[time-nuts] Z3805A cooling requirements?

Volker Esper ailer2 at t-online.de
Sun Dec 16 13:57:29 UTC 2012

It's the same as with the SR620 TIC. As long as you have only one common 
chamber for all parts, you have to make tradeoffs for everyone:
the power supply needs cooling (as much as it can get), the control loop 
of the oven is not designed for additional cooling, and comparators and 
further electronics don't need extremely low but stable temperatures, 
that means no air flow.

If you are ready for a change of your mechanical design, (e.g. placing a 
fan at/in the case), place a(n) (isolating) sheet between oven and 
switching supply, then cool the supply bricks abundantly. Make sure that 
the air flow of your fan does not penetrate the seperate oven chamber.

Arranging for a seperate chamber for your oven keeps the natural air 
flow due to convection undisturbed.

I guess, placing the additional sheet shouln't be too much of work.


Am 12.12.2012 02:20, schrieb SAIDJACK at aol.com:
> Stu,
> a fan is about the worst thing you can do for your Z3805 it will
> significantly worsen the stability of the output frequency. The oven inside does  get
> warm, that's why it is an oven :)
> The power consumption will go down once it heats itself up, the unit is
> designed to work without a fan sitting on a desk etc. Just make sure the vent
> holes are not clogged.
> Sounds like your Z3816 had a failure that caused the units power  supply to
> overheat.
> bye,
> Said
> In a message dated 12/11/2012 16:22:10 Pacific Standard Time,
> stewart.cobb at gmail.com writes:
> This may  be a newbie question, but I'm a newbie, so:
> Do the HP telecom GPSDOs  (Z38xx) require external airflow for cooling?
> They don't have built-in  fans, but they sorta look like they depend on a
> rack-level cooling fan,  which a telecom rack would almost certainly have.
> I ask because I  bought a Z3816 awhile back which worked for about a week
> and then failed. I  traced the failure to an internal power supply brick,
> which had a big  finned heat-sink attached but nevertheless smelled
> overheated and was  shorted internally.
> I never found a replacement power brick, and I  don't have time to mess with
> it right now, so I recently bought a Z3805A.  It, too, looks like it's
> working, but it started to feel awfully warm after  a few hours, so I
> unplugged it for now.
> It probably wouldn't take  much of a fan to bring the internal temperature
> down close to ambient, and  the fan could be powered easily enough from the
> supply rails. But that  might create a temperature gradient where the
> designers didn't intend one.  Or it might cause problems I don't even know
> about yet.
> At the  moment, the Z3805A is in a fan-less 19-inch rack with a bunch of
> other  equipment, in a lab environment. Should it have its own  fan?
> Cheers!
> --Stu
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