I agree with CH inverters are cheap and can be fine on efficiency.
The laptop's line-charger power supply , is often the weakest part from an
efficiency point of view.
The wiring to the lighter socket, often is inadequate if running off the
vehicle battery directly. This can cause quite a big drop in output voltage
above 100W.
One thing you need, is a much larger inverter than you might guess from rated
energy use of laptop.
Typically many laptops use a nominal 70W but the inverter required, needs to be
rated at at very least double that, because of poor power factor of switchmode
supplies used in laptops. My laptop often causes the inverter to hiccup at
startup because of wiring drops to the lighter socket. When inverter is
operated directly off of battery, then no problems. It is a ~200W unit.
A very good if more expensive option for a seperate battery to charge directly
off the car one, is the optima series of starved electrolyte wound cell
batteries. If kept topped up these will easily last more than 10 years. I
have some smaller cells of the same design still operating after 15years with
more than 50% capacity.
The Optima come in two ranges : automotive ones and deep discharge ones , but
both are capable of good cycling under deep discharge and have good guarantees.
They are often available a bit cheaper from Costco, as well as autostores.
They run a little over $100 I seem to remember for a 60Ah?
Tim Hughes
--- On Thu, 7/16/09, C.H.Ling <ch_photo@xxxxxxxxxxxxx> wrote:
From: C.H.Ling <ch_photo@xxxxxxxxxxxxx>
Subject: Re: [OM] speaking of batteries
To: "Olympus Camera Discussion" <olympus@xxxxxxxxxxxxxxxxx>
Date: Thursday, July 16, 2009, 1:00 AM
This is not necessary true, an inverter can draw very little power when
there is no load, it depends on the design, here is an example:
http://www.dcacpowerinverters.com/itemdesc.asp?ic=PW200-12
C.H.Ling
----- Original Message -----
From: "Larry G. Griffin"
Long time lurker here. I've had some experience with inverters and
batteries. An inverter will draw amps equivalent to about 10% of it's
wattage rating just connected to the battery, whether you are using it
or not. Back to lurking.
Larry
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