Re: (ET) Harry's suggestion of using DC to power 115VAC devices

[jim <fiskfarm mediaone net>]

Not sure if this was mentioned but never use a tool with a variable speed 
trigger
as well as you can kiss the variable speed solid state unit good-bye. Been 
there
and done that with a Magnum Hole Hog on a DC alternator rig. Situation 
would be the
same off the ET and a DC 120 unit.

Jim

Steven Naugler wrote:

> To Harry and the "List",
>         One potential danger of using DC to power tools sold for 115VAC 
> use that
> have universal motors is that most have AC rated power switches.  An AC
> rated switch will fail prematurely when used on DC, sometimes by welding
> closed (on).  The problem is that AC switches depend on the current
> dropping to zero 120 times a second.  At that zero current any arcing
> stops.  The same switch on DC has to break the current at full current
> because (sorry for being obvious) the current never drops to zero with 
> DC.
> A DC rated switch generally has larger contacts.
>         I am not saying you should not use these tools on DC, but rather 
> be
> careful unless you know the device was designed for both AC and DC use.  
> If
> an AC switch when used with DC fails there is a high likelyhood of 
> failing
> welded in the on position.
>
> Steve Naugler
> snaugler earthlink net
>
> > [Original Message]
> > From: harry landis <hlandis hotmail com>
> > To: <elec-trak cosmos5 phy tufts edu>
> > Date: 9/28/00 9:25:07 PM
> > Subject:
> >
> > To the list:
> >
> > I suppose since there is a flurry of interest in inverters, I will put 
> > in
> my
> > two cents. I built a device last spring that solved the problem for me.
> > Since I don?t want to use anything except tools with brush type motors
> with
> > power from the ET, I don?t need AC. So I took 4  Vicor 150 watt 48v to 
> > 48
> > volt dc-dc converters and connected the inputs in parallel and the
> outputs
> > in parallel. (They are made to run on 36-72 volt input, but actually 
> > work
> > down to 28v) So now I have 600 watts (12 amps) of 48V isolated power.
> Then I
> > took a 48v to 15v 150 watt (10 amps) converter and wired the input in
> > parallel with the other inputs, and put the output in series with the
> other
> > outputs. So now I have 10 amps or more of 63 volt power. Now I put this
> > output in series with the battery pack. Now I have 10 amps or 
> > more(1000w)
> of
> > 99v DC power. Which is just about right to run universal motors. They
> prefer
> > it to 110 AC. Better life, more power, fewer losses. The converters 
> > cost
> > about $100 ea from Vicor. I have about enough surplus ones to make 
> > maybe
> 2
> > more converters. They are about *? x 3? x 5?. It?s called a full brick
> > package. You can probably find them on the Vicor site. I screwed them 
> > all
> to
> > a 1/8? aluminum plate that sits across the front of the E12 under the
> hood
> > (over the batteries). It doesn?t get in the way of anything. The input 
> > is
> > taken from the PTO outlet. The output is an outlet on the plate.It also
> has
> > a switch/circuit breaker to turn it on and protect it from overloads. 
> > The
> > converters are 85% -95% efficient.  It has worked fine from the moment 
> > I
> > first turned it on. I use a weed whacker, chain saw and rotary hammer
> with
> > it, no problem. I haven?t seen a source of these things surplus. I got
> mine
> > in a one time deal. I suppose I would part with a set for  $150. The
> buyer
> > would have to make the mounting plate and wire it all together. I
> probably
> > also have a circuit breaker and  outlet.
> >
> > Harry Landis
> > _________________________________________________________________________
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>
> --- Steven Naugler
> --- snaugler earthlink net