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View Full Version : Power Cuts and the effect on telephone exchanges - thought you might like to know



Roscoe
07-10-2014, 12:17 PM
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.

paulw
07-10-2014, 02:05 PM
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..

dugimodo
07-10-2014, 03:25 PM
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.

pctek
07-10-2014, 04:17 PM
Once upon a time they all had generators.

Agent_24
07-10-2014, 05:09 PM
Interesting! I did not know that.

tweak'e
07-10-2014, 06:45 PM
anyone know why some old houses had batteries connected to the phone lines at the house ?

Roscoe
07-10-2014, 07:03 PM
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.

dugimodo
07-10-2014, 10:46 PM
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 https://www.youtube.com/watch?v=xZePwin92cI 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.

pctek
08-10-2014, 06:34 AM
When I first started with the post office I learnt how to maintain gear basically like this https://www.youtube.com/watch?v=xZePwin92cI 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.

dugimodo
08-10-2014, 07:35 AM
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 :)

paulw
08-10-2014, 07:36 AM
When I started in Auckland we were using this stuff well an earlier version of it..http://www.youtube.com/watch?v=ZwOlSgL--iM&feature=related

R2x1
08-10-2014, 09:22 AM
This sort of stuff (https://www.youtube.com/watch?v=ZAJpionUxJ8) didn't seem so weird back in the day, but it was for the outside world, not NZ in the main.
Even if that old test gear was working perfectly now, it would be of amazingly little use today. It was bleeding edge then though, real magic stuff, and almost impossible to describe to outsiders. LOL
Instead of watching tv, bored people stuck at home could listen to the party line.

paulw
08-10-2014, 10:17 AM
This sort of stuff (https://www.youtube.com/watch?v=ZAJpionUxJ8) didn't seem so weird back in the day, but it was for the outside world, not NZ in the main.
Even if that old test gear was working perfectly now, it would be of amazingly little use today. It was bleeding edge then though, real magic stuff, and almost impossible to describe to outsiders. LOL
Instead of watching tv, bored people stuck at home could listen to the party line.:+1:

B.M.
08-10-2014, 11:20 AM
Boy, those links bring back memories. :)

I worked on the old Rotary, pre 2000, and 2000 switching in Hamilton before moving to Carrier & Toll, later to become known as Transmission.

Anyone got a photo of the old Wellesley Street battery room?

That was what real lead acid ďplanteĒ cells looked like. :D

pctek
08-10-2014, 01:25 PM
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 :)

OK, PM, he might know you.
He didn't work in the Waikato but did go there....

paulw
08-10-2014, 06:06 PM
Boy, those links bring back memories. :)

I worked on the old Rotary, pre 2000, and 2000 switching in Hamilton before moving to Carrier & Toll, later to become known as Transmission.

Anyone got a photo of the old Wellesley Street battery room?

That was what real lead acid “plante” cells looked like. :D

No, but I can remember it as if it was yesterday. Always had the endcell switched in.. Carrier and Toll. Now there's a name I haven't heard for a few years.. Been there done that. I remember being on power room duties and having to read both the 52 volt main batteries and the two 130 Volt carrier batteries and the two 24 Volt toll batteries...

Those weren't the years take it from me.. The only fun thing was cranking up the ac > dc motor generator set to keep the batteries going during the morning and afternoon rush hours and watching the girls go past..

B.M.
08-10-2014, 07:03 PM
No, but I can remember it as if it was yesterday. Always had the endcell switched in.. Carrier and Toll. Now there's a name I haven't heard for a few years.. Been there done that. I remember being on power room duties and having to read both the 52 volt main batteries and the two 130 Volt carrier batteries and the two 24 Volt toll batteries...

Those weren't the years take it from me.. The only fun thing was cranking up the ac > dc motor generator set to keep the batteries going during the morning and afternoon rush hours and watching the girls go past..

Yep, the end cell was called the 25th cell and was switched in if the voltage dropped to 48v.

And if you wanted a real wake-up call, get tied up between the ringing current busbar at 75v 16 2/3 hz ac, (sawtooth), and +130v plate voltage busbar for the carrier room. I kid you not, it got your attention when the ringing voltage went negative and there were amps in abundance. :D

And yes, diving down to the generator shed in the middle of the night under emergency lighting (read torch) to crank up a couple of massive caterpillar diesels where you had to start a petrol starter motor and then make sure the Caterpillars were decompressed before throwing the starter into gear and pulling down one compression lever at a time, so starting the Caterpillars one cylinder at a time. After that you had to synchronise the two units so they were in phase otherwise when you threw them onto load all hell would cut loose and there would be circuit breakers and fuses popped everywhere.

Yep, on your own in the middle of a filthy night in a shed on the banks of the Waikato River doing battle with the emergency power supply was exciting all right, well character building anyway. :D

But Iím buggered if I can recall any girls going by. :confused:

prefect
08-10-2014, 07:06 PM
I remember as a kid batteries in cupboard round red ones quite tall never seen any like it since. We were on party line even remember the number 604 Ngatimoti. When I lived in Havelock I recall phone number 1 Havelock which was the garage I think..

tweak'e
08-10-2014, 07:58 PM
when i was crawling under the house fixing the bathroom floor (before garage blew out) i found a couple of those big read top drycell? batteries still connected to a telephone cable. mind you i think its 10 pair? cable, no idea where it runs to.
i've come across those batteries quite a few times in older homes.

R2x1
08-10-2014, 08:32 PM
Those fat dry cells were good value, The zinc remaining in the case was handy for zinc plating, or making acid into killed spirits, the carbon center electrode had many uses, plus there were two Fahnstock clips on some, screw terminals on others.
The paste and bag was good for making chooks try to spit, they'd peck the bag, then dance about trying to get rid of it.

paulw
09-10-2014, 07:37 AM
Y

But I’m buggered if I can recall any girls going by. :confused:

Day time . Open the side door to the street to let the cool air in..

Roscoe
09-10-2014, 09:05 AM
But Iím buggered if I can recall any girls going by. :confused:

Auckland University is at the top of Wellesley St and we used to watch the sweet young things walk to and from Queen St and the university. It was a great distraction. Even the senior tech used to join us in this popular pastime. That was one of the perks of working in the Wellesley St Exchange.

prefect
09-10-2014, 04:57 PM
Auckland University is at the top of Wellesley St and we used to watch the sweet young things walk to and from Queen St and the university. It was a great distraction. Even the senior tech used to join us in this popular pastime. That was one of the perks of working in the Wellesley St Exchange.
Watching tarts walk by is an excellent pastime.