A UPS, or uninterruptible power supply, is a device that provides emergency power to a load when the input power source fails. A UPS differs from a generator in that it will give nearly instantaneous power by supplying energy stored in batteries, supercapacitors, or flywheels. In contrast, a generator takes several seconds to several minutes to start up. A UPS is typically used to protect electronic equipment from harmful power surges and is also used to provide backup power in the event of a power outage.
Currently, in the market, there are two categories of UPS available, one is a cheap short-time backup with low load capacity and another one is an expensive long-time backup with high load capacity. There are no UPS available with long-time backups with low load capacity.
The primary target of this project is to build a custom UPS that is cheap to make and provides a long-time backup for 300W of load, which is sufficient for a standard work-from-home setup.
The whole project is designed, manufactured and assembled in-house.
What You Will Learn
- How to modify a UPS?
- How to upgrade UPS for long battery backup?
- Background knowledge of Electrical Systems
- Background knowledge of UPS
- Background knowledge of Battery
- Background knowledge of Mechanical Assembly
Hardware Bill of Materials
- Cheap 300W Computer UPS – 1pc
- 26Ah 12V UPS Battery – 1pc or More
- Heat Sink (Different Sizes) – 5pc
- Misc Passive Components
- Thick Copper Wire – 2 meters
Making the DIY Long Backup UPS
Teardown of Cheap UPS
There are three primary components in a UPS. They are Switching Circuit/PCB, Battery and Transformer. The primary problem of cheap UPS is longevity and the reason they don’t last long is their lack of ability to handle the heat generated under long runtime. The switching FETs and the Transformers are the places where the heat is generated and under long runtime, it can damage itself due to overheating.
The first step is to dismantle any cheap UPS and extract all the primary components. I recommend Zebronics ZEB-U725 UPS.
Modification of Transformer
To prevent overheating of the transformer and to prevent it from burning the coil we have to add an external heat sink on all the periphery of the transformer. I have also used active airflow using a BLDC fan for additional cooling. The heatsinks can be stuck to the body of the transformer using thermal glue.
Modification of FET Heatsink
There are four FETs that are used to switch(invert) the DC12V to AC12V during discharging/backup mode and rectify AC12V to DC12V during charging. A major amount of heat is generated during the process and a larger heatsink will keep the FETs cooler and extend their lifetime.
An additional heatsink is stuck to the existing heatsink with thermal glue. It is recommended that you use a single block of a large heatsink.
Assembly of Modified UPS
I used an old APC UPS chassis to fit the big 26Ah 12V battery and the electronics from the Zebronics UPS.
Two sets of batteries are used. One is the 26Ah 12V battery, the other one is two 7Ah 12V batteries in parallel. The smaller batteries are secondary backup batteries and are not in parallel to the primary battery. The secondary batteries are used only when the primary 26Ah battery is discharged. This provides a longer battery backup. in Total, they provide 40Ah of backup. For a WFH setup of 150W of load including a laptop and a monitor, you can expect a backup of at least 3 hours.
All Rights Reserved Copyright (c) 2022 Arnab Kumar Das THE PROJECT IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE PROJECT OR THE USE OR OTHER DEALINGS IN THE PROJECT.