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From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: Pure sine wave inverter ?
Date: Sat, 23 Sep 2006 13:45:47 -0400
Message-ID: <>

You don't need a sine wave inverter for an oxygen concentrator.  It'll
run just fine on a cheap one.  I ran my dad's portable unit on a
Vector 400 watt unit and then on a 1kw unit.  Starting was iffy on the
400 so I upgraded.

1kw inverters are widely available for under $100.  I'm sitting at a
Love's truck stop right now and saw that they were offering a Xantrex
1kw for $79.  Harbor freight has a nice 2kw unit for $149 unless it's
cheaper on sale.


From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: Pure sine wave inverter ?
Date: Sat, 23 Sep 2006 16:43:14 -0400
Message-ID: <>

On Sat, 23 Sep 2006 19:03:47 GMT, "JerryD\(upstateNY\)"
<> wrote:

>Thanks for that information Neon.
>I wasn't sure a cheap inverter would run the oxygen concentrator and because
>of the importance of it working properly, I didn't want to take a chance.
>I already have a 700 watt modified sine inverter so I can use that or the

You're welcome.  There isn't anything in the concentrator that is at
all sensitive to power quality.   Just a motor running some sort of
air pump and a logic board that runs on filtered, DC power.

Take note of what Sorbonne said about power consumption.  Now I don't
for a moment believe that the thing will draw 4 amps X 120 volts worth
of real power.  Small AC motors are notoriously low in power factor.
The real power consumption will probably be on the order of 250 watts,
about right for a quarter horse electric motor.  Even 250 watts,
however, is a considerable drain on a 12 volt system.  That would be
about 22 amps to the inverter.  That will require a pretty large
battery bank AND a high amperage charger to deal with.

I should comment in passing that I'm VERY impressed with the batteries
on my semi truck.  They're 8D type maintenance-free.  Four of 'em in
parallel.  Private labeled for International and marked "dual
purpose".  Like most truckers, I have a large inverter in the truck
and several continuous loads such as the mini-fridge.  By my
measurement, the inverter draws at least 25 amps just for the base
loads (fridge, cell charger, camera charger, computer, etc.)

I can park for 10+ hours with the engine off and this stuff running
and have still have the engine spin right to life.  The truck has a
low voltage cutoff which is supposed to reserve enough power for
cranking.  It has never tripped.

As impressive, I can turn on the toaster and the microwave at the same
time which draws right at 150 amps from the system, and not have the
lights dim at all. Even with the engine off.

I noticed these batteries on display at the International dealer
priced at $120 each so they're not outrageous.

I haven't had time to investigate these batteries fully so I'm not
necessarily making a recommendation.  Just relating a couple weeks'
experience since I've had this brand new truck.


From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: Thanks, for all the responses.
Date: Sat, 15 Dec 2007 16:09:05 -0500
Message-ID: <>

On Sat, 15 Dec 2007 10:52:04 -0500, GingerJools <> wrote:

>On Wed, 12 Dec 2007 11:18:36 -0500, Neon John <> wrote:
>>On Wed, 12 Dec 2007 07:52:39 -0800 (PST), GingerJools <> wrote:
>>>What are the advantages of _modified_ sine wave inverters?
>>Cheaper and somewhat more efficient than pure sine inverters.  Few products care what
>>the waveform looks like so the MSW type works fine.
>Thanks John, and Will. I enjoyed your discussion of the details.
>I think, if the cost differences are shrinking, I will look for a pure
>sine inverter next year.  Lazy Lady didn't come with one at all.  Her
>solar panels are used solely to recharge the batteries, which is a

You're welcome.

While the gap in EFFICIENCY between MSW and sine wave inverters is narrowing, I
haven't noticed a big change in the price premium mfrs charge for sine inverters.
Mostly because the market will support the premium prices and not because sine
inverters are that much more expensive to make.

As with most other things RV, I recommend sitting down and analyzing your planned
usage before deciding.  MSW inverters operate just about everything OK nowadays.  The
one glaring exception that I'm personally experienced with is DeWalt's cordless tool
battery chargers.  Maybe other brands too but that is the only brand I have
experience with.

About the only place where MSW inverters don't do so well is with SOME but not all
audio-visual equipment.  Some cheap stereos will pick up a hum from the sharp edges
of the waveform.  Some cheap TVs will pick up noise bars from the same cause.

This is becoming much less of a problem as switching power supplies (that don't care
whether the power is AC or DC) get designed into more and more consumer appliances.

A popular but false myth is that computer gear doesn't like MSW power.  Going back to
the first PCs and laser printers, I've yet to experience any of those alleged
problems.  Currently on my computer desk is a Brother laser printer, a Canon scanner,
an HP inkjet printer, this laptop, several external hard drives, a 13 port USB hum
and a DVD burner, all powered from a quite old MSW uninterruptible power supply.  A
UPS is just a fancied-up inverter, battery charger and battery.

If you want to buy a sine inverter just to have the best, that's perfectly OK, of
course.  But unless you have some quite special application to power, there isn't any
technical reason to spend the extra money.


From: John De Armond
Subject: Re: taiwan ebay sine inverters -- crap or good?
Date: Fri, 28 Dec 2007 23:33:25 -0500
Message-ID: <>

On Fri, 28 Dec 2007 11:18:12 -0800, "Ulysses" <> wrote:

>The general consensus is that it's bad to run a refrigerator (compressor
>type) from a MSW inverter.  Would it be safe (safer) to run one from MSW
>with one of these filters?

I don't know about that.  I run two chest freezers and a refrigerator here in my
cabin on my MSW UPS.  I also run a conventional compressor fridge in my MH on an MSW
inverter.  Many moons ago I ran my office 'fridge along with all my computers and a
laser printer on a pure square wave inverter-based UPS.

The compressors get a little warmer than normal - the harmonic content causes higher
hysteresis losses in the iron - but not enough to worry about.

The filter would reduce the harmonic content and thus the heating so yes, if you're
worried about the heat, the filter will help.


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