/diy/ - Do It Yourself

>>402143
>>402143


I guess it will not last longer.


what are you using those leds for? indoor grow or what?

>>402189
I wish, I have a job interview this friday and had to quit last week.

This is for my truck, it doesn't have a light in the cab.

>>402265
I would imagine this would do it-
http://www.amazon.com/Converter-Power-Supply-Module-Non-isolated/dp/B00A71A42Q

I don't know how many amps your lights will pull, but note that if it's going near or over 3 it looks like you'd want to run two of those, otherwise one should be fine.

>>402277
>http://www.amazon.com/Converter-Power-Supply-Module-Non-isolated/dp/B00A71A42Q
thanks, they're only like 4.5w max, so it shouldn't be heavy amp draw.

If you were asking what they're intended for originally - they're for battery operated custom lightsabers meant for sparring (led in hilt rather than tube).

Just use a resistor. Or am I missing something here?

12v - (2 * 3,7V) = 4,6V (to be dropped by a resistor)

LED mA max.:1000 mA

R = V / I = 4.6V / 1A = 4,6 ohms
P = V * I = 4.6V * !A = 4.6 watt

So, use 2 LEDs in series with a 4.7ohm. 10 Watt resistor
$1.80
http://www.ebay.com/itm/Ceramic-Wirewound-Resistor-4-7-Ohm-10-Watt-5-/330503536642?pt=UK_Sound_Vision_Speaker_Parts&hash=item4cf38bc002

Or, to add a safety factor, go up to 5.6 or 6.8 ohms
$1.20
http://www.ebay.com/itm/5-6-Ohm-10-Watt-5-Ceramic-Wirewound-Resistor-/230799984764?pt=UK_Sound_Vision_Speaker_Parts&hash=item35bcc0487c

I would go with a 6.8 ohm because a car battery can go up to 14 Volts
@14 V, resister voltage is 6.6V
I = 6.6V / 6,8 ohms = 0.97A (CHECK)

>>402536

>>402536
>Or am I missing something here?
he wants MUH EFFICIENCY
I'm not sure if a voltage regulator would actually be any more efficient anyway, and it probably doesn't matter

>>402536
>>402538
now that I've had my morning coffee...
1000mA is MAX
so, use 800mA max to have a 20% safety factor
R = V/I = 6.6V / 0.8 = 8.25ohms
P = V*I = 6.6V * 0.8 = 5.2 watts
use an 8.2ohm 10 watt resistor in series with 2 LED's

>>402536
Use 3 LEDs in series. Instead of burning energy through the resistors, use it to light up.
You still need a resistor though, maybe around 1 ohm, do the claculations i'm too lazy now.

The ONLY ONLY ONLY way to run anything LED is with those buck/boast pucks. aka, mini switchmode PWM voltage and current converters.

If you cannot afford to (?!?) , the the next viable option is using (wired in a configuration of being) a constant current device using a 317T regulator. It generates heat if your source voltage is muchly different to the LED total voltage. Limit current. Heat = inefficiency.

THe ghetto option (ie: bad) is a series resistor.

The absolute worst option is directly wiring a LED (or series of them) to a battery. Your LEDs lower resistance the hotter they get. lower resistance = more current when voltage stay the same.

current kills LEDs quicker than an americunt cop tazering a downy.

>>402861
It would be too sensitive to voltage changes. Current would drop to 0 @ = ~11.1V

>>402874
OP here again, do you agree with this anon's suggestion? >>402277

Seoul P4s work just fine with buck converters. They slap 'em together into flashlights all the time. In fact since your alternator is going to cause some spikes and Vf varies between LED samples, you really should use a current regulating driver in that application. Just make sure your converter is good for more than 12V because your electrical goes above that occasionally.

Nominal current through one of those LEDs is 350mA, though they'll take up to an amp with sufficient cooling.

You don't want to put an amp through them for a dome light though. You'd need to cram a big heat sink up there and they'd be too bright anyway.

A linear regulator is also easy to DIY- use an inductor to pull the voltage down and feed it through a regulator like an AMC7135 (outputs 350mA, so one per LED). iirc the 7135 tolerates up to 5V so you'd pull down to a bit under that with the inductor.

Linear regulators don't use PWM, so no variable output but also no stroboscopic effects.

>>403129

You don't want to use one of those supplies for the LED you've chosen unless you can test and cherry pick your LED first. The forward voltage of a P4 can vary between 3.0V and 4.0V.

Giving it access to 3A@3.7V could have very unexpected results depending on where your piece sits in that range.

fuck the p4, get some xm l2's. Also decide how many watts you want to use and buy an appropriate regulator.

>>403205
will pick up some of those regulators immediately, already ordered the buck converters last week.

I have had alternator spikes bothering me without even mentioning it, I'm glad you said something about it.

>>403228
The voltage is identical to the LEDs I mentioned, so I may use those with a regulator like the anon above you mentioned, I've already ordered 2 buck converters like I mentioned in OP, but I can use them for other trinkets.

>>403266
checking these out in another tab right now, they look pretty good, thanks for the mention.