[time-nuts] Re: PRS-10 heatsink design

[Bob kb8tq]

Hi

All of these small “telecom” Rb’s suffer the same way. The form factor is similar
and they all dump a lot of heat out the baseplate. None of them do well with a 
“down facing” simple heatsink

“Simple” answers:

1) Use a fan / forced air. That’s how they typically where used in most (but not
all …) telecom gear. 

2) Go off to any of the many online heatsink outfits and buy a chunk of extrusion
better suited to the task. Even with 30 mm fins, down facing isn’t great.

3) Flip the unit so the fins face up

Best is still going be fins that are up/down in the vertical plane (if that makes
any sense at all …) and get good airflow from bottom to top. 

If you go with a fan, be careful to isolate it a bit. Rb’s do have vibration sensitivity. 
One plus with a fan is that you can servo it to maintain accurate temperature. 

Bob

> On Jun 23, 2021, at 7:00 AM, Dana Whitlow <k8yumdoober at gmail.com> wrote:
> 
> I mount my PRS-10 vertically (so that the channels between the fins are
> vertical),
> with the connector on top.  This orientation was chosen simply for best
> access to
> the connector, but yields heat sink temperatures down around 45C to 50C.
> The
> unit is open and fully exposed to the air.  I run it at 24Vdc.
> 
> The open mounting is obviously best for natural convective cooling, but does
> leave the stability somewhat vulnerable to ambient temperature variations,
> drafts, etc, although I've not had obvious problems with this.
> 
> If you want to combine good cooling with low dependence on rapid variations
> in ambient temperature, I suspect the best way is to interpose a very thick
> aluminum (or copper) block between the heatsink flange of the PRS-10 and
> the heatsink.  The block will add minimal thermal resistance, but will
> serve as
> a thermal lowpass filter.  The downside to this is that full warmup of the
> PRS-10
> will take longer.
> 
> Dana
> 
> 
> On Wed, Jun 23, 2021 at 2:05 AM James Wilson <jmw at fastmail.com> wrote:
> 
>> My limited experience with the factory heatsink for the PRS-10 has left me
>> pretty unsatisfied. It seems ok for brief bench evaluation but not for
>> permanent enclosure installation. Reported unit temps are in the 70 - 75 °C
>> range with it sitting on a bench in a 25 °C room. It needs to be turned on
>> its side or upside down for any convection to take heat away, or for fans
>> to be directed at the fins. There are no side or top screw holes on the
>> PRS-10 so you can’t mount it in that orientation. Has anyone found or built
>> a better heatsink that can use active cooling?
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