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Thread ID: 138115	2014-10-07 00:17:00	Power Cuts and the effect on telephone exchanges - thought you might like to know	Roscoe (6288)	PC World Chat

Post ID	Timestamp	Content	User
1385729	2014-10-07 00:17:00	Most people know that telephone exchanges continue to operate when the power goes off and are aware that the reason that they continue is because all telephone exchanges have batteries, but it is well less known why they run on batteries. Many people think that the batteries are there as a back up for when the power goes off, but that is only a side benefit and if the power does go off for a long time, the batteries will run out and the exchange will stop working. Some of the more important exchanges have a back up generator (such as the big major exchange in Airedale St in Auckland City) while others may have to rely on portable generators. So if the batteries are not there as a back up, why do they have them? Firstly, you cannot impress speech on AC current. So why not just convert the AC current to DC and use that? The reason is that the AC supply is not constant which means that the resulting DC current would not be constant either and constant DC current is required for speech, so they use the not so constant AC supply to charge the batteries which supply the constant 50 volts required. That is the real reason why exchanges use batteries. Just thought you might like to know.	Roscoe (6288)
1385730	2014-10-07 02:05:00	Well the exchanges work or 48 volts DC supplied from the batteries which are charged from the commercial power supply. When the commercial power goes off the batteries keep the system going until the backup generators kick in some times started manually. If there were no batteries installed then you would have to have some sort of "No Break" system like we had back in the 1940s ~ 60s where a motor generator set with the large flywheel were installed. This allowed enough time for the diesel to be started . These were designed for low load situations. If there were no batteries in a modern environment then the diesel generators would have to run 24 / 7 (I'm sure the neighbors would love this) or if the power goes off the exchange would stop until the generators were started. They would have to be pretty grunty to take the cold start load of an exchange the size of Airedale street or remers.. Batteries also do power smoothing as we..	paulw (1826)
1385731	2014-10-07 03:25:00	Yeah the batteries work as a smoothing capacitor for the output of the 50V rectifiers as well as reserve power for outages and pretty much all telephone/ isp equipment runs on 50V DC (or 24V for some mobile gear). One thing that's not obvious right away with the slow move to fibre and voip type telephone services is the surprisingly large power saving to the phone company when they no longer have to supply power to your house for the landline. In future if you want your phone to work in a power cut you may need to provide your own backup power to keep the equipment going, some people may be in that situation already. Myself for example, I have no landline and just use a cell phone or occasionally skype. I know of at least one exchange that has in the past been used to pump power back into the grid when hydro lake levels were getting low as it's diesel generators have quite a bit of spare capacity. Spark has to be one of the power companies larger consumers I'd imagine.	dugimodo (138)
1385732	2014-10-07 04:17:00	Once upon a time they all had generators.	pctek (84)
1385733	2014-10-07 05:09:00	Interesting! I did not know that.	Agent_24 (57)
1385734	2014-10-07 06:45:00	anyone know why some old houses had batteries connected to the phone lines at the house ?	tweak'e (69)
1385735	2014-10-07 07:03:00	anyone know why some old houses had batteries connected to the phone lines at the house ? That was in the days of the manual exchanges which did not supply the voltage for speech. In the earlier phones the speech batteries were incorporated in the telephone housing which is why the manual phones of those days were so big. Nowadays the speech battery is supplied by the exchange.	Roscoe (6288)
1385736	2014-10-07 10:46:00	Yep and the old phones with the crank handle generated an AC ring current to alert the operator a call was incoming. Things have come a long way in a short time. When I first started with the post office I learnt how to maintain gear basically like this www.youtube.com but pretty soon spent years replacing them with the current Neax exchanges throught he 2nd half of the eighties. Now the exchanges are getting pretty long in the tooth and it looks like telephone services will move to the same network as the internet rather than be a separate service. It's coming around full circle as initially the internet was a service carried by the telephone network and now telephony is a service often carried by the internet.	dugimodo (138)
1385737	2014-10-07 18:34:00	When I first started with the post office I learnt how to maintain gear basically like this . youtube . com/watch?v=xZePwin92cI" target="_blank">www . youtube . com but pretty soon spent years replacing them with the current Neax exchanges throught he 2nd half of the eighties . . Really? Whats your name? Husband started in 1964 . Step-by-step, crossbar all that . Then when the Americans came over, he went round the upper north island with them putting in the first NEAX stuff . They asked him to go work for them, they were going to Egypt next . . . . but he hated the digital stuff . He did discover we had access to the exchanges via home phone but sadly went and told them and they corrected that so you couldn't anymore . He stayed for a bit, I remember his colleague went on holiday and he had a DOS laptop, I had to go to work with him for a few days, I'd run the software, he'd hook it up to the equipment then replace whatever needed replacing and he absolutely hated the whole business . He took redundancy on the second round in 1991 .	pctek (84)
1385738	2014-10-07 19:35:00	Well our careers overlap by about 6 years so if your husband worked in the waikato during that time we probably met. If you like I can PM you my name, not sure I want to post it publicly :)	dugimodo (138)
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