Problem with solar panel charger

I have found a schematic for constructing a solar panel charger for charging a Sealed Lead Acid battery, but I have a problem.

The schematic is this:

solar-charger-circuit/

The problem is that on input (the voltage that comes from the solar panel) I measure 8,1 Volt instead of 12 Volt (ok I didn't have too much sun today), but the output I get is 1,8 Volt. If I have understood the circuit correct, shouldn't I have the (input voltage)/2 at the output (so 4 Volts), or I am wrong?

Also, I didn't connect the VR as in the schematic. I connected the "middle" pin to the upper circuit, and one of the "side" pins to the ground. Am I wrong?

OK, I'll take a guess.

The battery is probably "dead" and pulling-down all of the voltages. You might just need more time and/or a bigger solar panel (or a smaller battery).

What voltage do you get out of the solar panel with nothing connected?

Does the potentiometer do anything. Since the description says to adjust it for 9V, I assume that means without the battery connected. (And of course, you won't get 9V if you're only getting 8 out of the solar panel.)

shouldn't I have the (input voltage)/2 at the output (so 4 Volts), or I am wrong?

No, it's a voltage regulator so you should get whatever voltage its adjusted for. Of course it requires a little more voltage-in, so you probably need about 10V in to get 9V out (you can check the "dropout voltage" on the datasheet).

Then, there's the Zener-transistor voltage limiting circuit that's supposed to intentionally mess-up the regulation and limit the output. (Make sure the Zener is not backwards.)

How big is the solar panel in terms of power and maximum current.
Its most likley that the charger is simply pulling the solar panels voltage down because the panel cant supply enough current.

alex5678:
Also, I didn't connect the VR as in the schematic. I connected the "middle" pin to the upper circuit, and one of the "side" pins to the ground. Am I wrong?

the link says they use an LM317, a variable voltage output regulator.
you say you did not follow the circuit
and that you are not getting what you expected.
the schematic in not a picture of the actual part. and the LM317 is in/out/adj on the pins. The output is the center pin
so you might have done it right.
usually we ask that you post your schematic, the one you made, listing your part numbers.

I have measured the output of the solar panel today, and it gave 11,3 Volts. Then I measured the output of the solar charger and again it gives me 1,81 Volt. Nothing changed. I checked the circuit and it is correct. I cannot understand what is wrong. On the website, I have posted in a previous post, as I have read from the messages people say the circuit works...

This is the circuit.
On the left is the input (2 solar panels in series, each one 6V, 3.5Watt, ~560mA)
On the right is the output (where I connect the Sealed Lead Acid battery)

the_circuit.jpg

Your layout and soldering job looks good alex5678, but unfortunately it doesn't let you properly test your circuit. There are several differences between your reference circuit and your own one. You need to build it on a breadboard so you can make changes easily before soldering it together.

Try starting out with this circuit to make sure you have the LM317 properly adjusted:

Play with the variable resistor and note the maximum voltage of the output. Put a 1K resistor across the output plus and minus and test the output again. Then add the diodes and test the output again. Then add the zener/transistor (make sure the zener is in the correct orientation) and check it once more.

What are the voltages for each of these. You will need ... 13 volts or so, under load, to charge your battery. I doubt your 6 volt, 500mA panels will get there.

ps, I made a mistake in the drawing. Connect the top part of the pot to the + wire with a (~180 ohm) resistor.

You MUST have the recommended capacitor on input side of the LM317 (0.1 uF) and 1 uF on the output is strongly recommended.

Also, you should measure your voltage at the input pin of the VR, not the output of the solar panel.
your voltage drop across the diode will have some effect as to your input voltage.

Ok, I will build it again, in a breadboard this time, to see if it works to me also, and find what is wrong to the soldered circuit...

ChrisTenone : that's NOT the way to adjust a LM317:

It requires a 1.25V drop between Vout and Vadj...

Add a 220R between Vout and Vadj to make this work, together with stabilising caps.

And , OP I'm pretty sure the original circuit's problem is that it presumes the zener doesn't conduct before it's turn on voltage .This isn't true - they leak a lot. Add a 1K resistor between the zener's anode and 0V to fix this.

Allan

allanhurst:
ChrisTenone : that's NOT the way to adjust a LM317:

It requires a 1.25V drop between Vout and Vadj...

Add a 220R between Vout and Vadj to make this work, together with stabilising caps.

And , OP I'm pretty sure the original circuit's problem is that it presumes the zener doesn't conduct before it's turn on voltage .This isn't true - they leak a lot. Add a 1K resistor between the zener's anode and 0V to fix this.

Allan

Is it possible to provide me a drawing in order to understand how to connect them?

I don’t think the idea is brilliant, but the enclosed modded circuit ought to work.

Allan

spla.pdf (22.9 KB)

An LM317 seems a poor choice for a charging circuit (high dropout voltage).

How big is this solar panel, and how many cells.
You need at least an panel open circuit voltage of 18volt to charge a 12volt battery.

If the panel is small, then a simple backflow protection diode (or p-channel mosfet diode) with a shunt regulator on the panel side might be enough.
Leo..

allanhurst:
I don't think the idea is brilliant, but the enclosed modded circuit ought to work.

Allan

C1,C2 are electrolytic or it doesn't matter?

Doesn’t matter. But electrolytics are cheaper.

Allan

I bought the components today, and I assembled the circuit on a breadborad. The maximum output I got is 4,97 Volt for input of 10,9 Volt as you can on the attachments. The problem is that I cannot get 6 Volt on the output, this is due to the input, or should I add/remove something on the circuit?

input.jpg

Wawa:
An LM317 seems a poor choice for a charging circuit (high dropout voltage).

How big is this solar panel, and how many cells.
You need at least an panel open circuit voltage of 18volt to charge a 12volt battery.

If the panel is small, then a simple backflow protection diode (or p-channel mosfet diode) with a shunt regulator on the panel side might be enough.
Leo…

2 solar panels in series, each one 6V, 3.5Watt, ~560mA

I want to charge a Sealed Lead Acid 6V battery.

I assume the amp-hour rating of that battery is at least 10x of the panel's current rating.
If so, then you don't need current limiting.

Allan's circuit should work, but with poor performance in low light conditions.
A simple diode between panel and battery should perform better,
but needs a "brake" on the solar panel side when the battery is full.
Plenty of shunt regulator examples on Google with a TL431 and a PNP power transistor.
Disadvantage of a shunt regulator is that is gets hot when the battery is full.
I calculate about 4watt with two of those panels in full sun, so only a small heatsink on the power transistor.
Leo..

This one could be converted to 6volt.

Wawa:
I assume the amp-hour rating of that battery is at least 10x of the panel's current rating.
If so, then you don't need current limiting.

Allan's circuit should work, but with poor performance in low light conditions.
A simple diode between panel and battery should perform better,
but needs a "brake" on the solar panel side when the battery is full.
Plenty of shunt regulator examples on Google with a TL431 and a PNP power transistor.
Disadvantage of a shunt regulator is that is gets hot when the battery is full.
I calculate about 4watt with two of those panels in full sun, so only a small heatsink on the power transistor.
Leo..

This one could be converted to 6volt.

What modifications should I do?