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From: Rob Sicade (no email)
Date: Fri Mar 02 2001 - 13:01:53 EST
I promised myself I'd stop posting, but just one more - In the interest of
safety, please do not hook up a 'large capacitor' to the motor .
As a rule of thumb you can expect most AC motors to draw seven times their
normal load when they start. Most inverters allow for a much higher than
normal load for a short time for exactly this reason. My heart 1000W inverter
will supply around 30amp of surge - this is slightly more than 3.5 times it's
continuos power rating. I would expect other inverters to have similiar surge
ratings.
A few comments about inverters and the use of multiple smaller ones in place
of a large inverter, check the specs of a few if this is news.
1. A heart freedom 10 is 93% efficient. The average for smaller, cheaper
inverters is much less (as little as 80% efficient). And before we question
the Heart efficiency numbers, why should I believe the manufacturers of the
others any more than heart. My own measurements on my own boat put the
efficiency at over 90%.
2. The bigger inverter's voltage control will be twice as constant.
3. The bigger inverter's frequency control will be much more accurate.
4. A Heart Freedom 10 draws 0.12 amps when there is no AC load and is pretty
easy to shut off when you're not using it, most of the small inverters
actually draw more when there is no load.
I would have a hard time making a case for multiple small inverters over a
large one, especially if you already own one like a heart or a trace. If I was
powering anything other than something computer-like, I would get at least the
equvalent of a Heart or Trace.
Just my opinion, I'm sure there are much more interesting jury-rigs if the
easy way is too boring.
Rob Sicade
R Hepler wrote:
> I believe a motor can draw 2 to 3 times its 'normal' load
> while starting. What you might be running into, though, is
> that by applying a sudden, large load your batteries might
> drop below the threshold voltage of the inverter, causing
> it to shut off. Do you have a multimeter that will retain
> min/max readings? If so, hook it up and plug in the 'frige
> and see what happens.
>
> I *think* you might be able to hook a large capacitor in
> line with the load to absorb some of the startup load, but
> really wouldn't hazard a guess as to how to size it, or
> even how to hook it up.
>
> -Rob
>
> --- "Rich, Michael" <> wrote:
> > I like the idea of multiple small inverters and that
> > might be my problem. I
> > wanted to run the small (4.2cubic feet) fridge off the
> > inverter. We figured
> > earlier the fridge draws about 4.5 amps. However this
> > fridge over powers my
> > 500/800 peak watt and 600/1000 peak watt inverter when it
> > is plugged in. So
> > do I assume it draws far more when it is powered on. Is
> > there a number for
> > minimum watt inverter I need to power this fridge or is
> > there a way to hook
> > both inverters up to get more capacity? Mike
> >
> > -----Original Message-----
> > From: R Hepler [mailto:]
> > Sent: Thursday, March 01, 2001 5:20 PM
> > To: Live Aboard
> > Subject: Re: lv-ab: inverters
> >
> >
> > I *think* the small (<300w) inverters are actually in the
> > 90's, efficiency-wise. If it is the difference between a
> > $300 printer (was that a canon that was mentioned at that
> > price?) at 12v and a $40 printer and $40 inverter at 120v
> > (and $30 blender and $190 in rum), I know which way I'd
> > spend my $300 >;-P (hic)
> >
> > -Rob
> >
> > --- Jim Lynch <> wrote:
> > > Assuming you've got the opion of running the printer
> > from
> > > either 12 VDC
> > > or 110VAC and the efficiency of the device is the same
> > in
> > > either mode,
> > > then the quick answer is yes. The practical answer is
> > > that it depends
> > > on the inverter. Many of the inverters today are
> > better
> > > than 80%
> > > efficient so the answer remains yes, but not a lot.
> > >
> > > Jim.
> > >
> > > > Roger Crawford wrote:
> > > >
> > > > Rob tcbH mentioned using an ac printer and hooking it
> > > up to a small
> > > > inverter to change the dc to AC. Does this method
> > suck
> > > the batteries
> > > > down faster than a 12 volt appliance?
> > > >
> > > > Roger
> >
> >
> > __________________________________________________
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