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From: spacecriter (Bill C) on 10 Jun 2010 20:24 So snag, which way are you going for this? BTW, if you do use a voltage reg, you still need to use a current limiting resistor, or you could blow the LEDs.
From: Snag on 10 Jun 2010 21:06 spacecriter (Bill C) wrote: > So snag, which way are you going for this? > > BTW, if you do use a voltage reg, you still need to use a current > limiting resistor, or you could blow the LEDs. Yeah , I just tonight found that out . I might be in over my head here ... so I guess I better learn to swim ! BTW , I will be going with a voltage reg , set at 10v . 5 LED's in series that want a nominal 2v . So how does one size a current limiter ? Got a big bag of 1/4w carbon film resistors in various sizes ... bet I'm gonna need the specs on my LED's . -- Snag "90 FLHTCU "Strider" '39 WLDD "PopCycle" BS 132/SENS/DOF
From: Snag on 10 Jun 2010 21:23 Snag wrote: > spacecriter (Bill C) wrote: >> So snag, which way are you going for this? >> >> BTW, if you do use a voltage reg, you still need to use a current >> limiting resistor, or you could blow the LEDs. > > Yeah , I just tonight found that out . I might be in over my head > here ... so I guess I better learn to swim ! > BTW , I will be going with a voltage reg , set at 10v . 5 LED's in > series that want a nominal 2v . So how does one size a current > limiter ? Got a big bag of 1/4w carbon film resistors in various > sizes ... bet I'm gonna need the specs on my LED's . > -- > Snag > "90 FLHTCU "Strider" > '39 WLDD "PopCycle" > BS 132/SENS/DOF OK , looked it all up . Not as hard as I thought , there's a wizard to calc it all for me ! Plug in the values and push the button ... -- Snag "90 FLHTCU "Strider" '39 WLDD "PopCycle" BS 132/SENS/DOF
From: spacecriter (Bill C) on 10 Jun 2010 21:39 Snag wrote: > spacecriter (Bill C) wrote: >> So snag, which way are you going for this? >> >> BTW, if you do use a voltage reg, you still need to use a current >> limiting resistor, or you could blow the LEDs. > > Yeah , I just tonight found that out . I might be in over my head > here ... so I guess I better learn to swim ! > BTW , I will be going with a voltage reg , set at 10v . 5 LED's in > series that want a nominal 2v . So how does one size a current > limiter ? Got a big bag of 1/4w carbon film resistors in various > sizes ... bet I'm gonna need the specs on my LED's . 1/4 W ought to be OK Use the calculator I sent you. It will give you the nearest common resistor value. Ignoring the voltage regulator, plug in 12, 10, and 20. It says you should use 120 ohms and it will burn .04 watts. Well within .125 W. You could dial it up a litle to derate the LEDs. Using 13.5, 10, and 18 yields a 220 ohm resistor. 1/4 W still works. -- Bill C. "I am NOT lost... I'm *exploring*"
From: Snag on 10 Jun 2010 23:52
spacecriter (Bill C) wrote: > Snag wrote: >> spacecriter (Bill C) wrote: >>> So snag, which way are you going for this? >>> >>> BTW, if you do use a voltage reg, you still need to use a current >>> limiting resistor, or you could blow the LEDs. >> >> Yeah , I just tonight found that out . I might be in over my head >> here ... so I guess I better learn to swim ! >> BTW , I will be going with a voltage reg , set at 10v . 5 LED's in >> series that want a nominal 2v . So how does one size a current >> limiter ? Got a big bag of 1/4w carbon film resistors in various >> sizes ... bet I'm gonna need the specs on my LED's . > > 1/4 W ought to be OK > > Use the calculator I sent you. It will give you the nearest common > resistor value. > > Ignoring the voltage regulator, plug in 12, 10, and 20. > > It says you should use 120 ohms and it will burn .04 watts. Well > within .125 W. > > You could dial it up a litle to derate the LEDs. > > Using 13.5, 10, and 18 yields a 220 ohm resistor. 1/4 W still works. > > -- > Bill C. "I am NOT lost... I'm *exploring*" Your email (??) must be lost in cyberspace ... I found a calculator , using 5 of the 2v/25ma LED's in series and 10v it calls for a 1ohm 1/4 watt resistor for each string . Shorter strings/higher voltages result in much higher resistor values , but 1/4 w is still recommended . My main concern if I use an unregulated power supply is the widely varying voltages . I wonder if they'll be bright enough at the lower voltages if I allow for the higher ones ... this circuit may see anywhere between 11 or so up to 14 volts . -- Snag "90 FLHTCU "Strider" '39 WLDD "PopCycle" BS 132/SENS/DOF |