[time-nuts] External cooling fans - source

[Dr. David Kirkby]

On 18 December 2017 at 23:11, Charles Steinmetz <csteinmetz at yandex.com>
wrote:

> From time to time, the subject of external cooling fans comes up -- for
> example, in discussions of the HP 5370A/B with their steaming hot
> heatsinks.  I have several times recommended very quiet, all-metal, 4" desk
> fans as ideal for the job, but have not been able to suggest a source.
>

For what it is worth, my 5370B run very hot, which forced me to check my
mains voltage as I knew every time I had done a quick measurement, the
voltage was above 230 V. So for a few days I logged the voltage, and found
it was consistently high. The maximum permitted here in the UK is 253 V,
but I measured mine at 255.x volts. It was the heat of the 5370B that
forced me to contact the electricity supply company (UK Power Networks),
who logged the voltage for 4 days. I have a 3-phase supply here, which is
unusual for a domestic property, but each of the 3 phases was consistently
high. I managed to get the supply company to reduce the voltage by 5%. That
made a *significant* difference in the heatsink temperature of the 5370B,
and a significant difference to to the exhaust temperature of my HP 70000
series system.

I'm not saying an extra fan is not a good idea, but it is certainly worth
ensuring the mains voltage is not too high. I was told by UK Power Networks
that they aim for 245-250 V in rural areas - this is despite the UK is
supposed to be 230 -6%/+10%. On equipment with linear power supplies, a few
extra volts can lead to a significant increase in the amount of heat the
regulators produce. 10% extra voltage does *not* equate to 10% extra power
dissipation, but considerably more.

I found quite a reluctance on the part of the UK Power Networks to reduce
the voltage. Even though it was was on average more than 5% high, the
technical manager who took ownership of the problem only wanted to reduce
the voltage by 2.5%, despite they could easily reduce it 5%. Luckily, when
the engineers came to adjust the supply voltage, (which they do by changing
the taps on the 11 kV primary), I managed to convince them that there were
very few properties on the transformer, and the furthest was an old couple
that used very little electricity. So they did reduce it 5%, which is the
maximum they could. But they warned me that if there were complaints of low
voltage, they would have to increase it 2.5%. Luckily for me, nobody
locally noticed the reduction in mains voltage, and it is still on average
over 230 V.

It would be interesting to know how low the AC input can go on a 5370B
before the regulators fail to regulate. Given they are the sort of
instrument one might want to run for long periods, running one on a UPS,
with a transformer to reduce the output of the UPS, might not be such a bad
idea.


> Charles
>

Dave