IP Server 900 Hardware Installation Manual
External connections
H.2
From this point, UPSs can be further broken down by inverter types, which determine output. These are:
•
Square wave
.
•
Modified sine wave
(or
quasi sine wave
).
•
Sine wave
.
Most devices with wall-mounted chargers, such as cordless drills or screwdrivers, can behave erratically —
sometimes not allowing the charge circuit to engage at all — when operating with modified sine or square
wave inverters. Small wall-based transformer-style power supplies, similar to those ESI phone systems use,
can experience overheating problems with modified sine or square wave outputs, which occur while some
UPSs are operating in battery mode. This overheating could eventually cause damage to the power supplies;
and, in time, the damage could cause a spike through the phone system — seriously damaging some of the
static-sensitive components inside the casing.
While the
true
sine wave UPS output power curve smoothly increases to its peak, then smoothly
decreases (allowing connected loads and equipment to operate the same as they would from utility supplied
wall power), the
modified
sine wave and square wave UPS output power curve will shoot straight up, level off
at peak voltage and then drop straight down. Additionally troublesome is that the modified sine wave sits at
zero voltage for a short period during the transition to or from batteries — which is the main difference
between it and the square wave output of some UPS. Please note that this short interval during which the
modified sine wave UPS sits at zero voltage can directly affect the transfer time of the UPS and could,
theoretically, be enough to cause the phone equipment to reset or even “freeze.”
Though it is hard to predict exactly when different ESI systems will have problems with modified sine wave or
square waveform UPSs (meaning during a power failure event or the recovery from one), it’s fair to assume
that a problem will eventually arise from the use of such UPSs.
Therefore, ESI recommends that only true
sine wave output UPSs provide backup power to our phone systems and equipment.