# Solar Panel used in Conjunction with a DC to DC Step Up

Good morning all, I am trying to put a little project together where I used a 1 watt, 6v solar panel in conjunction with a 0.9V - 5V to 5V DC to DC boost converter. I hooked up the solar panel to a multimeter and tested it in dim lighting and it was outputting about 3.5V and 130mA. 3.3V is well within the tolerance for the boost converter so I hooked it up to the boost converter.

I took a volt reading at the connection point and now the voltage dropped to about 0.2V. I have tried this with multiple panels and regardless of the no load voltage, it seems to drop to about 0.2V.

The boost converter also has a USB output and when I plug it in to my phone, nothing happens. I have confirmed the boost converter works because when I attach the dc inputs to a 1.5V alkaline, the system powers up. What do you guys think the issue is? Do I need to input a stable voltage/current?

I have linked the products below: Boost converter: http://www.ebay.com.au/itm/DC-DC-USB-0-9v-5v-to-5vdc-Boost-Step-up-Power-Supply-Module-Mini-PFM-Control-DA-/151285075110?pt=AU_B_I_Electrical_Test_Equipment&hash=item23394b0ca6&_uhb=1

• How much current it takes from 1.5V alkaline? – Kamil Apr 22 '14 at 23:47
• Have you tried to add some capacitor before converter? Maybe it needs bigger current for startup (to charge that huge 100uF capacitor and coil initially). – Kamil Apr 22 '14 at 23:49
• I did not measure the current from the 1.5 alkaline but I think its something like 200ma as this is what the boost converter specs seem to dictate. – darkzen15 Apr 23 '14 at 0:04
• Also keep in mind that solar panels don't really act like batteries or supplies powered from the wall, they have complex I-V characteristics. Getting good efficiency out of them requires a power converter which can do maximum power point tracking (MPPT). – Zuofu Apr 23 '14 at 0:28

I'm assuming that you tested the panel voltage into an open circuit (just test leads across the panel) and the panel current into a short circuit (again, just test leads across the panel). This is not a valid test. When you put your ammeter across the panel, it acts as a short circuit. So the panel is putting out 130ma at almost no voltage!

As soon as you connected the regulator to the panel, it drew enough current to pull the voltage below what it could handle.

Look at it this way: a 1W 6V panel will put out 1/6 amps (167ma) at 6V in full sunlight. There's no way it's going to put out anywhere near that in dim light.

• Yea, he probably did. People are not aware how weak solar panels are... – Kamil Apr 22 '14 at 23:57
• Yes, I tested it in a short circuit. I am assuming the boost converter acted as a load and as a result showed only 0.2V when connected with 0 amps being output. How would I resolve this though? Can I use the panel to charge a battery bank and then run the boost converter off this bank? – darkzen15 Apr 23 '14 at 0:00

Are you trying this inside? Those panels just can't produce any usable power indoors under normal incandescent or fluorescent light.

In general, a solar panel will output most of it's rated voltage until the light output becomes quite dim (sometimes to as low as 10% or ideal). However, current starts to drop immediately as light brightness drops from full sunlight.

So if your 6 volt panel was only producing 3.3 volts, his would suggest that you were under very low light conditions. I am very surprised that you measured any current. Under load I am willing to bet there is no current in that low light condition.

Go outside on a very bright and sunny day and try again - it should work!

Solar panels just don't work inside. Although they will work at less then 100% through a window facing the sun!

Let us know if you succeed.

Good luck!

Edit: I just looked at the solar panel you bought. It has a low current. If you get this to work, it will take a long time to charge your phone. I would recommend putting two or three of hem in parallel and the. You would get a reasonable charging current.

• Thanks guys, you have all been very very helpful, this problem was keeping me up all night and all my research proved fruitless. My first time posting on a SE forum and I'm very impressed with the speed and quality of the assistance offered! – darkzen15 Apr 23 '14 at 0:23
• Hi Filek, yeh I was hoping to use the low current to trickle charge at less than C/10 for a li-ion (with in built charge controller) or nimh battery. – darkzen15 Apr 23 '14 at 0:30
• My main aim was to have an in=car GPS-tablet solution where the tablet was constantly topped off via a solar trickle charger instead of from the cars own battery. – darkzen15 Apr 23 '14 at 0:35
• OK, I understand. As long as the GPS has built in charge controller because it is bad ad dangerous to trickle charge a Li-ion without charge controller/PCB protection. It should work through the car's window if sun is shining bright. I have used similar boost converters with solar panels with success. – Filek Apr 23 '14 at 5:09

I used a 1 watt, 6v solar panel

According to the linked page, the open circuit voltage is 6V and short circuit current is 0.183A.

A first order model, under full sunlight, is then a 6V voltage source in series with a $\frac{6V}{0.183A} = 32.8 \Omega$ resistor.

tested it in dim lighting and it was outputting about 3.5V and 130mA

That doesn't compute.

$0.13A$ through a $32.8 \Omega$ resistor is 4.26V so, under full sunlight, the output voltage should be $6V - 4.26V = 1.74V$ and, with dim light, much less.