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DEC-20 Day!

m_thompson

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In honor of DEC-20 day I just booted TOPS-10 7.03 on the RICM's DECSYSTEM 2020 #4224. The system was originally installed at the University of Massachusetts, Dartmouth (formerly Southeastern Massachusetts University). It currently has a RP06 disk modified to run on 2-phase 110/220VAC power, an RM03, and two TU45 tape drives.
http://www.ricomputermuseum.org/Home/equipment/dec-pdp-10-decsystem-2020-4224
DEC-20-2017.jpg
 

acollins22

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Leicester, UK
Excellent :)

The first machine I used on my Computer Studies course in 1980 was a system 20 over a dial up line and an acoustic coupler.

Everyone knows the PDP-8 and PDP-11 but the System 20 is a bit forgotten. Great to see one still running.


Cheers

Andy.
 

bqt

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Just booted the DECSYSTEM-2020 on DEC-20-20. I booted TOPS-10, but should have swapped the disk pack and booted TOPS-20.

Very appropriate. Too bad MRC aren't with us anymore. He always liked to remind people of Dec-20.

Happy Dec-20 everyone.
 

daver2

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Yep, we have 3 phases - others have two phases at 180 degrees apart. So you can simply add the two AC voltages together.

Assuming 110 Volts single phase will give 220 Volts when operated across two phases.

A 2 phase USA piece of equipment should, therefore, work on a single phase UK supply...

Dave
 

m_thompson

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Two phase ?

The processor, and tape drives are plugged into single-phase 30A 115VAC outlets. They can be reconfigured to run from 220VAC.

The RP06 disk drive says that it is 20A 220VAC three-phase. It isn't. The 115VAC fans are wired in series across the two lines to get 220VAC. The spindle and blower motors and electronics are 220VAC. You can daisy-chain three RP06 drives from a single power cable and they rotate the phases from drive to drive to balance the load. There is a plug on the input wiring box that can be changed to configure the drive for three-phase delta, or three-phase wye. I modified the plug to configure the drive for two-phase input, and wired the outlet to match. It works just fine on two-phase 220VAC power.
 

Gary C

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The processor, and tape drives are plugged into single-phase 30A 115VAC outlets. They can be reconfigured to run from 220VAC.

The RP06 disk drive says that it is 20A 220VAC three-phase. It isn't. The 115VAC fans are wired in series across the two lines to get 220VAC. The spindle and blower motors and electronics are 220VAC. You can daisy-chain three RP06 drives from a single power cable and they rotate the phases from drive to drive to balance the load. There is a plug on the input wiring box that can be changed to configure the drive for three-phase delta, or three-phase wye. I modified the plug to configure the drive for two-phase input, and wired the outlet to match. It works just fine on two-phase 220VAC power.

Ah, I see.

Two phase is a big no no at work because it can make our induction motors run backwards so it sounded odd.

Never seen or used any two phase equipment in near 40 years in the power industry :)

We tend to use 415V three phase (415 between phases) and develop 240V single phase to neutral.

But I bet there is some UK thing out there I have missed :)
 

bqt

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The processor, and tape drives are plugged into single-phase 30A 115VAC outlets. They can be reconfigured to run from 220VAC.

The RP06 disk drive says that it is 20A 220VAC three-phase. It isn't. The 115VAC fans are wired in series across the two lines to get 220VAC. The spindle and blower motors and electronics are 220VAC. You can daisy-chain three RP06 drives from a single power cable and they rotate the phases from drive to drive to balance the load. There is a plug on the input wiring box that can be changed to configure the drive for three-phase delta, or three-phase wye. I modified the plug to configure the drive for two-phase input, and wired the outlet to match. It works just fine on two-phase 220VAC power.

Very few things DEC did ever truly required 3 phase. It was mostly load balancing and getting lots of power out without going to silly large fuses...

Trying to recall, I know the VAX-86x0 really requires 3 phase, as it has 3phase motors for the fans (I know of someone who wired one up backwards and overheated the thing - fans running in reverse). Trying to remember if the RP07 might actually have needed it as well, but am unsure...
Otherwise I can't think of anything. I wouldn't be surprised if the VAX-9000 series would want it, though.
But there is certainly a lot of equipment I've never played with, so maybe some other do require it as well. I've worked on DEC-2060s, and I can't remember seeing anything in there that actually needed 3phase, but that thing wanted power. :)
 

m_thompson

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Two phase is a big no no at work because it can make our induction motors run backwards so it sounded odd.

In the US 2-phase is normal for a house, and 3-phase is almost impossible to get in a house. The 2-phase is two 120V 60 Hz lines and a neutral. The two lines are 180 degrees out of phase so line-to-line is 240V.

In a business you will sometimes see an electrician wire just two phases of a 120Y208 3-phase circuit to a 2-phase 240V receptacle, so you get 208V.
 

m_thompson

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Trying to remember if the RP07 might actually have needed it as well, but am unsure...

The RP07 manual says that it can run on 208/220/240 3-phase delta or 380/400 3-phase wye, 50 or 60 Hz. It needs 7A to operate and 40A to spin up. I couldn't find schematics, so I don't know if it really uses 3-phase.

I've worked on DEC-2060s, and I can't remember seeing anything in there that actually needed 3phase, but that thing wanted power. :)

Most of the KL10s had three low efficiency 1-phase switchers connected to each of the 3 phases and needs about 21.6kW power for just the CPU box. I think that the core memory was about 2kW for 256k words, plus 2kW for each RP06.
 

Gary C

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Just been reading up on the US systems and glad its much simpler in the UK, I suppose it was an advantage of a national, government owned monopoly that produced a symmetrical nationwide system :)
 

m_thompson

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I suppose it was an advantage of a national, government owned monopoly that produced a symmetrical nationwide system :)

It started here with both DC and AC distribution systems. AC eventually won because transformers would allow for transmitting the power for long distances at high voltages. Even for AC systems there were lots of different voltages and phasing. There are still small pockets of unusual voltages used with old equipment. Until recently one of our local power companies supplied 400VDC for elevators near a power plant.

At least we don't have Japan's problem with both 50 and 60 Hz in use.
 

Gary C

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At least we don't have Japan's problem with both 50 and 60 Hz in use.

Could see that would be a big problem if something big enough was closed between them.

About 4 years ago, I synchronised one of our generators to the grid, but because of a fault with the sync indicator, I closed the main breaker about 12° late, the operator in the turbine hall said everything 'moved' in a sort of subsonic 'boom'

3 years later, we opened up the turbine for its routine maintenance and found damage to the main bearing between the generator and the turbine where the shaft had hit the bearing shell at about 200° from TDC. Fortunately, all the vibrations were fine (actually slightly better as I recall) and the coupling between the generator and turbine shaft (transmitting about 2 million Nm) had slipped slightly.

Ooops :)
 

Terry Kennedy

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Trying to recall, I know the VAX-86x0 really requires 3 phase, as it has 3phase motors for the fans (I know of someone who wired one up backwards and overheated the thing - fans running in reverse).
I'd be surprised, because I had 3 8650s at one time and did the breaker panels / input power for them. I don't recall any warning in the site prep or installation guides about ensuring correct phasing. Plus, there is an airflow sensor that trips the entire system offline if there is insufficient airflow. Simply trying to slide the reusable filter out of an 86x0 will trip the airflow sensor. Trivia - the 86x0 doesn't need that ridiculously expensive Russel Stoll 60A watertight connector. I ran our first one happily on am adapter cable I made to power it fom the L21-30R receptacle we used for the 785 it replaced.

Trying to remember if the RP07 might actually have needed it as well, but am unsure...
It did, although thankfully it had a "phase error" indicator and wouldn't start the spindle unless all 3 phases were present in the correct sequence.
 

Terry Kennedy

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In the US 2-phase is normal for a house, and 3-phase is almost impossible to get in a house. The 2-phase is two 120V 60 Hz lines and a neutral. The two lines are 180 degrees out of phase so line-to-line is 240V.
Not necessarily. All the houses on my block are powered from a dedicated transformer vault and all are on the same 2 legs of 3-phase power. The poles have the old "racks" where 3 individual wires ran (3 phases plus neutral) but the wires are all cut and modern braided 3-conductor distribution cable installed. But even after they replaced the transformers, they are still giving us 2 legs of 3-phase.

This is common enough that things like room air conditioners, electric water heaters and so forth are either configurable for 208/240 or are de-rated when running on 208.

In a business you will sometimes see an electrician wire just two phases of a 120Y208 3-phase circuit to a 2-phase 240V receptacle, so you get 208V.
Unless the business is big enough that it maintains its own transformer farm, you're always going to get that. Aside from autotransformers or MG sets, there is no way to get large amounts of 240V when the building service is 208 Wye.
 

Terry Kennedy

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It started here with both DC and AC distribution systems. AC eventually won because transformers would allow for transmitting the power for long distances at high voltages. Even for AC systems there were lots of different voltages and phasing. There are still small pockets of unusual voltages used with old equipment. Until recently one of our local power companies supplied 400VDC for elevators near a power plant.
NYC's (and nearby) subway systems and some other consumers run on 600 to 750VDC. Until not that many years ago, parts of the older (IRT) subway system signals ran on 25Hz AC. This is because electric railways were prevalent enough early on that there was a huge "installed base" problem which prevented conversion from DC to AC. In fact, the only system I know of that converted from DC to AC was the Newark City Subway, when they wholesale replaced their PCCs with LRVs.

This is an area I'm painfully familiar with. A transit museum I work with has its office and traction power from one electric utility (converted to DC from 3-phase 4160VAC with a rectifier set, although the old MG is still there and presumably operable). The tracks end there, but extend 1.5 miles in the opposite direction, in an area where all of the power comes from a different electric utility. So we have 600VDC overhead wire with return through the track on the ground. Some new buildings were put up down the line in that second utility's service area and electric service was ordered. HUGE amounts of paranoia and paperwork all around. The electric utility wanted to run their 5KV power conduits at least 12 feet below the tracks. Unfortunately, that puts them below sea level. They wanted disconnects on both sides of the tracks. The planning department demanded disconnects near the building on both the input (utility) side of the transformer and the output side of the transformer, both before and after the metering toroids.
 
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