10 Watt leds

[BloodyDuck]

I want to build a light for fishing. It will require the 12v 10 watt led from EBay. I can not understand why I put 2 in series and I can hardly see they are energized. HOWEVER If I put just one to my 12 volt car battery it is BLINDING and THEY ARE HOT.

So to recap. 7 total 10Watt led Generic from China. No writing or model number on them. I want to wire them so that I can use them at night for fishing. What do I need to build so that they work?

 

[crutschow]

Do you have a specs on them?

They obviously work. How is it that you want them to work?

10W LEDs will require mounting on a heat sink to avoid overheating.

 

[dougy83]

Can you show which LED you are using?

I just did a search on Ebay and the first six 10W LEDs I saw had a forward voltage of 9-12V; this is because there are multiple lower power LEDs in the 10W LED assembly, in series and parallel connection. They will get very hot as well - you'll need to heatsink them, and potentially use a fan to help cool the heatsink.

If they have a forward voltage of 9V, then you could use a resistor for each LED to set the current to 1A and then wire the seven LED/resistor sets in parallel to run from the 12V source. This will be wasting 21W in the resistors.

If the forward voltage is higher (e.g. 12V), you may wish to build a boost flyback converter, regulating the current and driving all LEDs in series. This will be more efficient.

 

[BloodyDuck]

I wanted to use them under water. I have a Clear polyurethane that is water proof that I was/will put on them to waterproof them.

 

[BloodyDuck]

**broken link removed**

This is the ones I purchased.

 

[audioguru]

Their rears are supposed to be bolted to an aluminum heatsink.
If you insulate the heatsink with polyurethane then it must be larger.

You must guess about the size of the heatsink.

 

[crutschow]

The LEDs need to be on a heat sink and you need to limit their current to below the maximum allowed as dougy83 stated.

 

[BloodyDuck]

When I reduce the amp and I coat them in urethane and I only use them when they are submersed in the water wouldn't that provide all the cooling they would need?

 

[audioguru]

Name-brand LEDs have a detailed datasheet that has details about cooling them in air, not in water.
Your cheap Chinese LEDs have no datasheet and no details about anything.

How will you measure their temperature?
How will you reduce the current?

 

[BloodyDuck]

Reducing the current is what I wanted help with. I didn't know if there was a diagram of a board that I could build.

 

[dougy83]

When I reduce the amp and I coat them in urethane and I only use them when they are submersed in the water wouldn't that provide all the cooling they would need?

I'm not sure of the thermal conductivity of polyurethane but its likely not particularly good. You would do better to mount the LEDs on a piece of thermally conductive material, e.g. metal, which is exposed to the water. That should cool it sufficiently that whatever coating you use on the emitting side of the LEDs doesn't crack or melt or burn.

Reducing the current is what I wanted help with. I didn't know if there was a diagram of a board that I could build.

Methods to limit the current were addressed in post #3. If you wish to go the resistor route, it would be safest to assume the minimum specified forward voltage of the LEDs is the actual value.

 

[audioguru]

You can reduce the current in an LED simply by adding a resistor in series with it. The resistor is called A Current-Limiting Resistor.
Then the resistor gets hot.

You can make a complicated circuit that pulses the LED on and off at a high frequency called Pulse-Width Modulation.
A wide pulse produces a high average current and a narrow pulse produces a low average current. The transistor or Mosfet that switches on and off gets only a little warm.

 

[audioguru]

If you wish to go the resistor route, it would be safest to assume the minimum specified forward voltage of the LEDs is the actual value.

But the cheap Chinese LEDs do not have any spec's. They could be measured instead.

 

[dougy83]

But the cheap Chinese LEDs do not have any spec's. They could be measured instead.

forward voltage values are provided on the page he linked to previously.

 

[audioguru]

forward voltage values are provided on the page he linked to previously.

No.
A forward voltage spec is ALWAYS listed with a certain current. They don't say anything about current.
Maybe at 9V they barely light and at 12V they get so hot they burn out in a couple of minutes.

 

[BloodyDuck]

Thank You for all the help and advice. I am going to 86 these lights and start over.

 

[dougy83]

Thank You for all the help and advice. I am going to 86 these lights and start over.

That seems a bit extreme. If you want the actual forward voltage measurement at a certain current, then measure it!