Power Systems FAQ
 
 

How much power is required?

Pulsecom communication equipment requires -48Vdc, usually supplied by 120Vac to -48Vdc “rectifiers”.

  • Look at the “Practice” or instruction manual for each product to be powered to determine how many milliamps (mA) of current the product requires (a milliamp is 0.001 Amps, or 1,000 mA = 1 Amp). An example: Pulsecom’s DS3 EXPRESS (DS3 over 4 twisted pairs) requires 200mA.
  • Add the current requirements from all of the products you wish to power from a power supply. For example, if you plan to install two (2) DS3 EXPRESS units at a site, they’d require a total of 200+200 = 400mA.
  • Finally, select a suitable power supply. In this case, assuming the products will be installed indoors, Pulsecom’s 2100-0300 120Vac to -48Vdc, 1A (1000mA) power supply would be more than adequate.

What size Fuse is required?

It’s best to allow a significant safety factor when selecting fuse sizes for low power communications equipment such as that offered by Pulsecom. The fuse needs to open if a wiring short or catastrophic equipment failure occurs, but should not accidentally open due to repeated power on-off cycles or fatigue or because it’s operating at its design limits.

Pulsecom shelves are often equipped with 0.75A (750mA) fuses per card slot to accommodate the heaviest expected power demands. For example, Pulsecom’s O3-3D3P unit (OC3 to 3 DS3s with integral optical protection switching) requires 380mA (0.38A). The 0.75 fuse size provides approximately a 2 to 1 safety factor – a good rule of thumb.

How much Battery Reserve do I have?

Pulsecom’s POWER NODE/6A is equipped with four 12V, 7AH (Amp-Hour) batteries. The four batteries are connected in series to provide a 48V battery “string. The result is a 48V battery system that can deliver 7AH.

Simplistically, that means the batteries could provide 1 Amp for 7 Hours. Or, 7 Amps for 1 Hour. In reality, the 7AH capacity rating is based upon a slow discharge – faster discharge rates reduce the Amp-Hour capacity.

A typical 0.5A load (representing a couple of different Pulsecom units) could be powered from the 7AH batteries for about 14 hours. For longer battery back-up times, Pulsecom’s POWER NODE+ is designed to use 14AH batteries.

What’s Span Powering?

Span Powering means that equipment at a far-end site is being powered from a near-end site over telephone wire linking the two sites. The technique is common for T1 and HDSL equipment. In fact, home telephones are often powered from telephone company equipment located down the street or in telephone company buildings.

However, high speed equipment - such as SONET multiplexers - have always required too much power to make remote powering practical. Business-quality DS3 circuits have required that a SONET multiplexer be located in a business site and be powered via local (business site) power supplies and battery back-up systems. This approach is not only expensive in terms of power equipment, batteries and battery maintenance, it’s less reliable than telephone company power systems that often include generator back-up systems.

The exceptionally low power required by Pulsecom’s DS3 and GigE equipment has made span powering of business data circuits not only practical but highly cost effective. Even the migration from copper to fiber-fed DS1 circuits is easier by remotely powering Pulsecom’s OC3 to DS1 units with our Span Power units.

What’s the Range of Pulsecom’s Span Power Units?

Just determine the amount of current required and then refer to the following chart to determine the range based upon wire size.

Maximum Load (mA)
Loop Resistance (ohms)
Range in kFt (4 pairs)
22 GA
24 GA
26 GA

160

450

57

36

22

180

400

50

32

20

200

360

45

29

18

225

320

40

25

16

250

290

37

23

14

300

240

30

19

12

360

200

25

16

10

400

180

23

14

9

450

160

20

13

8

500

140

18

11

7

600

120

15

10

6


 

 
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