Simple Power Backup Build

Power Backup Build

Power Backup Build

What I needed?

When loadshedding began, I was staying in a townhouse complex and needed a backup solution. Mainly for a few lights and my laptop and when all work is done my – media center. This article describes some of the steps I followed to build a simple power backup.

What followed afterward was some research, the main sources being:

  • Manga Guide to Electricity (eBook or Print format available)
    – Jogged my memory on High School Physics and added a little more detail on electron transfers, etc.
  • MJ Lorton videos (Youtube Solar Series)
    – Provided the considerations, equipment and methods required for solar installations but mainly used it to understand limitations with batteries for now.
    – Also identified what concepts I needed to brush up on if I needed to progress.
  • Battery School
    – Direction on what procedures should be followed when installing, maintaining and charging batteries, charger types and application considerations.

*Various other forums – fill in the gap knowledge

After the research I decided that whilst I will not need a huge setup , I wanted something that:

  • I could mess around with
  • perhaps grow a little
  • tear apart when I need to
  • repair and tinker with easily

My Setup:

I decided on the following setup based on the requirements above.

  • 2 x 50 AH batteries SABAT 722 (reason: easy to get and slightly easier to carry up townhouse stairs)
  • 4 x battery clamps (to wire batteries in parallel to create a 100 AH power bank)
  • Wire from old booster cable 5.6 mm +-140 amp (battled to get a decent price on wire, so just ripped apart an old booster cable)
  • 1 x a fuse holder (wanted extra safety when I connect a low power inverter into the cigarette lighter plug)
  • 1 x cigarette lighter plug (to allow simple inverters to be plugged in and swapped quickly)
  • 1 x shuko plug to 3 pin adapter (had to build this one, not easy to get unless you order from bushpower – often inverters have a shuko plug (euro 2 pin plug) outlet, which is not really an option if you have a 3 pin laptop adapter)
  • 1 x CTEK MXS 5.0 Battery Charger (I was only going to use the power bank when there was loadshedding, so imagined 10 hours to charge 50A worth of battery would be fine)
CTek MXS 5.0 Charger - 5A Charger

CTek MXS 5.0 Charger – 5A Charger

  • 1 x Autopro (Autozone Brand) 200W  Modified Sine Wave inverter (reason: I did not plan on powering anything that required a Pure Sine Wave Inverter e.g a motor or  a large amount of power since all of the electronics I wanted to run used an average +- 100W.
Power Bank Setup

Power Bank Setup

How much power do I need and for how long?

  • When I sized the system I knew I wanted something that could cater for 2 scenarios:
    • Scenario 1) Charge my laptop while I use it for at least 5 hours and place lights around the house and keep them running for +- 3 hours
    • OR
    • Scenario 2) if not using for laptop or lights, keep my media player and led screen running so I can watch or listen to something

To understand what I hardware I need to power the above, I did the following:

Ellies Efergy Meter

Ellies Efergy Meter

  • I took an Ellies Efergy 3 Plug Adaper Meter (very similar to a Kill-a-Watt used in the US and UK) and measured the power draw of all the components I needed to run. Geewiz have something similar on their site here (have not used it myself but have seen others using it).
  • Scenario 1)
    • The Laptop drew Max 50W and averaged a frugal 20-30W in general use. The LED lights were DC 3W bulbs so I assumed they would pull a max of 5W without measuring them.
    • As such to run the Laptop + lights I needed around 50W of continuous power (excluding any inefficiencies experienced in power transfer)
  • Scenario 2)
    • Further to the above, I wanted the option of being able to power a media center in case I wanted to listen or watch something, the media center and all components drew 120W on full load and around 100W on average.

Okay, now I had my 2 scenarios: either run my laptop and a few lights or my media center for a short while. To calculate what I could run based on the 100 AH power bank I was going to build, I used the following equation:

How many Amps are drawn per hour in each scenario?

Power (Watts hours) = Voltage (V) X Amperage (A)
To understand what Amps will be drawn on per Hour from the batteries, we reverse the equation to:

Amperage Hours (AH) = Power (Watt hours) / Voltage (V)
Where: Voltage = 12V;

Scenario 1:

Power for scenario 1 = Laptop + 2 Led Lights
= 30W + 10W

Therefore: Amp Hours = 40W / 12V
= 3.33 Amps per hour

Scenario 2:

Power for scenario 2 = media centre
= 100w

Therefore: Amp hours = 100/12
= 8.33 Amp per hour

Note: Batteries that are sold as ‘Deep Cycle” Lead Acid batteries by retailers are not necessarily true deep cycle batteries because they cannot be depleted regularly passed 50% without damaging them. True deep cycle batteries at the time of this post were still prohibitively expensive,so I decided just to cater for the 50% rule.

Note: inefficiencies are generally are present in every connection and conversion of electricity. our calculations do not take inefficiencies into account to keep the math simple, however one could make the assumption that one looses +-20% or some arbitrary percentage when converting electricity from one medium to another.

Based on our scenarios how long can we run the scenarios on my proposed power bank.

How long can the Power Bank run each scenario for?

Using the formula: Total usable amp hours / Amp hour draw = No. of hours. (estimated)

Where Total usable amp hours = Power Bank total * 50% (to cater for 50% discharge rule)

= 100 * 50%

= 50 usable amp hours.


Scenario 1 draws: 3.33 amp hours
Scenario 2 draws: 8.33 amp hours

So, 50 Amp hours / scenario amp hours = duration we can possibly run

So, scenario 1 = 100*50%/3.33
= 15+- hours

So, scenario 2=100*50%/8.33
= 6+- hours

To illustrate your considerations that you should take in a sequential list :

  1. How much power do you need to run your scenario?
  2. How long do you need to run the scenario for?
  3. What batteries would support the Scenario, taking into account the 50% rule if needed?
  4. Do you need a Pure Sine Wave inverter to support the scenario? or will a Modified Sine Wave work fine?

In conclusion:

This setup worked well for me until I moved and my requirements changed. I have actually re-purposed the system to backup my alarm, cctv and wifi router. The only change I made was to swap out the battery charger for a 10A Hawkins ABC1210 Switch mode charger, so I could keep the power backup online all the time as opposed to leaving it on standby.

Hawkins ABC1210 Switch mode 10A Battery Charger

Hawkins ABC1210 Switch mode 10A Battery Charger

Depending on interest in this article, I will consider posting on the procedure I followed to install a changeover switch connected to an inverter and batteries. The setup allows me to switch-over the lights from Eskom to an inverter connected to batteries and back.

On the side:

In the interim I am also experimenting with solar and inspired by Toby Kurien’s article and MJ Lorton have been looking into getting smaller setups working. Fortunately I should be able to take these Power Bank setups solar If I feel the need later.

Hope you enjoyed, any comments or directions appreciated

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