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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment.

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Old 11th Jul 2020, 8:15 pm   #1
govjohn
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Default Plessey power supply PS112

HI This might not be in the right section but it has got a NATO part no. I'm Hoping that the collective knowledge of the forum might be able to help with some information on my latest toy. This is a very heavy power supply 22.5Kg/49.6lbs made by Plessey for the Military. As can be seen from the Photo's it doesn't give many clues on the front about its capabilities. The door just covers the mains voltage adjustment switches. The toggle switch is a momentary action centre biased type. In use it switches on if its held up but the O/P doesn't latch on and it switches off when the switch is released. When on it gives 30V no load, 25V with a 5Ω load, & 27.5V with a 10Ω load. As the mains transformer secondary is 37 0 37V 15A Something is obviously wrong. Does anybody recognise this unit or know where I can get any information on it?
It does not appear to have been modified apart from the removal of the O/P socket, and the replacement of the diode and capacitor at the rear seems to have been competently carried out. so I'm at a bit of a loss, short of reverse engineering it and dredging up long forgotten collage lessons on saturable reactors. Help.
John.
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Old 11th Jul 2020, 8:58 pm   #2
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Default Re: Plessey power supply

A bit of internet searching found: -


http://www.vmarsmanuals.co.uk/newsle...cles/ps112.pdf

https://www.blunham.com/Radar/Signal...sseyPTR175.pdf

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Old 11th Jul 2020, 9:12 pm   #3
John KC0G
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Default Re: Plessey power supply

http://www.vmarsmanuals.co.uk/newsle...cles/ps112.pdf
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Old 11th Jul 2020, 11:23 pm   #4
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Default Re: Plessey power supply

Once again the forum has come up trumps! The breadth of information available from members of the forum is astonishing. Thank you.
John.
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Old 12th Jul 2020, 11:41 am   #5
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Default Re: Plessey power supply

Hi John,
You don't say what you intend to power with the Plessey PSU, but, just in case, the offload voltage can be very high - >30v - and there is often a substantial spike in the output voltage - >40v - when you switch off the unit. The regulation of the output is not effective at loads less than 4A (from memory - its in the handbook) One way to avoid problems is to permanently wire a suitable resistor across the output so that the unit is always delivering 4A or more.
These units were designed to run dynamotors - specifically ARC52 and PTR175 - so will deliver large starting currents but with less than close regulation of the output voltage as a dynamotor is pretty insensitive to input voltage variation.
Good Luck
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Old 12th Jul 2020, 3:58 pm   #6
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Default Re: Plessey power supply

Hi Peter, thanks for your reply. You mention the Handbook is there any way I can get a copy of this especially the circuit diagram? The problem I have is the O/P is permanently stuck at 30 V supplying 5A with no adjustment possible. Looking closely at the wiring I'm not shure that someone hasn't been playing so I would like to check the wiring against the circuit. Can you help please?
John.
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Old 13th Jul 2020, 2:05 pm   #7
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Default Re: Plessey power supply

Hi John,
Somewhat to my surprise I cannot find a cct. diagram for the PS112 on my system - I was sure I had one.
If you can give me a couple of days i will continue to look on some other systems I use. I have a PS112 myself and was sure I had got the details for it as I like to acquire the documentation for stuff I use whenever possible.
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Old 13th Jul 2020, 8:01 pm   #8
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Default Re: Plessey power supply

Thanks for looking Peter, like you I like to have info on all the equipment I use. I hope you are successful. Regards.
John.
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Old 13th Jul 2020, 11:01 pm   #9
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Default Re: Plessey power supply

For anyone doing a bit of research around this sort of regulator, have a look for 'Magnetic amplifiers' and the black, variable, inductor is a 'transductor'.

In a transductor, an inductor has a core which makes it a large value inductor for the frequency and current involved. Part of the core has a DC field applied across it, transverse to the main field my another loop of core with its own winding (the control winding) This DC field is revved up enough to start saturating the bit of core material common to both loops of the core. This reduces the effectiveness of the core loop for the main winding and its inductance drops.

In this sort of power supply, this will drop the impedance in series with the main supply, allowing more current.

Some of these saturable reactor (=Transductor) systems had a high frequency ferrite core for the main path inductor, with an iron cored low frequency core (and control winding) used to saturate the ferrite.

Normally the control winding has many turns of fine wire to increase the effective current 'gain' but this high L means it is slow. So you have a gain/speed tradeoff.

The art in designing the cores is to ensure orthogonality of the two fields in the common bit of core. Otherwise the power field can induce huge voltages in the control winding.

Interesting technology. Not completely dead. Mag amp regulators can be found regulating lower priority outputs on some multi-output switch-mode power supplies to give individual regulation.

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Old 14th Jul 2020, 9:48 am   #10
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Default Re: Plessey power supply

John / Peter,

I have info in the PS112 here, so if you need a copy just let me know.

Cheers,

Martin
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Old 14th Jul 2020, 12:46 pm   #11
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Default Re: Plessey power supply

Hi All,
Found the circuit for PS112 - attached to the end of the ARC52/PTR175 documentation.
Copy attached.
Martin - thanks for the offer of help.
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Old 16th Jul 2020, 12:03 pm   #12
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Default Re: Plessey power supply PS112

I would like to thank everyone who has responded to my request for help with information on the PSU including Sparky 67 for additional info. With the aid of this I have got it working as intended . So thank you and goodby untill the next time.
John.
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