Mono block temp difference

[Disco-Pete]

Here's a strange phenomenon. First of all, many thanks to nattawa for stepping in and getting these up to standard +.

Okay, the left one idles about 4degF cooler than the right. But if I switch them around, the left one still idles 4degF cooler than the right. What's up?

 

[jacques antoine]

Here's a strange phenomenon. First of all, many thanks to nattawa for stepping in and getting these up to standard +.

Okay, the left one idles about 4degF cooler than the right. But if I switch them around, the left one still idles 4degF cooler than the right. What's up?

Spooky !!
Do you have a heating device on the right?
An air draft on the left?

 

[rayma]

Here's a strange phenomenon. First of all, many thanks to nattawa for stepping in and getting these up to standard +.

Okay, the left one idles about 4degF cooler than the right. But if I switch them around, the left one still idles 4degF cooler than the right. What's up?

How about a photo? Are they on a shelf, or the floor? What's close to them?

 

[Disco-Pete]

They're on the floor. Heat vent is about one foot away but absolutely no air hits the amp. I will temporarily block it off completely and report back. I suppose the overall ambient temp increases exponentially toward the vent though. I didn't think it would be quite that drastic.

 

[rayma]

They're on the floor. Heat vent is about one foot away but absolutely no air hits the amp. I will temporarily block it off completely and report back.

It's definitely the heat vent. You can use a heat shield such as a piece of cardboard to make a partition a little higher than the amps between them and the vent..

 

[Disco-Pete]

Yes, it is the heat vent. Even though no air directly hits the amp. The vents in the heat register are turned parallel to the amps. I can hold a lighter flame between it and the amp with no disturbance.

 

[nattawa]

If the duct under the floor runs underneath one of the amps it could make a slight difference in heat sink temperature.

 

[Disco-Pete]

Hi Shaoyi. It's not the duct work because my conclusion is a result of closing off the register completely. I wrapped it in a plastic grocery bag and stuck it back in it's place. Both amps are now the same or very close. But I'm surprised that there should be a difference since the amps are side by side with only a few inches between them. So it must be radiant heat from the air coming out of the register since no air from it hits the amp directly? Or simply mixture taking place in close proximity to the register that I'm not able to detect.

 

[AndrewT]

A passive heatsink, although not designed to be blown, is very much affected by forced airflow.
Even quite innocuous draughts can increase the air flow rate substantially and affect the effective cooling.

 

[jacco vermeulen]

side by side with only a few inches between them.

Think 3 heat sources in a row.
Which will be effected most by the other two ?

 

[Disco-Pete]

Thanks all for clearing that up. Now on to the next big discovery.

 

[jacco vermeulen]

Your next discovery is that part of the 4F temperature difference is due to the rapid change in W/C (C/W) for heatsinks that operate at less than 35F above ambient.

 

[Disco-Pete]

They are at 105F. Room temp is 73. What does W/C stand for?

 

[jacco vermeulen]

The reciprocal of C/W

 

[Disco-Pete]

Oh, you mean like a backwards running clock? A quick search turned up about 100 meanings, none of which referred to the topic at hand. I did find a reference to heat sink temp but still no specific terms for C and W. I gathered C stands for centigrade and W for time?

 

[AndrewT]

C = Celcius or Centigrade. But is a temperature DIFFERENCE. It is not a temperature as in °C

W = Watt. This is the Power to be dissipated.

W/C is the dissipation capability in Watts for each Cdegree above the ambient (temperature difference).

C/W is the rise in temperature due to power being input to the device/dissipator.

One is the reciprocal of the other.

 

[nattawa]

....and because it is the temperature differential that drives air convection (velocity) and determines temperature gradient towards the ambience, a heat sink operates more efficiently in terms of c/w at temperatures high above ambience than would otherwise. That's why jacco says what your next discovery could be.

 

[Disco-Pete]

I get it. Thanks.
Can you have too much heat sink in an audio amp?