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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


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