Date: Thu, 24 Jul 2008 21:48:12 -0400
Reply-To: David Beierl <dbeierl@ATTGLOBAL.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: David Beierl <dbeierl@ATTGLOBAL.NET>
Subject: Re: Inverter Questions
In-Reply-To: <fa0982d70807241812q52245f0ch291b2220fe8beb9b@mail.gmail.co m>
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At 07:12 PM 7/24/2008 -0600, Paul Connelly wrote:
>I thought that 100 amps seemed excessive (it was for short circuit
>protection not normal operation - it has 2 x 30 amp fuses on board
>for Short circuit protection,
Ok, internal fusing for 60 amps...
> as well as overload and over temperature shutdown protection too)
> and the wiring instructions calls for 10 awg (for cable runs of 10'
> or less, 8 awg for longer runs - I am using about 5' in the
> original plan). 500 watts at 12 Volts running at max would draw a
> little over 40 amps
Remember inefficiency, and the potential difference between watts and
volt-amperes. The unit is fused to carry 60 amps...
>the breaker box and run some fresh cables to the auxiliary battery.
>Maybe a 40 amp breaker might be a better idea than a 100 watt fuse
>(also solves the switch rating problem)?
A 40-amp *DC* switching breaker could be a good thing. Here's a
50-amp AC/DC unit from Blue Seas:
<http://www.shipstore.com/SS/HTML/BLU/BLU7228.html> $16, not bad --
unless you need to stick it in a Blue Seas panel to make it work.
>On the feeding the external circuit with the inverter rather than
>plugging directly to it, I don't see any major difference between
>doing that and say plugging an extension strip to the inverter and
>running a couple of small loads off of it.
Power strip is ok, as long as it doesn't have noise filtering
circuits in it. The stepped-square-wave output has lots of
high-frequency content, tends to burn up the filters.
> I'm talking like cell phone charger (.15 amps, laptop 1.5 amps, if
> not using the laptop maybe a small DVD player, nothing major).
> Although, if the inverter is accessible then so are the sockets -
> just kinda makes the stock sockets obsolete ( I never hook up to
> shore power unless I'm drawing the Dometic down at home before a trip.
*You* never...but what about your heirs and assigns, or your wife, or
the person who buys it after you are senile? Or the kid playing with
the 110v flap outside when you're running the inverter? You
absolutely must not hook up in parallel with a working 110v
input. No kidding. Really.
> Talking of the Dometic, that's the only potential high draw from
> that circuit if I forget to switch it from 110 volts to DC or
> Propane. (Sorry BTW, the 240 V thing is inured in my brain!)
>
>However, what the application of 110 VAC to the output of the
>inverter might do if that switch was left on (on the inverter unit
>or breaker) I do not know - might be worth a try first!!!
I can almost guarantee it would be much more exciting than you have
any interest for. And I'll give sporting odds that it could be
pretty exciting even if the inverter is not powered. In any case, as
I said before, you simply must not do this, it's far too likely to be
fatal to someone down the road. If you permanently disable the
external 110 input, then the remaining issue is whether neutral and
ground are bonded together inside the fan.
>Also, looking at the manual a little more, there is the phrase "Do
>not connect to ... any AC circuit where the neutral conductor is
>connected to ground or the -ve of the DC source".... which would
>mean the Dometic - which is connected to the distribution circuit
>for the 110 VAC.
I don't know if the Dometic neutral is connected to ground at the
fridge -- probably not. I don't know if the house wiring neutral is
bonded to ground -- might well be.
But I strongly recommend to leave the existing shore-power setup
intact, and keep the inverter wiring completely separate from it. Or
go the whole hog with a transfer switch.
--
David Beierl - Providence RI USA -- http://pws.prserv.net/synergy/Vanagon/
'84 Westy "Dutiful Passage," '85 GL "Poor Relation"
