converting solar to mains

[audioguru]

1) Connect the 0V of the LM317 circuit to the cathodes of the two LEDs.
2) Connect one end of the new 120 ohm resistor to the output of the LM317 and connect the other end of the resistor to the anodes of the two LEDs.
We do not know if the LEDs in each lantern match so use a separate 120 ohm resistor for each stripped lantern.

 

[Jagsy]

is this how you mean audioguru...and do I also need to take the old resistor out or do I just leave it there ( I googled 0v to see what it meant and nothing came up so im assuming 0v means the negative output because anodes ( long leg) go to positive and cathodes ( short leg ) go to negative ) am I right on that?

 

[audioguru]

The LM317 has a positive output voltage. The "ground" is 0V and is common to its input and to its output. It does not have a negative output.

You show the 120 ohm resistor correctly in series with one LED but your lantern has two LEDs.
Disconnect the wires to the LED circuit board and make the two cuts I showed then the existing 82 ohm resistor connects to nothing.

 

[Jagsy]

ok I have a new diagram with 2 ways ..number 1 and number 2...which is the correct way of doing it or are they both correct and I can do it either way

 

[audioguru]

Now you show two separate LEDs. Don't you want to have them on their circuit board where they are already connected together?
In post #39 I showed that you need to make two cuts on the board to disconnect the "blob" and I showed the anodes and cathodes of the LEDs. Then connect one end of the 120 ohm resistor to the output of the LM317 and connect its other end to one of the anodes solder joints, then connect 0V of the LM317 to one of the cathodes solder joints.

 

[Jagsy]

thanks audio, my resistors are being delivered on Monday so I,ll post back then

 

[audioguru]

I have many solar garden lights. My electrical utility company was giving them away for free so I asked if I could take two. The clerk said take as many as you want, we have thousands. I took ten.

I replaced the cheap Chinese Ni-Cad cells in them (they rusted away) with modern American Ni-MH cells that do not rust. I replaced the cheap Chinese LEDs that also rusted away with American ones that do not rust. In summer they glow brightly all night long.

But now it is winter and the sun is up for only a short time and is low in the sky so my solar garden lights are lit for only a couple of hours each evening following a sunny day.

 

[Jagsy]

yeah that's the same with mine audioguru, I live in the north of England in manchester and the solars just don't charge much in the autumn,winter time... summertimes ok but summer doesn't last very long that's why I thought I,d convert them to low voltage mains

 

[Jagsy]

hi audioguru, the resistors came this morning, I did as you said and it worked great.... am I ok connecting all 4 lanterns to one lm317 board, thanks

 

[Jagsy]

Hi audioguru... the globes are called lucia everbright globes https://www.bltdirect.com/everbrigh...ts?adcid=pla&gclid=CKKpks6Mt8ECFSXHtAodcwkAzw
I have done a diagram to show you how they connect together, I have 2 sets of these so there are 8 globes altogether
I also have another 4 globes that have there own solar panel each, I worked out that I needed a 220 ohm resistor n each of those globes from the 7.5v input and it worked

 

[audioguru]

I assume that each globe has a single white LED inside? Then its voltage is about 3.2V and the 120 ohm resistor will have a voltage of 7.5V - 3.2V= 4.3V across the resistor. The current is 4.3V/220 ohms= 19.5mA which is fine.
You could also make a small circuit board at the LM317 with a 220 ohm resistor feeding each globe.

 

[Jagsy]

how many globes could I connect to one lm317... is there a limit? and if there is a limit how do you find out what the limit is from a 7.5v output

 

[audioguru]

how many globes could I connect to one lm317... is there a limit? and if there is a limit how do you find out what the limit is from a 7.5v output

If you cool it with a heatsink, one LM317 can supply up to 1.5A but many go up to 2.2A. It is shown on its datasheet. If it gets too hot then it turns off, cools then turns on again. It is bad to let it repeat heating and cooling due to thermal fatigue.

With no heatsink in the TO-220 package an LM317 can heat up to 1.9W when it will be at its maximum allowed temperature before it turns off.
You will use a 12V supply (but a 9V supply will heat it less) and its output is 7.5V so it has 12V - 7.5V= 4.5V across it. Then its maximum current is 1.9W/4.5V= 422mA. Each globe will use about 19.5mA so one LM317 powered from 12V can power 422mA/19.5mA= 21 globes without a heatsink. With a big heatsink it can power about 193 globes when powered from 12V.

 

[Jagsy]

just another quick question audioguru.... when I run the cable in my garden can I power all the boards from 1 x 12v power supply like in diagram number 1 or does it have to be from 4 x 12v power supplies with 4 cables like diagram number 2...diagram pictures are below

 

[audioguru]

I cannot remember the rated current from your 12V power supply and I cannot remember the total current all your LEDs will use. Maybe only one transformer and only one LM317 will power everything.

 

[Jagsy]

so to work out I total all the ma from every led string and leds in the globes and laterns and total it all up.... the 12v dc adapter is rated at 2amps and the lm317 can handle 2 amps aswell........ so if it all totals under 2 amps the lm317 and 12v 2amp dc adapter can handle everything...am I right?
so I total 3 led strings at 150ma x3 =450 ma , lanterns 40ma x 4= 160ma, globes 20ma x 8 = 160ma, and another 4 globes I,ll be adding soon at 20ma x 4 =80ma..full total = 850ma in total, so I,ll be ok to use 1 x 12v 2amp power adapter and 1 cable to supply all the lm317 boards like in diagram 1 or even use just 1 board if I want to as the board is rated at 2amps as well and it has a heatsink on it....am I right?

 

[audioguru]

Yes you can use one 12VDC/2A adapter, one LM317 voltage regulator and some resistors.

 

[Jagsy]

thanks for helping me with everything audioguru, you`ve been brilliant

 

[cowboybob]

Post 10:

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.

Post 17:

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.

Post 58:

Yes you can use one 12VDC/2A adapter, one LM317 voltage regulator and some resistors.

Thank you, ag, for the confirmation.

CBB

 

[audioguru]

Cowboybob,
An LM317 can be connected as a current regulator to light ONE LED product like a string of fairy lights, globe or a lantern. But Jagsy has many different LED products he wants to light, each having different LEDs and different currents.
Therefore we decided to regulate the voltage to about 7.5V and use a separate series resistor to determine the current for each product.