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From: John De Armond
Subject: Re: 12 v dc inverter to 110 v ac questions
Date: Mon, 17 Jan 2000 23:22:56 EST
Newsgroups: rec.outdoors.rv-travel

BadRadd wrote:
> >Will KD3XR wrote:
> >Look up inverters ( HEART INTERFACE for example) for more complete
> >information.
> That's bad advice Will.  Heart Interface lies like hell in their promo material
> when they say that all your appliances will operate flawlessly on their
> invertors, which are modified sine wave units.  If you call them on this,
> they'll try to convince you that a small percentage of tvs have problems
> running on their rigs.  The reality is that 3 out of 4 of mine had scrolling
> horizontal lines while connected to it. I don't call that a small percentage
> and in my opinion Heart Interface are nothing less than corporate thieves in
> misrepresenting their products.

I've had the same experience with several brands of pseudo-sine
(sic) inverters and several TVs.  Some combos cause the picture to
roll or tear.  ALL combos have had some amount of hash in the
audio.  All that I've tested caused intolerable crap in the AM radio
(and by inference, to HF ham radio.)  I experimented with adding a
snubbing network* to try to soften the sharp edges of the square
wave with mixed success.  I could usually get the rolling to go away
but some buzz remains.**  Some inverters flat don't like the snubber
and show their displeasure by overheating, blowing fuses, letting
the blue smoke leak out or a combo of the above.

> Statpower makes true sine wave units which put out power that is just as clean
> or better than your local utility for about the same price as those other
> jerks.

That's the one I'm going with.  I've had good luck with Statpower in
the past for running sensitive electronic test equipment in a
service van.  The relatively small penalty in efficiency and cost is
worth it.

* The snubber is placed across the 120 volt output and acts as a
high pass filter, clipping off the sharp edges of the square waves
that make up the pseudo-sine.  Values have to be determined somewhat
experimentally but a good starting value is a 0.1uF poly cap in
series with a 4700 ohm 5 watt resistor.

** I'm sure someone will exclaim that their XXX brand (usually $$$)
TV works perfectly.  Irrelevant to this discussion, since so many
low cost TVs ARE affected.  I personally would not risk a good TV in
the RV.  Shaking a shadow mask out of alignment is a lot less
financially tragic to a $150 TV than to a $500 one.


From: John De Armond
Subject: Re: 300 watt inverter
Date: Wed, 16 Feb 2000 14:35:35 EST
Newsgroups: rec.outdoors.rv-travel

Brad Slaughter wrote:
> Leo <> wrote in article
> <14rq4.92531$>...
> > I have just purchased a small 300 watt inverter from Costco. I plugged it
> in
> > and hooked up a small 14" T.V. which  worked just fine,however I am quite
> > surprised at the amount of noise the internal fan makes while the
> inverter
> > is on. Watching the tube at night while laying in bed would certainly
> I bought a small inverter that is solid-state with NO mechanical cooling
> for my TV, therefore no noise. I think it claimed 140 watts continuous
> output.  You may want to see if you really need all of that 300 watt power
> and have to pay for it with additional cooling.  The little inverters sell
> for $29.99-$49.95.  It worked just fine for my TV and DirecTV receiver
> combination in my old motorhome.  Didn't get hot either, even in the
> overhead storage compartment.  I simply plugged it into the empty 12 v
> receptacle on the winegard antenna amplifier, then moved the TV plug to
> it's outlet.
>         Just an idea...Brad

One word of caution.  Many TVs require a large, momentary surge of
power to operate the degauss circuit when the set is plugged in or
turned on.  My Wallyworld special 12" combo TV/VCR is such a
critter.  A 140 watt inverter I started with would trip on overload
when the TV was plugged in.  I could bring the TV up on the
generator (the degausser doesn't fire again for several minutes) and
then plug it into the inverter and everything was fine.  I could
also "thump" the inverter several times (turn on, turn off, reset)
which gradually heated the degaussing thermistor enough to turn off
but I was highly uncomfortable to subjecting the TV to repeated
power surges.

My solution has been a 300 watt inverter.  Got mine from Autozone. 
Yep, has a loud fan.  I installed a small capsule thermostat inside
the inverter to turn the fan on and off as needed.  It has never
been needed.  I also mounted the inverter up under a shelf inside a
cabinet so that a closed door will shield the noise if the fan ever
does run.


From: John De Armond
Subject: Geneator/battery charger combos (was Re: Honda EU3000 generator  
Date: Wed, 10 May 2000 14:28:44 EDT
Newsgroups: rec.outdoors.rv-travel

BadRadd wrote:
> >I dry camp with 6 golf car batteries.  I charge them for 4 hours with a
> >60 amp charger every day.  Then run the inverter for everything except
> >air for the rest of the day and night.  Just running an air cleaner or
> >fan all night draws down the batteries big time.  My EX 1000 Honda will
> >not run my 60 amp charger, have to go with the EX 4500.
> 60 amps times 14 volts equals 840 watts. Why won't the EX1000 run your charger?
>  It certainly should.  

It's because the charger presents a highly reactive load to the
inverter inside the generator.  The charger only draws power over a
short portion of each 60 hz half-cycle when the voltage of the
transformer output + the diode drop is greater than the battery
voltage.  In addition to being rich in harmonics, this short
conduction angle draws a very high peak current that instantaneously
overloads the inverter.  This is why the AC generator/battery
charger combo is a bad idea.  Note that solid state converters
usually have the same input "power factor correction" that computer
switch-mode power supplies do and so don't draw such a high peak

The better setup is an engine-driven DC generator.  Example:  My
Honda EX350 inverter generator will not drive my 15 amp battery
charger at all, even though the apparent wattage is well within
range.  OTOH, the "cordless battery charger" that I build,
consisting of a similar small 2-stroke engine directly driving a
modified small car alternator, will easily charge at 60 amps.

I noticed in a recent Popular Mechanics that Subaru, of all
companies, is now making a small, portable combo AC and battery
charging generator.  According to the article, the generator is only
available at Subaru car dealers.  Go figure.


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