UPS customer answers

A lot of our customers are asking about UPS for their lasers - here is the skinny.

"What UPS do I need to run my laser?"

With all the useless loadshedding, this question is being asked more and more, and my stock answer is normally 2KVA or 3KVA online.

However … I have been doing some testing, and that is actually not all there is to it.

The more pertinant question is "How long do you want it to run?"

Looking for a 2000VA (2KVA) Online UPS on Takealot, there is a PSS brand for R4995, a Mecer Winner Pro for R4445, and other dodgy and cheaper ones. There are also a couple of more expensive ones.

A 2000VA Online UPS will easily run a 6040 HQ or 960 HQ with all the accessories (assuming inline silent fan), or a 30W / 50W fiber laser, along with a PC and screen (or a notebook).


The Mecer has 4 x 12V 9Ah batteries. This is equivalent to 36Ah of actual output. Considering that you do not want to completely discharge the batteries (and that they need quite a while to recharge), this will give you an effective 24 minutes of use to 50% battery capacity. You will then need 4 hours of charging to recover the batteries to 90%.

The PSS has 4 x 12V 7Ah batteries. This is equivalent to 28Ah of actual output. This will give you an effective 18 minutes of use to 50% battery capacity. You will then need 4 hours of charging to recover the batteries to 90%.

And this is while the batteries are still new and fresh. As they age, their performance will deteriorate.

Selling at R5329, the Mecer Winner Pro 3000VA On-Line Tower UPS seems to be a better deal. it has 6 x 12V 9Ah batteries, equivalent to 54Ah of actual output. This will give you an effective 36 minutes of use to 50% battery capacity. You will then need 4 hours of charging to recover the batteries to 90%.

So for anyone wanting to run their machines for an hour during loadshedding, a 3000VA system with additional battery packs (another 6 x 12V 9Ah) will work.

Calculations etc. available from me on request.

The Mecer UPS is also generator compatible as it is an on-line, double-conversion UPS, so with a 6KVA generator, (without the extra batteries) it will run as long as the generator has petrol …

A generator typically produces inconsistencies and fluctuations in voltage and frequency ranges. If the range is wider than what the UPS is willing to accept, your load will continue to run off the UPS and eventually deplete the batteries. This scenario would be typical with an off-line or line-interactive UPS system.

An on-line, double-conversion UPS system works differently and is the type of UPS that I recommend for use with a generator. An on-line UPS continually converts incoming AC power – whether from the main power supply or a generator – into filtered DC power, and then reconverts it back into AC power with a pure sine wave. That’s the clean feed of power your sensitive equipment needs. And as another benefit, an on-line UPS filters variations in frequency as part of its everyday operation, so battery life doesn’t shorten prematurely.

When it Comes to Generator and UPS Compatibility, Size Does Matter. Your standby generator set must provide computer-grade output power and be dedicated to run UPS protected IT applications only. Additionally, the continuous generator capacity rating must be at least twice the rated capacity of the UPS system used. As connected equipment cycles on and off, inrush currents can cause the UPS to switch between AC, battery and bypass modes. Over-sizing the generator relative to the UPS capacity will help prevent this from happening.

Don’t Forget About Earthing the generator. If you pull the plug on your UPS to move it from the Eskom power supply to the generator, you’re also pulling the plug on the electrical earthing. A sudden loss of earth on the UPS and all the equipment it powers could be a big problem: currents normally dissipated to ground through the UPS would find another path to get there, possibly through network cables, passing through other devices along the way.