voltage boost for halloween outfit

Discussion in 'The Projects Forum' started by jesterscup, Oct 7, 2014.

  1. jesterscup

    Thread Starter New Member

    Oct 7, 2014
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    Hi,

    It's been many years since I've done any electrical engineering work ( used to in high school, doing radio ham stuff etc). But for halloween this year I decided to add some lights onto my outfit, "no big deal" thought I , a few led's, how hard can it be......

    So after buying 40 - odd nice red led's and beginning to assemble them, I realised that my original design would require a huge number of batteries to power it !

    In essence, I have 2 circuits, one for the wings, and one for the mask.
    The led's in question require 1.7v and 3000mA ( I need to confirm the amperage )
    The wings have 24 leds in series , and the mask has 10 in series. This would require around 7 9v batteries !

    Since this seems a little excessive I did a bit of a google and discovered the 'voltage booster circuit', but I'm afraid it's a little over my head, I'm not sure I even understand the theory, let alone how to choose the components ( for fear of setting myself on fire). I'd really love to do this 'right', and after a few hours of searching for a solution I discovered this forum, and thought I'd at least ask. Push comes to shove I'll carry around a pile of batteries, but I hoped that someone here might find it an interesting challenge, or already know a solution and be able to help me out.

    Thanks ^.^
     
  2. MrChips

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    Oct 2, 2009
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  3. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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    A couple of observations. The 3000mA current is more likely to be 30mA. I doubt your discrete red LEDs require 3A. Also, that is a maximum current rating and the LEDs can be run at a lower current, with an appropriate current limiting resistor.

    Second, 9V batteries are likely NOT to last very long.

    Third, if you boost the voltage, you will have less current available. As someone once said TANSTAAFL (there ain't no such thing as a free lunch). Power equals voltage times current and remains constant, so if Voltage goes up, Current goes down.

    Try arranging the LEDs in series strings, each of which will require a constant current. Then parallel these strings. Then a pack of AAs can power multiple LEDs.
     
  4. jesterscup

    Thread Starter New Member

    Oct 7, 2014
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    I'll see if I can pull out the technical sheet for the leds, or failing that update the amperage on the op when I get home and can confirm. a quick search online shows similar leds requiring around 2mA.

    Actually this was one of the first things I tried ( using the mask, 2 series of 5 led's), the brightness drop across the parallels was distinct and noticeable, something I'd wish to avoid.

    Thanks, this is rather useful, it starts to cover what I'm looking for around chapter 7, at which point I'm already utterly confused/boggled..
     
  5. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    each string needs its own current limiting resistor and the supply voltage needs to be greater than the sum of the LEDs in each string.
    or just avoid the whole voltage boost thing just use a resistor for each LED.. all LEDs in parallel.
    much easier that way..
     
  6. jesterscup

    Thread Starter New Member

    Oct 7, 2014
    10
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    Perhaps I could've titled my thread a little better?

    I did that with the mask led's( each set has a resistor before it), I would have to assume the the change in brightness is due to resistance in the wires between the first and second 'sets' (the wires being longer for the second set), I'll try rigging the mask with wires of equal lengths to see if that minimises this effect, and report back.

    Setting up each led for the wing set ( the 24led's) wouldn't be practical, the leds are in pairs and each pair is at the end of a 1m 'bone' with 6 'bones' per wing ( think of a fan, with 'bones' spreading out from a point ).
    even if I could be assured of the brightness being relatively equal across all the pairs, it'd require over 24m ( or 48m for each led to be parallel ) of cable ( something I'd like to avoid if possible ), while running them in series allows me to connect them across bones (some elastic cord runs across the bones at 75cm, the wire can be integrated into that), giving a total wire usage of around 7m.

    Doing them in series seems to avoid the brightness drop, and saves on the cable, but at the expense of needing more voltage. That being said, if I ran the wings in parallel with each other, that potentially takes me down to 4 9v batteries. I can probably consider myself as happy with that, if it comes to it....
     
  7. jesterscup

    Thread Starter New Member

    Oct 7, 2014
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    sorry for the double post, I hope thats not considered bad form here.....

    How feasible is it to use a circuit based on the following?
    [​IMG]
    (Source: http://technologytutor.co.nz/technology-and-science-for-kids/01-build-your-own-joule-thief )

    Obviously changing the battery to a 9v, changing the resistor , and chaining a wings worth of leds rather than the single ( with a resistor at the beginning )?
    In addition, wouldn't having a differing number of windings for the inductors effect this? Say having twice the number of windings on the 'resistor' side ?
     
  8. Wendy

    Moderator

    Mar 24, 2008
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    That would work, but I have a couple of suggestions. Ignoring the battery type, how many power sources do you really need? It may be one per location, for the mask, for the wing, for the dress, etc. Define this first.

    Second, how many LEDs per power source? Most LEDs are fine with 0.01A per LED, maybe even a lot less. Just because an LED can use 0.03A (or with ultrabrights, 0.7A) doesn't mean you have to max the device out.

    Color of the devices is important. It dictates how many LEDs per chain (in series) you can have.

    So, lets start with a table, how many LEDs on a battery (type unimportant at this point), how many clusters of LEDs, and color of the LEDs. When we break it down you may find the requirements will design themselves.
     
  9. jesterscup

    Thread Starter New Member

    Oct 7, 2014
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    I'd like to keep the mask and the wings separate, so 2 sources.

    EDIT No... Brightness... it's burns usssss....
    ( brightness is kinda important, the brighter the better, but within limits, it's wont be possible to do maintenance on it if an led blows, well not easily.)
    All the led's are the same ( makes it easy I suppose ) red 5mm , 1.7 forward voltage , 30mA(tbc ).
    edit2: the spec on the led's is clearly wrong... I suspect the 1.7v is the minimum, and that the max voltage is either 2.5v or 3v, I'll test this at some point, but it gives some leeway I suppose.

    mask:
    2x 5 led 'clusters'

    wing x2
    6 x 2 led 'clusters'
     
    Last edited: Oct 7, 2014
  10. Wendy

    Moderator

    Mar 24, 2008
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    A 9V battery would work well, or a 3V watch cell. You could even use X2 AAA or AA batteries, depending on your size requirements. The AAA would give the most bang for the buck, as well as brightness.
     
  11. jesterscup

    Thread Starter New Member

    Oct 7, 2014
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    so it turns out I'm a bit of a dummy, I got home and looked at my mask to discover I'd used different resistors for each cluster, which accounts for the difference in brightness when the clusters are arranged in parallel (doh!).

    I assume that if I have all the clusters for the wings in parallel that the extra resistance from the extra cable ( min 6m longer - the last cluster on each wing is circa 3m away from the first cluster on the wing), there will be some dimming but hopefully not much?

    If I get the chance I'll post some pics of my work as it stands.
     
  12. MrChips

    Moderator

    Oct 2, 2009
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    You are making the assumption that the resistance in the connecting wire will have an effect and reduce the voltage to the last cluster. While theoretically this is true, you need to measure the resistance of the connecting wire. You will discover that the resistance is less than 1-ohm and hence will have no observable effect on the current or voltage.
     
    djsfantasi likes this.
  13. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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    Second MrChips observation. Wish I could type faster on this phone. The 3m cable resistance will be negligible compared to the other resistances in the clusters.
     
  14. jesterscup

    Thread Starter New Member

    Oct 7, 2014
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    You guys are awesome!!!
    I thought I'd show off a little if thats ok...
    Firstly here are the lights for the mask...
    [​IMG]
    not attached to a mask as yet. I've a few prototypes, but I've not found a mask design I want....

    wings...
    [​IMG]
    This is the inside of one of the wing 'blades', I can't really finish it off until I have all the other blades ready and I'm waiting for delivery of the metal 'bones'. What I can do however is begin wiring up the LED's as all the 'head' plates, I've enough components to wire up one wing .

    Belt & harness...
    Nothing much to show here, I've not really started on the belt ( it'll hold the batteries & switches), it's likely to be the last thing I work on. The backplate & harness ( the bit that holds the wings together and keeps them on my back ) is coming along, but there's not much to see ( a couple of pipes, some nuts & bolts, a bit of hardboard & 2 oven trays from Tesco ), and the harness straps are in the post....
     
  15. jesterscup

    Thread Starter New Member

    Oct 7, 2014
    10
    1
    So in the end, having all the lights in parallel, did cause one set of wings to be slightly brighter than the others, I suspect this was caued by a change in gauge of the wires ( I ran out near the end and had to use one length of thicker wire to complete the circuit). my biggest fail wasn't electronic, but the use of elastic governing the available 'spread' of the wings. I'm currently trying to think of a 'hack' to fix that.

    In the end I used 4xAA batteries ( 2 parallel sets of 2 in series )... worked a treat. Perhaps I could've added more, but I didn't want to risk blowing them.

    [​IMG]

    So onto, my next project... wings again, but this time I'm going for a simpler wing design, but making them open/close using motors of some sort... I'll likely post here for help/suggestions..

    Big thanks to everyone who helped.
     
    wayneh likes this.
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