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Thread: Resistors too hot (tri-cree stunt): nearly 200F

  1. #1

    Default Resistors too hot (tri-cree stunt): nearly 200F

    Note: this is not the final wiring, this is just a test to check long-term performance, I'll be adding a switch later (the first one I used literally fried). Also yes, I know the battery is huge, I built a custom hilt myself to fit it.
    I have 3 photo/deep red crees wired in parallel with a 1.2ohm 3w resistor each (from tcss: https://www.thecustomsabershop.com/1...istor-P22.aspx).

    The problem: after only 10 minutes of operation, when I tested the temperature of the resistors with a thermal probe, they were over 90C (193F) and rising!

    Not so great for either the safety of the internals or my hand, not to mention the not-so-insignificant loss of battery life being converted to useless heat energy.
    Does anyone have any ideas how to make the wiring more efficient and/or less dangerous using the existing power source?

    Last edited by vivid-dark; 11-23-2018 at 10:15 PM.

  2. #2

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    Giving off heat is what the resistors do.

    Youre direct driving them I assume from the diagram? If so, the only thing I could recommend is you use larger wattage resistors if you are that concerned about the heat. Also the third die isnt going to make that much of a difference in the brightness factor, so you could disconnect that if you absolutely had to.
    TCSS MODERATOR
    All n00bs READ these first (PLEASE)!!!:
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    "Yeah, yeah, I've heard it all before... you want blindingly bright, super loud, running 1138 blinkies off of the cheapest sound card you can find AND you want all of it to run on a battery the size of a dime, and run for a very, VERY long time. That one cracks me up every time..."
    My email: fjk_tcss@yahoo.com

  3. #3

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    Yeah, I get that it's what they're supposed to do, but presently I just have the resistors free-floating inside the hilt so they could potentially transfer that heat directly to the aluminium, or touch other wires. Thanks for the tip though, I'll try a higher wattage resistor. And I should probably anchor the resistors to a circuit board just for good measure, now that I've read what I just wrote lol.

    Edit: yes, direct driving, as buckpuck requires 5V sadly
    Last edited by vivid-dark; 11-23-2018 at 10:16 PM.

  4. #4

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    On second thought, I think I'll re-solder the crees in series and use a step-up/boost converter instead of resistors, since I have a lot of amperage to work with.

  5. #5

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    Quote Originally Posted by vivid-dark View Post
    On second thought, I think I'll re-solder the crees in series and use a step-up/boost converter instead of resistors, since I have a lot of amperage to work with.
    That wont work.
    TCSS MODERATOR
    All n00bs READ these first (PLEASE)!!!:
    1. Forum Guidelines
    2. FJKs Down and Dirty guide to Ohms Law

    "Yeah, yeah, I've heard it all before... you want blindingly bright, super loud, running 1138 blinkies off of the cheapest sound card you can find AND you want all of it to run on a battery the size of a dime, and run for a very, VERY long time. That one cracks me up every time..."
    My email: fjk_tcss@yahoo.com

  6. #6

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    Quote Originally Posted by Forgetful Jedi Knight View Post
    That won’t work.
    Why do you think this won't work? I don't think it's a great idea, but there's no reason it wouldn't work given the appropriate circuit. This is how power banks work. It's just another thing that wastes energy and gets hot to hit the correct output, though.

  7. #7

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    You have two possible options that will reduce the heat through the resistors:
    1. You can use two in series or one on each side of the LED. Instead of the single 1.3 you could use 2x .68. You could also common a resistor on one side.
    2. Depending on the power curve, a slightly higher value may decrease the power dropped across the resistor. The voltage drop across the LED will also decrease, increasing the drop you need to drop across the resistor, so it could nullify the current drop. You'll have to do the math (or better yet, take measurements) to know if it will help.

    Rather than keeping the resistors away form the hilt, letting the hilt sink some heat away may keep them cooler. If they are floating inside they will be hotter because they can't efficiently dissipate the heat. One thing you should definitely not do is insulate them further by using heatshrink or insulator. You'll just drive them hotter and potentially closer to failure.

    There is also a 3.7v 1000ma driver in the TCSS shop https://www.thecustomsabershop.com/1...ver-P1211.aspx

  8. #8

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    Quote Originally Posted by jbkuma View Post
    Why do you think this won't work? I don't think it's a great idea, but there's no reason it wouldn't work given the appropriate circuit. This is how power banks work. It's just another thing that wastes energy and gets hot to hit the correct output, though.
    Hell be able to crank out 7.5V out of a 3.7V battery (which is what he would need if he wired all theee LEDs in series)?
    TCSS MODERATOR
    All n00bs READ these first (PLEASE)!!!:
    1. Forum Guidelines
    2. FJKs Down and Dirty guide to Ohms Law

    "Yeah, yeah, I've heard it all before... you want blindingly bright, super loud, running 1138 blinkies off of the cheapest sound card you can find AND you want all of it to run on a battery the size of a dime, and run for a very, VERY long time. That one cracks me up every time..."
    My email: fjk_tcss@yahoo.com

  9. #9

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    Quote Originally Posted by Forgetful Jedi Knight View Post
    He’ll be able to crank out 7.5V out of a 3.7V battery (which is what he would need if he wired all theee LEDs in series)?
    It is possible. Dollar store power banks include a circuit to output 2+ amps at 5v. The circuit trades current for voltage. That 32650 should be able to pump out the amps, if he can find or build an appropriate circuit that will fit in the hilt.

  10. #10

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    @jbkuma the thing I find most confusing is how buckpucks aka step-down converters are seemingly hailed as the best possible solution to voltage regulation (esp in regards to being more constant regardless of battery charge), yet step-up converters have literally only ever once been mentioned in the entirety of this forum. They're two sides of the same coin, are they not? Really I'm just concerned with maintaining brightness for the full length of time before the battery is depleted, and I've seen it said over and over and over on this site that direct driving with just plain old resistors will result in dimming over time as the battery drains. I've also seen it stated in multiple places, including here, that buck/boost converters are more efficient than resistors.

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