UltraSound and...Resistors!!!

[dj2rbo]

I was pondering about using a 2.5 US with a red lux 3 but intead of using 6aaa batteries maybe instead using 2 3.7 li-ions. Can you do this by using a resistor going to the LED? I tried to find the answer but couldnt find it. Thanks for ant future inputs......

[Shadar Al'Niende]

if you are using a US 2.5 it will regulate the current and voltage for you when running the LED off the board.

You realize they are no longer in production though right? (US 2.5's)

[dj2rbo]

You dint even read the whole thing. You fast drawing typer!!!!

[Shadar Al'Niende]

I did i swear! :rolleyes:

[Roy's Blues]

In the US 2.5 product listing it has instructions for this situation.

Battery input voltage:
Maximum for board = 9.6V
Minimum/Maximum for Luxeon 3, K2, P4 = 4.5V / 7.2V (6V recommended)
Minimum/Maximum for Luxeon 3,P4 Red/Amber = 4.8V / 6.0V
Minimum for Luxeon 5 = 7.2V
IMPORTANT! (be sure to use the correct voltage/power with corresponding LED type)

6 AAA Nimh = 7.2v
6 AAA Alkaline = 9.0v

Using higher than the recommended input voltage will fry your board.

Use a 4AAA or 4 AA pack with Reds/Ambers

[Eco]

In the US 2.5 product listing it has instructions for this situation.

Battery input voltage:
Maximum for board = 9.6V
Minimum/Maximum for Luxeon 3, K2, P4 = 4.5V / 7.2V (6V recommended)
Minimum/Maximum for Luxeon 3,P4 Red/Amber = 4.8V / 6.0V
Minimum for Luxeon 5 = 7.2V
IMPORTANT! (be sure to use the correct voltage/power with corresponding LED type)

6 AAA Nimh = 7.2v
6 AAA Alkaline = 9.0v

Using higher than the recommended input voltage will fry your board.

Use a 4AAA or 4 AA pack with Reds/Ambers
You also did not read his post fully.
He wants to know if he can us a 7.4v Li-ion pack with a Lux III if he adds a resistor to the Lux III end to increase the voltage load and therefore reduce the strain on the board.


I've been kicking the idea around, myself, and can only see one problem: Using a resistor will neck increase your voltage draw from the board, but also neck down your current. For a Red Lux III, I don't think you'll get anywhere near the 1400mA that the specs call for. I don't see why it wouldn't work with something like a Rebel, that uses 700ma instead. The necked down current of the resistor will limit your current, but a Rebel doesn't use much current as is.
A brief calculation balancing the wattages of the board and LED will likely be a good first step towards your goal.

P=V*I
PBattery In=PLED+PResistor
Which would be...
(7.4*.9ma) = (2.9*.7) + PResistor
(6.66W) = (2.03W) + PResistor
(6.66W)-(2.03W) = PResistor
(4.63W) = PResistor
Resistors round up, so a 5W resistor. However, given that the board draws some voltage itself, I would recommend having a 3W resistor handy for testing purposes.

Using a simple http://led.linear1.org/led.wiz]LED Resistor calculator, (http://led.linear1.org/led.wiz) I calculated you'll need a 6.8 Ohm, 5W resistor.
I am by no means an expert at algebra, and I am probably incorrect in my numbers, so please do not quote me as accurate. I was merely demonstrating what I believe to be the correct process. The process for calculating the power of the resistor I am quite sure is correct, however I cannot say how the board will react to the resistor. I would strongly suggest getting a second opinion here.

[Roy's Blues]

My point was it's ridiculous to try to push the board that way and there is no point in doing it.

I've wired up over 30 US 2.5's. in various combinations
If anyone wants to discard the advice I give, it's their choice.
Just don't come crying to me when your board is toast.

[Novastar]

Listen to Roys Blues... you all should.

If anyone is planning to do:

Batteries --> US Board --> Resistor --> LED
... ... ... this =
BAD IDEA... in general, do ~NOT~ do this.

Especially if you're going to feed the board way more voltage than the LED needs (read: you have an LED that "wants" ~3.7v... you are trying for a battery solution of 7.2v or > )

Also of note... the US boards do not regulate current in the same fashion that the Crystal Focus boards do. The US boards (basically) burn off the excess voltage as heat. Which is why the US boards can physically get very hot if you're "excessive" with the battery solution. CF boards don't work this way--they utilize a decent portion of "excess" voltage (to a certain extent, within REASON) as current later on (less burnt off/wasted).

However...

If you wish to use ~7.2v... but yet you are heck-bent on using a Luxeon III Red (~2.95v fwd)... ok... so--use the correct diode or voltage regulator...

...BEFORE going to the board. As in:

Batteries (~7.2v or > ) --> 6v regulator? 5v reg? Whatever--the right diode... --> NOW the US board --> LED

That will still be pathetic and goofy (as you'll waste even MORE precious battery life/current/voltage/power as heat)... but... whatever. You could do it.

Oy... :rolleyes:

[Crystal Chambers]

...BEFORE going to the board. As in:

Batteries (~7.2v or > ) --> 6v regulator? 5v reg? Whatever--the right diode... --> NOW the US board --> LED



I've been considering/wondering about this myself. Thinking of saving space as apposed to 4AA or AAA. Though I do believe the question was with the resister in the wrong spot.

[Rhyen Skytracker]

It is just crazy to spend all the money for a US 2.5 that has a LED driver built into the board and has a setting for the Lux III red and then use a resistor for the LED. You would lose your blade lock up and flicker effect. Plus 2 Li-Ions is over the Max voltage input for the Lux III red setting. Just use 4 AA or AAA NiMH and you won't have any problems. If you use the AA NiMH you will get 2300 mAh which will increase your run time dramatically.

[FenderBender]

Whats so space saving about two 14500's? 4 aaa NiMhs soldered into a pack really doesn't take up any more space, and will not create these kinds of uneccessary quandries. It is silly to want to use resistors and voltage regulators in conjunction with a board that regulates voltage and current, even if it does a poor job of it:D

[Crystal Chambers]

A board will fit on top of 2AA size batteries but not 4AAA. Unless I'm missing something about voltage regulators like size/space( I don't know anything about them yet) then it seems it could save a lot of space.

Maybe the voltage regulator would fit in a choke but the US 2.5 and wires are too crammed for that space so they need to be mounted on top of the battery pack in the larger ID area.

[FenderBender]

Custom 4xaaa pack and US 2.5 have been fit into a 4" MHS section by yours truly;)

[Rhyen Skytracker]

A board will fit on top of a 4 AA NiMH custom batt pack with a little room to spare. By soldering your own 4 AA NiMH pack and putting heat shrink over them in a 2 x 2 configuration you can put a sound card on top very easily. I do that all the time. And with the 4 AA NiMH you get 4.8 Volts and 2300 mAh. Here is the type of set up I am talking about.

Batt Batt
Batt Batt

[Crystal Chambers]

A board will fit on top of a 4 AA NiMH custom batt pack with a little room to spare. By soldering your own 4 AA NiMH pack and putting heat shrink over them in a 2 x 2 configuration you can put a sound card on top very easily. I do that all the time. And with the 4 AA NiMH you get 4.8 Volts and 2300 mAh. Here is the type of set up I am talking about.

Batt Batt
Batt Batt

You can do this with a battery holder too.

Ideally I need to fit batteries, board and speaker in 4 inches or even a bit less would better...pushing a bit for a noob.

[Rhyen Skytracker]

I haven't tried 4 AA NiMH in a batt holder. Would a card still fit on top of the batt holder? That is why I make my own batt packs, you have a whole lot more room with out the batt holder.

[Crystal Chambers]

yep! 4AA batteries in holder, the US 2.5 on top inside a film container with room underneath for wire. For me it was too long for a mid-hilt choke with recharge port in a lit pommel and reverse speaker at the choke.

Without the recharge port and lit pommel it would've been fine.

[Shadar Al'Niende]

not a lux V....duh.... :oops:

[thejedilestat]

i as just going to say make your own 4AAA bat pack but fender got to it b4 me... so ya i was going to do it myself cuz the AA from my bat pack will pop out when im useing the saber

[Rhyen Skytracker]

I was talking about putting the card on top of the battery pack so the only space you take up long wise in the hilt is the length of the battery pack.


Card
Batt Batt
Batt Batt

Like that. You save lots of room doing it that way.

for a lux V config use 6 NiMH batts like this http://saberconcepts.50.forumer.com/viewtopic.php?f=3&t=107 The card will go on top of the 2 batteries like post 2 in this thread
http://saberconcepts.50.forumer.com/viewtopic.php?f=3&t=103

[Eco]

Okay. Ya'll beat my pathetic math with logic. :D

Rhyen, would you say that a four AAA NiMH pack would work with an MR board on top?

[Rhyen Skytracker]

You should get around 1 hour run time if you use 4 AAA 1000 mAh NiMHs. (If you use a 1000mA LED) The card fits on top of those easily.