[time-nuts] External cooling fans - source

[Bob kb8tq]

Hi

Yes, this *is* a bit off topic. Sorry about that … I’m sure it’ll never / ever happen 
again :) …. ummm …. today ….

The voltage that supply feeds are set to is as much a public relations issue as a 
technical one. People would routinely complain “the lights are to dim”. Voltage
gets bumped up. Complaints drop off. Eventually you are right at (or as you observe 
marginally above) the max limits. Since the power company is paid by the watt, the
added power usage (if any) is not a big deal. The call outs for checks *are* a big
deal to them ….. complaints impact the metrics by which they are judged ….

Bob

> On Dec 19, 2017, at 12:48 AM, Dr. David Kirkby <drkirkby at kirkbymicrowave.co.uk> wrote:
> 
> 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
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