AVR Trim bx1300lcd

[Anonymous user]

1. Why is the AVR TRIM feature not included in the BX1300lcd OR BX1500lcd?

2. Am I taking a slight risk of overvoltage with no TRIM feature?

3. What is the difference between surge supress and AVR Trim?

4. Are there any APC UPS models that have an LCD screen and AVR boost AND TRIM?

thanks

[Anonymous user]

Still not clear on surge supression vs AVR?

[Anonymous user]

First let me talk a little bit about voltage regulation.

External voltage regulation is something SMPS - Switched Mode Power Supplies - do not require per se. They have internal voltage regulation and have a somewhat wide tolerance for voltage fluctuations. Most SMPS can cope with fluctuations of 25% above it's norminal rating and 30% below without a problem. The only thing the SMPS do is at high frequency change the PWM pulse to keep the output voltages, 12VDC, 5VDC, 3.3VDC or whatever, tightly regulated. The SMPS draws more current (Amps) when the voltage is low and reduces the amount of current drawn when the voltage goes up. By doing this, the need for external voltage regulation is questionable. You can read more about that at:

http://www.teal.com/products/App%20note%20AN-2.htm

Since most PSU today is active power factor correted (APFC), these power supplies can work all the way from 80-270V without a problem. Trying to regulate the voltage externally is almost useless, it's a waste of energy, since voltage regulation methods do spend some energy.

In the end, most SMPS work harder to supply a tighly regulated output when the input voltage drops to let's say, 80 to 90volts. In some cases they can't supply all its rated wattage when operating at 80volts - apart form the APFC ones, that works beautifully either at 80volts or 270volts, on the fly! So, too low input voltage is worse than a somewhat high input voltage. The power supply "prefers" a higher input voltage than a low input voltage. Voltage sags and brownouts are more demaging to PSU than are some voltage swells.

Voltage regulators causes some bad behaviours as you will read on the website I told you above and if you can avoid it, it is better for the power supply. Having only the boost mode feature is something desirable for modern power supplies, not something to worry about, unless you really have problems in your house with excessively high voltage, let's say, 140, 150volts all day long. That's something the power company or an electrician should solve, not a voltage regulator. Voltage regulators do help in these cases, but you're not fighting the root of the problem here, your're trying to mask it with a voltage regulator, wasting a good deal of electricity trying to bring the voltage down.

[Anonymous user]

Thanks rau -

You made me feel better.....

[Anonymous user]

You're welcome!

I think this will become a trend, the newer UPS releases will come out without trim mode regulation and eventually (IMHO) without voltage regulation at all since SMPSes are becoming more and more common even for small devices like acess points, switches and the like and also more and more strict regulations are requiring active PFC.

It's been quite a while that monitors can work from 100 to 240volts and I'm not counting their tolerance margin. The need for greener products will push this trend forward since voltage regulation can contribute up to 10% of energy wastes inside an UPS. They'll still come out with surge protection though, which has no impact on the energy consumption nor any other side effect.

[Anonymous user]

AVR = Automatic Voltage Regulation. What it does is to regulate the mains voltage within a limited range. In the case of your UPS, it boost +12% when the incoming voltage is too low. Let's say the incoming voltage is at 80volts, the output then goes to 89,6Volts, +12% of 80 volts, which is still acceptable for most PSUs. When the UPS output reaches let's say, 115V with the boost mode on, then the UPS sends a command to a componet called relay so that the +12% compensation is turned off.

Basically the voltage regulation is a series of power transformers, it can either be a step-up transformers or a step-down transformers (doing the boosting and trimming work). They basically do the same thing a 220V to 110V step-down transformer does, or a step-up transformer does, when it gets 110V and transforms to 220V. The UPS senses the incoming voltage and comands a series of relays (which is an eletro-mechanical device where the clicking noise comes) to select a different transformer output or "tap", as they call it. An automatic voltage regulator can only work within a limited range as I've just said. Their "taps" are at a fixed rate lets say, +10volts. If the UPS have a 12% voltage trimming option and the incoming voltage reaches 160Volts, it can only trim 12% of that, which will result in 141 Volts.
Voltage regulator transformer can have as many "taps" as its developer wants, but it makes the unit much havier, it wastes more energy and generates more heat. It doesn't matter if the AVR has four "taps" or sixteen taps, it is still slow for suppressing voltage surges as I will explain below.

For you to understand a little bit better what an UPS voltage regulation feature is, think of it as actual taps with running water, the water here would be the voltage. For exemple, the "tap 1" is 90% open, the "tap 2" is 80% open, the "tap 3" is 110% open, the tap 4 is 120% open - the first two taps in these exeples works for voltage triming and the last two for voltage boosting. The UPS selects each one of this taps depending on the amount of "water" (voltage), coming from the wall outlet. There is about 8 to 33 miliseconds delay between sensing the voltage fluctuation and the actual regulated output...

Surge supression works differently. Surge supression is basically made to protect against high energy and fast rising surges or spikes that can be caused by lightning, electric motors being turned on or turned off, etc. Surges are essencially fast rising spikes and voltage swells are slow rising and low energy in nature. Surge suppresion can in some cases reduce voltage swells, but this is not its main purpose.

Surge protection is basically comprised of a component called MOV - Metal Oxide Varistor. An MOV works at diverting surges to ground. When operating at its nominal voltage, or the mains voltage, the varistor acts like a resistor with its resistence tending to the infinite, so it does not conduct electricity to ground at this state. When there is a fast surge, it instantaneously reacts (in nanosecods) by decreasing it's internal resistence, allowing the excess energy to flow to ground.

The voltage regulator can not act as fast as an MOV for suppresing high power and fast rising surges and would not be capable of that because of the nature of a power transformer. High energy surges must be diverted to ground and power transformers do not do that. Compared to the speed of an MOV, the voltage regulator is like a turtle.

There are some disadvantages regarding the use of MOVs for suppressing voltage swell. MOVs degrade very fast if frequent voltage swell are imposed to it, it gets too hot and it's internal chemistry degrades. MOVs are made to react fast and come back to it's initial state very quickly as well, which happens when a power surge occurs. That's why manufactures of surge protective devices use an mov that only triggers itself when the voltage is much higher then the mains voltage. If the MOV starts to conduct too early, it will degrade itself very quickly and on all power grids a relativelly high number of fast duration swells, do happen.

I invite you to google for MOVs and Surge protection if you are interested in knowing more about it.

I wish I could write a bit more about it, but I don't know if my english is good enough or my limited knowledge would allow me to do that. English is not my mother tongue...

[voidstar_apc · Accepted solution]

Allow me to summarize: the AVR and the surge suppression solve two different problems. The AVR can adjust the voltage of the line within a limited range to compensate for the voltage being too high or too low. However, the AVR does not respond quickly enough or have wide enough compensation to handle surges. Surge protection is capable of putting huge surge voltages into ground very quickly, but won't adjust the long-term voltage of the line as the AVR does. They're complimentary technologies.