converting solar to mains

[cowboybob]

First, without the resistor there's a good chance you'll either overload the regulator and/or the PS AND possibly fry the LEDs.

Now, not knowing the resistance per foot of the cabling you intend to use, it might be that its resistance is sufficient. Just don't know.

Also in that vain, using just the diameter of the cable I can't reasonably guess what current level the individual wires will tolerate. You might be able to google the cable's model # (or whatever) and find its Ωs per foot.

All things considered, I think that if you start with the lowest possible voltage level and gradually increase it (if need be), you'll be able to observe the LED string's response and be able to better decide your next course of action.

 

[audioguru]

We are guessing that a string of LED fairy lights do not have resistors built into it. The voltage-stepup circuit probably regulates the output current at 150mA so the 200 LEDs can glow dimly for 8 hours from a 1200mAh AA cell.
A 10 ohm resistor with 150mA in it will have a voltage of (10 ohms x 150mA=) 1.5V across it and the white LEDs will have 3V to 4V so the LM317 regulator should be set to 4.5V to 5.5V. Then the LM317 needs a minimum input of 7.5VDC.
If you use a 12V input and the output of the LM317 is 4.5V then it heats with (12V - 4.5V) x 150mA= 1.13W so it will be fairly hot but will not need a heatsink if the TO-220 package is used. Each string will need its own LM317 regulator.
The current for each LED string is very low at 150mA so any small wires can be used.

 

[Jagsy]

hi..ive ordered the parts I need...12v power adapter..the voltage step down regulator and the 5w 10 ohms resistor..... just 1 thing confusing me.... cowboybob said earlier in the thread that I could possibly power all strings from this setup... but audioguru is saying I need 1 regulator for each string.... can you clarify which it is... thanks and if it is 1 regulator for each string can they all be joined to the same power adapter or will each regulator also need its own power adapter.. cheers lads

 

[audioguru]

We are still guessing that a string of fairy LEDs uses about 3V to 4V. Why don't you measure one string that is powered from a voltage stepup and current regulated circuit and a charged AA rechargeable battery cell and tell us?

One string of 200 fairy LEDs uses a 10 ohm series resistor and its LEDs have a certain voltage. Another string of 200 fairy LEDs has a different voltage.
A string of 100 fairy LEDs needs to have a series 20 ohm resistor and it also has its own voltage.
It might be possible that all your strings use the same voltage but probably not so a separate LM317 regulator and series resistor is needed for each string. All the regulators can be powered from one 12VDC adapter.

The datasheet for the LM317 shows that it needs a 120 ohm resistor, a 270 ohm resistor, a 200 ohm trimpot, a 0.1uF ceramic capacitor and a 2.2uF electrolytic capacitor. Then its output voltage can be adjusted from 4.1V to 6.1V.

You also have lanterns and globes but we have not discussed how to light them and we do not know their spec's.

 

[Jagsy]

cheers audioguru... im going to get my head round the led strings first and try to get them working before I start asking questions about the lanterns and globes...im taking it one step at a time lol

 

[Jagsy]

hi, im back again..... ok ive wired the lights together to the lm317 board connected to a 12v dc adapter ... I firstly wired a set of 200 warm white string leds.... i used a 5w 10 ohms resistor and then slowly turned the voltage , i got to about 4.5v and was happy with that brightness..... i thought i,d experiment a little and wired the 200 string with a 100 string and a 50 string and they all came on, the voltage had to be set around 7.5v for the brightness to be ok.... only problem with the 3 sets together is the resistor is getting quiet hot .. is the resistor made to get that hot so i can have the 3 sets together on the lm317 board or could I put a different value resistor between the output and led strings...if so what value would you think would do the job

 

[audioguru]

How much heat in the resistor?
Measure the voltage from one end of the resistor to its other end then multiply it by itself (squared) then divide by the resistor value (10 ohms). The result is how much power the resistor is dissipating as heat. If you measured 4.5V then the heating is (4.5V squared)/10= 2W.

The resistor is rated for 5W and will be very hot with 5W. At 2W it will be very warm.
Usually we operate a resistor at no more than half of its power rating to avoid it melting plastic insulation on wiring or melting a plastic capacitor.

You are lucky that all your LEDs are well matched.

 

[Jagsy]

would it stay cooler if I just replaced the 5w 10 ohms resistor with a 20w 10 ohms resistor

 

[audioguru]

A 20W resistor is much larger than a 5W resistor and has much more surface area to feed the heat to the surrounding air so at only 2W it will just be a little warm.

 

[Jagsy]

thanks audioguru...it looks like I have the string leds sorted then..... if you don't mind I,d like to do the globe lights next.... I,ll post in a couple days ..I,ll see if I can get the specs of them , I take it it,ll probably be the same sort of setup as the string ones... the globes are 4 single led lights and they each have there own wire all connected to the solar panel, so that's 4 sets of wires going into a solar panel that feeds off 2 AA 1.2v batteries.......... I have 2 sets of these leds... so that's 8 leds altogether and if possible I,d like to run them all from the same board using a 12v power adapter and another lm317 voltage regulator if its possible

 

[audioguru]

Does your 12V adapter and LM317 get hot when lighting all your strings of fairy LEDs? If not then they can also power your globes but the globes will need their own resistors. The resistors will be different, smaller and much higher ohms.

The color of an LED roughly determines how much voltage it uses. Red is 2V, bright green is 3.2V, blue and white are also 3.2V. So only a red one might work (poorly) from two rechargeable AA cells without having a voltage stepup circuit.
Ordinary LEDs are 5mm in diameter and use 20mA. I have some Super-Lux LEDs in a square 4-pins package that are very bright at 60mA and they use the 4-pins to take away the heat. Please describe the size and color of the LEDs in the globes.

 

[Jagsy]

hi audioguru, ive decided to do the globes last and if its ok I`d like to do the 4 lanterns first if that's ok.... they run off a single AA 1.2v battery...ive took 2 pictures of the leds..the colour is white, there are 2 leds in each lantern and it sounds like there the same kind of leds you described in your last post ... also no the 12v adapter or lm317 didn't get hot at all with the led strings, just the resistor but im hoping the 20w resistor I ordered will sort that out, thanks

 

[audioguru]

You did not say the diameter of the LEDs so we do not know how much current is their maximum. They appear to be the same as the 5mm diameter Chinese LEDs in my solar garden lights that operate at 20mA.
I don't know if the LEDs are in series or in parallel. The 82 ohm resistor might be rated at half a Watt so if the LEDs are in parallel with 40mA then the resistor has 3.3V across it and it dissipates 0.13W of heat so it will be fairly warm.
If the LEDs are 3.2V white then the LM317 should have an output of about 6.5V.

Today in a store I saw LED candles on display. They flickered something like real candles except they repeated dim, brighter, brightest, dim, brighter, brightest over and over with the same rhythm.

 

[Jagsy]

so can I just clip off the solar wires and battery wires and hook this straight up to an lm317 board ...with the - and + on the circuit board of the leds to the - and + side of the lm317 board and then slowly turn the voltage regulator until the leds get bright?

 

[audioguru]

The solar panel charges the battery cells. The battery cells power a voltage stepup circuit that feeds the LEDs and 82 ohm resistor.
I do not know what S+, S-, B+ and B- are.
You MUST measure the current or you will destroy the LEDs. Stop when the current in each LED is 20mA.

But we are just guessing that the LEDs are in parallel. Post a photo of the solder side of the board that will show S+, S-, B+ and B- wiring.

 

[Jagsy]

the s+ and s- is for the solar panel connections and the B+ and B- is for the battery connections, please could you give me step by step on how to measure the current, i do have a voltmeter/multimeter

 

[audioguru]

The solar panel does not connect to the LEDs. Instead it connects to the battery charger circuit and also might be used to activate a transistor that turns the LEDs on when the solar panel is dark and turn the LEDs off when there is light.
The battery also does not connect to the LEDs. Instead it connects to a transistor that connects it to the LEDs when the solar panel is dark.
I wonder if there is a battery charger blob-on-board and transistor switch on the back side of the LED board? Where is the photo?

IF (your entire circuit is full of IF's) the LEDs are in parallel and IF the 82 ohm resistor is in series with them then measure the voltage across the resistor when the LEDs are lighted and use ohm's Law to calculate the current.

 

[Jagsy]

hi, I measured the voltage across the resistor and it showed as 2.15v... the diameter of the leds are 5mm... here are the pictures of the underside of the board aswell

 

[audioguru]

I was correct.
The black thing is an integrated circuit blob-on-board that is a battery charger, a voltage stepup circuit and a transistor switch. It must be disconnected from the LEDs.
I was correct again because the LEDs are connected in parallel.

It might be difficult to measure the voltage of the LEDs when powered by that blob because the voltage is probably pulsing at a high frequency that your voltmeter cannot accurately measure.

You said your LM317 is set to 7.5V for the fairy LEDs and is not hot so it can also be used to power these lanterns. Guessing that the LEDs use 3.2V then a new resistor is (7.5V - 3.2V)/40mA= 107.7 ohms which is not a standard value. Use 120 ohms. The heating power in the resistor is (7.5V - 3.2V) squared / 120 ohms= 0.154W so a 1/4W resistor is fine. Use one 120 ohm resistor for each lantern. If they are too bright then use 220 ohms or 330 ohms.

Here is how to separate the LEDs from the blob:

 

[Jagsy]

thanks audioguru, do I solder the + and - leads directly to the back of the leds or do I solder + and - leads to the B+ and B- On the circuit board and can I put one resistor between the + or - output of the lm317 and the 4 leads of the lanterns going into it ( would i need a higher watt resistor if I did this )like I did with the fairy strings