Alpha VMX Series User Manual

VMX

Standby Power Supply

Technical Manual

VMX Series Standby Power Supply

Effective: October, 2007

Alpha Technologies

Alpha Technologies

Power

®

VMX Standby Power Supply

017-940-B0-001, Rev A

Effective Date: October, 2007

Copyright© 2007

Alpha Technologies, Inc.

member of The Group

NOTE:

Photographs contained in this manual are for illustrative purposes only. These photographs may not match
your installation.

NOTE:

Operator is cautioned to review the drawings and illustrations contained in this manual before proceeding. If
there are questions regarding the safe operation of this powering system, please contact Alpha Technologies
or your nearest Alpha representative.

NOTE:

Alpha shall not be held liable for any damage or injury involving its enclosures, power supplies, generators,
batteries, or other hardware if used or operated in any manner or subject to any condition not consistent with
its intended purpose, or is installed or operated in an unapproved manner, or improperly maintained.

Notice of FCC Compliance

Per FCC 47 CFR 15.21:

Changes or modifi cations not expressly approved by the party responsible for compliance could void the user’s authority to operate the
equipment.

Per FCC 47 CFR 15.105:

This equipment has been tested and found to comply with the limits for a Class A digital device, pursuant to part 15 of the FCC Rules.
These limits are designed to provide reasonable protection against harmful interference when the equipment is operated in a commercial
environment. This equipment generates, uses, and can radiate radio frequency energy and, if not installed and used in accordance with the
instruction manual, may cause harmful interference to radio communications. Operation of this equipment in a residential area is likely to
cause harmful interference in which case the user will be required to correct the interference at their own expense.

TM

Contact Alpha T echnologies: www.alpha.com

or

For customer service (7 AM to 5 PM, Pacifi c Time), call:

For complete technical support, call: 1-800-863-3364

7 AM to 5 PM, Pacifi c Time, or 24/7 emergency support

In the UK call: [phone]

In Germany call: [phone]

To report errors in this document, send an email to:

[e-mail]

1-800-863-3930

3

Table of Contents

Safety Notes .......................................................................................................................... 7

Utility Power Connection Notes .................................................................................. 9

Signal Ground ............................................................................................................11

1.0 Introduction to the VMX Power Supply ..................................................................... 12

1.1 Connections Overview ................................................................................... 13

1.2 Inverter Overview ...........................................................................................14

1.3 Optional Status Monitoring Modules .............................................................. 15

1.4 Optional Features .......................................................................................... 16

2.0 Theory of Operation ..................................................................................................17

2.1 AC (Line) Operation ....................................................................................... 17

2.2 Standby Operation ......................................................................................... 17

2.3 Charger Operation ......................................................................................... 18

3.0 Installation.................................................................................................................20

3.1 Installation Procedure .................................................................................... 21

3.2 Service Power Inserter Connections.............................................................. 22

3.3 Installing the Coax Cable Connector Outputs ................................................25

4.0 Confi guration ............................................................................................................26

4.1 Micro Board Setup ......................................................................................... 26

4.2 AC Output Voltage Reconfi guration ...............................................................27

5.0 Operation ..................................................................................................................28

5.1 Start-up and Test ............................................................................................28

5.2 Smart Display ................................................................................................. 31

5.2.1 Operation Normal ................................................................................ 33

5.2.2 Additional Information Display............................................................. 34

5.2.3 Setup Menu ......................................................................................... 35

5.2.4 Alarm Indications................................................................................. 38

5.2.5 Control Panel LEDs............................................................................. 40

5.2.6 Detailed Menu Structure and Navigation ............................................ 41

5.3 Smart Display Glossary .................................................................................43

5.4 Automatic Performance Test .......................................................................... 45

4

017-940-B0-001, Rev. A

5.5 Providing Power via External Source............................................................. 46

5.5.1 DC Powering ....................................................................................... 46

5.5.2 AC Powering ....................................................................................... 46

5.5.3 Using a Truck-mounted Inverter or Generator .................................... 47

5.6 Resumption of Utility Power ...........................................................................48

6.0 VMX Power Supply Maintenance ............................................................................. 49

6.1 Check Battery Open Circuit Voltage .............................................................. 49

6.2 System Information ........................................................................................ 49

6.3 Check Battery Voltage Under Load................................................................ 50

6.4 Check Battery Charger Voltage ..................................................................... 51

6.5 Check Battery Terminals and Connecting Wires ............................................ 51

6.6 Check Output Voltage .................................................................................... 51

6.7 Check Output Current .................................................................................... 51

6.8 Replacing the Metal Oxide Varistors ..............................................................52

6.9 Maintenance Log ...........................................................................................53

7.0 Specifi cations............................................................................................................54

7.1 Safety and EMC Compliance .........................................................................55

8.0 Troubleshooting ........................................................................................................ 56

8.1 Return/Repair Information.............................................................................. 56

8.2 Parts Ordering Instructions ............................................................................56

8.3 Emergency Shutdown .................................................................................... 57

017-940-B0-001, Rev. A

5

List of Figures and Tables

Fig. 1-1, VMX Power Supply ............................................................................................... 12

Fig. 1-2, VMX Terminal Block Overview .............................................................................. 13

Fig. 1-3, Inverter Overview .................................................................................................. 14

Fig. 2-1, Charger Modes...................................................................................................... 18

Fig. 2-2, VMX Block Diagram .............................................................................................. 19

Fig. 3-1, SPI Cover Removal ...............................................................................................22

Fig. 3-2, Coaxial Cable Insertion and Securing ................................................................... 22

Fig. 3-3, Cover Replaced, SPI Switched On ....................................................................... 23

Fig. 3-4, SPI Grounding Lug ................................................................................................23

Fig. 3-5, Enclosure Ground Bar ...........................................................................................23

Fig. 3-6, Wire/Connector Assembly .....................................................................................23

Fig. 3-7, SPI to Output 1-4 Connection ............................................................................... 24

Fig. 4-1, Micro Board Settings ............................................................................................. 26

Fig. 4-2, Transformer Output Tap Connector ....................................................................... 27

Fig. 5-1, Confi guration Screen............................................................................................. 28

Fig. 5-2, Smart Display ........................................................................................................31

Fig. 5-3, Additional Info Display ...........................................................................................34

Fig. 5-4, Setup Menu Display .............................................................................................. 37

Fig. 5-5, Smart Display LEDs .............................................................................................. 40

Fig. 6-1, MOV Removal ....................................................................................................... 52

Fig. 6-2, MOV Replacement ................................................................................................ 52

Table 5-1, Setup Menu Parameters ..................................................................................... 36

Table 5-2, Major Alarms ....................................................................................................... 39

Table 5-3, Minor Alarms ....................................................................................................... 39

6

017-940-B0-001, Rev. A

Safety Notes

Review the drawings and illustrations contained in this manual before proceeding. If there are any questions
regarding the safe installation or operation of this product, contact Alpha Technologies or the nearest Alpha
representative. Save this document for future reference.

To reduce the risk of injury or death, and to ensure the continued safe operation of this product, the following
symbols have been placed throughout this manual. Where these symbols appear, use extra care and
attention.

ATTENTION:

The use of ATTENTION indicates specifi c regulatory/code requirements that may affect the placement of
equipment and /or installation procedures.

NOTE:

A NOTE provide additional information to help complete a specifi c task or procedure.

CAUTION!

The use of CAUTION indicates safety information intended to PREVENT DAMAGE to material or
equipment.

WARNING!

WARNING presents safety information to PREVENT INJURY OR DEATH to the technician
or user.

Safety Precautions

• Only qualifi ed personnel may service the VMX Power Supply.

• The VMX shall be installed in an appropriate enclosure in accordance with the requirements of IEC
60364-4-482.

• Verify the voltage requirements of the equipment to be protected (load), the AC input voltage to the power
supply (line), and the output voltage of the system prior to installation.

• Equip the utility service panel with a properly rated circuit breaker for use with this power supply.

• When connecting the load, DO NOT exceed the output rating of the power supply.

• Always use proper lifting techniques whenever handling the power supply or batteries.

• The VMX Power Supply contains more than one live circuit! Even though AC voltage is not present at the
input, voltage may still be present at the output.

• If batteries are being stored prior to installation, charge at least once every three months to ensure
optimum performance and maximum battery service life.

• To reduce the chance of spark, and wear on the connectors, always switch the inverter’s battery circuit
breaker off before connecting or disconnecting the battery pack.

• The battery pack, which provides backup power, contains dangerous voltages. Only qualifi ed personnel
should inspect or replace batteries.

• In the event of a short circuit, batteries present a risk of electrical shock and burns from high current.
Observe proper safety precautions.

• Always wear protective clothing, insulated gloves and eye protection (safety glasses or face shield)
whenever working with batteries.

017-940-B0-001, Rev. A

7

Safety Precautions, continued

• Do not allow live battery wires to contact the enclosure chassis. Shorting battery wires can result in a fi re
or possible explosion.

• Always replace batteries with those of an identical type and rating. Never install old or untested batteries.

• Avoid using uninsulated tools or other conductive materials when handling batteries or working inside the
enclosure.

• Remove all rings, watches and other jewelry before servicing batteries.

• Spent or damaged batteries are environmentally unsafe. Always recycle used batteries. Refer to local
codes for proper disposal of batteries.

Battery Safety Notes

• Always refer to the battery manufacturer’s recommendation for selecting correct “FLOAT” and “ACCEPT”
charge voltages. Failure to do so can damage the batteries.

• Verify the VMX battery charger's “FLOAT” and “ACCEPT” voltage settings. See Section 5.2.3, Setup
Menu.

• Batteries are temperature sensitive. During extremely cold conditions, a battery’s charge acceptance
is reduced and requires a higher charge voltage. During extremely hot conditions, a battery’s charge
acceptance is increased and requires a lower charge voltage. To compensate for changes in temperature,
the battery charger is temperature compensating.

• If the batteries appear to be overcharged or undercharged, fi rst check for defective batteries and then
verify the correct charger voltage settings.

• To ensure optimum performance, inspect batteries every three to six months for signs of cracking,
leaking, or unusual swelling (note that some swelling is normal).

• Check battery terminals and connecting wires. Clean battery terminal connectors periodically and torque
to manufacturer's specifi cations. Spray the terminals with an approved battery terminal coating such as
NCP-2.

NOTE:

If installed, disconnect the AlphaGuard (AG-CMT) prior to measuring battery voltage.

NOTE:

Even with a AG-CMT present in the system, any battery which fails the 0.3V load test must be replaced with
an identical type of battery.

• Check battery voltages UNDER LOAD. Use a load tester if available. Differences between any battery in
the set should not be greater than 0.3Vdc.

• Refer to the battery manufacturer’s recommendation for correct charger voltages.

• Number the batteries (1, 2, 3, etc.) inside the enclosure for easy identifi cation (refer to the appropriate
enclosure installation guide).

• Establish and maintain a battery maintenance log (see Section 6.9).

NOTE:

Always verify proper polarity of cables before connecting the batteries to the power module. The batteries are
clearly marked for polarity. If the cables become interchanged at the batteries the battery breaker will trip.

8

017-940-B0-001, Rev. A

Utility Power Connection Notes

ATTENTION:

Connecting to the utility should be performed only by qualifi ed service personnel and in compliance with local
electrical codes. Connection to utility power must be approved by the local utility before installing the power
supply.

ATTENTION:

UL and NEC require that a service disconnect switch (UL listed) be provided by the installer and be connected
between the power source and the VMX Power Supply. Connection to the power supply must include an
appropriate service entrance weather head.

NOTE:

In order to accommodate the high-inrush currents normally associated with the start-up of ferroresonant
transformers (400A, no-trip, fi rst-half cycle), either a “high-magnetic” or HACR (Heating, Air Conditioning,
Refrigeration) trip breaker must be used. Do not replace these breakers with a conventional service entrance
breaker. Alpha recommends ONLY Square D breakers because of increased reliability in this powering
application. High-magnetic Square D circuit breakers and BBX option (UL Listed service entrance) are
available from Alpha Technologies.

Description Alpha P/N Square D Part Number

230V Installation — HACR (15A) 470-224-10 QO215
BBX — External Service Disconnect 020-085-10 QO2-4L70RB
BBX — External Service Disconnect 020-141-10 QO8-16L100RB

VMX Line Cord Options Alpha P/N

Line Cord,3C, #14, SCHUKO/320 C19 RECT, 1M (EU) 875-432-10
Line Cord, 3C, #14, SCHUKO/IEC 320 C19 REPT, 2.5M (EU) 875-433-10
Line Cord,3C, #14, BS546/IEC 320 C19 RCPT, 1M (India) 875-434-10
Line Cord,3C, #14, BS1363/IEC 320 C19 RCPT, 2M (UK) 875-435-10
Line Cord,3C, CHN/IEC 320 C19 RCPT, 1M (China) 875-436-10
Line Cord, 3-conductor, 12AWG, NEMA 6-15P (US) 875-471-10

017-940-B0-001, Rev. A

9

Utility Power Connection Notes

ATTENTION:

In most cases, the following confi gurations qualify for service entrance use when wiring a duplex receptacle
to a service disconnect. Other codes may also apply. Always contact your local utility to verify that the wiring
conforms to applicable codes.

240Vac Service Entrance, VMX 225V, U.S. Domestic Models

These confi gurations are equipped with a 240Vac duplex receptacle to provide power to the power supply
and peripheral equipment. The receptacle, NEMA 6-15R, is protected by a single, 2-pole, common trip 15A
circuit breaker located inside the service entrance. Wiring is typical 14AWG per NEC code, and a grounding
clamp, located on the enclosure, facilitates dedicated grounding.

NOTE:

To bond the box to a neutral plate, use the long green bonding screw provided (Alpha P/N 523-011-10).

220, 230, 240Vac Service Entrance, VMX 225V, International Models

Typical 220, 230, 240Vac 15A Service Entrance Wiring, International

Line (Black)

Copper Ground Wire

#8 AWG (Minimum)

Breaker

Grounding Point Made

to Enclosure Wall

To Utility

Neutral (White)

Neutral Bus

LI

10

017-940-B0-001, Rev. A

Grounding Connection Notes

In order to provide a ready, reliable, source of backup power, it is necessary to establish a grounding system
that provides for the safety of service personnel and for the proper operation and protection of equipment
within the network.

Safety Ground

The safety ground is a two-part system. The fi rst part is a return path for stray current back to the input
breaker, and the second is a return path from the Alpha enclosure to a second ground rod.

Typically, the utility ground provides a return path to the input breaker or fuse panel by means of a connection
to an appropriate driven ground rod at the base of the power pole. This path must meet all local and national
standards and regulations.

The second part of the safety ground arrangement is the ground path between the Alpha enclosure and a
second ground rod located at least six feet away from the driven ground rod at the power pole. The second
ground rod and enclosure are connected via #6AWG solid copper wire buried at a depth of 8 to 12 inches. The
wire is connected to a ground lug on the back of the cabinet (for pole-mounted enclosures), or to a ground
lug inside the cabinet (for ground-mounted enclosures). Connection to the ground rod is made with a listed
grounding clamp suitable for direct burial, or by exothermic weld. Normally it is specifi ed that the impedance of
this ground can be no greater than 25 ohms at 60Hz. However, if dual ground rods are installed approximately
eight feet apart, it is not necessary to measure the impedance of the ground rods (it is assumed that the
impedance specifi cation is met).

Signal Ground

For proper operation, the Service Power Inserter (SPI) must be securely grounded to the enclosure chassis.
For systems utilizing ESM/DSM status monitoring, the coax drop ground connection is made through a
separate chassis ground block (Alpha P/N 162-028-10).

Strike (Lightning) Ground

Lightning strikes, grid switching, or other aberrations on the power line all have the potential to cause “fast
rise-time currents” that can cause damage to the powering system. Without a low-impedance path to ground,
the current, while traveling through wires of varying impedance, can produce high voltages that will damage
the powering equipment. The most viable method available to protect the system from damage is to divert
these unwanted fast rise-time currents along a low-impedance path to ground. A low-impedance path to
ground will prevent these currents from reaching high voltage levels and posing a threat to equipment. The
single-point grounding system provides a low-impedance path to ground, and the key to its success is the
proper bonding of the ground rods, so the components of the grounding system appear as a single point of
uniform impedance.

WARNING!

Low impedance grounding is mandatory for personnel safety and critical for the proper
operation of the cable system.

017-940-B0-001, Rev. A

11

1.0 Introduction to the VMX Power Supply

The Alpha family of VMX Uninterruptible Power Supplies is designed for powering signal processing
equipment in cable television and broadband LAN distribution systems. The VMX provides a critical
load with current-limited, regulated, AC power that is free of spikes, surges, sags and noise.

During AC line operation, AC power entering the power supply is converted into a quasi square wave
and is regulated by a ferroresonant transformer at the required output voltage. The regulated voltage
is connected to the load via the O
to the battery charger to maintain a fl oat charge on the batteries.

When the incoming AC line voltage signifi cantly deviates from normal, the VMX Power Supply
automatically switches from the AC line to Standby mode, maintaining power to the load. During the
switch to standby operation, energy in the module’s ferroresonant transformer continues to supply
power to the load. While in Standby mode, the VMX powers the load until the battery voltage reaches
a low-battery cutoff point.

When utility power returns, the VMX Power Supply waits a short time (approximately 10 to 20
seconds) for the utility voltage and frequency to stabilize, and then initiates a smooth, in-phase
transfer back to AC line power. Once the transfer is complete, the battery charger recharges the
batteries in preparation for the next event.

Key components of the VMX Power Supply include a line-conditioning ferroresonant transformer,
resonant capacitor, transfer isolation relay, and inverter. The inverter contains circuitry for the three­stage temperature-compensated battery charger, DC to AC converter (inverter), AC line detector, and
Smart Display. An optional communciation module provides remote status monitoring.

UTPUT 1-4 ± terminal block connections, and some power is directed

The VMX Power Supply features:

• Line Interactive Ferro Technology (LIFT)

• Smart Display

• Built-in programmable battery self-test

• 3-stage temperature compensated battery charger

• Automatic battery detection

• Field programmable fl ash memory

• Four-Output Protection Interface Module

• Digital status monitoring (optional)

12

Fig. 1-1, VMX Power Supply

017-940-B0-001, Rev. A

1.0 Introduction to the VMX Power Supply, continued

1.1 Connections Overview

Below is a brief description of each terminal.

Connections:

• AUX OUT (Auxiliary Output): The Auxiliary Output is an uninterruptible supply of power

that can be used to power external devices such as cable modems or ethernet hubs. The
auxiliary output is rated at 220V 150W and uses a 2A 250V fast blow fuse (Alpha P/N
460-157-19).

• LRI (Local/Remote Indicator): The LRI lamp option connects to the LRI ± terminals on
the terminal block. The LRI circuit is rated at 12Vdc, 250mA. This option duplicates the
function of the red ALARM LED by illuminating an externally mounted red lamp.

• Voltage Out: The Protective Interface Module (PIM) allows the VMX Uninterruptible
Power Supply to provide programmable current limits for four output channels. The
Service Power Inserter (SPI) connects into the Voltage Out terminals.

• Ground: A ground wire (up to 6 AWG) can be connected to the ground lug to
permanently tie the chassis to utility ground. This may be desired when an AC generator
is connected to the power supply, because the chassis ground through the line cord is
removed when the line cord is plugged into the generator.

• V SEL (Voltage Select): The voltage select jumper can be confi gured for either the 63V
output or the 48V output. The voltage values may vary between models.

Voltage Select (VSEL) Jumper

Ground Lug

LRI

AUX OUT

Voltage Out: Modular Ouput Terminal

NOTE:

If using the Alpha SPI with the VMX power supply, cut the Anderson connector off of the SPI and strip the
wires 3/8" and connect them to the output terminal.

017-940-B0-001, Rev. A

Fig. 1-2, VMX Terminal Block Overview

13

1.0 Introduction to the VMX Power Supply, continued

1.2 Inverter Overview

The inverter provides uninterrupted power to the ferroresonant transformer (via the batteries)
during line failures. During line operation, the inverter charges the batteries using a three­stage (Bulk, Accept, and Float) charger.

Components:

• Smart Display: All operational functions, system testing, setup items, and alarms are

available via the Smart Display panel on the front of the VMX Power Supply (the Smart
Display is covered in detail in Section 5.2). Display functions are accessible by pressing
any of the four keys: ESCAPE, UP, DOWN, and ENTER. Backlighting is activated when
any of the four keys are pressed, and stays illuminated for one hour. There are four levels
of menu items: Operation Normal, Additional Information, Setup, and Alarms. Press
ENTER to display one level lower. Press ESCAPE to display one level higher. Press
ESCAPE to toggle between the main menu and alarm menu when alarms are present.

• Battery Breaker: The battery breaker disconnects the batteries from the inverter's
DC circuit. With the battery breaker turned off, the VMX Power Supply will not transfer
to standby mode, the inverter is disabled, and the battery charger cannot charge the
batteries. If an overcurrent is detected in the DC circuitry the breaker will trip.

• Battery Input Connector (Red = Positive; Black = Negative): The batteries plug directly
into the inverter’s battery connector. The connector is color-coded and fi ts in one direction
only.

• Inverter Cooling Fan: The inverter is equipped with a cooling fan that operates during
standby operation, or when the inverter heatsink temperature reaches 85°C. The fan
stays on until the temperature drops below 75°C. The fan also operates any time a self­test is in progress.

• Battery Temp Probe Connector: The Remote Temperature Sensor (RTS) plugs directly
into the temperature probe (RJ-11C type) connector. The sensor end of the RTS is routed
to the battery compartment and taped directly to the side of the center battery. The RTS
provides battery temperature measurements used to adjust the battery charge voltage.

Smart Display

Battery Breaker

Inverter Cooling Fan

14

Status LEDs

Fig. 1-3, Inverter Overview

Battery Input

Battery Temperature
Probe Connector

017-940-B0-001, Rev. A

1.0 Introduction to the VMX Power Supply, continued

1.3 Optional Status Monitoring Modules

The VMX Power Supply supports a number of Alpha Technologies communications modules.
The modules may be ordered factory-installed or as user-installed fi eld upgrades.

CAUTION!
Handle these modules with extreme care. Circuit boards and logic upgrades are static-sensitive and

susceptible to damage.

AlphaNet™ Ethernet Status Monitor (ESM)

The AlphaNet ESM (Alpha P/N 745-814-40) allows monitoring
of your VMX Power Supply via a network connection. Advanced
features and networking services provide for quick reporting and
access to critical powering information, keeping your broadband
network running reliably.

The AlphaNet ESM supports the standard networking protocols
required for effective power network management. The ESM
provides effi cient network status monitoring and diagnostics using
Simple Network Management Protocol (SNMP) and standard
MIBs. A Web interface enables authorized personnel direct
access to powerful, advanced diagnostics using a common Web
browser. No custom software is required. Refer to the AlphaNet

ESM Technical Manual, Alpha P/N 704-782-B0, for more
information.

AlphaNet™ DOCSIS Status Monitor (DSM) and Euro DSM

The AlphaNet DSM (Alpha P/N 745-825-30) and EuroDSM (745­814-43) provide the same funtionality as the AlphaNet ESM, but
feature an environmentally hardened embedded DOCSIS® cable
modem for convenience and reliability. Refer to the AlphaNet

XP-DSM Technical Manual, Alpha P/N 745-814-B0, for more
information.

NOTE:

A hardware kit (Alpha P/N 745-818-22) is available for the ESM, DSM,
or EuroDSM, communications modules. This kit contains sheetmetal and
interconnect cabling, and should be ordered along with the modules.

AlphaGuard™ Battery Charge Management System

The AlphaGuard Battery Charge Management System
extends battery life by providing the precise voltage required
for each battery. You can replace single batteries as they
fail, not the entire string. It spreads charge voltage equally
across batteries, and batteries no longer need to be matched.
It adjusts for battery changes as they age. The optional
communications module monitors individual battery voltage
during inverter operation, protecting against damage from over
discharge. The AG-CMT-3 model supports 36V battery strings.
The AG-CMT-4 supports 48V battery strings. Refer to the

AlphaGuard Installation Instructions, Alpha P/N 012-306-C0,
for detailed information.

AlphaNet ESM

AlphaNet EuroDSM

AlphaGuard CMT

017-940-B0-001, Rev. A

15

1.0 Introduction to the VMX Power Supply, continued

1.4 Optional Features

The following options can be factory installed, or upgraded in the fi eld by the user:

Local and Remote Indicator (LRI)

The LRI (red) lamp is located on the outside of pole-mount enclosures. During normal AC
line operation, the LRI remains off. The LRI comes on only when the power supply is running
in Standby Mode. Whenever a fault is detected during self-test, the LRI fl ashes to indicate
that service is required. The LRI is a simple form of status monitoring that allows operators to
check the operational status of the power supply without having to climb the pole and open
the enclosure (Alpha P/N: 740-139-20).

AC Indicator (ACI)

The AC Indicator (green lamp) is located next to the LRI on the outside of pole-mount
enclosures. As long as there is voltage present at the output, the ACI remains on. As with the
LRI, it acts as a simple form of status monitoring that allows cable technicians to check the
output status of the power supply without having to climb the pole and open the enclosure.
Alpha recommends using the ACI-LL (long life LED) because it provides much longer life
than the original light bulb design. Models for 60V and 90V are available. ACIs are not
recommended for ground mount enclosures (Alpha P/N: 740-167-21).

LA-P+ 240V (Lightning Arrestor)

The LA-P+ plugs directly into the enclosure’s convenience outlet, to provide additional
protection from voltage spikes caused by lightning and other power disturbances. It
eliminates the need for hard-wired MOVs. No additional wiring is necessary (Alpha P/N: LA­P+240)

ATTENTION:

Utility safety ground must meet all local and national standards and regulations.

16

017-940-B0-001, Rev. A

2.0 Theory of Operation

2.1 AC (Line) Operation

During AC line operation, utility power is routed into the primary winding of the ferroresonant
transformer through the contacts of the transfer isolation relay. At the same time, power is
directed to the rectifi er circuitry in the inverter which provides power for the control circuitry.
The bidirectional inverter also serves as a battery charger during AC line operation. The
ferroresonant transformer and an AC capacitor form the resonant tank circuit, which provides
excellent noise and spike attenuation, output short circuit current limiting, and output voltage
regulation. The ferroresonant transformer produces a quasi square wave output which
resembles a rounded square wave.

CAUTION!
To minimize the possibility of the transformer entering unstable operation, the VMX Power Supply

requires a minimum load of at least one ampere connected to the output. Unstable transformers will
self-correct as soon as a load of one ampere or greater is connected to the power supply.

2.2 Standby Operation

When incoming AC line voltage drops or rises signifi cantly, or a complete power outage
occurs, the VMX line monitor activates standby operation. During the transfer from AC line to
standby operation, the battery powered inverter comes on-line as the isolation relay opens to
prevent AC power from back-feeding to the utility. The energy contained in the ferroresonant
transformer continues to supply power to the load. The following changes also occur within
the VMX Power Supply:

• The control logic drives the inverter fi eld-effect transistors (FETs) on and off. This

switching action converts the DC battery current into AC current in the inverter winding of
the ferroresonant transformer, which provides regulated power to the load.

• The control logic, which includes a microprocessor and other circuits to protect the

inverter FETs from overcurrent damage, monitors the condition of the batteries and the
inverter during standby operation. Since a prolonged AC line outage would severely
discharge the batteries, resulting in permanent damage, the control logic disables the
inverter when the batteries drop to approximately 10.5Vdc per battery.

When acceptable AC line voltage returns, the power supply transfers back to AC line
operation within 10 to 20 seconds. This delay allows the AC line voltage and frequency to
stabilize before the control logic phase-locks the inverter’s output to the utility input. The
control logic then de-energizes the isolation relay, reconnects the AC line to the primary of
the ferroresonant transformer and disables (turns off) the inverter. This results in a smooth,
in-phase transfer back to utility power without interruption of service to the load. The battery
charging circuit then activates to recharge the batteries in preparation for the next power
outage. In the case of a prolonged AC outage where the inverter shuts off due to low battery
voltage, the output will return as soon as the AC line voltage returns.

NOTE:

The duration of battery-backed standby operation depends upon the type and number of batteries and the
load on the power supply.

017-940-B0-001, Rev. A

17

2.0 Theory of Operation, continued

2.3 Charger Operation

The VMX Power Supply uses a three-stage, temperature-compensated battery charger.
During AC line operation, the inverter winding on the ferroresonant transformer feeds the
charger circuit which provides BULK, ACCEPT, and FLOAT charge voltages to the batteries.

Charger Modes:

TEST: When the power supply fi rst starts, transfers back to line, or when batteries are fi rst

connected, the power supply will indicate the charger mode is TEST for a period of up to
10 minutes. The charger will operate the same as BULK mode, but with a slightly different
battery detection method. The charger mode will also indicate TEST during self-test.

BULK charge is a “Constant Current” charge. The maximum charger current is 10 Amps.
As the charge is returned to the batteries, their voltage increases to a specifi c threshold
(2.27Vdc per cell). This cycle ends when the charging current into the batteries becomes less
than 0.5A.The charger then switches to ACCEPT mode. The BULK charger mode generally
returns the battery charge state to 80 percent of rated battery capacity.

ACCEPT charge is a “Constant Voltage” charge. This voltage, 2.40Vdc (adjustable) per
cell, is temperature-compensated to ensure longer battery life and proper completion of the
charge cycle. This cycle is complete when the charging current into the batteries becomes
less than 0.5A, or approximately six hours from the time ACCEPT mode was entered. When
the batteries are fully recharged the charger switches to the FLOAT mode of operation.

FLOAT charge is a temperature-compensated “pulsed voltage” charge, averaging about

2.27Vdc (adjustable) per cell. During FLOAT mode, the batteries are fully charged and ready
to provide backup power. The charger provides a small maintenance charge to overcome the
batteries self-discharge characteristics and other minor DC loads within the power supply. As
the battery voltage reaches the “full charge” level the time delay between pulses increases.

The cell voltage is temperature-compensated at -0.005Vdc per cell per degree Celsius
(adjustable) to ensure a safe battery cell voltage and maximize battery life. The temperature
compensation is limited to an absolute battery voltage minimum of 2.20V per cell and a
maximum of 2.50V per cell regardless of the temperature compensation settings.

18

2.40

2.25

2.15

2.05

10

9
8

7
6
5
4
3
2
1
0

Charger Current

Bulk Accept Float

Fig. 2-1, Charger Modes

Volts Per Cell

017-940-B0-001, Rev. A