[time-nuts] External cooling fans - source

Jeremy Nichols jn6wfo at gmail.com
Tue Dec 19 11:20:04 EST 2017


I put a small external fan on my 5370B, which keeps the heat sink at a
reasonable low temperature (Time-Nut content) -but- (Nixon segué) the power
company here also runs the voltage all the way up to the limit (126VAC)
because "many of our [rural, like me] customers are all-electric and the
load tends to pull the voltage down during times of peak use." The voltage
got so high I finally put a recorder on it and walked the results into
their office. In response, they attached their recorder to my connection
and ran it for a couple of weeks before agreeing with me. Then they
reluctantly turned the transformer down a notch so we stay below 126VAC now.

Jeremy

On Tue, Dec 19, 2017 at 5:44 AM Bob kb8tq <kb8tq at n1k.org> wrote:

> 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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