Inverters

[AndyD]

For running computers, laptops and the 'better quality' LED lighting, you do not need a pure sine wave convertor, and a square wave is more than adequate.

I'd suggest take it on a case by case basis it very much depends on how their switch mode supply is built. Some may not play very nicely with modified sine supply especially if it's got actice PFC built into it. You may also find they run very hot, again this would vary depending on the design. If it's hi-fi equipment or TV then any common mode noise that carries though the power supply will result in interference and buzzing.

[Justloadit]

PFC works on attempting to fill the blank areas of the sine wave by making a boost switch as opposed to a buck switch during the peaks therby reducing the current draw during this time, so effectively reducing the power factor. The PFC still rectifies the sine wave into a DC voltage, and the PFC attempts to reduce the saw tooth which is characteristic of DC rectification under load, where during the dips, the circuit has to both supply the circuit with power, and charge the capacitors up for the next cycle, effectively doubling up the current draw from the supply.This simply means that the PFC will work better with a square wave inverter with a small dead time between positive and negative half cycles. In the case of electronic equipment, because of the low power they draw, the PFC circuits are relatively light and probably would be happy with the modified sine and square wave with dead time.

With respect to the noise on audio equipment, yes that can be a factor, and especially during a power failure, silence augments the hum and buzzing.

[HR Solutions]

I phoned PSS - they are going to give me a quote. Hopefully they get their sines and peaks in line

[HR Solutions]

This just sent to me - can you please give opinions on this ?
Power Caddy Brochure HT-C-M1000.pdf


[3x-a-d3-u5]

I've worked with Powerbackups.co.za they have a handy power calculator: http://powerbackups.co.za/index.php?main_page=page&id=1 to work out the size batteries you'd need. But keep in mind as AndyD said, you'd be looking for a balance between length of time and amount of equipment.

Sometimes the most reliable and cost effective solution is a combination of generator and UPS. An inverter is part of a UPS. So "A UPS consists of an Inverter, Transformer, Voltage regulator, Charger and Batteries." The UPS kicks in as the power failiure starts giving the jenny time to kick in, or when the jenny runs out of juice, the UPS saves the day long enough to get more fuel...

[HR Solutions]

3x - I cannot have a genie due to our office park. I have to have an inverter, therefore I am looking for guidance on what to get to last me up to 4 hours.

[ians]

Your quote for that unit must have been around R5000?

[HR Solutions]

Your quote for that unit must have been around R5000?

Yes .... And I'm wondering how long it will last ? Ie will it last 4 hours ?

[CLIVE-TRIANGLE]

I have discovered that re-charge time has now also become critical. That info sheet refers to between 6 and 12 hours, which is probably ok.

I don't know what my UPS is supposed to be, but when we had occasional power-outs it allowed us more than enough time to safely shutdown our NAS (network attached storage) box and then it would happily keep our routers and access points going for about two hours.

Now, when the power goes off it does not hold the NAS box for even long enough for me to shut it down; I would say 3 minutes and it's dead. The unit is less than a year old so I assume the battery is ok. Many (probably most) off the shelf UPS are "online" and so the net charge is minimal. With these rolling load shedding power offs, it has no hope of reaching full charge before the next out.

I mention this because most commercial units are made for developed countries where power failures are the exception, not the norm, so that issue is suddenly a factor.

The previous units I had were supported by a standby generator. I suspect the generator's voltage regulator was really dodgy because it killed the UPS units pretty quickly. I changed from desktops to laptops with external monitors and wireless keyboards and mouse so that the laptops' battery became the UPS and at least the computer hibernates and ultimately does a soft shutdown when that battery gets low.

I am afraid there is no way out; if it is important that you work through power outages and more importantly, you value your data, you have no choice but to throw money at it.

If your desktops are recent powerful beasts, the power supplies are almost certainly 300 watt units and if so then I doubt the unit you posted will be adequate.

[Justloadit]

Hi Clive,

I am in no doubt that the battery in your UPS is dead. This happens when low cost batteries are used. Most suppliers, to keep the cost of the UPS as low as possible to compete, use the low cost batteries.
You will need to open the inverter, and replace with what is called a deep cycle battery. Will probably cost 3 times more than the low cost units.
The main problem with UPSs are that they continuously trickle charge the battery, and this kills the battery over time. One should also at least once a month run the UPS off the battery, so that the battery can cycle and keep the electrolyte going. Also for a full charge, you need a 24hour cycle.

With respect to the generator killing UPSs, it is simply too small for the application, making the generator hunt around the 50Hz excessively, making the UPS switch in and out attempting to maintain a constant power to your computers, this hunting, causes excessive voltage to be developed which takes out the UPS protection (MOVS or surge arresters).

If a generator hunts up and down, stop and get a larger one. Just remember up here on the highveld, you lose 40% of the generator capacity because of the thin air, add to it that it will be a Chinese made in whcih the specs have been inflated, and divide the rating by 50% to get a rough idea of its true capacity.