Date: Sun, 4 Dec 2005 10:12:50 -0500
Reply-To: Dennis Haynes <dhaynes@OPTONLINE.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Dennis Haynes <dhaynes@OPTONLINE.NET>
Subject: Re: Inverter at Radio Shack
In-Reply-To: <11dcddf80512040405i11e50628q1ee1788bc4c781ba@mail.gmail.com>
Content-type: text/plain; charset=us-ascii
3,000 watts requires 250 amps assuming 100% efficiency and 12 volts. If
you really need 3,000 watts, you need to add ~15% for inefficiencies and
if starting motors, you need to add for a reserve capacity. Also,
batteries will not stay at 12 volts under this load. A battery is
considered discharged at 10.5 volts so you really need at least 300 amps
for this load. Optima's like many batteries should be discharged at a 5
hour rate. They will be destroyed if discharged too rapidly for any time
period. Assuming 60 A/hour rating, that leaves one capable of delivering
12 A/h, so you really need 20 of them to run this thing at capacity for
any length of time. Most RVs with inverters this size use 4 or 6 225 A/H
6 volt golf cart batteries. Trojan GC-2 is the favorite.
If the cable length is significant, you need at least 1 gauge. 1/0 will
work best.
Dennis
-----Original Message-----
From: Christopher Gronski [mailto:gronski@gmail.com]
Sent: Sunday, December 04, 2005 7:05 AM
To: Dennis Haynes
Cc: vanagon@gerry.vanagon.com
Subject: Re: Inverter at Radio Shack
Canadian Tire has inverters at 10% off right now. They had one that
was 3000W for around $450 Canadian. What kind of gauge wire would you
need to sun something like that? And how long would it take to deplete
an Optima or typical strater battery at any kind of load?
Chris
On 12/3/05, Dennis Haynes <dhaynes@optonline.net> wrote:
> The real problem with most inverters is not how they are rated, but
the
> way they are feed power. A 300 watt inverter needs 30 amps minimum. If
> you need to reach a 400 watt peak, than you need well over 40 amps.
The
> hard part to understand is how a 300 watt inverter can be expected to
> work with a cigarette lighter plug. In the VW, things are really bad
as
> the lighter socket is connected with a 20 gauge more suitable for 8
amps
> at best. The Radio Shack 300 watt inverter has no problem running a
> laptop and charging it's battery as long as the wiring and the
cigarette
> lighter socket has been upgraded or the unit is wired directly. Larger
> inverters will work even worse if the wiring is not adequate.
>
> Dennis
>
> -----Original Message-----
> From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On
Behalf
> Of Greg Potts
> Sent: Saturday, December 03, 2005 12:38 PM
> To: vanagon@GERRY.VANAGON.COM
> Subject: Re: Inverter at Radio Shack
>
> Hi Joy,
>
> Have you looked at high-end laptops recently? Extra-bright 17"
> monitors are common. DVD-burners are standard equipmment, and
> powerful speakers to go with them. They throw off a ton of heat, and
> to do that they draw a lot of watts. That means that they're built
> with large-capacity batteries, and if you want to RUN the laptop and
> charge it at the same time you're drawing twice as much power.
>
> And as I mentioned in an earlier post, the ratings on inverters
> recently has little or nothing to do with what they actually produce.
> True output is more like a third of rated output.
>
> If someone wants to try to run and charge an "executive class" laptop
> I wouldn't recommend purchassing anything less than a 300W rated
> inverter.
>
> Happy trails,
>
> Greg Potts
> Toronto, Ontario, Canada
>
> 1973/74/79 Westfakia Conversion **Bob the Tomato** LY3H
> 1977 Sunroof Automatic L63H/L90D
> http://www.pottsfamily.ca/westfakia
> http://www.busesofthecorn.com
>
>
>
>
> On 2-Dec-05, at 9:31 PM, Joy Hecht wrote:
>
> > I'm baffled as to why folks need these huge inverters for laptops!
>
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