24
1
\$\begingroup\$

You can use a solar charge controller. This will limit the voltage and current from your solar panel to the batteries. These are commercially available as pre-built modules.

|improve this answer|||||
\$\endgroup\$
  • \$\begingroup\$ I was hoping for a cheaper solution... Is there no component that exists that I can hack and clip on? \$\endgroup\$ – Tristan Trevissick May 28 '17 at 19:13
  • \$\begingroup\$ You could use a buck-boost converter rated for 24V input and anywhere from 15-18V output (I assume you're using it with the charger in the image.) \$\endgroup\$ – kva May 28 '17 at 19:21
  • \$\begingroup\$ Awesome. My friend just told me that Lazerhacker managed to do what I am trying to do with a buck-boost converter on a similar system. Will try the same and see if it works. Thanks for the advice!!! The day I build a bigger system I guess a charge controller would be more appropriate. But for now cheap and cheerful will do! \$\endgroup\$ – Tristan Trevissick May 28 '17 at 19:32
1
\$\begingroup\$

Not sure if you need any supercap at the panel input. No solar panel charger you can buy on the market has any of them. Rather you would need a capacitor bank with higher voltage rating 35V, 50V,.. and so on depends on open circuit voltage of the panel.

|improve this answer|||||
\$\endgroup\$
0
\$\begingroup\$

Thanks to those who replied and gave helpful advice. I found a solution that works for me without having to buy different parts.

I hook up an imax B6 LiPro balance charger to the caps once they are reading just below 16.2 volts. When I have 6 batteries plugged in to charge the voltage stays consistent even with low light i.e. sun behind trees and the caps don't risk over heating. Given the flight time of 7 mins, this is the perfect set up given the charge time. The only catch is that one needs 12 batteries in order to always have a battery ready.

Still looking into the buckboost converter as that looks interesting too.

|improve this answer|||||
\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.