(ET) Re: Driving modern 120 VAC accessories - Chris Tromley's question about paralleling cheapie 12vdc inverters

["John B Reinhard" <reinharj frontiernet net>]

The cheap 12vdc powered inverters are NOT usually sine wave.

I don't know how many different things should not be run on the Modified
Sine Wave inverters, but all the low end (MSW) Uninterruptible Power
Supplies (like APC Back-UPS model line) state that they should only be used
to power PC's - which have switching power supplies in them, and apparently
don't mind Modified Sine Wave power.  For other loads, APC recommends their
sine wave models - like Smart-UPS, or better.

I would think it is similar for power inverters  - and maybe it all depends
on how many steps in the wave - how closely it approximates a real sine
wave.

I think the 12vdc powered MSW inverters can power drills and similar if 
they
are universal motors - don't know if extra motor heating or other side
effects occur.

The power inverters and UPS's with Sine wave output all cost MUCH more than
equal wattage MSW models.

John
E-20's, Comuta Cars, B&D and Ryobi Cordless mowers, and anything else
battery powered I can find or build . . .


----- Original Message ----- 
From: "Chris Tromley" <chris_t microtrac com>
To: <elec-trak cosmos phy tufts edu>
Sent: Thursday, January 06, 2005 1:14 PM
Subject: Driving modern 120 VAC accessories (was: RE: (ET) Battery
maintainers)


Hi Chris,

You have touched on a major problem for me.  I'm closing in on my first 
year
in a new house with a nice big yard, which is why the concept of an ET
quickly went from an interest to a necessity.  Mowing is now a pleasure,
snow plowing is yet to be experienced (I'm ready and eager to try it), but
dealing with leaves and downed branches is still a major headache.

I got a Patriot electric chipper/shredder
http://www.patriot-products-inc.com/products.htm#eleccsv that I'm happy
with.  But the raking and shredding still takes a *huge* amount of time.
Since the shredder also acts as a vacuum, the most time-efficient solution
is to mount it on a tow cart and lift/shred the leaves in one pass.  But
that means powering the shredder from the ET.

It's rated at 120 VAC and 13 amps, but I'm not sure of the actual load 
under
varying conditions.  A 3600 watt inverter is maybe overkill.  But the only
thing I've found that runs from 36 VDC is a Tripp-Lite APS 3636(?)
inverter/charger.  Comfortable power "headroom", plus a nice charger, but
the low low eBay price is $820.  Way more than I paid for my ET.  Or the
shredder.  Finding an inverter that runs from 36 VDC is Very Difficult.
Hmmm, maybe get a bunch of us together for a volume purchase?

Does anyone think I might have any luck finding a more common 800-1000 watt
inverter that runs off 12 VDC that could be paralleled?  I'd run three to
keep the pack balanced.  I'm an electrical dummy, but I know there would
have to be a provision to synch the outputs.  Anyone heard of such a 
feature
on this type of inverter?

rest of original message chopped