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REMOTE POWER SYSTEM
”Turning your copper into gold”
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Eltek
What?
Powering remote electronics utilizing
the existing copper network
Also known as ‘span power’ or ‘line power’
Powering a broadband/xDSL network
Increased bandwidth requires active
components (DSLAM) closer to the end user
Solutions for power distributions required
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What?
CO site with
existing 48Vdc
system and
battery backup
Typical distance
to remote DSLAM
site is 5 to 10km
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Eltek
Remote Powering
concept
Existing twisted pairs now
made available for power
distribution. ±190Vdc,
250mA
Fed by existing
48Vdc or
integrated Rectifier
solution
AC or
DC
Remote
DSLAM
NODE
Central
Office
n numbers
of Remote
Nodes
Remote
DSLAM
NODE
Dc/dc converter in
the Remote End
supplying -48V
Remote
DSLAM
NODE
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Eltek
Why?
CAPEX & OPEX reductions
Utilize the existing infrastructure
Copper network, X-connects, etc.
Eliminate the requirement for batteries and local
power utilities
Reduces the size of the DSLAM significantly
Battery maintenance eliminated
Increased speed of xDSL roll-out
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Eltek
How?
RFT: Remote feeding telecommunication circuit
Remote Power feeding standard: IEC60950-21/GR-1089
Power limitation: 100W per channel (circuit)
RFT-C circuits:
Max. 60 mA, maximum 1667V (100VA)
normally limited to 800V
OR
RFT-V circuits:
200Vdc referred ground (400Vdc potential)
OVS and ground leakage current detection
Eltek only have this type of equipment, why?
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Eltek
How?
Block
schematics
based on Eltek
products
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Modules
System Solutions
Flatpack DC/DC Converter 48/190
Flatpack VA Limiter
Remote End Converter
Flatpack RPS Integrated
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Eltek
Central Office
modules
Flatpack DC/DC Converter
Flatpack VA Limiter
Input: 48Vdc (40-60Vdc)
Input: ±190Vdc
Output: 190Vdc of 1250W
Output: ±190Vdc 12 Channels
Reliable ”Flatpack” technology
(RFT-V Circuits) of 100W
Digital current sharing
Short circuit proof
High temp protection
Over voltage shutdown
Part no.: 241114.501
CE, UL and NEBS approvals
(250mA)
Current limiters
Over voltage protection
Ground leakage current protection
(trip current 60mA)
1.000.000h MTBF per channel
Part no.: 241258.724
IEC/UL60950-21 (”remote powering safety standard”)
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Eltek
VA Limiter
On/Off switch
I+ CURRENT SENSE
+190V input
from dc/dc
converters
Over load
detection
Over voltage
protection
Ground leakage
current detect
Secondary
protection;
gas
discharge
tube
Current limiters
for lightning and
AC power fault
protection
Over load
detection
-190V input
from dc/dc
converters
On/Off switch
I- CURRENT SENSE
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Eltek
Remote End
Converter
5 separate DC/DC converters
Primary surge protection integrated
Input voltage: 190V-380V
Output voltage: 48V
Output power: up to 380W
depending on site layout (typically
250W)
Flexible mounting, eats no space in
DSLAM rack
Part no: 241258.722
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Eltek
Flatpack RPS
2U Integrated
2U Integrated
2 DC/DC Converters
2 VA Limiters
24 output channels (RFT-V
Circuits)
Single or dual feed
19”/23” mounting
3U solution with Redundant
DC/DC converters is also
available
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Eltek
Flatpack RPS
6U Integrated
Flatpack 6U Integrated
Building block for larger
cabinet solutions and
expandable systems
Up to 6 DC/DC Converters
Up to 6 VA limiters
Up to 72 output channels
48Vdc feed configurable on site
1 x 250A
3 x 100A
6 x 50A
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Eltek
Real CO site
with RPS
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Site installation
System dimensioning
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Eltek
Safety
Crossover between telecom and power
Above 60V SELV level
Important
Qualification & identification of twisted pairs
Training of installation and maintenance people
Follow Eltek installation manuals (including the
configuration tool)
Grounding of people working on cables is
important!
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Safety – Voltage
levels
Classification of voltage levels (GR-1089)
A1: 200Vdc / 0.15mA maximum leakage current to ground
A2: 200Vdc / 5mA maximum leakage current to ground
A3: 200Vdc / 10mA maximum leakage current to ground
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Eltek
Safety – DC
IEC 60947-1 – Effects of current on
humans beings and livestock (DC)
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Eltek
Safety – DC
Dangerous
area
Our area
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Safety – AC
Remember difference between DC and AC
30mA AC is accepted as trip current
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Safety – Body
resistance
2kΩ
1,275kΩ
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Safety - Earth
leakage detection
VA Limiter takes care of the safety in the system,
on earth fault it trips on 60mA
190V/2,5kohm ≈ 72mA -> earth fault
2kohm (typical person) + 0,5kohm (typ. cables)
If the earth leakage current exceeds 60mA, the VA
Limiter shuts off within 5ms and runs in a hick-up
mode limiting the average current to ground to less
than 5mA.
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Safety –
Overload
Isolated (non grounded) person/user (should not
happen..)
380V/1,275kohm ≈ 300mA
VA limiter channel will go into overload and shut down,
but...
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Eltek
Safety – Marking
X-connect example
Proper
marking
DSLAM cabinet
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Safety –
cable qualification
From Eltek User Guide
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Basic electrical considerations
Block diagram
Fixed Parameters
Remote End Converter
Line Impedance
Stability criteria's
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Eltek
Block diagram
Central Office
Remote site
VA Limiter
Remote Unit
Line impedance
[Ohm]
190V-380V/48V
DC/DC Converters
I [mA]
VA limit
VA limit
Vco
[V]
Vremote
[V]
48V to DSLAM
+190
GND
-190
Cable length
[m, km, kft]
VA limit
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Eltek
Fixed Parameters
Central office voltage
±190Vdc = 380V
Max current
Derived from max output power, safety requirements (GR1089-CORE, IEC/UL60950-21):
100VA (W) per channel
380V
Imax = Pmax/Vco = 100W/380V = 263 mA
Safety margin and tolerances must be taken into account
The maximum input current of the Remote End Converter
must be limited to less than the maximum output current
of the VA Limiter (next slide)
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Fixed Parameters cont’
current
Maximum
263 mA
238 mA
235 mA
Tolerance VA Limiter (5%)
Worst case maximum
output current VA Limter
Tolerance Remote End
Converter (1%)
Worst case maximum
input current Remote End
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Eltek
Remote End Converter
Max input current: 235 mA
Efficiency: ~86%
This steals power from the CO
Power out = 86% of Power in
Pin = Vin * Iin
input
Output
losses
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Eltek
Line Impedance
Specific resistance for copper:
0.018 Ohm/mm2/m (at 30°C)
Resistance per km/kft for Cable size:
0.9 mm (AWG 19): r=27.6 Ohm/km, 8.4 Ohm/kft
0.6 mm (AWG 22): r=55.3 Ohm/km, 16.8 Ohm/kft
0.5 mm (AWG 24): r=87.8 Ohm/km, 26.8 Ohm/kft
0.4 mm (AWG 26): r=139.7 Ohm/km, 42.6 Ohm/kft
Max impedance:
The maximum line impedance is calculated from the
stability criteria
Next slides
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Stability 1
The obvious
The power consumption has to be less than the
power available
If the power consumption exceeds the power
supplied, the power train will collapse
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Eltek
Stability 2
Dc/dc converters has inverse impedance
characteristics (1/R)
The load is constant
If the input voltage drops, the converter will
draw higher current to maintain the output
voltage (with a constant power load)
When the converter draws more current, the
input voltage will drop further...
Constant power:
Pin  Vin  I in
Constant power load
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Stability 3
Too high line impedance will
result in decreasing output
power for increasing current
REC input power vs input current
Z line 
Rloop = 1200
80
Vco
Z line 
2  I max
Rloop = 1000
70
380 V
2  235 mA
Rloop = 800
Rloop = 600
Input power [W]
60
~ 800 
Rloop = 400
50
40
30
Unstable!
20
10
0
0
50
100
150
200
250
Input current [mA]
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Line Impedance cont’
Now we can find maximum cable length:
AWG 19: 13.6 km / 44.7 kft
Z max
lmax 
AWG 22: 6.8 km / 22.3 kft
2r
AWG 24: 4.3 km / 14.0 kft
AWG 26: 2.7 km / 8.8 kft
To increase length pairs can be paralleled
2 pairs – double length
3 pairs – triple length
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Paralleling of pairs
Cable resistance is increased
1
1
1
1
 

 ...
Rtotal R1 R2 R3
The current is shared between the pairs
If the cable resistance is equal, the current is
shared equally
The touch current remains the same
Only single wire out of and into the modules
connectors
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Eltek
Line Impedance cont’
How does the line impedance affect the
output power?
Linearly decreasing with increasing line
impedance
Max Output Power per channel vs line impedance
90
Output Power [W]
80
70
60
50
40
30
20
10
0
0
200
400
600
800
1000
Line Impedance [Ohm]
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Eltek
Line Impedance cont’
Knowing the max line impedance, the
minimum power per channel can be
calculated
Pout  Pin 
Pin  Vin  I in
Vin  Vco  Z line  I in
 Pout  Vco  Z line  I in   I in 
 Pout  (380  800  0.235)  0.235  0.86  38.8 W
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Configuration
Site dependent parameters
Power consumption
How many channels?
How many pairs?
Wire gauge
Calculated parameters
Max line impedance
Max Cable length
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Eltek
Site Dependent parameters
Power Consumption
This is what the power system do; deliver a
certain amount of power to the Remote End
How many channels?
Adding channels means adding power
How many pairs?
Adding (parallel) pairs means increasing cable
length
Wire gauge
As seen, the wire gauge affects the line
impedance. Use as low AWG as possible...
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Eltek
Calculated Parameters
Max line impedance
The maximum line
impedance is calculated from
the maximum power drop of
the lines
Max Cable length
The cable length can easily
be calculated from the
maximum impedance as long
as you know the gauge
Vco
Pmin
Z

2
I max n   I max
Z
l
r
r  139.7 Ω/km
for 26 AWG
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Excamples –
Cable Calculator tool
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