Charging a 1.2V cell from 3V Solar Cell. Need help.

[hiayushman]

Hi there!

I'm building a circuit and having a little trouble while setting up a 3V solar Cell(~100mA) in the circuit as attached.

When i tested the solar cell the open circuit voltage was above 1.8V but while connected in the circuit, it just aint rising anything above 0.75V. The battery voltage is 1.25V while the led has a forward voltage of about of 2.8V.

Is the battery charging if the solar cell is put in light?

It is to be noted that the 22K ohms resistor isnt working in my circuit, so i have replaced it with a 500 ohms resistor. It sets its sensitivity to cut off the led if it is placed in ample amount of light. The website from where i took this idea says the resistance should be of high value, i.e., more than 15k+ ohms but in my circuit it only works for 500-1K ohms resistance. Any suggestion?

Thanks

 

[Doc Hudson]

Welcome to the forum, your question appears to be more electronic based rather than just electrical. This forum is primarily aimed at electricians and issues related to fixed wiring of commercial and domestic premises. So replies may be sparse. But do check back later, as some of our members dabble in the components and electronics side of things as well.

Doc H.

 

[kme]

a 500 ohm resistor on the base of q1 seems very low - you need to be careful you haven`t fried the tranny

I can`t find this project on his website - but something ~"feels" wrong at a quick glance through the circuit diagram. I`ll try to have another look later, and see if I can tell you anything else.

KME

 

[hiayushman]

Welcome to the forum, your question appears to be more electronic based rather than just electrical. This forum is primarily aimed at electricians and issues related to fixed wiring of commercial and domestic premises. So replies may be sparse. But do check back later, as some of our members dabble in the components and electronics side of things as well.Doc H.

That was very humble of you Doc Hudson. Not many mods do that. Glad to be a part of your community

Cheers!

kmeRe: Charging a 1.2V cell from 3V Solar Cell. Need help.

a 500 ohm resistor on the base of q1 seems very low - you need to be careful you haven`t fried the tranny

I can`t find this project on his website - but something ~"feels" wrong at a quick glance through the circuit diagram. I`ll try to have another look later, and see if I can tell you anything else.

KME

Yes, a low resistance might damage the transistor Q1 but i tried using higher resistance value which only dampens its sensitivity and doesnt cut off the led. And oh, by the way, i am using BC548 for Q1 and Q2 presuming that its equivalent to the suggested 2N4401 in the diagram.

As for R2, the led lits brightest for 500 ohms resistor as against 1k ohms. Nothing less nothing more...just 500 ohms :-D

The link for the project is

1.5 VOLT WHITE AND UV LED DRIVE CIRCUIT

Thanks for the help KME.

The idea is to make the circuit self sustained so that the solar cell could charge the battery whenever its potential gets higher than the battery's potential.

 

[ProDave]

I'm looking at that circuit, and struggling to understand what it's trying to do.

Strip it to basics (ignore the transistors and inductor) and you have a solar panel, connected via a diode to the battery. The forward volt drop of the diode will be about 0.6V So with a 1.2V cell, any voltage greater than 1.8V from the solar panel will start charging the battery.

But what are the two transistors and the inductor trying to achieve?

It looks like it's some form of switch mode boost regulator, but what's making it oscillate? And even if it does manage to oscillate, is it's sole purpose to illuminate the LED?

A link to where you got the circuit might reveal an explanation of how it's supposed to work.

I take it you have a multi meter, if so set it to mA range and connect it in series with the battery, that will tell you if it's charging or not.

 

[hiayushman]

:-D

Okay, about the circuit, its a type of boost converter which drives a led having a forward voltage of 2.8 from a 1.2V(or 1.5V) battery source. In short, it step ups the voltage. The inductor in the circuit is custom made by me. The attached image below will help you get the idea. Its a type of oscillator which produces short pulses to drive the led. The more detailed version of its working can be found in the link i'd provided in the above post .

I tried connecting the solar panel with the battery by placing a schottky diode(forward voltage is 0.3V) between them. Sadly my multimeter isnt able to measure current due to some internal fault(maybe its fused). Now, before connecting, solar panel shows 2V but after connecting it to the battery...it shows the battery's potential of 1.27V. As per my knowledge, it should have between 1.27V and 2V, depending upon the internal impedance of both the devices if i am not wrong.

Maybe its time i should borrow a multimeter from someone

Thanks again!

View attachment 3876

 

[NozSpark]

But it only steps up the voltage to the LED, not the battery

The diode and Q1 are only there to shut the oscillator down while the solar panel is producing 0.6V more than the battery - at which point it should be charging the battery

 

[Doc Hudson]

Maybe its time i should borrow a multimeter from someone

Are you in the UK, (not sure because of your country flag?), if yes, our forum sponsor has a good range of multimeter's including some decent quality low budget option. Digital & TRMS Multimeters - ISSWWW It may be worth you while saving up a bit of cash and sending a PM to our sponsor, View Profile: megger mark - Talk.electricianforum.co.uk... a forum with a difference., asking what he has in your price range. Many of our members have used his services and can vouch for good value for money, quality and customer service.

Doc H.

 

[hiayushman]

But it only steps up the voltage to the LED, not the batteryThe diode and Q1 are only there to shut the oscillator down while the solar panel is producing 0.6V more than the battery - at which point it should be charging the battery

True. Thats what it ideally should do. But upon checking the potential across the battery when the solar panel shuts the oscillator the multimeter reads 1.27V, the battery voltage. Is it okay? Or should it be between 1.27 and 2V(Solar panel volatge output)?

I hope i'm not being a pain in the ass here but i've been working on this really bad for this needs to be gifted to someone.

Are you in the UK, (not sure because of your country flag?), if yes, our forum sponsor has a good range of multimeter's including some decent quality low budget option. Digital & TRMS Multimeters - ISSWWW It may be worth you while saving up a bit of cash and sending a PM to our sponsor, View Profile: megger mark - Talk.electricianforum.co.uk... a forum with a difference., asking what he has in your price range. Many of our members have used his services and can vouch for good value for money, quality and customer service.

Doc H.

Doc Hudson, i am sorry but i'm from India. Thanks for the help though. Appreciated!

 

[Doc Hudson]

Doc Hudson, i am sorry but i'm from India. Thanks for the help though. Appreciated!

Oh dear, that would rather mess up the postage costs! never mind.

Doc H.

 

[NozSpark]

True. Thats what it ideally should do. But upon checking the potential across the battery when the solar panel shuts the oscillator the multimeter reads 1.27V, the battery voltage. Is it okay? Or should it be between 1.27 and 2V(Solar panel volatge output)?I hope i'm not being a pain in the ass here but i've been working on this really bad for this needs to be gifted to someone.

Doc Hudson, i am sorry but i'm from India. Thanks for the help though. Appreciated!

Well, you are always going to have a 0.6V PD across the diode, so if the panel is giving out 2V you will only ever see 1.4V at the battery even when it's fully charged. When it's discharged the battery will draw current from the panel and the voltage will drop (especially with a low power panel)

 

[hiayushman]

Well, you are always going to have a 0.6V PD across the diode, so if the panel is giving out 2V you will only ever see 1.4V at the battery even when it's fully charged. When it's discharged the battery will draw current from the panel and the voltage will drop (especially with a low power panel)

Yes but its true for a general purpose diode(Silicon based). Since, i am using a schotkky diode which has a PD of 0.3V across it, the potential shouldnt be lower than 1.7V.

I suppose measuring the current flow using a multimeter be worthwhile . I'll get it done by tomorrow and report back.

There is just one more thing that is bugging me. The resistance R1 connected with Q1... why in my case it so less? The author in the weblink specifically mentions that it should be higher than 15K ohms for the right sensitivity but i'm only getting it at 500 ohms. What could be the reason?

Q1=Q2= BC558

Is it possible that i'm using not so suitable transistor?

 

[kme]

Without digging out my transistor reference books (which I`m not doing now, because:

1. its late.

2. I think they`re up the loft.

3. I`m a bit knaffered.

I think the alterations you`ve introduced have affected the circuit - but q1 base resistor "feels" wrong, if you know what I mean?

If you`re reading 1.27V, and you expect a reading of 1.27V-2V.........then you haven`t got a problem, have you??

Need to measure current on battery cable - DC ammeter, pref. centre zero (if analogue) will tell you if batt is charging.

 

[binky]

Think you are confusing yourself - PV panels when 'stalled' display a higher voltage than when they are supplying power. For instance, my own set of panels displays around 340V at the inverter on start-up, which drops to around 245V when being used to actually generate power and some current is flowing.

 

[hiayushman]

Think you are confusing yourself - PV panels when 'stalled' display a higher voltage than when they are supplying power. For instance, my own set of panels displays around 340V at the inverter on start-up, which drops to around 245V when being used to actually generate power and some current is flowing.

Now i dont want to sound total noob(as i completely am) but i aint really sure whats happening with the panel.

I took the panel to my Univ to check the current values.

At 2.2V, the short circuit current was 0.5mA(peak). I checked the value twice, thrice but it just showed 0.5mA as against the rated Isc current of 100mA. I called the seller and he says he got lot many similar feedbacks from his customers and he advised them all to check the Solar panel by putting a load like a small motor. I'll check back on that later. :-(

After connecting the battery directly(1.27) to the solar panel (Voc 2.2V), the voltage shown was 1.27(battery's potential) although, 0.3mA current was flowing to the battery from the panel.

You ever encountered for your panel to behave like this?

Is this the reason why R1 in my circuit is so low(500 ohms)?

Time to buy another panel?

Thanks for the help

 

[NozSpark]

If I were you I'd leave R1 a.t the value in the diagram, it's there to limit the base emitter current

 

[binky]

Now i dont want to sound total noob(as i completely am) but i aint really sure whats happening with the panel.I took the panel to my Univ to check the current values.

At 2.2V, the short circuit current was 0.5mA(peak). I checked the value twice, thrice but it just showed 0.5mA as against the rated Isc current of 100mA. I called the seller and he says he got lot many similar feedbacks from his customers and he advised them all to check the Solar panel by putting a load like a small motor. I'll check back on that later. :-(

After connecting the battery directly(1.27) to the solar panel (Voc 2.2V), the voltage shown was 1.27(battery's potential) although, 0.3mA current was flowing to the battery from the panel.

You ever encountered for your panel to behave like this?

Is this the reason why R1 in my circuit is so low(500 ohms)?

Time to buy another panel?

Thanks for the help

Sounds like a ****ged panel (though I could be wrong as I normally only play with 200W units). The panel when tilted directly at sun, should show the full Isc. We normally check a panel by connecting the leads together and using a clamp ammeter, but measuring mA might be abit hard unless you have a very sensitive instrument. I used to measure by sticking probes into ends of connectors, but that tends to cause a few sparks on a big panel, but should give same result!!

PS don't worry about being a Noob we all were once and learn't from asking questions

 

[kme]

The panel Isc as stated is under "standard test conditions" (stc) - the manufacturers standard irradiance / temp tp provide stated output.

If, under good lighting conditions (irradiance reading?) you`re only getting 5% of rated Isc (what Voc are you getting relative to panel spec.?) - then the panel sounds carp.

 

[hiayushman]

If I were you I'd leave R1 a.t the value in the diagram, it's there to limit the base emitter current

But what if there is negligible current supplied by the panel? :-(

Sounds like a ****ged panel (though I could be wrong as I normally only play with 200W units). The panel when tilted directly at sun, should show the full Isc. We normally check a panel by connecting the leads together and using a clamp ammeter, but measuring mA might be abit hard unless you have a very sensitive instrument. I used to measure by sticking probes into ends of connectors, but that tends to cause a few sparks on a big panel, but should give same result!!PS don't worry about being a Noob we all were once and learn't from asking questions

Thanks Binky. I dont think my 3V panel can produce sparks that could be detected but i'd measured the voltage and current under a good quality multimeter.

Anyways, i will give it a last try again once i get back home.

The panel Isc as stated is under "standard test conditions" (stc) - the manufacturers standard irradiance / temp tp provide stated output.If, under good lighting conditions (irradiance reading?) you`re only getting 5% of rated Isc (what Voc are you getting relative to panel spec.?) - then the panel sounds carp.

KME, i'm too having the feeling of receiving a crappy panel. It was tested under a well illuminated surrounding(not under direct sun).

At the time of testing, Voc was 2.2V but dont have the irradiance reading. I will test thoroughly this time and report all the measurements on Tuesday along with the irradiance reading.

Thanks a lot everyone. Really appreciate your concern.

 

[NozSpark]

I've just had a look at the data sheet for your transistors

Full saturation is achieved with an Ib of 0.5mA, Ic of 10mA and Vbe of 0.7V