Wiring BIG W LED's ?

[piesrule58]

Hi guys,

Below is a picture of how I understand the Big W Led's should be wired up using a big 24v AC transformer. Am I right? Do I have to use the 180 Ohm resistors? If not, could someone please correct me.

Cheers, Terry

[polar bear]

looks good to me , will you be dimming these?
i suspect you will need a rectifier for the DC ???

[fj]

is that wiring something that is specific to the BigW lights or is that all LED's in general?

i want to get some LED's and throw away the transformer and controller that come with them and hook them up directly to the SSR's running at 24VAC, which is what most lights here in AUS run at with the supplied transformer. is wiring in that resistor something that i would have to consider as well?

[piesrule58]

looks good to me , will you be dimming these?
i suspect you will need a rectifier for the DC ???

Yes, I will be dimming these. I am not sure what you mean (rectifier for the DC ???) They will be running off 24v AC.

[aussiephil]

Hi guys,

Below is a picture of how I understand the Big W Led's should be wired up using a big 24v AC transformer. Am I right? Do I have to use the 180 Ohm resistors? If not, could someone please correct me.

Cheers, Terry

Terry

The resistor value will need to be calculated for each of the colours.

The actual voltage output of the transfprmer will need to be taken into account as they are usually higher than the nominal rating, ESPECIALLY under light loads.

For the Big W Leds refer to http://doityourselfchristmas.com/forums/showpost.php?p=94315&postcount=35 for my measurements on all colours except the warm white.

For AC the peak voltage needs to be taken into account.
24v = 33.9v Peak
26v = 36.7v Peak, probably the most likely value 300w Toroids though i haven't measure one for a while
28v = 39.6v Peak, typical of the voltage out for smaller transformers with a 24v rating.


Example
RED set based on measurements in other post.

29.6v forward voltage for 20mA
10v need to be dropped across a resistor from the peak of 39.6v (28v RMS)
= 500 ohm resistor

or
4v need to drop across a resistor from peak of 33.9 (24v RMS)
= 200 ohm resistor

if a 200 ohm resistor is used based on expected 24v RMS voltage and 28v is actually supplied then the peak current would be 50mA, this value should be inside the peak rating for most LEDs.

All the other colours would use lower value resistors.

When used with AC most 24v nominal LED strings i have found to be fine without resistors just watch the actual transformer output voltage.

The pain of taking into account all the voltage calcs for AC was one of the driving forces for switching to DC.
DC is just so much easier for low voltage lighting especially LED's.

Cheers
Aussiephil

[David_AVD]

The pain of taking into account all the voltage calcs for AC was one of the driving forces for switching to DC.
DC is just so much easier for low voltage lighting especially LED's.

Not to mention eliminating any chance of flickering caused by the half wave operation when used on straight 24Vac.

[piesrule58]

Thanks guys,

Firstly, I know next to nothing about electricity. So the above examples really only confuse me. What I need is (preferably a picture) a simple explanation of the easiest way for me to wire up the Red, Blue and Green Big-W Leds so I can run and dim them from a big adjustable variac ( 0 to 240v AC) transformer. A picture is worth a thousand words, especially for me.

Thanks, Terry

[polar bear]

if you could explain to me how to up load a drawing i could give you an example of what i did for mine, i used 240v leds from k mart no dimming but they certainly flashed ok

[piesrule58]

Hi Polar Bear,

To upload a drawing you have to click on "Go Advanced" at the bottom of the Quick Reply. Then click on the paper clip to attach a picture.

[Goldie]

Hi Piesrule58

the attached file is how l setup my Bridge rectifers, you can add a resistor, in there to, l just cut up some bread board, put the 24v to the connector soldered a socket in place and a connector to the other end, you need to cut the track between the socket, you can put a resistor between the bridge and connector also.

Hope this helps,

PS l'll get you a picture of one with the resistor on it tonight

[polar bear]

here's a wiring diagram of what to do ( very rough) but it should put you on the right track. you can buy from jaycar etc ready made rectifiers or buy some diodes and vero board and make your own look at Goldie's photo (very well done i recon) . Hope this helps

[Tabor]

To keep the parts count down and cost and time assembling.

You can place a bridge rectifier directly to the transformer and supply the triacs with a full wave rectified signal.

That way multiple SSR's can be supplied from one large bridge rectifier.

[polar bear]

not that i have tried it but do triacs switch dc?

To keep the parts count down and cost and time assembling.

You can place a bridge rectifier directly to the transformer and supply the triacs with a full wave rectified signal.

That way multiple SSR's can be supplied from one large bridge rectifier.

[Tabor]

It is not DC.

It just a fullwave rectified AC signal, which triacs can still work from.


I used this for my entire display this year.

[Goldie]

Hi Piesrule58

Took a little longer than l expected, attached are pic's of the bridge and resistor together, hope this helps, there is also a pic of the holder that you could use

[piesrule58]

Thanks guys for all the great info. I bought a rectifier and some resistors today so I will give it a try. One more question, I told the guy at Jaycar that I wanted to run 24 Big W 120ct strings from the one rectifier. He sold me the 12amp version. Is that OK?

[David_AVD]

I think each string draws ~ 250mA so that should be fine.

[slyfox04]

let us know how its goes piesrule, I might go that way myself.

[piesrule58]

I have connected up one string and it is working well.

[slyfox04]

How the bridge rectifier circuit look like for your piesrule58

Does it go
24VAC Transformer --> Rectifier --> SSRez

I'm assuming that's the way its being done by talk in the thread.

[smartalec]

hi all,
im using the Big W leds on my arch's using a simple 24v ac tranformer for testing, they all seem bright to me.
but they will be going on a 24v dc system later on.(i see them flickering with the ac.)

so do i need a bridge rectifier or diodes to enable dimming with these LED's?
i have'nt got a renard an dc ssr to try them on yet.

[slyfox04]

Good thread I got one of my SSRez's running full rectified AC. One thing I notice is:

The unloaded voltage is only 30V.
1 String no resistor: 28V
2 String no resistor: 26V
4 Strings w\470Ohm resistor: 24V

Something funky going on there? The voltage might keep dropping with more load? Or might flatten out on 24V I would of though the voltage would of been much higher.

I've got a 600V 50Amp bridge rectifier and 500VA 25VAC toro.. Could be resistance in the join somewhere will check that.

[David_AVD]

The transformer output will be slightly higher with no load.

Also the diode bridge will have lower losses when lightly loaded.

Are you trying to measure the rectified AC voltage? If so, I doubt you'll get sensible readings with most multimeters.

[slyfox04]

Yeah I'm trying to measure the rectified AC voltage. But I think its my multimeter reading wack, at one stage the low batt symbol pops up and it read 55V unloaded. And its a fairly cheap thing so I guess your right about not getting sensible readings.. Plus the ripple noise won't be helping

Also loving my setup for mounting SSRez's in a enclosure, makes testing pretty easy. Its a B&R Q10 power box I managed to get or $100 (retail $260+)

[smartalec]

sorry what does rectified AC voltage mean? or are they meening DC?

cause i thought rectified AC was unfiltered DC?
an unfiltered DC is a supply with no caps to filter it.

could someone help me here..

[slyfox04]

Well yeah its Unfiltered DC, I'm just calling it rectified AC because everyone else is haha. But yeah.

[smartalec]

phew, i thought my memory was going on me for a second..

it's hard when the whatsitmacollit connects to the thingymagig connected via some doflicky, that makes it work..