| valterdaw |
| Is there any easy way to "dyno test" an amp to measure it's power output with acceptable accuracy? |
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| Stocker |
| Monitor output voltage and current while driving a load. Multiply the one by the other and you've got your output power. |
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| jackinnj |
| You measure the output voltage and current to derive the power with the lowest impedance that you are likely to subject the device to BUT you should also measure the temperature on the heatsink of the amplifier -- you can use a RatShack weather digital thermometer, or a cooking thermometer as sold at BednBath -- you really don't want the heatsink to get over 75 or 80 degrees C (167F). Higher than this and you will experience the bad side of "Mean time between failures". |
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| Perry Babin |
Go to #102 in the directory of my car audio site. It gives the basics for testing power output.
Before testing any amplifier, you should realize that some are poorly designed and will not survive long term testing with a sine wave at full power. Many times, the heatsink is so poorly designed that only a small part of it will get hot. The aluminum is too thin to conduct the heat quickly enough to make use of all of the sink. In short, if you're testing budget amplifiers (particularly class AB amps), be prepared to quickly disconnect main power from the amp. |
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| jackinnj |
In fact, thinner aluminum will conduct heat more quickly
Joules/Time = Conductivity * Cross Sectional Area/Length
That's why your aluminum baseboard heaters are more efficient than your old cast-iron radiators. |
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| Perry Babin |
| The thinner aluminum will get hot within a small area of the transistors. Thicker aluminum will more efficiently transfer the heat away from the transistor. For normal audio, the thin heatsink will transfer the heat away from the transistors well enough but when testing at full power, the transistors (and a small area of the sink) will reach a much higher temperature than they will on a thicker sink. |
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| jackinnj |
| quote: | Originally posted by Perry Babin
The thinner aluminum will get hot within a small area of the transistors. Thicker aluminum will more efficiently transfer the heat away from the transistor. For normal audio, the thin heatsink will transfer the heat away from the transistors well enough but when testing at full power, the transistors (and a small area of the sink) will reach a much higher temperature than they will on a thicker sink. |
Cornell Physics Department:
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| Perry Babin |
If we were discussing interface materials (between the semi and the sink), this may be valid.
If this applied to heatsinks, amp manufacturers would use aluminum foil for heatsinks. They'd save millions on shipping alone. |
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| valterdaw |
| quote: | Originally posted by Perry Babin
If we were discussing interface materials (between the semi and the sink), this may be valid.
If this applied to heatsinks, amp manufacturers would use aluminum foil for heatsinks. They'd save millions on shipping alone. |
Exactly! Assuming heatsink/semi thermal contact is perfect and not depending on thickness of heatsink, the bigger "heat accumulator" or "integrator" you have, the slower resulting temperature will change depending on power, semi trying to dissipate at each particular moment. Big heatsink can be represented as set of thin ones, with the perfect thermal contact to each other. |
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| jackinnj |
the problem with a very low mass heat sink is that it will change shape -- basically once you top up the heat sink with the amount of energy it can store you're done -- after this point it must either radiate or change state, and the radiation is proportionate to the surface area and a thermal transfer coefficient.
i have some huge heat sinks used in CNC -- #2 son got them on a dumpster-dive when he was at Carnegie Mellon. |
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