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

["Steven Naugler" <snaugler earthlink net>]

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 ½? 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