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Old 14th November 2012, 10:27 AM   #2371
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In that case we need to correct the ratings specified on the posts for hotrod stages.
20W+ will quickly roast the 12W 1Rs specified for the stage 3 (2A).
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Old 14th November 2012, 11:47 AM   #2372
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The 20W will be on each Mosfet not on each setting resistor. We should only note that different leds or Mosfet batches may ask for lower than 1 Ohm to reach 2A.
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Old 14th November 2012, 11:57 AM   #2373
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Quote:
Originally Posted by Salas View Post
The 20W will be on each Mosfet not on each setting resistor. We should only note that different leds or Mosfet batches may ask for lower than 1 Ohm to reach 2A.
So what wattage resistors will be needed for 2As?
I am asking because if we need 12W for 1,2A (10V across), I would expect something around 20W for 2A
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Old 14th November 2012, 12:01 PM   #2374
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I don't know what you are expecting at over 1 amp... You're risking big time malfunction and something bad to happen to your audio equipment... Can you really hear a difference over 600-800mA?

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Old 14th November 2012, 12:10 PM   #2375
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Quote:
Originally Posted by dimkasta View Post
So what wattage resistors will be needed for 2As?
I am asking because if we need 12W for 1,2A (10V across), I would expect something around 20W for 2A
#2370 I already wrote that the resistor dissipation is just what voltage is on the actual resistor times the set current. Measure your set resistor pin to pin, what is it? 1.2-1.4V now that you are set at 1.2A?
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Old 14th November 2012, 12:14 PM   #2376
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If you will burn say 4W on a self sinking resistor, 12W to 15W nominal will be safe. I would not recommend less than 3x for long term reliability because it heats up on 100% cycle due to constant current operation.
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Old 14th November 2012, 12:15 PM   #2377
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Quote:
Originally Posted by pinnocchio View Post
I don't know what you are expecting at over 1 amp... You're risking big time malfunction and something bad to happen to your audio equipment... Can you really hear a difference over 600-800mA?

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He uses an output coupling capacitor.
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Old 14th November 2012, 12:58 PM   #2378
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Quote:
Originally Posted by Salas View Post
#2370 I already wrote that the resistor dissipation is just what voltage is on the actual resistor times the set current. Measure your set resistor pin to pin, what is it? 1.2-1.4V now that you are set at 1.2A?
That s what I thought, but I got confused from #2368 to #2370 where I asked if it was the measured 1,2V and you told me no it was 10V and 12W.
Anyway
So it's currently 1,1V x 1,2A = 1,32W on the resistors.

My initial question was if that 1,32W is enough to make 10W resistors run so hot? 70C on the cement body?

@Pinnocchio
Yes there is a difference, but I think 1-1,2A will be my limit mostly for practical reasons like heatsinking limitations and as you say general reliability and safety.
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Old 14th November 2012, 02:37 PM   #2379
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In DC duty cycle, yes a cement self sinking box can accumulate temp. You experienced it yourself on those 10W of yours, didn't you?

P.S. I thought you were asking about the 70C estimated internal temp of IRF240-9240 I had analyzed before that.
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Old 14th November 2012, 02:40 PM   #2380
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Yep.... they were pretty damn hot...
Really disturbing
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