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Electric Question

 
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padme9055 (Tabitha McCurdy)
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PostPosted: Mon Sep 02, 2013 4:20 am    Post subject: Electric Question Reply with quote

Forwarning: I'm a NOOB! I know just about nothing concerning electric stuff, other then the basic, basic stuff about postive and negative and that it flows.

That said: I'm wanting to make two lightsabers for my younger siblings. I want to use LED's from the custom saber shop. Not planning on sound at this time. So my question is: How much voltage (how many of what kind of battery) do I need to get say 4 hours of light from a LED from the custom saber shop?
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SuperFLY (Dave)



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PostPosted: Mon Sep 02, 2013 10:01 am    Post subject: Reply with quote

that depends on what you actually want to do?

do you just want light or both sound and light?

if you want sound and therefore will be after a petit crouton or crystal focus board for example then you'll need a proper 7.4v li-ion battery to power it.

i believe they have a 5v output (must admit when i built mine i just builit it from parts i knew worked together, didn't actually check the voltages.

if you just want light then a 3x or 4x aa/aaa battery pack will be fine; its more the amp-age you have to pay attention to. at 1500mah for a 3x battery pack you'd probably get about 40mins light depending on the luxeon. probably more if you used standard leds but obviously they won't be as bright.

you could get a buckpuck to control the resistance and be able to adjust the power usage (i've not used one personally.. just heard about them)

probably a good idea to pop over toe the tcss forum or saberforum.com and have a look on there. the people on there know a lot more than me Very Happy

the other decision you need to make is whether you use a luxeon or led string for the blade. personally, i'd always use a luxeon and poly blade just for the fact its so durable and a lot less work than an led string, plus if my luxeon (tri-star rebel BBW) anything to go by it's definitely bright!

I've built a couple of sabers.. one was a cheapy one from a hasbro plastic saber. i ripped out the soundboard, rewired it and added different LEDs for a bladeless custom saber. my second was a proper attempt and that's my ANH luke saber with petit crouton board with full luxeon and removable blade. very proud of that one.. looks and sounds great, but certainly not cheap compared to my eco-board (hasbro) derived one
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padme9055 (Tabitha McCurdy)
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PostPosted: Mon Sep 02, 2013 1:20 pm    Post subject: Reply with quote

I'm going for just light, so okay, the aa/aaa batteries should work.

I want to go with the poly-carb blade, because I want to be able to duel with my siblings with our blades Smile. Thank you Smile .
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Drazhar ()
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PostPosted: Tue Sep 03, 2013 12:16 pm    Post subject: Reply with quote

Short answer: it depends on the LED you're using

Long answer, it will serve as an equation reliant upon capacity of the battery/batteries you use, as well as the forward voltage and current draw of the LED in question.

Though this is really more of the domain of www.fx-sabers.com/forum in my humble opinion.
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darachim (Dane Braun)
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PostPosted: Tue Sep 03, 2013 2:21 pm    Post subject: Reply with quote

You should use this kit:

http://www.thecustomsabershop.com/Build-Your-Own-Seoul-P4-Electronics-Kit-P469.aspx

Thats the easiest way to build a light function in the saber. Wink
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rogue9607 (Nick)
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PostPosted: Thu Sep 05, 2013 9:57 pm    Post subject: Reply with quote

FX or TCSS forums will have a LOT of information on the subject, but the downside is that they have a LOT of information. Smile

I'll try to go a bit into the math, hopefully without going too far. A plumbing analogy for electricity from HowStuffWorks (http://science.howstuffworks.com/environmental/energy/question501.htm): "The voltage is equivalent to the water pressure, the current is equivalent to the flow rate, and the resistance is like the pipe size."

Your voltage will be determined by your battery or battery pack. Li-ion batteries are typically 3.7v, alkaline AA are 1.5v, and Ni-Mh rechargeable AA are 1.2v. Note that batteries will be slightly higher when fully charged and slightly lower when nearly depleted. Three rechargeable AA batteries will be 3.6v for example, when wired in series.

Battery capacities are measured in either amp hours (Ah) or milliamp hours (mAh) (1 Ah = 1000 mAh). Saying that a battery has a capacity of 1500 mAh means that it can supply one hour of current at 1500 mA, two hours of current at 750 mA, three hours of current at 500 mA, etc. Divide the capacity by either the required current or the desired run time to get the other value. These will be rough numbers, but should get you in the right ballpark.

How bright the LED is will generally be a function of the specific LED and how much current it's using. Too little current and the LED will not turn on. As the current increases, the LED will become brighter. Go with too much current and the LED will burn out. You can regulate the current by adding resistors to the circuit. TCSS has a calculator for resistor values on their site, though the math isn't too hard. Some LED/batteries will not need a resistor if the forward voltage (Vf) of the LED is close to the voltage of the battery pack. The difference between the forward voltage of the LED and the voltage of the battery pack is typically made up for as heat dissipated by resistors. But, the Vf of an LED isn't constant, so it can change depending on how much current is passing through.

Since I mention heat, I should note that for saber applications you'll want some kind of heat sink for the LED to dissipate additional heat.

To give an example that I'm familiar with, I recently put light in one of my hilts that I've been very happy with. The LED is a cheap RGB LED (http://dx.com/p/3w-led-emitter-on-star-multicolored-rgb-4530), it uses one 3100 mAh li-ion (3.7v) battery, one resistor for the red color, and a set of piano switches in the hilt to turn the different colors on/off independently. It also has a recharge port, but that's aside from the actual function of the light.

The LED is rated for:
Red: 2.5V ~ 3.0V, 350mA
Green: 3.2V ~ 3.8V, 350mA
Blue: 3.2V ~ 3.8V, 350mA

At 350 mA, the LED is reasonable for saber purposes, but it can be overdriven fairly well (and pretty cheap if you blow one). Without a resistor and a fully charged battery, blue and green run at around 800 mA. With an external heat sink (essentially a piece of aluminum on the back), I haven't had any issue with the LED. Red went above 1.3A when i tested it without a resistor, so I quickly unplugged it and added a resistor, though I don't recall the value, and got it back into the 700-800 mA range as well.

With this setup, I can get red, green, blue, yellow, cyan, purple, and "silver" blades by turning the different colors on/off. The more colors, the shorter the battery life. I've had cyan (blue + green) on for 3-4 hours before noticing a dip in the brightness. (If you're doing the math and noticing that things don't add up, as the voltage drops, the current will drop too. It will not stay at the full 800mA for very long, though I never measured it in the middle of the battery life.)

For reference, here's the saber I mention. The saber on the bottom of the top comparison shots is a Mace MR. The bottom left shows the lens holder/heatsink module.


Ok, that got a bit carried away... please feel free to disregard what I said, or ask questions. Smile
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