Date: Sat, 18 Dec 1999 13:41:27 -0800
Reply-To: Davidson <wdavidson@THEGRID.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Davidson <wdavidson@THEGRID.NET>
Subject: Re: What Size Inverter Do I Need?
Content-Type: text/plain; charset="iso-8859-1"
Kevin,
A few points:
1. When possible it is preferred to run appliances with 12 volt because
there is some loss of power in the inverter.
2. You cannot use all the amp hours that a battery is rated for... count
on maybe 2/3 to 1/2 depending on things like temperature.... that's because
the voltage would drop way below 10 volts and it is harmful to the life of
your battery to be deeply discharged much below 10 volts.
3. There are many postings over the past year regarding the set up of an
auxiliary battery. Noone has all the answers and it is a good education to
follow the discussions. It is typically set up so that the auxiliary battery
charges off the alternator when the engine is running and is isolated by a
switch when the engine is off so your appliances do not drain the starter
battery. There are many choices when it comes to the switch... all discussed
in posts you will find in the archives. But a more important factor than
choice of a switch is the size of the wiring between the + post of the
starter battery and the + post of the auxilliary battery. The size of the
stock wire is too small in most if not all of the Westy campers.... it may
be large enough in the weekender versions. In any case, the wire should not
be smaller that a #8 wire or there is danger of fire.
4. An alternative to having more than one auxiliary batter would be to
have additional sources of charging. You could start the engine
periodically, but the noise and fumes are a problem. Also you can get a
solar panel or two that would help out on sunny days.... it even possible to
have a small windmill on a portable tripod.
5. Leaning to conserve/manage power reduces the need for additional
auxiliary batteries and/or alternative power sources.
Bill
90 Westy Syncro
>Like many of you have already done, I'd like to install an onboard
>electrical system for some interior lights, Propex heater, stereo, 'puter,
>etc. all run off of an Optima battery.
>
>The Optima battery rates at 52 amp/hrs. I've calculated my max daily
>consumption at roughly 35 amp/hrs. According to West Marine you should have
>at least 20% of your inverter's rating in amp-hrs of battery capacity.
>Therefore, I come up with about a 300 watt inverter (20% of 300 watts = 60
>amp/hrs. compared to the Optima's rating of 52 amp/hrs.).
>
>West Marine says that this calculation roughly "allows you to run your
>inverter for two hours at half power while consuming 50% of the battery's
>energy." Huh? I don't get it. Is this overkill, or not enough? Can a 300
>watt inverter handle lights, heater, stereo, and 'puter running all at the
>same time for a few hours?
>
>Now one of the ftp files I got off of gerry.vanagon.com says your battery
>capacity should be double your expected daily amp/hrs. consumption.
>According to this, I'd have to be driving around with 90 pounds of Optima
>batteries, i.e. two Optimas! Yikes! And who has room for two Optimas?
>
>I'd also like this setup to recharge itself as I'm motoring down the road.
>
>I'm really flying blind here. I've just read enough to make myself
>dangerous. Any guidance will be appreciated.
>
>Hope you're all enjoying a big vat of figgy pudding.
>
>Kevin
>'89 Syncro Westie
>"Anchored, down in Anchorage - Alaska"
>
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