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----- Original Message -----
Sent: Friday, January 25, 2002 11:57
AM
Subject: Re: [pvusers] Issue 34 re: EMI from
SW4048
>
> That is true, and I pretty much
operate under the same scenario as you. But also remember that the better the
wave form and the better the power factor, the less power your AC appliance will
consume. That translates to slightly less PV & battery.
Yes, it may be that the appliance would use a
little more power on mod. sine....but modified sinewave inverters generally have
a slightly higher efficiency rating than do sine-wave - but - and here's the
major hitch - all inverters I've heard of only reach peak efficiency when
operating at 75% to 85% of their continuous duty rated output.
So when used for the high efficiency appliances
(especially the lighting) universally recomended for RE installations a house
sized inverter, say 1500W - 4000W, would be providing power at around 20%
efficiency or worse. EEEK!
I'm no mathmetician and don't need to be one to see
the flaws in promoting such a scheme.
The efficiency of conversion , or lack
thereof, makes a good argument in favor of buying a small dedicated
inverter for low draw, long run time items such as computers.
Another frequently raised point against the use of
less than pure sinewave is that the life-span of appliances will be
lessened.
I haven't had my t.v., washing machine, coffee
maker, electric mixer, shop vac, etc. etc. for twenty years to find out -
but can see how this could be so.
So......should one spend 70% to 100% more on a sine
wave inverter to possibly ensure a longer working life of intermittent use,
inexpensive appliances, or not? What about the computer? It wasn't so
cheap.
> I am using DC motion detectors, which operate a relay to
switch on and off the AC outdoor lighting. But the DC detectors are
pricey.
They sure are, especially in the RE catalogs. And
the range of detection is often less than A.C. counterparts.
However there are alternatives - parts and/or kits
may be obtained from electronics retailers, or existing products might be
modified to suit the purpose.
The majority of security/surveilance
equipment (both radio-signal and hard-wired) operate on D.C. power, many
have relays to activate A.C. loads such as lights.
In some instances one may bypass the supplied A.C.
to D.C. transformer, replace it with their own D.C. power supply and presto
chango - you got it.
With cheap battery powered units such as Harriet
Carter catalogs' "Driveway Announcer" ($29.95 sender/reciever),
simply bypass the battery compartment with your own power supply and you're
in business for cheap.
> It is also more expensive to wire a
home for DC. For example, my home's DC circuits use #2 wire for the main runs,
and have #8 wire for outlets and hard-wired DC appliances. #12 or #14 Romex is
cheap, cheap, cheap.
The expense of
D.C. wiring could be prohibitive in a retrofit job, but would certainly be worth
considering in new construction.
The cost of D.C. light ballasts for both
flourescent tube and compact flourescents added over half again to the actual
wiring cost.
Our total expense for D.C. wiring, (12V system)
consisting of 10ga.stranded wire running from a total of five 10A D.C.
breakers to both outlets and hard wired fixtures was $279.72 - far less
than the cost of the additional panels we would have needed to provide for the
conversion losses attendant with constant inverter use.
Case in point: We use a home-made D.C. fan for heat
distribution in winter. Fan performance is comparable to that of a standard
twenty inch A.C. box fan on "low" speed.
The widely available A.C. model spins at 450 rpm
and uses 50W, ours spins at 468 rpm (average) and uses 12W.
This fan operates 24/7 during cold weather.
Consider the difference in power consumption,
then figure the A.C. equation at 20% inverter
efficiency...........
Then we have my aquarium lights.......
<Then you also
have to deal with making sure that you have good receptacles for your DC plugs.
Cigarette lighter types suck. I like to use AC type plugs for DC receptacles.
But in order to make sure that I don't accidentally plug a DC appliance in an AC
receptacle, for the DC I use the standard 20 amp receptacles & plugs. They
have one vertical blade and one horizontal blade so they will not accept the
other kind with 2 vertical blades.
Not only do I do away with those nasty cigarette
lighter plugs, but that silly 14ga. or 16ga. appliance cord goes out the back
door too. I do have one female lighter receptacle in the living room for testing
gadgets prior to wrecking the warranty.
I once saw an expensive three speed D.C. box fan
that used 50W on one setting (don't remember which setting), this fan came with
a six foot or so long 14ga. cord with cigarette lighter plug. The proud owner of
this device was also utilizing two 14ga. cigarette lighter plug extension cords
on the grounds that "they wouldn't be selling these things if it weren't
o.k."
Maybe it is o.k.- but not on Goat
Hill.
May the sun shine upon you freely and
consistently
Teri
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