[PLUG] Do it yourself Linux UPS...

Fri Aug 14 22:30:17 UTC 2009

At 02:40 PM 8/14/2009, you wrote:
>I know I need an inverter/charger and a rectifier.  What I haven't
>found out is how many batteries and what kind to use.

12 batteries come in deep cycle and auto starting. Get the deep 
cycle. You will find an amp-hour rating (at the 20 hr rate). This is 
what a new battery will put out before it is discharged. Multiply by 
, say 11v, to get watt-hours.

Find the watts of what you want to drive and divide into the above 
watt-hours, then toss out 20-30% to get APPROX. hours the battery 
will power your stuff. A 60 a-hr batt will  run 500 watt for around 
an hour. Measure your computer - you'll probably find it draws far 
less than you would expect form the power supply rating.

>  I see a Coleman
>1000 watt inverter on ebay and it supposedly shuts down automatically
>when it's about to deplete the battery...

Size the inverter for the expected load - computer + monitor +??

All modern inverters automatically shut down on low battery (as well 
as over voltage.)

Be sure to check both Harbor Freight & Fry's - for inverters. Will 
probably be cheaper than Ebay + shipping. and easy to return.

>but how do I signal the
>computer that the batteries are about to be drained completely?
>I don't know if the Coleman unit is a charger as well or just an
>inverter.

I have only seen one unit at Fry's/Harbor Freight with a charger and 
it was not automatic. (There are units with charger & auto switch 
available from Trace and their competitors.)

>A UPS needs surge suppression capability and undercurrent
>protection and most of the time power should be applied w/o using
>the batteries.
>
>The nicest way to do signaling would be to use say a PIC micro
>controller and put a signal out over the local ethernet line.

I am using a setup with a simple 3PDT relay:
Use two poles to switch the power out between the wall socket and the 
inverter out.
Use one pole to switch the inverter on (wire across its on-off switch)

Remaining item is charger. Ideally  it will sense a low battery and 
take the battery up to 14-14.5v them revert to 13.6 for float. I got 
one of these form harbor freight a few years back, but they don't 
seem to have these anymore.

>So, what kind of batteries should I use?
>
>   I don't like the typical sealed lead acid because where do you
>   get them A and how do you revive them without special equipment B?

Fry's has sealed lead acid.

>   Nickel metal hydride batteries are a possibility where the AA
>   variety are available at most electronic stores.  Nickel metal
>   hydride RC car packs might be ideal.  Another possibility is
>   to see about getting say D cells.

NMH = expensive.

>   There are some AA Lithium ION batteries, but I don't think these
>   are typically rechargeable batteries.

More expensive

>   There are laptop battery packs, but using these might be a bit of a
>   challenge and expensive.
>
>So I am thinking car batteries as they pack a lot of punch, are
>available practically everywhere, and they are recoverable without
>special equipment.  However, open lead acid batteries are not
>appropriate for use on a desktop.  I've also heard if these
>batteries don't vibrate that they will sulfate up much faster.

Phone company used to (and may still) use stationary liquid lead 
acid. Get deep cycle.

>So say I start with 2 12V car batteries.

One may do - look at the run time required. 200 watts for 2 hrs 
should be easy for one battery.

Thanks
JK

>A do it yourself UPS doesn't make much sense unless the
>UPS you are replacing is say an APC Matrix UPS, so let's
>pretend that we are doing just that.
>
>For the inverter, do I need a 1000 watt capacity?  Do I need
>more than that?  How do I figure out how many batteries to
>hook to it?
>
>For the rectifier/charger, do a typical say car battery
>charger if I'm using lead acid auto/marine batteries?
>Will the typical marine/auto battery battery charger
>stop charging when the battery is fully charged?  How
>do I monitor the state of charge and report that on the
>network?
>
>Perhaps for the rectifier/charger and inverter I should
>build my own, but how do I do that?
>
>Well, here are the results of a quick google search:
>
>http://www.dansdata.com/diyups.htm
>
>http://www.wikihow.com/Build-Your-Own-Uninterruptible-Power-Supply
>
>http://www.diy-computer-repair.com/UPS-Uninterruptible-Powe-Supply.html
>
>http://dev.emcelettronica.com/ups-uninterruptible-power-supply-reference-design
>
>
>
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