- This topic has 28 replies, 1 voice, and was last updated 2 weeks, 2 days ago by Olegabaft.
21st May 2005 at 09:31 #41108Ranjeet JhaGuest
I am working with a GSM provider in India.
Q: Why do we use – 48 V DC supply in Telecom Equipments.
RANJEET KUMAR JHA13th June 2005 at 03:27 #41109dr.kumarGuest
we are using -48V, in order to avoid battery drain up. U want still clarification ur mail ID.
dr.kumar18th June 2005 at 11:36 #41110werGuest
i think in Telecom we use -48 v coz at -ve voltage less noise or interference from outside.20th June 2005 at 02:46 #41111dr.kumarGuest
of course true, but for interference and noise we provided filters in the switch.6th July 2005 at 08:11 #41112diwGuest
Which filter your r talking about….
Clarify pls.20th July 2005 at 12:35 #41113Ashish GoelGuest
The noise pulses tend to go towards positive end. So the higher the voltage towards positive end the higher the noise and interference. Hence the volyage used in telecom is -ve.21st July 2005 at 07:13 #41114B G NaiduGuest
Do you explain more about wht do you use -48v in telecom.
Naidu21st July 2005 at 09:04 #41115ashishGuest
Hi Friends, Basically I am an electrical engineer, working with a mnc. I know little bit about telecom electrical utility. I am very keen to enter in this field for installation & maintenance of switching network (BTS/BSS). Please let me know courses /certification running in India gives more knowledge about telecom electronics. How can I go for such jobs?10th August 2005 at 07:35 #41116Omer AhmedGuest
The -48V voltage was selected because it was enough to get through kilometers of thin telephone wire and still low enough to be safe (electrical safety regulations in many countries consider DC voltages lower than 50V to be safe low voltage circuits). 48V voltage is also easy to generate from normal lead acid batteries (4 x 12V car battery in series). Batteries are needed in telephone central to make sure that it operates also when mains voltage is cut and they also give very stable output voltage which is needed for reliable operation of all the circuit in the central office. Typically the CO actually runs off of the battery chargers with the batteries in parallel getting a floating charge.
The line feeding voltage was selected to be negative to make the electrochemical reactions on the wet telephone wiring to be less harmful. When the wires are at negative potential compared to the ground the metal ions go form the ground to the wire instead of the situation where positive voltage would cause metal from the wire to leave which causes quick corrosion.12th August 2005 at 11:33 #41117katGuest
noise pulse can be neg(-) also, there is no specific reason to be it pos(+).
can u explain more on your point??
-thanks12th October 2005 at 12:46 #41118sukuGuest
I feel that , the power supply can’t generate negative voltage .
only the polarity is changed , with respective to the chassis of the equipment .
incase of -48v system , the +ve bus bar is grounded , if is’t +48v system the negative bus bar is grounded .13th October 2005 at 07:40 #41119shaleen srivastavaGuest
Actually the earth is consider to be positive so we apply negative supply to our BTS so that when lightening occurs the charge travels to the positive terminal like earth not to the BTS. if we apply positive to our equipment then both the equipment and the earth will be connected and our instrument can be damaged during lightening
So negative polarity seperates our BTS from earth.
One more thing which i had heard is that all the digital equipments are configured to work on negative polarity
CH2MHill Communication group ltd.13th October 2005 at 17:09 #41120sukuGuest
I have seen Motorola BTS , BSC , XCDRs have a positive +48V design also .
in this what will happen .14th October 2005 at 08:30 #41121Shaleen SrivastavaGuest
actually this reason which i had told about the +ve supply ,told by one guy from philipines he is expert in telecom
i’ll try to find ur answer and get back to u soon
can u please give me ur email id
firstname.lastname@example.org November 2005 at 00:19 #41122dexturGuest
i believe it is -48 to avoid cathodic reaction. You can read on this in the book Telephony by HARB.