# AC external Xmas lights

#### pmslater

Joined Oct 25, 2020
12
Ok sorry for posing here but can't find the answer. (Which I think is quite simple in theory,)

Im powering some LED fairy lights off a car battery. Boosted to 31v.
But the lights at AC and only half light up.

How can I make a simple inverter (without stepping up the voltage creating safety issues)

I ideally off there shelf, I know little but very handy so know maybe I will have to make something using some Mofets.

Help very much appreciated.

#### ericgibbs

Joined Jan 29, 2010
16,747
hi pm,
Welcome to AAC.
Is it possible to split the lights into two strands, run the two in parallel.
Make sure the split divides the load equally.
E

#### ronsimpson

Joined Oct 7, 2019
2,515
Are the lights lighting/not-lighting by odd/even 1,3,5,7,9 work and 2,4,6,8,10 not working?
OR
Are lights 1-15 working and 16-30 not working?

#### pmslater

Joined Oct 25, 2020
12
No, they are two strands, they are ac to make them flash by adjusting the frequency of the polarity +- or -+ I don't care if they flash tbh.

#### djsfantasi

Joined Apr 11, 2010
8,652
How are the lights normally powered? Fairy lights that I am familiar with run off a few olts DC. A coin cell battery or two is used.

If you connect the string to the normal source of power, do they work? 31V seems unusual...
UPDATE: Your last post clears some of my questions up.

Except how are they normally powered?

#### Dodgydave

Joined Jun 22, 2012
10,583
Can you post a picture of the original PSU ?

#### pmslater

Joined Oct 25, 2020
12
Normally mains adaptor 100/240 AC to 30v Ac 0.12a. (ZH-K009C-0300120-S-03)
Power pack claims it a DC output but IT IS NOT it's AC.

They have 8 pre-set patterns, wired in 2 channels each light in turn on the opposite polarity.

Most modern LED XMAS lights are wired this way, cheap and effective. Just not ideal for be wiring them up in the park. I have previously powered via a telegraph pole arrangement but its only time till the council or management company come knocking as my cables cross the road on the estate.

#### pmslater

Joined Oct 25, 2020
12

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#### pmslater

Joined Oct 25, 2020
12
More pics

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#### Dodgydave

Joined Jun 22, 2012
10,583
That's a DC output, but it will be pwm and reversing to make the alternating LEDs work.

If you want to just put the LEDs on without any flashing, just put them on a 15V AC supply .

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#### pmslater

Joined Oct 25, 2020
12
So how do I get from 12 or 24v DC to AC.

Its the AC I don't know how to do

How do I make or buy the inverter that I need??

Thanks

That's a DC output, but it will be pwm and reversing to make the alternating LEDs work.

If you want to just put the LEDs on without any flashing, just put them on a 30V AC supply .

#### Dodgydave

Joined Jun 22, 2012
10,583
Like I said, the LEDs are wired back to back in series, so one half work one way +/-, and the other half work the other way -/+, so DC won't be any good as only one set will work, you need AC .

#### pmslater

Joined Oct 25, 2020
12

#### sghioto

Joined Dec 31, 2017
3,652
So is the idea I assume is to use the driver to clockwise and then anti clockwise repeatedly using the code?
Correct. I'm showing a stand alone driver using the LM555 but the Arduino is perfectly fine and you won't have to construct anything. You would be basically switching the polarity of the motor driver at the same frequency as the AC line voltage, 50 or 60Hz.

#### Dodgydave

Joined Jun 22, 2012
10,583
Why not use a 15V Transformer straight off the mains.?

#### sghioto

Joined Dec 31, 2017
3,652
Why not use a 15V Transformer straight off the mains.?
Apparently the lights run off 30 vac. and the TS is using a 12 volt battery for power. So a small DC to AC converter with a step down transformer to 30 volts should work.
More expensive solution but less work.

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#### Tron Jockey

Joined May 3, 2020
19
Ok sorry for posing here but can't find the answer. (Which I think is quite simple in theory,)

Im powering some LED fairy lights off a car battery. Boosted to 31v.
But the lights at AC and only half light up.

How can I make a simple inverter (without stepping up the voltage creating safety issues)

I ideally off there shelf, I know little but very handy so know maybe I will have to make something using some Mofets.

Help very much appreciated.
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https://www.amazon.com/15v-plug-transformer-110v-input/dp/B0041X3D5Q