30v two wire "chasing" LED light string query

[diyer]

Hi guys,
I bought a 500 LED warm white light string off of an Aussie eBay seller, it was an acceptable price and I needed a warm white set.
On opening the package I was surprised to see that there is a fig 8 cable running to the lights, I checked the plug pack, a 30 volt switching supply and sure enough it has a multi function chaser built in.
How does this work with only a two wire feed? Maybe the LEDs are wired with opposite polarities, but how do all of the LEDs light at once?
Any ideas on ho I best bypass the MFC?

 

[diyer]

Re: 30v two wire "chasing" LED light string query

I just found the Lytworks from Bunnings thread, that answers a lot of questions

 

[David_AVD]

Yep, lights like that are basically useless to most people here.

 

[diyer]

Re: 30v two wire "chasing" LED light string query

Thanks David,

So for all the lights to be illuminated the transistors (T1 & T2) have to be switching very fast so that they appear to be steadily illuminated, correct?

 

[David_AVD]

The 2 wire light sets have 4 transistors used in a bridge configuration. They swap the polarity every few milliseconds. The dimming occurs within each of those half cycles.

The only easy way to have all of the LEDs appear to be on at the same time is to feed the string AC. You can't mod the MFC to do this.

 

[diyer]

Here is a possible solution for two wire LED strings to make then alternate, I am sure that you electronics wizards might be able to improve on this!

 

[David_AVD]

Yeah, a relay will work to use the every other LED alternately, but as you say it will only be one at a time.

 

[diyer]

Re: 30v two wire "chasing" LED light string query

Do you guy’s think that a circuit board to control two wire strings would be worthwhile?
With my (very) limited electronics knowledge I don’t think it would be that difficult, I imagine maybe three dimmer channels driving an IC switch selecting the output polarity with a flip-flop switching the ‘all on’ function? Possible?
I need someone with a lot more digital experience than I to suggest a circuit layout, I don’t mind taking the time to do a prototype and trying to make it work as a community project.
If required, shortening of the light string should be possible at the series join locations, but a reduced voltage would be required to run these.

 

[David_AVD]

I've actually already made a 2-wire driver board that accepts standard DC controller outputs.

It's all built so I should get around to testing it one day.

 

[diyer]

Re: 30v two wire "chasing" LED light string query

That's great David, I would be very interested in the outcome.

 

[diyer]

Re: 30v two wire "chasing" LED light string query

The controller failed tonight, the LEDs all work fine, so half of them are now illuminating from a 24v ac supply.
I'll open the controller up tomorrow to try to determine what has failed