[ARC5] UPS Transformers

[Peter Gottlieb]

All the sine units I worked on used PWM. 


Peter

> On Nov 19, 2015, at 10:28 PM, Brian <brianclarke01 at optusnet.com.au> wrote:
> 
> Hello Wayne,
> 
> Most quasi-sine output UPS devices have two transformers.
> There is one for charging the batteries and running the management circuitry off the mains. And there is one that takes the output of the oscillator / low impedance power amplifier and shifts it to your desired line Voltage.
> It would be nice to get the design data on the latter transformer to discover what duty cycle it was designed to meet. Some UPS devices, whose specs I have read, have a hold up time at 70% of rated load of 5 minutes. When I did the maths, the overall energy conversion efficiency was about 40%. I suspect some loss of efficiency would be down to a cheap transformer designed by an accountant. When I was designing transformers, if the efficiency test results didn't get near 99 to 99.5%, I would dismantle and reassemble.
> When a UPS device's specs claim an efficiency in excess of 80%, I look very carefully at the output waveform. It is very easy to get high efficiency the closer the output resembles a square wave. With a square-wave output, less cooling is required than if the output resembles a sine-wave. The maximum efficiency you can get out of a Class AB amplifier is pi/4, or 78.5%. No-one uses Class A with its maximum efficiency of 25%. However, Classes C, D E, F, G ... can easily exceed 80% efficiency at the expense of waveform purity.
> 
> With respect to adding outboard batteries to increase the hold-up time, look at the back panel. If there is an external battery socket, then you can safely add batteries.
> 
> 73 de Brian, VK2GCE.
> 
> On Friday, November 20, 2015 2:45 AM , you wondered:
> 
> I would assume that you would want to use transformers of a similar size/capacity if you want to approach the full capability of the device.
> 
> I have seen people afflicted with an extended power outage ask if they can charge the battery for their UPS and then use it to run their computer.  I assume the answer to this is "No," that the UPS is designed not only to use a battery of a given capacity but also to run on that battery power for that length of time, not several times longer.  I have seen very little evidence of active cooling or extensive heatsinking in UPS units either for the transformers or the solid state components.
> 
> Wayne
> WB5WSV 
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