[time-nuts] HP and other equipment failure

David Kirkby david.kirkby at onetel.net
Fri Jun 14 09:13:32 UTC 2013


On 14 June 2013 05:48, Perry Sandeen <sandeenpa at yahoo.com> wrote:

> There are two long standing truths about
> electronic equipment.  One you can’t have
> too much filter capacitance.  Two, you
> can’t cool too much.  (Please spare me
> the  liquid nitrogen or submarine battery
> comments.)
>
> Regards,
>
> Perrier

Well, I have to disagree with both comments.

More filter capacitance in a standard linear power supply means the
diodes take more current for a longer period of time. For any given
diode, that puts more strain on it. At very high levels of
capacitance, the amount of stored energy is huge, and can be
dangerous. In the event of a fault, higher stored energy has the
potential to do more damage than lower stored energy. Once you have
sufficient capacitance, which includes calculating the effects of
reduced supply voltage, minimum capacitance of device with tolerances,
and some safety factor, I don't see what more capacitance does other
than increase costs, weight, and the potential for more damage in the
event of a fault.

Whilst it is well known that increasing temperature gives rise to
shorter component lifetimes, more cooling also requires more noise,
and so a compromise has to be met. I have here an Air Control
Industries VBL9 blower, which I want to sell in fact. That will move
about 1000 cfm at 6" of water pressure. It happens to take 2.8 kW from
the mains, the startup current is too large to not blow a normal mains
fuse in a plug here in the UK, and the noise is enough to get
neighbours wondering what the hell it is, despite I live in a detached
house, some 50 m from the nearest property. So while a HP 5370B needs
far more cooling than provided, I think the VBL9 would certainly
provide too much cooling air.

Engineering is always a compromise. HP usually got that balance about
right, although in some instances, like the 5370B, that is not true. I
know mine got pretty damm hot, and I'm quite near sea level. I would
imagine for someone at a high altitude, it would be even worst.

I have to agree with you about the serviceability of older HP
equipment though. It is much more serviceable than modern equipment.
However, you would have to go back a long way before finding equipment
which one could guarantee one could keep going, as most things I'd
contemplate buying will have a ASIC and/or some other specialist
component which if it failed would be impossible to get except by
taking one from a similar piece of equipment.

Dave



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