On the expensive end, some homeowners may be able to spend between R100,000 to R200,000 to equip their homes with a solar power system to escape load shedding, but for most of us on the lookout for budget-friendly solutions, a relatively affordable UPS (uninterrupted power supply) backup system is the most accessible (and temporary) way to keep electrical appliances going for a few hours while the power is off. 

With a wide range of mostly affordable products on sale – from a few hundred rand to a hundred thousand rand – it is important to make the kind of informed choices that match our energy needs. 

“You need to be aware of the power rating of the appliance you need to service. Ordinarily, you wouldn’t necessarily have to know that, but considering the energy situation that we find ourselves in, unfortunately we all have to get a grip on what these numbers mean,” says Kinesh Chetty, an energy consultant with a focus on solar (PV) energy systems, and a former director of the Maxx Solar academy in Johannesburg. 

Below, he explains the difference between three measurement units that are often used to indicate the energy potential of UPS backup batteries by retailers – namely, watts, volts and amps.

Say Watt? 

Chetty explains that while the science might sound complex, one of the simplest ways for the average consumer to work the appropriate UPS backup system is by understanding the power rating of different appliances. 

One example: On the back of a typical flat screen television, there’s a little sticker with a nameplate rating providing information such as voltage and watts. On a typical 49-inch smart TV, the sticker might indicate a power rating of 100 watts. 

Effectively, this means that the television requires just a little under 100 watts of power. Hence, if a consumer was looking for a UPS backup to run just the television for 4.5 hours of Stage 6 load shedding, they would multiply the 100 watts rating by the 4.5 hours to figure out the approximate amount of energy they would need from the UPS, which in this case would be approximately 450wh (watt hours). 

Another user might be shopping for backup power for 2.5 hours during Stage 4 daytime load shedding, so that they stay connected to their Wi-Fi and perhaps be able to able to charge their laptop and phone. 

Here too, Chetty advises they follow the same formula by adding up the power ratings indicated on the different appliances that they plan to plug into the UPS, and multiplying them by the number of hours they think they will need the power for. And then making sure that the UPS will have enough watt hours.

In the absence of watts, there will be maths 

However, not all appliances will have the watt power rating indicated. Some, especially those that use minimal energy – such as routers and smartphones – will have separate unit measurements for volts (V) and amps (A) only. In that case, there will be one extra calculation. 

Simply multiply the two – that is, the voltage indicated by the amps measurement, to get the watts measurement. As explained above, double-check to see if the watt output of the UPS will be sufficient for what you need. 

One example: If you turn a 2017 MacBook Pro upside down, you’ll see indicated a voltage rating of 20 volts and a maximum of 4.3 amps. Multiply those two and you get 86 watt hours. Hence you can safely assume that is the maximum energy required to run the computer, although on average it will use a little less.

Some UPS units will only show the mAH units, which indicates milli-Amp hours. Although this might seem a bit more technical, a 1,000 mAh is the same as 1 Amp Hour. So while that cheap USB might sound impressive when promising 8,000 mAh, keep in mind that is just eight amp hours, and multiply that by the indicated voltage.

For example: The battery size of the standard iPhone 13 is 3,227 mAh (3.2 amps). The battery voltage is rated at 3.8 volts. Multiply 3.8v by 3.2A, and you get an approximate watt hour measurement of 12.16 wh. If you want to avoid doing the maths, you can also simply google the watt hour rating.

If you needed enough power to charge an iPhone as well as keep a MacBook Pro laptop and an average router requiring 7 wh of energy plugged in, you would add the laptop’s 86wh to iPhone’s 12,16wh and the router’s 7wh, for a total of 105,16 wh. Over two-and-a-half hours, those three appliances would require a maximum of 263 wh.

One small UPS that is currently for sale at a local retailer for R1,900 is indicated to have a capacity of 57wh. In this case, this would be far from sufficient for all three, but if you take the laptop out of the equation by charging it prior to load shedding, such a UPS would be sufficient to charge the phone and keep the router going. 

Considering that the phone would likely need about an hour to charge fully, you would have even more watt hours to spare to keep the router powered up since the phone won’t be plugged in for all 2.5 hours. 

Say no to lead – go with lithium batteries

UPS systems with lead batteries are typically cheaper to buy. However, lithium batteries will discharge a consistent amount of power throughout the charging cycle, whereas lead batteries will discharge significantly less power the longer one charges. 

So while it might take an hour to fully charge the iPhone from a lithium battery powered UPS, due to the drop in power of the lead battery, the rate at which it charges slows down the longer one charges, which could add more hours to charging time as it releases less and less energy as the battery starts to go flat. 

Additionally, in terms of lifespan, lead batteries have approximately half the lifespan of lithium batteries. 

Chetty explains: “The thing about lead acid batteries is that even though you might have 12 volts multiplied by 100 amp hours, and it looks like we have 1,200 watt hours available, we don’t actually have 1,200 hours available because when it comes to lead acid, you don’t want to damage the units by depleting more than 50% of the battery. So effectively, what you have is closer to 600 watt hours.”

Spend a bit more – it’ll last longer 

“Right now, it’s a bit of a gold rush. The market is flooded with gimmicky items,” says Chetty, when we show him some of the cheaper options from a popular online retailer. 

“They might keep your modem running for a couple of hours, but in a year, they’ll be so depleted that you’ll have to replace them. It’s like putting a piece of sellotape over a gushing volcano,” he adds. 

Among some of the options under R10,000 that Maverick Life showed Chetty, he says the more reliable options will have lithium batteries instead of lead, and will also display a clear indication of the wattage. 

He advises that consumers rather go for the ones clearly identified as lithium, and with clearly identified watt hours, rather than try to work out various unit measurements that might be confusing.

In brief:

• Work out your power needs by adding up the wattage indicated on the appliances.
• Multiply the total watts by the number of hours you think you will need the backup for, and buy a UPS that is indicated for those watt hours.
• If appliances don’t have the wattage indicated, multiply the voltage indicated by the amps indicated to get the watts.
• If possible, avoid buying lead batteries and rather go with lithium.

DM/ML

In case you missed it, also read Load shedding 101 – what to consider when buying LED emergency bulbs for your home

Load shedding 101 – what to consider when buying LED emergency bulbs for your home

This story was first published on 13 July 2022.