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### Topic: How to limit solar panel voltage? (Read 2762 times)previous topic - next topic

#### RudiAhlers

#30
##### Jun 29, 2018, 05:25 pm
Sorry for the late response, it took some time to get all components for testing.

I've ordered a few solar panels:
53x30mm, 5V 0.15W (30 mA)
68x36mm, 5V, 0.3W (60 mA)
100x28mm, 5,5V, 0.22W (40 mA)

plenty of zener diodes for different voltage and BAT54 schottky diode.

After some testing I decided to use 5,5V, 0.22W solar panel, 1N4733A (5.1V) zenner diode to limit voltage and BAT54 schottky diode to prevent discharging.

With 1N4733A I got voltage drop ~0.1V (without load), it's appropriate as for me.
BAT54 has reverse leakage current 2μA at 25V, it also fits my requirements.

Thank you for help.
How long does it take to recharge the supercap, once discharged?

#### jremington

#31
##### Jun 29, 2018, 05:36 pmLast Edit: Jun 29, 2018, 05:37 pm by jremington
Quote
How long does it take to recharge the supercap, once discharged?
Depends on the illumination intensity, the capacity and the solar panel current.

From the capacitor equation Q = CV, it is approximately true that (delta t) = C*(delta V)/I.

#### RudiAhlers

#32
##### Jun 29, 2018, 05:44 pm
Depends on the illumination intensity, the capacity and the solar panel current.

From the capacitor equation Q = CV, it is approximately true that (delta t) = C*(delta V)/I.
Yes, I know all of those factors play a role. I wanted to know from the OP, with the components he brought, how well it works.

#### jremington

#33
##### Jun 29, 2018, 06:44 pmLast Edit: Jun 29, 2018, 07:00 pm by jremington
If you bother to do the experiment yourself, you will discover that it works as well as it is predicted to work.

These devices obey the laws of physics, so you don't actually need to depend on someone else's results.

#### RudiAhlers

#34
##### Jul 03, 2018, 10:33 am
If you bother to do the experiment yourself, you will discover that it works as well as it is predicted to work.

These devices obey the laws of physics, so you don't actually need to depend on someone else's results.
seriously??? I am curious to find out how well the combination of components he brought worked. If you bother to give me the components he used, I will gladly experiment it myself. But I am mot interested in finding out if what he brought worked as well as he hoped it would.

#### strange_v

#35
##### Jul 12, 2018, 11:02 am
How long does it take to recharge the supercap, once discharged?
It depends on whether, but let say it takes less than an hour to charge a supercup on a sunny day.

I've bumped into another issue with this remote sensor. After some time (usually days) nrf24l01 starts to consume much more than it has to. I've found a few threads about such a behavior in other people.
So, for now, this project is postponed.

#### alexsh1

#36
##### Nov 10, 2018, 10:41 pm
FYG - I have several solar panels with sensors. And I do not have any issues with nrf24l01+
In my latest setup I have a small 3V solar panel with 2.7v Zener diode charging two parallel 30F 2.7v supercaps used to power a node with the nrf24l01+

#### MarkT

#37
##### Nov 12, 2018, 03:42 pm
The problem you will face is that when the cap is discharged it will never let the panel produce power.

The cap will demand a HUGE amount of current from the panel which will drop it's voltage down too low to charge the cap at all.
No, thats not how it works.  A PV panel will produce constant current charging the cap linearly until the
voltage approachs the panel's open-circuit voltage whereupon the current falls.
Quote
It might work a little, but it certainly won't be efficient at all.

So if the cap is down to a voltage which kills your project, say 2V, the cap will pull the panel voltage down and keep it down at 2V.  The panel might be in direct sun and able to produce 0.2W, but not at 2V, it might produce 0.02W.

As a minimum you will need some kind of PWM controller to allow the panel to be operating at a higher voltage than the discharged cap.
A simple resistor and diode can be used, charges through resistor, discharges through diode to the load when
the load demands current.  If the resistor is large enough the panel voltage will be high enough to power
the load in full sun too.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

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