Home > Hardware > Longer UPS Life

Longer UPS Life

A good UPS (Uninterruptible Power Supply) is an important part of any reliable computer system, but they’re expensive.  When I found one of mine with four legs in the air one morning, I decided to give it a shot of Liquamycin instead of taking it to the slaughter-house.  Fixing the UPS seemed “greener” and I hoped I could make it better-than-new without giving too much money to the vet.

Common UPS in Action

Common UPS in Action

If you’ve made it this far you either want to know more about ranching cyborg cattle or you’re willing to wade through the ramblings of a crazed software engineer to find out more about UPS technology.  Read on for the latter.

A UPS provides power similar to what you get from the electrical outlets in your home.  Plug it into a wall outlet and then plug your electronic equipment into the UPS.  When Mains power is available, the UPS simply connects its output to its input.  It may also charge its batteries in preparation for power outages.  When the Mains power drops or stops altogether, the UPS continues to provide power to your electronic equipment by converting energy from its batteries into AC current with “inverter” technology.  The batteries discharge as this happens.  The rate they discharge at depends on how much power the equipment you connected to your UPS requires.

UPS systems are expensive.  Small units can only run equipment with meager power requirements for a short period without Household electricity.  Larger units will power more equipment for longer periods of time.  They use bigger batteries and cost much more.  A UPS that will power your PC for an hour or more could easily cost $300.  See this example for reference.  Much pricier units also exist.

The Problem

I have a computer system at home that performs many duties all day, every day.  It provides home phone, is a media hub, and fills a long list of other roles.  It’s painful when a power outage causes my server to go down.  Even worse is the potential harm an unexpected death can do to a computer.  Performing a graceful shut-down ritual on the server during a power outage is only possible with a UPS.

The batteries in a UPS will eventually die.  When that happens, your UPS acts like it’s just had its fill of green hay.  It won’t bloat, but don’t lift its tail.

After about 5 years of reliable service, my APC Back-UPS Pro 1100 bucked the kicket.  The batteries were dead.  While the batteries can be replaced, it’s often just as cheap and/or easy to replace the entire unit.  I have purchased replacement units several times over the years, but decided to try something different this time.

The Project

My idea was to replace the small, sealed OE (Original Equipment) batteries with Automotive batteries.  The larger units should provide sustenance for longer outages and are cheaper than sealed gel-cells, which is what the UPS initially contains.  While there are some potential problems with this solution, it didn’t seem like anything too crazy.

Disclaimer:  Attempt this project at your own risk.  There are a number of potentially deadly hazards when working with these components.  Dangers include electrocution, severe acid burns, explosions, and other nasty things.

After a little bit of searching on the web, it appears that other people have had the same idea.  There are a few project pages outlining the idea.  One of my coworkers has even tried it!  Check out the link below for a great example project.


After planning the project for a while, I decided to take the plunge.  The system would include the following elements:

  • Use battery boxes to keep battery acid contained and protect curious onlookers from touching terminals.  Terminals are likely to contain AC line current in addition to their DC component.
  • Fuse battery power for protection against shorts in the system or other craziness.
  • Use a larger battery for longer backup time, but not one that’s so big it wouldn’t charge properly.
  • Not cost much more than a new UPS unit.
  • Be reliable.

Quick Project Overview

  1. Remove stock internal batteries.
  2. Use the 60A fuse that connected the OE 12V batteries together to short the battery spade terminals together inside the UPS.  This allows use of the “battery disconnect” plug in back of the UPS to get power into the UPS with external batteries.
  3. Convert battery disconnect plug into a cable for external batteries.
  4. Put batteries in battery boxes and connect them with wing-nuts and cables.  The UPS requires 24V, so two batteries are connected in series.
  5. Connect the batteries to the UPS once they are snug in their boxes.
  6. Test it!

Project Pictures


Battery, cables, battery boxes

The batteries were about $70 each.  I bought 6 gauge cables because they were relatively cheap and easy.  They’re definitely overkill in the size category.  $10 for all the cables, $15 for both battery boxes, and $6 for the battery terminals nets a total project cost of about $170.

OE Batteries

Stock Batteries and Fuse

The stock batteries are connected with a 60A fuse.  I used it to short the battery connectors inside the UPS so the external battery disconnect plug can be used to route power from outside the unit into the circuit.  The fuse provides protection against over-current situations.  I would like to fuse each battery within its box for greater safety, too.

Battery Disconnect

Battery Disconnect Plug

The plug is a convenient way to take the batteries “out of circuit” for the stock UPS.  The plug looked like a great way to get power into the unit from external batteries.  It’s a very rugged connector designed for full battery current.  I sliced up the cable coming out the back so it could be connected to longer wires.  The wires would connect to my external batteries.

New Fuse Home

Fuse In Place of OE Batteries

A fused “short” where the OE batteries used to connect.  This is so we can use external batteries instead.

Battery Cable WIP

Battery Cable WIP

Working on the battery cable construction.  I used red electrical tape to mark the positive wire to make final installation easier.  Connecting the battery cables backwards would be dangerous.

Finished Battery Cable

Finished Battery Cable

The finished cable makes connecting and disconnecting the batteries a breeze.  It protects the batteries from accidental shorts and creates a reliable way to get power into the UPS.  I didn’t have to drill any extra holes or substantially change the UPS design.  I could simply solder the plug together again if I wanted to return it to stock configuration.

Battery Connections

Battery Connections

Batteries are wired together, but not to the UPS yet.  The new system is 24 volt just like the OE configuration.

New Running System

New Running System

Plug in the batteries and it’s ready to go.

New vs Old Battery

New vs Old Battery

Hoping the new system will provide much more capacity with similar reliability.  I’m not sure if the UPS will charge the batteries properly since they’re so much bigger than the OE units.  I’m testing it on my workstation and will move it to the server room pending a few weeks of reliable operation.

  1. No comments yet.
  1. No trackbacks yet.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )


Connecting to %s

%d bloggers like this: