[Lab] AC adapter question

[Raj]

That's a good point.  If you increased the voltage from 5V to 15V, you
could put 7 leds in series with a single 91 ohm resistor and reduce current
comsumption by 1/7 or around 1A.  This would also reduce heat produced from
7x5=35W to 1.134 x 15 = 17W, making the whole thing much cooler too.

7*1.6=11.2 (combined forward voltage drop for 7 LEDs in series at 1.6V
each).
15-11.2= 3.8 (voltage across the resistor)
3.8/91=0.042A (current through each resistor / each LED)
188/7=27 (resistors / branches required - you would actually end up with
189 LEDs since 27*7=189)
0.042*27=1.134A (total current required)
1.134 * 15 = 17W (total power)





On Fri, Jul 12, 2013 at 8:36 AM, Chris de Groot <cdegroot at adobe.com> wrote:

> Depending on how consistent you need the output of the IR LEDs you can
> always put two or three in series and reduce the size if the resistor, this
> would reduce the over amps used and make the whole thing more efficient.
>
> C
>
> Sent from my iPhone
>
> On 2013-07-11, at 5:55 PM, "Michael Grant" <michael at krazatchu.ca> wrote:
>
> That's almost 9 amps ...
>
> Michael
>
>
> On Thu, Jul 11, 2013 at 7:42 PM, Britta Evans-Fenton <
> technical at artengine.ca> wrote:
>
>> sorry that was a Maybe I AM drawing too many Amps.  (thanks for the help
>> Darcy)
>>
>> Britta
>> *Technical Coordinator *
>> Artengine.ca
>>
>> Ottawa Mini Maker Faire
>> Aug. 31 & Sept. 1 2013
>> www.makerfaireottawa.com
>> @MakerFaireOTT
>> #MMFO
>>
>>
>> On Thu, Jul 11, 2013 at 4:41 PM, Britta Evans-Fenton <
>> technical at artengine.ca> wrote:
>>
>>> Maybe I'm drawing too much Amps.  Would you recommend this AC converter
>>> over the last one:
>>> http://www.digikey.ca/product-detail/en/LS150-5/285-1817-ND/1918828
>>>
>>> I would have Amps to spare on this one.
>>>
>>> Britta
>>> *Technical Coordinator *
>>> Artengine.ca
>>>
>>> Ottawa Mini Maker Faire
>>> Aug. 31 & Sept. 1 2013
>>> www.makerfaireottawa.com
>>> @MakerFaireOTT
>>> #MMFO
>>>
>>>
>>> On Thu, Jul 11, 2013 at 4:32 PM, Britta Evans-Fenton <
>>> technical at artengine.ca> wrote:
>>>
>>>> There are 188 IR leds:
>>>> http://www.digikey.ca/product-detail/en/QED233/QED233-ND/187410  All
>>>> connected in parallel each with their own Resistor ( 91 OHM 1/4W 5% CARBON
>>>> FILM)
>>>>
>>>> Britta
>>>> *Technical Coordinator *
>>>> Artengine.ca
>>>>
>>>> Ottawa Mini Maker Faire
>>>> Aug. 31 & Sept. 1 2013
>>>> www.makerfaireottawa.com
>>>> @MakerFaireOTT
>>>> #MMFO
>>>>
>>>>
>>>> On Thu, Jul 11, 2013 at 4:00 PM, Ken <klmckinnon at rogers.com> wrote:
>>>>
>>>>>  It should power a LOT of LED's.  How many were you using and what
>>>>> sort of current limiting resistor did you have....a quick circuit diagram
>>>>> would tell a lot.
>>>>>
>>>>> Ken
>>>>>
>>>>>
>>>>> On 7/11/2013 6:49 PM, Britta Evans-Fenton wrote:
>>>>>
>>>>>  A little question about AC adapters.
>>>>>
>>>>>  I have an artwork that I did that I used an AC adapter to get power.
>>>>>  It was on for 4 days during a show, and I was surprised on how hot it got.
>>>>>  (I almost burned myself).  I did have duct tape on it holding it to the
>>>>> back of a wall, so that may have been half the problem.
>>>>>
>>>>>  I'm showing the work again, but I'm wanting to make sure everything
>>>>> is safe.  I need to hide the adapter due to aesthetic reasons, so I wanted
>>>>> to create a little white box around it with air holes, and I was suggested
>>>>> a fan, although it if it getting hot due to over working, adding another
>>>>> fan might not be a good idea.
>>>>>
>>>>>  It is only a bunch of IR leds that it is powering, so I'm surprised
>>>>> at the power I am needing.
>>>>>
>>>>>  any help would be very well appreciated.
>>>>>
>>>>>
>>>>>  Here is the Adapter I used :
>>>>>
>>>>> http://www.digikey.ca/product-detail/en/VGS-25-5/102-1928-ND/2045659
>>>>>
>>>>>
>>>>>  Here are the IR LEDS:
>>>>>
>>>>> http://www.digikey.ca/product-detail/en/QED233/QED233-ND/187410
>>>>>
>>>>>
>>>>>  And the Resistors I have on them were 91 OHM 1/4W 5% CARBON FILM.
>>>>>
>>>>>
>>>>>   Britta
>>>>>  *Technical Coordinator *
>>>>>  Artengine.ca
>>>>>
>>>>> Ottawa Mini Maker Faire
>>>>> Aug. 31 & Sept. 1 2013
>>>>> www.makerfaireottawa.com
>>>>> @MakerFaireOTT
>>>>> #MMFO
>>>>>
>>>>>
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