PDA

View Full Version : started on new string blade



ooty99
02-09-2016, 11:00 AM
Hi,

I have started work on my very first led string blade. I hav e 120 LEDs ready to be connected, with 30 being already connected. I have my hilt, blade, foam, and batterypack (a 2x aa holder). However, when I see some of these threads , I tend to come across people saying "don't wire all the LEDs in parallel or else it will heat up and the voltage drop will ruin the blade". I was planning on just making a simple stunt saber with no sound and a simple switch to turn it on/off. What else do I need to worry about? I don't want to keep working until I can be sure about the outcome afterward. Thank you!

ooty99
02-09-2016, 12:19 PM
I guess my question is, Would it be okay to wire up 120 LEDs in parallel and run off of 3v from a pack without catching on fire. If this is not good, how would I wire it to make it safe?

Hermitjensen
02-09-2016, 12:50 PM
Running that many LEDs in parallel at only 3v, will be completely safe, because most will probably barely turn on. In parallel LEDs share the current but all have the same voltage, and its the current that really makes an LED light up. And in Series configuartion the voltage is shared and current is the same everywhere. I think most people would say do the combination method, or series-parallel, circuit. Where you have groups of LEDs in parallel but then those groups are wired in series with the other groups. I maybe be wrong on this, but i do have a fair knowledge of elecronics, so hopefully someone will correct me if im wrong.

smsno
07-28-2016, 01:10 PM
so, because im very new to this..................... in theory

if i have a 200 green string, resisted down to 3.7 volts off a 9v battery. I would be better off having 4x50 led's off the battery for better power distribution?

because i have 100 in single row and there............. ok, but i expected better? so wiring them in groups will give better results?

smsno
07-28-2016, 01:10 PM
so, because im very new to this..................... in theory

if i have a 200 green string, resisted down to 3.7 volts off a 9v battery. I would be better off having 4x50 led's off the battery for better power distribution?

because i have 100 in single row and there............. ok, but i expected better? so wiring them in groups will give better results?

FenixFire
07-28-2016, 02:37 PM
Most 9v batteries are only in the 500mAh capacity.

A 2aa pack would have double the capacity for almost double the runtime, and your not bleeding off as much of the excess voltage as heat through the resistors.

An 18650 rechargeable could have as much as 3 times the run time.

jbkuma
07-28-2016, 03:19 PM
There are always trade-offs in this sort of thing. A lot of the strings I've seen are 6-8 segments. You'll have to do your calcs to figure out the voltage and current marks that will match best with your source and maximize your run time. The less you need to cut down your source with resistors and regulators, the better. The segments also allow for an extension and retraction effect if you upgrade with the right electronics later on.

It's often been said that strings aren't great for dueling because there are a lot of break points which make it fragile. Various methods have been discussed here and elsewhere regarding methods to offset that.

Sincenatic
07-29-2016, 03:36 PM
I would recommend using a 18650 Li-ion battery and a complete parallel setup. Depending on the specification of the LEDs you should add a resistor, but if you’re willing to gamble with the life-time of the LEDs you can in some cases skip the resistor. For red LEDs it is clear that you need a resistor, but for blue or green you could “gamble” – depending on YOUR preferences. I have a green blade with 80 LEDs without any resistor and so far I haven’t had any problems. A fully charged battery would provide 4.2v and if the LEDs are rated at 3.3v for 20mA, the resistor that I didn’t include (given the 80 LEDs) should have been 0.5625 Ohm. In your case (given the example of 3.3v) it would be a resistor of 0.375 Ohm. Keep in mind that I am not overly concerned about if they eventually would die, because I enjoy the building process. I have to underline that it is your preferences and your choice, and also I don’t know the specifications (or quality) of the LEDs. So far I have built two blades in complete parallel and only the last one was with the series-parallel setup.

If you want the scrolling (and have a soundboard or an arduino based solution), then it would be a natural choice to build 6 segments (in combination of parallel and series). Without this, I cannot see much of an argument to drop the complete parallel setup - just add a resistor if you would like to play it safe. Also, keep in mind that you would need two batteries in series (i.e 2*3.7v or 2*4.2v when fully charged) for the combinational setup.

profezorn
07-31-2016, 05:45 PM
For scrolling blades, I recommend building a PL9823 blade, see http://fredrik.hubbe.net/lightsaber/blade1.html, works like a charm.