Date:         22 Sep 1995 11:35:59 -0700
Sender:       Vanagon Mailing List <vanagon@vanagon.com>
From:         "Harvey Chao" <Harvey_Chao@smtp.svl.trw.com>
Subject:      Re: 110 volt power inverter

                      RE>110 volt power inverter                   9/22/95


>I know that some of the bus folks have 110 volt power installed in their 
>VWs, some with major enhancements (solar panels, multiple batteries, i.e. 
>David, Sami).  Wanting to have 110 v for misc stuff (battery rechargers, 
>etc), I was recently given a unit marked as follows:
>R.L. Drake Co.
>Miamisburg, OH 45342
>Model DC-4 Mobile Power Supply
>12 DC Negative Ground
>650 VDC, 250 VDC, and -45 to -65 VDC
>or 110 VAC (330 Hz) @ 150 W
>There is an inspection tag on it that says Tested 9-17-68

>The friend that gave it to me said that it was a power supply for a mobile, 
>tube-type ham radio he had.

Looking at the info from the label, that's consistant.

>It has a normal AC type plug on the unit, and wires that fasten to the 
>battery.  Is it OK to use this unit?  Isn't normal AC 60 Hz?  Would this be 
>OK to plug a laptop computer into?

NOT  repeat NOT, with emphasis NOT NOT NOT NOT!!!!!!

1)  The DC voltages will at the least knock you on you butt if you accidently
get "across" them, possibly much worse
2)  Unless your laptop's power plug  is a so called "switching" type design,
and that's not highly probably (and very hard to determine without opening it
up and examining the "guts"), if you plug a standard transformer type  power
cord into this - if you are lucky, it just won't work.  If you are less lucky,
something will "break".  

If all you need is a few watts to run a laptop, your safest alternative is to
see if the laptop mfgr. makes a +12 VDC power cord for your laptop.

Next alternative is to go buy two devices 1)  a 12 VDC to 120 VAC power
converter( aka inverter), and 2) some kind of power conditioner to filter out
spikes and surges. Caution - some transformer powered devices DON'T LIKE the
waveform that comes out of most inverters, and may run "hot" or may overheat
and fail.  Most devices with transformers like a nice smooth sine wave that
the wall outlet supplies, most inverters, no matter what the lable says
provide what effective is a "square wave" output.  

Actually, instead of the second alternative, go buy what is called an
Uninterruptable Power Supply (UPS).  Normally, this plugs into the wall and
your computer plugs into it.  What it does is pass 120VAC through (usually
filtering out spikes as well) and also keeps an internal 12VDC sealed lead
acid backup battery charged.  When the power goes out (120VAC power failure),
the UPS senses this and immediately draws power from it's internal battery,
converts it to 120VAC and feeds your computer.  Usually the battery is
relatively small, because it only is supposed to give you a short time to
quickly stop what you are doing and implement an orderly shut-down of your
computer.  If you get a UPS that  you can verify accepts 12VDC as an input
from it's internal battery, and choose one that is rated to support a full up
desk top configuration, (big power loads like monitor, hard drives etc) it
should be able to run a lap top for an extended time without overtaxing the
12VDC => 120VAC electronics if you replace the 12VDC internal battery with
power from your car battery.  I say this because there should be a big
difference in power draw between a laptop and a desktop computer, and because
the intended use of the electronics is for a very brief period measured in
minutes.  IMPORTANT QUALIFICATION "If all you need is a few watts to run a
laptop" --

If you also want to run other things, go back to alternative 2 and choose an
inverter with the appropriate capacity to what else you want to run.

Harvey