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| Kiriakos-GR:
With out the use of proper wires - cables .. what ever , any measurements are inaccurate . For 1.5 A constant juice , 1mm or 1,5mm car cables are the minimum diameter , that will keep them cold enough, so to not have an high resistance or thermal losses .. |
| slburris:
--- Quote from: Simon on September 19, 2010, 09:22:22 pm ---66% efficiency does not sound very good, considering the controllers are targeted at a specific current they will always operate at they should have nailed it at 80-90% for the target output --- End quote --- I'm not sure I follow your calculations. The input is 11.98v @ 0.956a, which is 11.54 watts Output is 8v (if the datasheet on Vf for the LED is right) @ 1.238a, which is 9.90 watts Dividing 9.90 by 11.54, we get 0.857 or 85.7% With alligator clips and less than ideal wire sizes, this is a lower bound on efficiency. Wired into the landscape system, which is 16gauge wire -- 1 mm for the metric world (everyone but the US it seems), I don't expect any issues. Scott |
| Kiriakos-GR:
--- Quote from: slburris on September 19, 2010, 10:26:55 pm --- With alligator clips and less than ideal wire sizes, this is a lower bound on efficiency. Wired into the landscape system, which is 16gauge wire -- 1 mm for the metric world (everyone but the US it seems), I don't expect any issues. Scott --- End quote --- I do not see why, just the words are stopping you from testing it , with better cables. |
| Simon:
--- Quote from: slburris on September 19, 2010, 10:26:55 pm --- --- Quote from: Simon on September 19, 2010, 09:22:22 pm ---66% efficiency does not sound very good, considering the controllers are targeted at a specific current they will always operate at they should have nailed it at 80-90% for the target output --- End quote --- I'm not sure I follow your calculations. The input is 11.98v @ 0.956a, which is 11.54 watts Output is 8v (if the datasheet on Vf for the LED is right) @ 1.238a, which is 9.90 watts Dividing 9.90 by 11.54, we get 0.857 or 85.7% With alligator clips and less than ideal wire sizes, this is a lower bound on efficiency. Wired into the landscape system, which is 16gauge wire -- 1 mm for the metric world (everyone but the US it seems), I don't expect any issues. Scott --- End quote --- yes sorry your right I forgot to consider the lower current in, another silly late night post |
| Zero999:
--- Quote from: Kiriakos-GR on September 19, 2010, 09:51:13 pm ---With out the use of proper wires - cables .. what ever , any measurements are inaccurate . For 1.5 A constant juice , 1mm or 1,5mm car cables are the minimum diameter , that will keep them cold enough, so to not have an high resistance or thermal losses .. --- End quote --- It depends on the length of the cables. Have you actually done any calculations or are you just guessing? 0.5mm2 should be more than enough to satisfy the thermal requirements and shouldn't effect measurements too much for short runs (under a meter). The resistance of a two core 0.5mm2 piece of cable is 93m? per meter, if the current is 1.5A the loss will be 209mW, if the power dissipated by the LED is 10W the inaccuracy due to the cable is just under 2.1%. Even better, measure the voltages directly at the board (which is what he's doing according to the photograph), that way the cables will be taken out of the equation. |
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