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Why Solar Panel Voltage Drops When Connected The Radio? Answered


I own a Brunton Solaris 6 solar panel with the power rating of 12v 6W and short circuit voltage of 19v. We were living together just fine until I got a Yaesu Vx-8dr Radio. It charges on 12v 0.5A AC adapter. I decided to charge it with my PV but when I connect the panel voltage drops under 12v to 9v and Radio doesn't charge showing a External DC tag which indicates the lower voltage. The only time I get a charge with this setup is when the panel oriented to the sun perfectly in high solar conditions which is too perfect to sustain. I tried to wire it with 80 Ohm resister to limit the current but didn't help. How can I stabilize the voltage and also carry the solution in my backpack? Thank you for your attention and help.


Your problem is that the charging requires more power than your little panel can supply.

Its working perfectly, and in accordance with the numbers you;'ve given. A solar panel is rated at full sun, normal to the sun's direction "too perfect to maintain" is a great description.

Unfortunately, a 6W system needs 6W from the panel.

Incidently, you can't HAVE a short circuit VOLTAGE of 19V.

"limiting current" will only make matters much, much worse.


Thank you for your quick answer.

There is one thing left bothering me.

This panel generates some power even it is slightly lower then the device needs. I want to take that in use somehow. Charge speed isn't a matter.

12v voltage is the only thing that radio needs to get the charge. If I'm right about it current is a matter of charge time.

If there is a way to stop radio to pull that much current, the voltage will rise right? If current limiting with a resistor does harm then good, any other solution left? I can go to the end since this panel is the only reasonably light one that I can carry in to the mountains.

May be should I store that power somehow and then charge the radio? But direct charging will be a lighter solution for my backpack.

I've just reviewed the manual for the radio, the charging spec is definitely 12V 1 amp ! Can you check the charger rating ?


The original wall adapter came with the radio was 12V 0.5A. Now I'm using a 12v 1A adapter. both are working fine.

I had a spare solar panel which is rated 10W. I tried it with my Brunton Solaris 6w in the same light conditions right now.

10w panel managed to charge it showing 16v
Solaris 6 couldn't and showed 10v

I hope these will help.

Have you any way to measure the real charging current ?


I mesured it. ammeter started from 0.45A and stabilized at 0.35A

Thank you for your kind efford. Now I know that it wont be possible with this panel. Thank you.

Please don't forget to mark this as the Best Answer, for other's reference !


Get a second (identical) panel, wire in parallel.


Thank you for your answer. Since I have limited space in my packpack and the cost of this king of CIGS solar panels are some 100$ I need to stick with the one I have right now.