Date: Sat, 22 Apr 2006 09:46:12 -0400
Reply-To: Edward Maglott <emaglott@BUNCOMBE.MAIN.NC.US>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Edward Maglott <emaglott@BUNCOMBE.MAIN.NC.US>
Subject: Re: battery-inverter-charger-battery loop
In-Reply-To: <e3a689eb4abd.44477b7b@optonline.net>
Content-Type: text/plain; charset="us-ascii"; format=flowed
I'll have to do a few more tests on the inverter to see how it behaves in
various failure scenarios. I am pretty safety conscious, and this project
is starting to raise some flags for me.
I'm not sure where the voltage potential you describe would come from. The
scenario where a failing component on the van would allow some AC current
to leak to the chassis. How would that translate to potential to earth
ground? Seems like the potential would be to the ground of the inverter
directly through the chassis rather than through the high resistance route
of wet tires to ground back to gas station pump, back up wet hose to filler
neck.
My goals for this project are to get away from having to manually
disconnect the fridge plug under the sink to reconnect it to the inverter
under there, and turn the inverter on. Then have to reverse that process
later to go back to shore power. Have to remove the pots and pans and
stuff to do that. Secondly, I'd like to have an outlet with easy access to
occasionally plug in a cell phone charger, camera battery charger, or other
small consumers of AC power. So maybe switching the whole AC system of the
van from shore to inverter is not the way to go. I'm open to suggestions!
Somebody asked how I was going to switch the inverter on and off. I was
just going to put another switch in parallel with the power switch of the
inverter. It's a low current switching situation.
Edward
At 12:15 PM 4/20/2006, you wrote:
>However, Once you hard wire that inverter into the Vanagon, it is now a
>permanent installation and it should meet NFPA and RVIA reqiurements
>including being UL listed for the application. The floating potential can
>cause all sorts of safety issues. Imagine this scenario: you are using the
>inverter to power the refrigerator while driving. The heater element is
>starting to fail and you are getting some current leakage or voltage
>potential to the vehicle chassis. You then pull into a gas station and it
>is raining, wet tires. You place the filler nozzle into the van filler and
>you complete that circuit and create a spark right at the filler. If you
>had a proper inverter, with a neutral properly wired, that ground would
>have become a short and tripped the circuit breaker or blown a fuse or at
>least ripped a GFCI. This is what grounded wiring systems are all about.
>How about that same scene with the defect and you pull into a campground
>and go to connect the water? That could be ni
>ce shock.
>
>Cheap inverters are designed for appliances to be connected directly to
>them. And those appliances should be the double insulated or isolated
>type. Laptops, cell phone chargers, and things of that nature are fine.
>Even TV's with some of the power supply connected to chassis ground can
>present problems.
>Use them as intended and avoid getting fancy unless you are ready to spend
>the money to do it right.
>
>Dennis
>
>
>----- Original Message -----
>From: John Bange <jbange@GMAIL.COM>
>Date: Thursday, April 20, 2006 11:22 am
>Subject: Re: battery-inverter-charger-battery loop
>
> > >
> > > I plugged that into my inverter today and it said "open ground."
> > I opened
> > > the inverter, and the ground does go to the inverter case, and
> > is not
> > > common with the neutral pole. I read with a meter, and got
> > about 40 volts
> > > between ground and neutral. I did a little test of wiring the
> > ground and
> > > neutral into the van's AC system and left hot disconnected. As i
> > > expected,
> > > I was seeing that 40 volts throughout the system including the
> > male plug
> > > on
> > > the outside of the van.
> >
> >
> > Actually, that's normal. Since inverters are not considered
> > "permanent"installations, the National Electrical Code doesn't
> > apply, but instead just
> > UL458. The UL regs are more relaxed and allow them to supply half the
> > voltage from each side ("hot" and "neutral") rather than forcing
> > the NEC's
> > strict "single phase 120V hot to ground bonded neutral" rules.
> >
> > I have a beefy DPDT switch I was going to use for this project,
> > but I was
> > > hoping to use one pole to turn the inverter on when I switch to
> > it. Now
> > > where is that drawing board...
> >
> >
> > If you're going to leave the inverter turned on and you think
> > people might
> > be fiddling with the shore power connection, yeah, I suggest
> > switching both
> > poles. Anything below 50V is considered "low voltage", but it can
> > still give
> > you a quite unpleasant shock. Also, if you plug in with the
> > inverter powered
> > up, even if the single pole switch is thrown, you'll likely get a
> > "groundfault" alarm from the inverter as shore power has neutral
> > tied to ground.
> >
> > As for controlling the inverter through the switch, are you
> > switching the
> > inverter power leads, or does your inverter have a remote power
> > switchingoption? If the former, that'd have to be one hefty switch...
> >
> > --
> > John Bange
> > '90 Vanagon - "Geldsauger"
> >
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