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From: David Lesher on 10 Apr 2008 00:38

So I'm trying to protect a 5 ton heat pump from power flaps, the
kind that occur when heavy winds blow trees across the primary feed
to a rural home.

The HVAC industry seems to have some prepackaged solutions, such as the
ICM491 <www.icmcontrols.com/downloads/icm491_ig.pdf> but I'm wondering..

It seems to say it samples the power for 5 seconds before acting. That
strikes me as way too slow. I want to drop the compressor offline in a
second or two, so it does not attempt to resume after falling to say half
speed or so.

But it appears to be popular in the HVAC industry...

What say the learned ones here?


--
A host is a host from coast to coast.................wb8foz(a)nrk.com
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433
From: Phil Allison on 10 Apr 2008 02:25

"David Lesher"
>
> So I'm trying to protect a 5 ton heat pump from power flaps, the
> kind that occur when heavy winds blow trees across the primary feed
> to a rural home.
>

** Is a " power flap " the same as a " power flop" or different ?

Perhaps the latter is a prime cause of the former ?




........ Phil


From: Martin Brown on 10 Apr 2008 05:40
On Apr 10, 5:38 am, David Lesher <wb8...(a)panix.com> wrote:
> So I'm trying to protect a 5 ton heat pump from power flaps, the
> kind that occur when heavy winds blow trees across the primary feed
> to a rural home.

I guess what we would call a power brown out in the UK where
incandescent lamps dim etc. Ours used to dim when it was wet and
stormy as strips of the antique perished insulation would bridge two
phases. They replaced the old cables with aluminium 3 phase with a
steel hawser core a few years back - that proved strong enough to
support a fallen tree! Although it did bend all the power line poles
along the road as a result.
>
> The HVAC industry seems to have some prepackaged solutions, such as the
> ICM491 <www.icmcontrols.com/downloads/icm491_ig.pdf> but I'm wondering..
>
> It seems to say it samples the power for 5 seconds before acting. That
> strikes me as way too slow. I want to drop the compressor offline in a
> second or two, so it does not attempt to resume after falling to say half
> speed or so.
>
> But it appears to be popular in the HVAC industry...
>
> What say the learned ones here?

The spec seems to say 50mS response to a total power disconnect and a
5s of 12% under or over voltage set point. And then a preset lockout
time before it retries if the power resumes normality. That seems
fairly reasonable to me. Although I would hope that it might act a bit
quicker if it found the line voltage suddenly at 1kV.

Regards,
Martin Brown
From: David Lesher on 10 Apr 2008 14:31
Martin Brown <|||newspam|||@nezumi.demon.co.uk> writes:

>On Apr 10, 5:38=A0am, David Lesher <wb8...(a)panix.com> wrote:
>> So I'm trying to protect a 5 ton heat pump from power flaps, the
>> kind that occur when heavy winds blow trees across the primary feed
>> to a rural home.

>I guess what we would call a power brown out in the UK where
>incandescent lamps dim etc. Ours used to dim when it was wet and
>stormy as strips of the antique perished insulation would bridge two
>phases.

A brown out [to me...] is gentle. A power flap is anything but that; as
the limbs short/unshort in the wind, the line voltage dives and restores
suddenly. The compressor, winding down to a stop, lurches back toward
full speed, only to have the line drop again.


>The spec seems to say 50mS response to a total power disconnect and a
>5s of 12% under or over voltage set point. And then a preset lockout
>time before it retries if the power resumes normality. That seems
>fairly reasonable to me. Although I would hope that it might act a bit
>quicker if it found the line voltage suddenly at 1kV.

The question is: is "total" zero volts, and do you really get zero in a flap?
Not 25% or so, but zero?


--
A host is a host from coast to coast.................wb8foz(a)nrk.com
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433
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