"Mr.T" wrote in message
news:49614d0d$0$12942$afc38c87@news.optusnet.com.au...
>
> "GlennP" wrote in message
> news:49603c92$0$3799$afc38c87@news.optusnet.com.au...
>> Nice thought but no.
>> Motors, refrigeration compressors (fridge, freezer, air conds.), actually
>> themselves cause a brownout on start-up & are not affected by the brief
>> milliseconds drop in voltage,
>
> Of course, but a sustained "brownout" can be a killer. A millisecond drop
> in
> voltage DOES NOT qualify as a "brownout".
>
>>they can easily handle a 30-35% dip in voltage
>> without damage.
>
> For a few seconds, or maybe even minutes, sure.
>
>> As a motor starts, (depending on the motor & how it's wired to start), it
>> can draw up to or over 10 times the full load current. i.e 5 amps full
> load
>> at 240 V can be around 50 amps at 240 V on start up, which depending in
> the
>> size of the motor & it's load can last anywhere from 1 second to 20 or so
>> seconds, & as you increase the current with a fixed resistance/impedance
> the
>> voltage drops, (thus self created brownout).
>
> Your definition of "brownout" here is completely fallacious.
>
>> Brownouts can last for a few seconds or a few hours depending on what
> caused
>> it & how it's controlled. Long lasting minimal voltage drop ones can
> damage
>> motors,
>
> Depends on *your* definition of "minimal".
> By a more reasonable definition that would be less than 10% and should
> cause
> no problem with a properly designed motor.
>
>>but internal overload circuits usually trip out long before that
>> happens, protecting the motor.
>
> IF they are fitted and work properly, then possibly yes. The number of
> fridges and freezers killed by longer term brownouts over the years would
> prove this is not always so. In fact last months Silicon chip has a
> circuit
> for a brown out protector to shut off the mains in just such an
> eventuality.
>
>> Short (millisecond) ones of large or small
>> voltage drop (like happens during storms) is more likely to damage the
>> electronics controlling the motor or other electronic items, than it is
>> to
>> damage the motor itself.
>
> Which is NOT a brownout. But in any case short voltage DROPS will not kill
> electronics, a resulting sharp increase MAY however.
> Some items do not like having the mains turned off AND on again rapidly,
> but
> name one item that cannot cope with the mains simply being turned off?
>
>> It's not necessarily the lower than expected voltage that kills
>> *electronics* is the rapid rises & falls in voltage that they don't like.
> As
>> I said before, electronics like smooth regulated voltages.
>
> Funny then that most power amps for example are unregulated, and often
> survive for decades, and being turned on and off when needed.
> As I said, rapid FALLS in the mains voltage do not kill electronics. In
> fact
> almost ALL electronic items suffer just such a drop every time the power
> is
> turned off! For many that is every day, or even more.
>
> Hell, even a light bulb will fail at switch on, not switch off, and for
> quite obvious reasons.
> I'm very surprised they are not obvious to you.
>
> But hey, you can believe in the tooth fairy if you like, I'm not about to
> care.
>
> MrT.
>
>
>
Believe what you want.
Are you an electrical engineer? If so I'll stand corrected & believe you.
I'm an electrical tech. (1 step down from engineer) I've been doing this for
over 20 years, my Father & Grandfather were are electricians, so I have been
involved with it one way or another all my life.
Millisecond voltage drop DOES qualify as a brownout, any surge that will
make an incandescent light bulb noticeably flicker is a voltage drop below
nominal voltage & 0 volts, which is the definition of a brownout.
Your definition of minimal voltage drop at less than 10% wouldn't harm a
motor because it isn't a brownout, it's still within the nominal allowable
voltage range. At 240v a minimal voltage drop would be (210v may just scrap
in) but 205-190v is minimal voltage drop, below that working overloads
should start tripping out.
As for fridges & freezers being killed by longer term brownouts, that
concludes to me 1) It is probably old & may be ready to die anyway, 2) It's
obviously not working properly & any change in the electricity supply
potentially has the ability to kill it.
As for light bulbs failing at switch on & not off, maybe you should tell me
the obvious reasons cause I have seen many light bulbs fail at or within
seconds of both switch on & off, & light bulbs failing has nothing to with
the surge or rise & fall of voltage (that's a factor, but not the cause).
The cause of a light bulb failing is due the expansion & contraction of the
metallic element that runs white hot.
Answer me this though, if the rapid fall in voltage (not total loss of
voltage i.e. turning it off) doesn't kill electronics, then why does the
rapid increase (back up) kill them, when the voltage doesn't rise back up to
anything over what they were working at possibly milliseconds ago?
In real world situations, during a storm a distant lightning strike may
instantly & briefly (milliseconds) earth the energy in power lines & drop
the voltage making your lights flicker, when the lines are re-energized the
voltage comes back up. If it was at 240v before the lightning strike, it
returns to 240v not more, not even briefly, so why do so many electronic
components fail during storms when no direct or close (within 500m)
lightning strikes occur?
A direct lightning strike is different & may raise a 240v supply to 1000's
of volts, & more than just your electronic components will fail.
Glenn.
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