Post by: ferrari_rulz_02 on August 10, 2005, 04:42:00 AM
i am planning on making a new case for my xbox, and runnign a lot of leds in it. it would be great to be able to use teh xbox psu to power it, but i dont think it can handle the amount of wattage i want to pull from it.
i want around 150 leds, draing about 20ma each
a bit of quick maths says that 3amps......i woudl rather run them at 5v instead of 12v
i coudl probably run a microATX psu (roughly like this one)
what do you guys think? i dont think the xbox psu will dish out that much, what do you think?
cheers
Post by: SICKdimension on August 10, 2005, 05:13:00 AM
Post by: ferrari_rulz_02 on August 10, 2005, 05:18:00 AM
QUOTE(SICKdimension @ Aug 10 2005, 10:24 PM)
Xbox PSU puts out 13.2A on the 5V line.
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Title: Xbox Psu Limitations
Post by: SICKdimension on August 10, 2005, 05:30:00 AM
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I've hooked up 106 LEDs and 2 cathodes with no problems. You'll be fine.
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Title: Xbox Psu Limitations
Post by: ferrari_rulz_02 on August 10, 2005, 05:42:00 AM
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Post by: SICKdimension on August 10, 2005, 05:30:00 AM
Post by: ferrari_rulz_02 on August 10, 2005, 05:42:00 AM
QUOTE(SICKdimension @ Aug 10 2005, 10:41 PM)
I've hooked up 106 LEDs and 2 cathodes with no problems. You'll be fine.
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Title: Xbox Psu Limitations
Post by: SICKdimension on August 10, 2005, 06:27:00 AM
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LEDs were on 5V, Cathodes on 12V. The LEDs were drawing 2.12A.
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Title: Xbox Psu Limitations
Post by: ferrari_rulz_02 on August 10, 2005, 06:48:00 AM
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Post by: SICKdimension on August 10, 2005, 06:27:00 AM
Post by: ferrari_rulz_02 on August 10, 2005, 06:48:00 AM
QUOTE(SICKdimension @ Aug 10 2005, 11:38 PM)
LEDs were on 5V, Cathodes on 12V. The LEDs were drawing 2.12A.
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Title: Xbox Psu Limitations
Post by: pablot on August 10, 2005, 07:28:00 AM
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if you want to be sure you can allways measure the amps consumed by the xbox when its pushing hard (eg, when playing a game)
it involves cutting the 5v wire (or wires, depends on psu) to measure the current.. its up you you =)
/pablot
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Title: Xbox Psu Limitations
Post by: mikeymikeuk on August 10, 2005, 09:37:00 AM
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Title: Xbox Psu Limitations
Post by: ferrari_rulz_02 on August 11, 2005, 12:29:00 AM
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Post by: pablot on August 10, 2005, 07:28:00 AM
it involves cutting the 5v wire (or wires, depends on psu) to measure the current.. its up you you =)
/pablot
Post by: mikeymikeuk on August 10, 2005, 09:37:00 AM
QUOTE
ok, thanks. i think ill start this project with the xbox psu. i might run half of them on 12v, to reduce the current on the 5v rail.
If your using the 12V supply as well capitalise on the fact you can run more than 1 LED in series from 12V. That way you can keep the current down.Post by: ferrari_rulz_02 on August 11, 2005, 12:29:00 AM
QUOTE(pablot @ Aug 11 2005, 12:39 AM)
if you want to be sure you can allways measure the amps consumed by the xbox when its pushing hard (eg, when playing a game)
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Title: Xbox Psu Limitations
Post by: mikeymikeuk on August 11, 2005, 02:51:00 AM
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Look at it this way. if I have 3 LEDs, each LED has a forward voltage of 3V and I want 20 mA through each, I also want to wire them to the 12V supply then I have two options :-
In parallel
Itotal = 3 * 20 mA = 60 mA.
Vfoward total = 3V
(12V-3V)/60 mA = 150 ohms series resistor.
Power dissipated in the resistor would be (12V-3V) * 60 mA = 0.54W
In series
Itotal = 20mA (since the same current flows through each LED)
V forward total = 3 * 3V = 9V
(12V-9V)/20 mA = 150 ohms series resistor.
Power dissipated in the resistor would be (12V-9V) * 20 mA = 0.06W
So its clear that wiring the 3 in series to the 12V supply you draw only a 1/3 of the current of wiring them in parallel. In the parallel circuit most of the power is being lost in the series resistor.
Another bonus of wiring them is series is that if one blows then they all go out, which isn't really a bonus, but if one of the LEDs in the parallel circuit blew then the other two will be getting another 10 mA each. If your supplying Imax in the first place another 10mA is going to damage the remaining two until they are all blown.
In short series rocks. Not as easy to wire as parallel but far better in the long run.
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Title: Xbox Psu Limitations
Post by: ferrari_rulz_02 on August 11, 2005, 03:06:00 AM
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Post by: mikeymikeuk on August 11, 2005, 02:51:00 AM
QUOTE
well they will all be arranged in parallel circuits. and i dont think in what sort of circuit theyre arange in will make any difference to the load they place over the circuit.
Of course it will!! The same current flows through all components in a series circuit.Look at it this way. if I have 3 LEDs, each LED has a forward voltage of 3V and I want 20 mA through each, I also want to wire them to the 12V supply then I have two options :-
In parallel
Itotal = 3 * 20 mA = 60 mA.
Vfoward total = 3V
(12V-3V)/60 mA = 150 ohms series resistor.
Power dissipated in the resistor would be (12V-3V) * 60 mA = 0.54W
In series
Itotal = 20mA (since the same current flows through each LED)
V forward total = 3 * 3V = 9V
(12V-9V)/20 mA = 150 ohms series resistor.
Power dissipated in the resistor would be (12V-9V) * 20 mA = 0.06W
So its clear that wiring the 3 in series to the 12V supply you draw only a 1/3 of the current of wiring them in parallel. In the parallel circuit most of the power is being lost in the series resistor.
Another bonus of wiring them is series is that if one blows then they all go out, which isn't really a bonus, but if one of the LEDs in the parallel circuit blew then the other two will be getting another 10 mA each. If your supplying Imax in the first place another 10mA is going to damage the remaining two until they are all blown.
In short series rocks. Not as easy to wire as parallel but far better in the long run.
Post by: ferrari_rulz_02 on August 11, 2005, 03:06:00 AM
QUOTE(mikeymikeuk @ Aug 11 2005, 08:02 PM)
So its clear that wiring the 3 in series to the 12V supply you draw only a 1/3 of the current of wiring them in parallel. In the parallel circuit most of the power is being lost in the series resistor.
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Title: Xbox Psu Limitations
Post by: SICKdimension on August 11, 2005, 03:14:00 AM
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Ya, never question mikeymikeuk regarding electronics. He knows his stuff. 'Nuff said.
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Title: Xbox Psu Limitations
Post by: mikeymikeuk on August 11, 2005, 04:01:00 AM
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Title: Xbox Psu Limitations
Post by: ferrari_rulz_02 on August 11, 2005, 04:27:00 AM
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Post by: SICKdimension on August 11, 2005, 03:14:00 AM
Post by: mikeymikeuk on August 11, 2005, 04:01:00 AM
QUOTE
Ya, never question mikeymikeuk regarding electronics. He knows his stuff. 'Nuff said.
Cheers SICKdimension QUOTE
but ill be having 16 leds in a parallel circuit, so if one blows, it doesnt matter any.
Fair play. Just make sure they are wired to 5V.Post by: ferrari_rulz_02 on August 11, 2005, 04:27:00 AM
QUOTE(mikeymikeuk @ Aug 11 2005, 09:12 PM)
Fair play. Just make sure they are wired to 5V.