Lipo solar lamp design

Thread Starter

Gwenbino

Joined Apr 23, 2020
4
Good morning,

I am a student in electronics & would like to ask about my solar lamp design which is far from perfect.

I want to use a 6V solar panel to charge a lipo through the TP4056 charging board. On the side I would like to do a night detection circuit to activate my solar lamp when the sun is down enough.

I have first tried to build it with 2 NPNs as described in the attachement LT spice simu with the name " solar led driver NPN". The design seems to work but I am not really in total control of what is going on there. I would like to understand how to tune my circuit resistors & values in order to for example switch it on when the solar panel voltage drops lower than X Volts. Could someone enlight me onmy mistakes & which parameters to tune there please?

I then found someone on the internet telling to use a PNP which seems to give me a much better result, even tho I am really having a hard time understanding how that circuit works. I have again no control over the system & would like to understand it & be able to tune the parameters in a comprehensive way.

thank you for your time & consideration.
Best Regards;
Gwen
solar lamp design.PNG
In blue I plotted the solar panel discharge voltage; In green the current flowing through the LED.
 

wayneh

Joined Sep 9, 2010
16,399
I am a student in electronics & would like to ask about my solar lamp design which is far from perfect.
So this is homework?

I have first tried to build it with 2 NPNs as described in the attachement LT spice simu with the name " solar led driver NPN". The design seems to work but I am not really in total control of what is going on there. I would like to understand how to tune my circuit resistors & values in order to for example switch it on when the solar panel voltage drops lower than X Volts. Could someone enlight me onmy mistakes & which parameters to tune there please?
What controls the conduction of the two transistors? Do you see a way to manipulate those controls?[/QUOTE]
 

ci139

Joined Jul 11, 2016
1,696
there are ready made (low quiescent power) modules (controllers) on the market ← it's hard to beat by something made of discreet parts

? are you trying to make this as a real thing or just simulate in spice

if it's to build - it might go tricky as you increase the number of the required options . . .

? your power input profile
  • simple - assumes the clear sunny day
  • complex - can boost the input at cloudy day / low sun
? your power output
  • simple - goes (fading) , as long as there is power avail
  • complex - uses switched CC output . . . perhaps goes to a beacon mode at low power
? module control
  • simple - (no controller) current limit charger / enough batteries to ensure they never overcharged
  • complex - device controller ← here it requires to detect the system state (if there is enough power from solar or battery input for it to run) , etc. ... a lot of things to consider/add/control as programmatically as and extra "harware" to detect system parameters . . .

Hacking an LED solar garden light - Blogs - Virtual Classroom for ADI University Program - EngineerZone ← a commercial variant
 

Thread Starter

Gwenbino

Joined Apr 23, 2020
4
First of all thank you for your time & consideration on my question.

So this is homework?

No, it is not, this is for my personnal learning curve, I am repairing my moms solar lamp, & it is quite easy since it is often just changing the Nimh battery or resoldering a faulty button. Yet I have noticed that there are either a joule thief circuit ( on the super cheap ones I believe) or some using dedicated ICs & Nimh battery. I enjoy working on electronics on my spare time & made few instructables already. As a project I decided to use what I had laying around & try to make my own solar lamp (not optimal but with a proper working concept) using my lipos, the charging board I had & no MCU, just a night detection IC thatshould be easy to make.

What controls the conduction of the two transistors? Do you see a way to manipulate those controls?
[/QUOTE]

I wanted to do it just with the dropping voltage of the solar panel & some PU/PD, yet this is maybe where I am making a mistake..
 

Thread Starter

Gwenbino

Joined Apr 23, 2020
4
first of all, thank you for your answer.I replied to your questions right below;

there are ready made (low quiescent power) modules (controllers) on the market ← it's hard to beat by something made of discreet parts

I know about these but I want to use my components laying around & acquire more knowledge on those NPN & PNPs.

? are you trying to make this as a real thing or just simulate in spice

I actually built the NPN circuitery on PCB board & plugged it to my solar panel & charging board, it kind of works as the simu, yet I am not fully in control which means I didnt understand everything I did, therefore I asked for help here.

if it's to build - it might go tricky as you increase the number of the required options . . .

? your power input profile -> Simple
  • simple - assumes the clear sunny day
  • complex - can boost the input at cloudy day / low sun
? your power output -> Simple
  • simple - goes (fading) , as long as there is power avail
  • complex - uses switched CC output . . . perhaps goes to a beacon mode at low power
? module control -> Complex, even tho I am aware that it is dangerous to mistreat Lipos & misshandling them could end up with a fire. I am trusting this Lipo TPU board charger. Since my solar panel is a cheap 6V, with a low current output, I am assuming nothing too bad would occur & therefore I am really focusing on the transistor part of the circuit, that night detection circuitery.?
  • simple - (no controller) current limit charger / enough batteries to ensure they never overcharged
  • complex - device controller ← here it requires to detect the system state (if there is enough power from solar or battery input for it to run) , etc. ... a lot of things to consider/add/control as programmatically as and extra "harware" to detect system parameters . . .

Hacking an LED solar garden light - Blogs - Virtual Classroom for ADI University Program - EngineerZone ← a commercial variant
Thank you again.
Gwen
 

ci139

Joined Jul 11, 2016
1,696
https://lygte-info.dk/review/Review Charger TP4056 UK.html
hints the LiFePo is not supported by that particular charge controller ???
+cite from the site "The board needs a 5 volt power supply," so you may want to add 1N4004... + 1N5817... to get apx. 1V drop
? what's the exact battery model you are using ?

you are almost right about your experiments

Fig_1-1.gif Fig_1-2.gif Fig_1-3.gif the R=0 may cause the simulation to hang or not start at all use "NO RESISTOR" or 2µΩ instead of 0Ω superconductor
 
Last edited:

Thread Starter

Gwenbino

Joined Apr 23, 2020
4
https://lygte-info.dk/review/Review Charger TP4056 UK.html
hints the LiFePo is not supported by that particular charge controller ???
+cite from the site "The board needs a 5 volt power supply," so you may want to add 1N4004... + 1N5817... to get apx. 1V drop

Good call for the voltage drop, my bad on that.

? what's the exact battery model you are using ?
I am not using the proper terms on that, sorry, I have Li-ion batteries, 18650. Max charge is 4.2V & I believe they're supported by the TPU, having a look at the chart they give us.
 
Top