Ultrasound 2.5 questions.

[Invisas1979]

Ok guys, I need a bit of a hand with this one as I'm not sure if a couple of things are possible and what the implications of doing what is in my head will have on the board.

So.....

I have scavenged a US 2.5 out of my older saber, mainly because I have space issues in the saber which is in developement. (See Pic)



It also doesn't help that it has a Crystal Reveal Chamber which I want to have powered by a 1watt led.

So first question,

Can a 1 watt luxeon run off of the additional led pads on the board and if it can what would the battery drain implication be, would it be the same running a 1 watt led directly?

Which leads onto my second question

The batter solution I want to use is 2 x 3.7v Trustfires, which = 7v. If i used a 5W Lux, that would leave around 2-3v power being pumped into the board, creating a hot board, unless the 1w led was taking a peice of that.

Would a couple of volts extra be too much?

Could it work like this? My brain is saying it's wishful thinking, but some of you would know better.

[FenderBender]

First, the pads on a 2.5 are WEEEAAAAAKK! They only put out enough to light the weakest of accent LEDs. Second, a LUX V (if that is what you are using) is usually 6.8v+ so under a load the 7.4V pack will just cover it.

[Rhyen Skytracker]

Fender is correct (as usual ) and the US 2.5 needs more than 1/2 a volt and less than 1.5 volts of the LED forward voltage. So if you are using a Lux V it should be just enough. The LED pads on the US 2.5 will NOT be enough to power a 1 watt LED. You CAN use the LED pad to go to the base of a transistor and the batt + to the transistor emitter and the LED + to the transistor collector. (Use the correct resistor of course) Be sure to use a PNP transistor. The TIP42 should work great. If you don't want to use the transistor off of the LED pads just run the 1 Watt LED in parallel to the main LED. Again, be sure to use the correct resistor.

[Invisas1979]

First, the pads on a 2.5 are WEEEAAAAAKK! They only put out enough to light the weakest of accent LEDs. Second, a LUX V (if that is what you are using) is usually 6.8v+ so under a load the 7.4V pack will just cover it.

Ahh I didn't know the FV of a LUX 5 I assumed it would be similar to the Lux three, in so far as the FV of a Lux 3 is around 3v if that makes sence.

Good to know it 6.8, but does that means that when the batteries get low the board will cut out?

If you don't want to use the transistor off of the LED pads just run the 1 Watt LED in parallel to the main LED. Again, be sure to use the correct resistor.

Ok so should I run the leds in parallel would that be off of the board, I'm assuming that's what you mean. And we resistor the lower watt led to aviod blowing it.

Because current is current it will flow identically through the wires to the leds at the same power so I'd just need the difference in the FV and the leds FV limit. Right?

[Rhyen Skytracker]

Yes, run the Main LED and the CC LED in parallel and resistor the CC LED. Since the US 2.5 puts out 6.8V to the LED output (for a Lux V) then you would use the LED resistance formula to calculate the size resistor you need. In order to do that you will need the Vf and current of the 1 W LED. The formula is as follows: (Vsource - Vforward) / LED current = resistance You will probably not find a resistor of the exact size you need but you can use the next size up of one that is available.

[Invisas1979]

Yes, run the Main LED and the CC LED in parallel and resistor the CC LED. Since the US 2.5 puts out 6.8V to the LED output (for a Lux V) then you would use the LED resistance formula to calculate the size resistor you need. In order to do that you will need the Vf and current of the 1 W LED. The formula is as follows: (Vsource - Vforward) / LED current = resistance You will probably not find a resistor of the exact size you need but you can use the next size up of one that is available.

Ok having looked at the Ohms law tutorial i think i'm with you.

I'll get the readings and figure it out.

Thanks for all your help guys

[Rhyen Skytracker]

No problem. Glad to help.