From: ems@michael.apple.com (E. Michael Smith)
Newsgroups: sci.energy
Subject: Re: Why not 120 VDC ?  Why invert?
Date: 25 Jan 93 20:53:34 GMT
Organization: Circle 'C' Shellfish Ranch, Shores-of-the-Pacific, California

In article <1k0635INNrkq@gap.caltech.edu> carl@SOL1.GPS.CALTECH.EDU writes:
>In article <1993Jan25.014943.1904@michael.apple.com>, ems@michael.apple.com (E. Michael Smith) writes:
>>>True.  However, if you care anything at all about energy efficiency, you don't
>>>use resistive heat sources.
>>
>>Blanket statements don't always hold ...  speaking of which, what 
>>non-resistive electric blankets are you aware of? ;-)
>>
>>There ARE places where resistive heat continues to make sense...
>
>Electric blankets (except, perhaps, in hospitals) don't fall into one of those
>places.  Maybe an electric blanket is useful when treating someone for
>hypothermia.  For any application where the person using the blanket is capable
>of generating heat, other alternatives work equally well.  For moderate (i.e.,
>above -20 degrees F) conditions, simple wool blankets are quite useful (you
>might need to use a few of them, but they work).  For lower temperatures, a
>blanket with an aluminum core works quite well.

Two things:  1)  I'm allergic to wool.  (We use a fluffy comforter) and
2)  My wife uses a heating pad for lower back pain.  I suppose I could
have taken the time to clarify this, but wanted to avoid the wasted
bytes.  But since the point was pressed, I'll waste em...  There is
no way I'm going to get my wife off of her heating pad. (Endo...). 
There a other folks who use electric blankets similarly...

>Jus how is it that you, known, unless I'm confusing you with someone else, for
>favoring energy conservation, are now advocating electric blankets in
>situations where they're not required?

I, personally, hate electric blankets for my own use.  (The leave me
feeling 'drained' the next day.  I don't know why.).  But I've known
many folks who use them rather than heat the whole room in winter.

I've slept under a ton of blankets in cabins in the mountains in
winter.  It was OK, but I can sympathise with folks who live in
places that are very cold and want an electric blanket.  I HAVE
found them personally useful for pre-warming the bed, then turn
them off when I get in.  (Headonism known no bounds! ;-)

I've very much in favor of any conservation that a)  Doesn't require
a change of my rather comfortable lifestyle and b) would be stupid to
NOT do.  I'm not in favor of conservation that is a pain or not very
cost effective.  Guess I'm a bit like John DeArmond in that sense,
aint nothing gonna get me to give up my big 4x4 truck, but I've got
nothing against putting a better more efficient engine in it (or 
driving my Honda most of the time and only using the truck when
justified).  I'm not going to dictate to folks that they can not
use electric blankets.  Many folks like them and it isn't my place
to tell them they are wrong.  It is a personal decision, but useful
to me as an example.

>>>Switching
>>>to DC means you've probably got to replace your refrigerator, your vacuum
>>>cleaner, your television set, your stereo....
>>
>>Um,the original posting stated clearly that I was looking at a mixed
>>mode system.  (In particular, I stated that an inverter would be
>>needed for electronics, misc. electrical outlest {like for the vac}
>>and the refridgerator).  
>
>So you're going to run TWO sets of wires throughout your home, one for AC and
>one for DC?  Once you've committed to the expense of having an inverter in the
>first place, the cost of increasing the capacity of the unit under
>consideration is relatively small.

That was the plan.  And, as I also pointed out in the post you are
responding to (but which lines you have deleted), on reflection I 
thought that the complication of dual wiring was probably why it
wasn't done.  

BTW, the cost increases may or may not be 'relatively small'...
I ALREADY have dual wiring in my house.  Part 120 VAC, part 220 VAC.
The cost of adding a small part of 12 VDC is trivial.  (One battery
at about $100 and a panel mounted next to the main panel into
which the re-directed wires could be moved.  Call it $150 total DIY.)

To go to 120 VDC would be no harder, but would, as was pointed out
by others, raise the entry point cost of batteries (since it would
take at least 5 batteries (24 VDC are available) and more likely
10 or 20 ( 6VDC )  to get deep cycle types.  Then there is the 
charging complication ...  I think this is the 'coup de gras'.

If you have a big enough system to need 10 to 20 batteries, you
will not notice the extra cost of the larger inverter so much.
That is likely to be less cost than converting the motor in 
one or two major appliances, such as the heater fan.

If you don't have a big enough system to need 10 to 20 batteries,
you don't have anything drawing enough watts to require 120 V
to push it down 12 ga. wire, so 12 VDC is enough.  So why take
on all the complications of a big battery and charge management
for a small system?  

And why go with complicated double wiring schemes if you already 
have a bundle sunk into a large battery bank and would rather 
avoid the need to dink with 120 VDC motor conversion?  

Much more direct reasoning that quibbling over whether or not
folks should use electric blankets...

-- 

E. Michael Smith  ems@apple.COM

'Whatever you can do, or dream you can, begin it.  Boldness has
 genius, power and magic in it.'  -  Goethe

I am not responsible nor is anyone else.  Everything is disclaimed.