Date:         Wed, 28 Mar 2007 22:59:28 -0500
Reply-To:     Matt Roberds <mattroberds@COX.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Matt Roberds <mattroberds@COX.NET>
Subject:      Re: Using a UPS unit as inverter
Comments: cc: Martin Jagersand <jag@CS.UALBERTA.CA>
In-Reply-To:  <20070329012628.FWUF26573.eastrmmtai111.cox.net@eastrmimpi03.cox.net>
Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed

> From:    Martin Jagersand <jag@CS.UALBERTA.CA>
> Date:    Wed, 28 Mar 2007 16:12:27 -0600
>
> I've experimented with using a computer Uninterruptible Power Supply
> (UPS) in place of an inverter and charger.

A couple of things to keep in mind if trying this:

- In "charge" mode, some UPSes don't use their internal transformer as
   an isolation transformer - parts of the circuit can be at full AC
   line potential.  This is perfectly fine for charging the internal
   battery but can get exciting if you're also charging a battery
   mounted in your van.

- In "inverter" mode, the UPS is designed to run for maybe 30 to 60
   minutes until the battery is discharged.  Then, it will be off
   for a minimum of a couple of hours while the battery charges back
   up.  This means that the heat sinking inside the UPS might not be
   up to long-term use.

Tripp-Lite (and, I think, APC) sells some inverter-chargers that are
meant to be used this way.  The charger is isolated and the inverter
is rated for continuous duty.  Typically these are a box with a cord
and plug, a 120 V outlet on the front, and two big studs with wing
nuts for connection to an external battery pack.  They aren't cheap,
though.

Matt Roberds