Electrical Circuit for DIY LED, need input

[Interestor]

Really not feel comfortable with any Vdc above 50

[mark0308]

Hi, another option is to get a switch mode power supply, there are 12VDC, 24VDC and 48VDC on the market, if you buy more unit, you could have the bargain power. A transformer with a rectifier may cause you $10 + $5 but you still have to include your labour cause. Switch mode power supply are more efficient and the price should be around $15 to $25 at Sim Lim Tower. Can check it at Sim Lim.
Best regards
Mark Tan

[limsteel]

Beauty of DIY is cheap with lots of elbow grease What's the point of spending more than 50% of a off-the-shelf unit? It more professionally done, both internal and aesthetically...

I can purchase a Computer PSU ranging from 300W to 1KW from SimLim Sq, but no fun! Aiya I can as well salvage working PSU from my dead computers! HOW COME I DIDN'T THINK OF THAT MOD abit should be able to support a few hundreds high power LED and yet comes with Overload, overheat, surge, etc protection!

Shall use 4pin Molex and 4pin 12V P4 Adapter

[sacy]

he Led tube light look very simple. but i still not sure are there any regulator hide at the back of the LED. Cause, if u telling me that it is using straight 240VAC power with a simple Rectifier to covert the VAC to VDC. it is dam scary man.

ya. Pc power supply is a good idea. u just need to short pin14 and pin15 to turn on the power supply.

[sacy]

normally a $30 pc power supply will have 3.3vdc at 15amp~20amp max for u to run as many parallel LED circuit as u like. and if u use up the 3.3vdc .. u still got +5vdc at 18amp~24amp max for u to use. ^^

[limsteel]

The shorting of the pin is a drag. I can easily whip a contact switch... But how to turn it on auto without manual intervention.

go old shop and see if I can find a AT PSU easier to connect if you ask me.

[sacy]

that easy. just short pin 14 and pin15 all the way. then use a timer will do.

AC socket <---> Timer <---->power supply

[limsteel]

You sure? Usually when PC hangs, we press the power button for 4 sec++ and the system will shut down. So effectively shorting 14 & 15 meaning the system will power on and then turn off in 4 to 5 sec?

OK tomorrow I go office try my PC I will hold on to the power button then turn on Power Source... If it turns on and stay on then problem solved...

But how come, you only suggested that I use the 3.3V and 5V connection.. there are so many 12V connection eg. 4pin power for IDE HDD, 4 Pin Power for FDD.

[sacy]

the 4sec thing is be cause it control by the motherboard. cause your power button are connect to motherboard. u can try just unplug all the molex connector from your pc. and make sure all power connector has being remove from the motherboard and device(hdd,cd/dvd rom..ect). then u short the pin 14 and 15 of the 20/24pin atx molex connector. right after u short both pin , u will see the fan from the power supply start running.

haha. 12v also can. but base on the 3.3v u can connect around 120 LED rating at 3.4v/100mA each in parallel. easy right

[Shadow]

he Led tube light look very simple. but i still not sure are there any regulator hide at the back of the LED. Cause, if u telling me that it is using straight 240VAC power with a simple Rectifier to covert the VAC to VDC. it is dam scary man.

ya. Pc power supply is a good idea. u just need to short pin14 and pin15 to turn on the power supply.

what so scary about? Your PL or T5 or MH also connected directly to 240V

[sacy]

haha. ya forgot. but AC got sine wave. 0V to 240 to 0V to -240V
DC straight wave all the way 240V that the killer

that just me only. not trying to mislead ppl ^^

[Shadow]

actually the killer is the curent. For example electro static discharge, althought it is more than 2000V but it won't kill you because very small current.

However I do agree that in this DIY case a bit more dangerous because it is close to water. without proper insulation 240V might cause hazard to the fish and you.

[sacy]

ya. shadow was right on current kills. Voltage shock u and make your muscle contractions .once your hand grad on to the item that shock u, u better pray hard that u can release your hand fast . before the current can pass thought your body to kills u. it only need around 90~100mA to stop your heart with open wound ... so don't play play!!! Voltage and current are evil brothers.. so that why got P=VI and I=V/R

think we a bit off topic

[limsteel]

Finally know the danger of using 240Vac direct covert to 240Vdc... Options available:

- Computer PSU (Few hundred watts)
Cheapest choice with enough power + safety and able to support many LED. and also support other peripherals like DC fan

Sacy Thanks for the tip... Should have known that PSU are not smart enough for the 4sec off thingy

- Laptop Charger or transformer adapters (usually < 60W)
Expensive and limited supported LEDs due to low wattage.

- Down light step down (240Vac to 12Vac) + Bridge + capacitor
Again the electrical circuit part a bit draggy.

Final verdict, Computer PSU is best suited for this application. For a little extra $, it offers power + safety.

[sacy]

u welcome. and remember to insulate all expose wire and solder point on your DIY item.
safety first ^^

[firethorn]

I was going on and on about electrical stuff but I shortened it somewhat. So here's my reply:

You'd be better off with a Huge step down transformer say 12v at 120VA (Should you have enough LEDs to require - in this case - 10 Amps), versus connected straight to the mains with, I assume, a simple resistor to limit the typical 13Amps available on the household mains.

This would also have the added benefit of decoupling the circuit from the mains which is essential in almost every circuit, especially for safety and the electrical noise you will get if you don't decouple the circuit.

From there you can do your ac-dc rectification with regulation, filtering and smoothing (these last 3 are essential in my opinion, regardless of the use). However, it should still work fine without it. Your house lights flicker on and off about 60 times a second but you don't notice it. The same goes for your TV which 'flickers' around 30 times a second. These of course flicker dues to AC current but the effect is similar with unsmoothed DC.

LEDs are diodes so you will need DC no matter what which brings you back again to an SMPS or a transformer. I once considered the possibility of running LEDs ala a rectifying circuit so unless you want to try this out...

At the end of the day, it would be cheaper for you to just buy it from a store, simply because they have something called mass production so unless there is a feature that you simply must have and is not available in stores, it is not cost-justifiable although it will definitely be fun to do.

[tawauboy]

some info;
a) 240vac bridge rectified gives you ~340vdc peak, not 240vdc. 240vac is a root-mean-square (rms) value.
b) 240vdc is no safer than 240vac
c) >50vdc is considered a high voltage. treat it with care.
d) led is a current driven device so you control the current through it. for a voltage increase of 0.1~0.2v, the led current can increase by 2x.
e) proper led current control requires a series resistor for each string of leds.
f) typical leds (<5mm) have a typical max current rating of 20~100ma. for higher power rating, you'll usually need surface mount devices (smd).

[limsteel]

some info;
a) 240vac bridge rectified gives you ~340vdc peak, not 240vdc. 240vac is a root-mean-square (rms) value.
b) 240vdc is no safer than 240vac
c) >50vdc is considered a high voltage. treat it with care.
d) led is a current driven device so you control the current through it. for a voltage increase of 0.1~0.2v, the led current can increase by 2x.
e) proper led current control requires a series resistor for each string of leds.
f) typical leds (<5mm) have a typical max current rating of 20~100ma. for higher power rating, you'll usually need surface mount devices (smd).

340VDC peak... would have shorten the life of the whole string of LED.

[Shadow]

not really just put more LED in series

[limsteel]

Yes, that it if I already know the peak is 340V...

Anyway, I got 10 pieces of 10 3W LED from ebay... 50&#37; cheaper then SimLim Tower. 3W White LED cost $10each...

Intensity Type: 110~120Lm
Viewing Angle: 120&#176;
Forward Voltage : 3.3V~3.5V
Forward Current: 700mA
Colour temperature : 6000k