converting solar to mains

[Jagsy]

hi.. im in the uk... I need to convert some solar leds to mains ( not much sun in winter to supply the panels and batteries ).... I need to convert about 4 strings of 200 leds a couple strings of 100 leds ( the fairy led string kind ) and also 4 lanterns with 1 led each in them... and finally 6 globe lights with 1 led each in them...the globes take 2 x 1.2v aa batteries direct to the solar panel and the string fairy leds all take 1 x aa battery each in the solar panel... I,ll need some kind of transformer that drops the power output from 240vac to about 3vdc ( will 3vdc be ok, the batteries are 1.2vdc but I understand the circuit boards would probs have a booster to output 3vdc to the leds ) .. I have a link for a converter here https://www.ebay.co.uk/itm/3306611029...%3AMEBIDX%3AIT ..can someone please take a look and tell me if this would do the job and also if it is doable with the converter would I need 1 for each 200 string of fairy lights or could I attach like 4 strings of 200 to one converter..thanks

 

[alec_t]

The supply you need will depend on how the LEDs are wired within each string. Series? Parallel? A combination of those? You may well need several different supplies to cope with that range of lights.

 

[audioguru]

An LED is not a hot piece of wire like an incandescent light bulb. If the voltage to a light bulb is a little high then it is brighter. If the voltage is a little low then it is dimmer.
But if the voltage to an LED is a little high then the LED burns out and if the voltage is a little low then it does not light.

The LED driver is designed to drive one 3W LED, not a bunch of low power LEDs. Its output is regulated at 600mA and the single 3W LED can have a forward voltage of from 3V to 5V.

An LED MUST be fed a limited current, not a voltage because each LED has a different forward voltage. If you feed 3V to a 3.3V LED then it will not light. If you feed 3.5V to a 3.2V LED then it will instantly burn out.
Maybe the fairy LEDs are all matched and are all in parallel but their current must be extremely low for 200 to be powered from a single AA battery cell. How will you limit the current?

Each string of LEDs, each globe and each lantern will need its own current source. A transformer is not enough because its output is an AC voltage and LEDs use only a DC current.

 

[Jagsy]

the transformer I linked to does convert 240v ac to 3v dc ... I think the led strings must be linked in series as I accidently cut a wire in the middle of the string and the lights after the cut stopped working but the lights before the cut continued to work , once I fixed the cut they all worked again.... I thought the leds that worked off a aa 1.2v battery were 3v leds and the board the battery is on would have some kind of booster to convert it to 3v...that's what I have understood by reading up anyway.. I was hoping to bypass the board altogether and wire direct to the string of leds..removing the solar panel and battery altogether... so would the transformer I linked to in my 1st post work and if so how many leds would it light up

 

[alec_t]

so would the transformer I linked to in my 1st post work and if so how many leds would it light up

As AG told you in post #3, "The LED driver is designed to drive one 3W LED, not a bunch of low power LEDs. Its output is regulated at 600mA and the single 3W LED can have a forward voltage of from 3V to 5V."

 

[Jagsy]

Hi thanks for clarifying alec_t ... would you know of the kind of transformer I would need to be looking at to drive the 200 string low voltage leds then

 

[KeepItSimpleStupid]

the transformer I linked to does convert 240v ac to 3v dc ... I think the led strings must be linked in series as I accidently cut a wire in the middle of the string and the lights after the cut stopped working but the lights before the cut continued to work , once I fixed the cut they all worked again....

That SUGGESTS parallel. The problem with parallel, it could any voltage under the sun, The series resistor for EACH determines the voltage the LED runs at. You can buy LEDS that operate at 5V or 12V and, I think 24 V. In some cases AC/DC, but these have LEDS have internal resistors and/or diodes or put two LEDs back to back.

Now, why don't you measure the voltage applied to the string with the solar set up? I think that might be a novel idea?

 

[alec_t]

would you know of the kind of transformer I would need to be looking at to drive the 200 string low voltage leds then

Not without knowing a lot more about the LED strings. Can you post a link to their datasheet or provide us with their full specification?

 

[Jagsy]

these are the lights I have **broken link removed** .. I cant find any data sheet ... I have 1x 200 string and 1x 100 string of warm white and 1x 100 string and 1x 50 string of white .... alls I know is that each string works off a 1.2v aa battery... I really didn't think it would be this hard to replace a solar battery powered light with mains... I just thought you would need to step down and convert 240v ac to input 1.2v to 3v of dc to the lights and I`d be good to go

 

[cowboybob]

Welcome, Jagsy, to ETO!

Seems to me that a simple voltage regulator circuit, using the output of the convertor you listed, would suffice.

For instance:

In a SIM it only supplies the current that the RLoad dictates (the resistance of the LED strings) with about 1.3mA being used by the regulator.

A very simple circuit to construct and probably capable of handling most (if not all) of your strings (up to the limit of the convertor - 600mA). I'd attach the strings, adding one at a time, and see what happens. Note that the LM317 will get warmer as you add load and might need a heat sink.

And, given the usage, probably wouldn't need the 20uF cap. If a Vo of 1.25Vdc is inadequate, it can be raised by adjusting the circuit.

 

[Jagsy]

Welcome, Jagsy, to ETO!

Seems to me that a simple voltage regulator circuit, using the output of the convertor you listed, would suffice.

For instance:
View attachment 88624
In a SIM it only supplies the current that the RLoad dictates (the resistance of the LED strings) with about 1.3mA being used by the regulator.

A very simple circuit to construct and probably capable of handling most (if not all) of your strings (up to the limit of the convertor - 600mA). I'd attach the strings, adding one at a time, and see what happens. Note that the LM317 will get warmer as you add load and might need a heat sink.

And, given the usage, probably wouldn't need the 20uF cap. If a Vo of 1.25Vdc is inadequate, it can be raised by adjusting the circuit.

hi cowboybob, thanks for your reply, so what your saying is I can get the Supply Transformer AC 85V-265V to DC 3V-5V 3W I linked to in my 1st post then attach the output of that to the input of an lm317...and then the string leds to the output of the lm317..... if thats correct will this prebuilt lm317 board be ok to get **broken link removed** .. I can then adjust the voltage of that to what I need

 

[audioguru]

If you use the string that has 200 LEDs and it is powered for 8 hours from a single 1200mAh battery then each string of LEDs gets only 1200mAh/8 hours= 150mA at 1.2V and gets only (1.2V/3.5V) x 150mA= 51.4mA at the LED voltage of 3.5V. Then each LED gets only 51.4mA/200= 0.26mA which is extremely dim. The voltage stepup circuit has some losses so each LED will get maybe only 0.2mA.

The ebay people know nothing about electronics. Their "transformer" is actually a converter.

 

[Jagsy]

hi would it be possible to just buy a 3v wall power adapter and wire that direct to the end of the led string, would that work? if it did I would just buy an adapter for each string and led globe and lantern ....adapters are pretty cheap

 

[audioguru]

The solar fairy LEDs are not powered from 3V. Instead they are powered from a voltage stepup and regulated current circuit that is powered from a solar-charged single 1.2V battery cell. The regulated current lights the LEDs properly at whatever voltage they need.
If you apply a 3VDC power supply then either the LEDs will not light, light dimly or burn out.

 

[Jagsy]

well how about getting a 3v or 12v wall power adapter then connecting that to a 12 or 3v to 1.2v stepdown module and connecting that to the battery terminals... so instead of getting power from the battery it will get the power from the mains but the circuit board inside will still be doing the same job...would that work?

 

[cowboybob]

hi cowboybob, thanks for your reply, so what your saying is I can get the Supply Transformer AC 85V-265V to DC 3V-5V 3W I linked to in my 1st post then attach the output of that to the input of an lm317...and then the string leds to the output of the lm317..... if thats correct will this prebuilt lm317 board be ok to get **broken link removed** .. I can then adjust the voltage of that to what I need

That would work.

And from your post#13, that also would work with a wall wart.

Just so long as you supply the LM317 based regulator PCB with an adequate minimum input voltage.

Adequate current from a single wall wart might be an issue, but starting with the lowest (1.25Vdc) voltage from the LM317 PCB and then raising the voltage slowly, you could observe the LED string(s) behavior.

The LM317 device is heat-sinked. It will get warmish as you add load(s).

Then add another string for a further comparison.

 

[audioguru]

An LM317 is a voltage regulator that you do not want for LEDs. But it can be connected differently as a current regulator to light LEDs.

 

[Jagsy]

ok..thanks guys.... this is what I have decided to do...... im going to buy this **broken link removed** which is a 12v 2amp power supply and then connect it to this **broken link removed** which will be set at 1.2v which can also be adjusted and then the only problem I have is do I bypass the solar panel circuit board and connect it straight to the led string or do I connect it the solar panel battery terminals ... I,d rather connect it straight to the led strings if that will be ok and put an on/off switch before the power adapter so I can manually turn lights on and off..... so can I connect straight to led strings so i can have manual on/off switch ?

 

[cowboybob]

An LM317 is a voltage regulator that you do not want for LEDs. But it can be connected differently as a current regulator to light LEDs.

True. But I get the impression the OP wants a ready made solution that will give him voltage level control.

So, in the interests of simplicity, Jagsy, you should put a 5W, 10Ω resistor (available from Radio Shack) in series with the output (either lead, + or - will do) of the regulator and the LED string. This should limit the current (as you adjust the voltage level) to acceptable limits without bleeding off too much voltage (to meet the minimum required voltage need(s) of LEDs).

I can't find any specs on your LEDs but my guess is that they are very low current devices (< 5mA), otherwise the miniscule solar panel provided could never generate the needed power to light them up.

And, no, I would not hook up your suggested circuit to the battery. Without knowing the battery composition, you run the risk of over charging it which could result in a fire.

An ON/OFF switch controlling the power source/regulator circuit would be fine.

 

[Jagsy]

True. But I get the impression the OP wants a ready made solution that will give him voltage level control.
So, in the interests of simplicity, Jagsy, you should put a 5W, 10Ω resistor (available from Radio Shack) in series with the output (either lead, + or - will do) of the regulator and the LED string. This should limit the current (as you adjust the voltage level) to acceptable limits without bleeding off too much voltage (to meet the minimum required voltage need(s) of LEDs).
I can't find any specs on your LEDs but my guess is that they are very low current devices (< 5mA), otherwise the miniscule solar panel provided could never generate the needed power to light them up.
And, no, I would not hook up your suggested circuit to the battery. Without knowing the battery composition, you run the risk of over charging it which could result in a fire.
An ON/OFF switch controlling the power source/regulator circuit would be fine.

what 2 core cable would you suggest.... I will have the 12v 2amp power adapter inside and then I will have to connect a cable to it and run it about 15 meteres where I will then connect that to the lm317 ( will be putting this in a waterproof housing and then from that the led strings will be connected.... so what cable would you suggest...would a 2core 1.5mm flex cable be ok and is the 5w 10 ohm resistor really needed