Submerged LED wall mounted light

[nippy161056]

Just want to ask if anyone knows where I can get a circuit to replace 1 x 32v 140w halogen wall-mounted pool light with a bank of 25 ultra-bright white LEDs.
I believe you can by them, however I'd like to have a go at making it. Thanks

 

[BioniC187]

Can you give a link to the LED's you were thinking of purchasing?

 

[nippy161056]

Thanks for your quick reply.
I have purchased 50 of the LEDs featured here **broken link removed**

 

[dougy83]

Can you design your own circuit with a description of the parts needed, or would you prefer a schematic? A simple method is to use a bridge rectifier followed by a 470uF capacitor, feeding two strings of 12 LEDs (that's 24 total, not 25, I realise), with a 220-ohm resistor in series with each string. This will give around 14mA through the LEDs if the transformer output is actually close to 32VAC. You can stress out your LEDs if the transformer output voltage is actually higher than specified. You can put a constant current controller on each string (using a couple of transistors) to remove this possibility.

 

[nippy161056]

I am a complete newbie to this sort of thing.
I was hoping to build something similar to this

Except mine will run from existing Stroud transformer and existing light.
The more info you can provide, the more likely it is that I will be able to make it.
So anything you can provide will help. Thanks

 

[dougy83]

Here's the schematic. Sorry for the quality, but I'm moving house and all my stuff is somewhere else. The bridge rectifier and capacitor are required because (I assume) your transformer provides 32 VAC; if it's not AC, then please say so. There are two strings of 12 LEDs, which simply means that you can omit the centre LED in your lamp array.

There should be around 44V on the capacitor, and around 14mA flowing through each LED.

 

[nippy161056]

Did you upload the image?
I cannot see an image.
It is AC

 

[dougy83]

Sorry, image is there now

 

[nippy161056]

Hi again. Just wondering if you could please explain / show me
1. how the transistors would be attached ?
2. the number for the trannies ?
3. what wattage for the resistors ?
4. what are constant current LED driver IC? (same as the tannies?)

 

[dougy83]

In the video you provided, they only use resistors to limit the current; that is what the above drawing is based on. The resistors can be 1/4W, though I'm not sure of the heat conductivity of your potting compound.

If you do want to use a constant current driver instead of a single resistor, you can use the circuit from **broken link removed** Note that the unconnected end of the 4k7 resistor can be connected to the collector of the upper BC547. You can use one of these circuits for each string of LEDs.