Author Topic: Desk test DC voltage box.  (Read 6164 times)

Offline Doc

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Desk test DC voltage box.
« on: January 23, 2014, 08:22:12 PM »
Here is my latest little project I did this afternoon. I had some old power supplies from some old computers that I salvaged. Took one and converted it to a nice little test box for my bench. I can get from 1 volt to almost 17 volts.
There is a 9 volt, 3volt, 6 volt, 12volt options it the high setting and more in the low setting. I need to make a map or label for the various voltages. I have a feeling this little box is going to come in handy.







George

Offline Doc

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Re: Desk test DC voltage box.
« Reply #1 on: January 25, 2014, 03:50:28 PM »
Put some finishing touches on test box.
I think this will be a nice addition to the work bench.

Labeled the posts.



Chart for the various voltages.



This was a pretty simple mod to preform on the power supply so don't throw those old computers out without salvaging those power supplies you may find a use for them.


George

Offline DavidA

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Re: Desk test DC voltage box.
« Reply #2 on: January 26, 2014, 02:53:12 PM »
Doc,

Great project.

Could I just add one note of caution to anyone else thinking of doing this.

These power supplies are NOT isolated from the mains in the same way as a normal linear PSU.

You can easily get in fatal contact with the supply voltage if you are not very careful.

That said,  have fun.

Dave. :zap:

Offline Doc

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Re: Desk test DC voltage box.
« Reply #3 on: January 26, 2014, 08:51:05 PM »
Always use caution when working with high voltages but this was a pretty straight forward rewire just make sure you check the out puts to the wires you use before you wire it up and you should be fine. Here is a video of my box in use testing a new tool grinder spindle I put together. I'm very happy with the little box's performance.

<a href="http://www.youtube.com/watch?v=qY_shjNIsUc" target="_blank">http://www.youtube.com/watch?v=qY_shjNIsUc</a>
George

Offline DavidA

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Re: Desk test DC voltage box.
« Reply #4 on: January 27, 2014, 11:12:43 AM »
Doc,

Thanks for the video.

I have,  at last count,  24 recovered PSUs. One that I know works,  the other 23 are to be the subject of much time wasting when things get quiet.
I should just strip them for bits,  and probably will ,  but the challenge is to get at least some of them working.

That was why I requested some advice a while back about 'scoping the mains.

Dave.

Offline Doc

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Re: Desk test DC voltage box.
« Reply #5 on: January 27, 2014, 12:07:53 PM »
  They will seem not to work when you plug then in you need to find the green wire and a black any of the black wires and connect them that will turn the power unit on. That would be in the high setting of the chart I made then for the low setting connect the green wire to an orange and it will be in lower voltage mode. So it it seems not to put out any thing when plugged in don't toss hook up the green wire then check again you maybe pleasentlysurprised.
George

Offline Baron

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Re: Desk test DC voltage box.
« Reply #6 on: January 27, 2014, 04:36:45 PM »
Doc,

Great project.

Could I just add one note of caution to anyone else thinking of doing this.

These power supplies are NOT isolated from the mains in the same way as a normal linear PSU.

You can easily get in fatal contact with the supply voltage if you are not very careful.

That said,  have fun.

Dave. :zap:

Actually they are isolated from a direct connection to the incoming mains !

However I would agree that caution be exercised when playing about inside whilst still plugged into the mains.  Also the main filter capacitors can hold enough charge to give someone a very nasty jolt should you happen to inadvertently touch a high voltage point.  In addition the case is grounded and this should be born in mind when using the PSU in conjunction with other equipment or circuitry that may not be isolated.

 

 
Best Regards:
                     Baron

Offline John Rudd

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Re: Desk test DC voltage box.
« Reply #7 on: January 27, 2014, 05:08:44 PM »
The majority of PC power supplies use  a Half  bridge configuration to generate the supplies on the secondary side ....
Most diagnosis (spelling?) can be carried out using a bench power supply and a scope to check the drive waveforms driving the switchers
eccentric millionaire financed by 'er indoors
Location:  near Hull

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Offline Baron

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Re: Desk test DC voltage box.
« Reply #8 on: January 28, 2014, 12:32:18 PM »
The majority of PC power supplies use  a Half  bridge configuration to generate the supplies on the secondary side ....
Most diagnosis (spelling?) can be carried out using a bench power supply and a scope to check the drive waveforms driving the switchers

Hi John,
It would be very dangerous to attempt to scope the mains input side of these or any other switch mode power supply utilising a direct mains connection.  Apart from risking ones safety, damage to an expensive scope could occur.

The only safe way to make these kinds of measurements is by using an isolation transformer between the mains and the device under test.  This type of transformer is specially constructed to ensure that no direct electrical connection can be made between input and output windings.

In any case keep one hand in your pocket !

Best Regards:
                     Baron

Offline John Rudd

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Re: Desk test DC voltage box.
« Reply #9 on: January 28, 2014, 01:51:14 PM »
Hi Baron,
I acknowledge your comments and that you have an understanding of the dangers.....but you're preaching to the converted....in my case....
I have a great fondness for electronics while I'm no expert, I enjoy it as a hobby now having served time as a tv engineer in a past career  :zap: ( along with many other jobs during my working career.....)
Now pursuing a career as a retired  ageing wannabe anything  :D
No intention to insult or bear malice towards anyone..... :coffee: Knowledge sharing is one of the greatest pleasures in life for me......I'm always prepared to listen, learn and share
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Offline DavidA

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Re: Desk test DC voltage box.
« Reply #10 on: January 28, 2014, 03:46:45 PM »
Thanks for the input on this subject.

I do intend to aquire an 1:1 220 Volt isolation transformer before I begin this investigation.

Funny,  the things we do to fill our golden years. :thumbup:

Dave

Offline Baron

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Re: Desk test DC voltage box.
« Reply #11 on: January 29, 2014, 09:43:05 AM »
Hi Baron,
I acknowledge your comments and that you have an understanding of the dangers.....but you're preaching to the converted....in my case....
I have a great fondness for electronics while I'm no expert, I enjoy it as a hobby now having served time as a tv engineer in a past career  :zap: ( along with many other jobs during my working career.....)
Now pursuing a career as a retired  ageing wannabe anything  :D
No intention to insult or bear malice towards anyone..... :coffee: Knowledge sharing is one of the greatest pleasures in life for me......I'm always prepared to listen, learn and share

Hi John,

My apologies !  No offence intended to anybody.  No offence taken either.

Its dangerous to make the assumption that everybody understands electricity.  Whilst I have no problems with re-purposing a computer PSU and think that this makes a useful addition to the bench,  there are those that will see this article and blindly grab an old PSU, and work on it without any thought to possible danger to themselves or others.

I am in full agreement with your last comment.  Its good to share.

Best Regards:
                     Baron

Offline RussellT

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Re: Desk test DC voltage box.
« Reply #12 on: February 03, 2014, 04:36:29 AM »
I have a similar box on the bench with a similar row of terminals.

Mine works just like it did in the computer and I am intrigued by

 
connect the green wire to an orange and it will be in lower voltage mode

I've not heard of that before.  How does that work then?

Russell

Offline awemawson

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Re: Desk test DC voltage box.
« Reply #13 on: February 03, 2014, 06:20:46 AM »
I can fully appreciate the utility of a box like this. I have a 'Weir Minireg' 0-30 volt 1 amp power supply that is pretty well always out. Gets used for testing bulbs, charging batteries, testing relay coils etc etc . . . It has not only the voltage adjuster, but also a variable current limit up to one amp which allows testing things gradually by turning it right down at first then cranking it up.

I bought it when I was an apprentice at Mullards in the late 1960's - it was surplus / retired then and I paid 1 for it. Since then I've acquired a couple more as they are so useful.
Andrew Mawson
East Sussex

Offline philf

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Re: Desk test DC voltage box.
« Reply #14 on: February 03, 2014, 07:47:16 AM »
I can fully appreciate the utility of a box like this. I have a 'Weir Minireg' 0-30 volt 1 amp power supply that is pretty well always out. Gets used for testing bulbs, charging batteries, testing relay coils etc etc . . . It has not only the voltage adjuster, but also a variable current limit up to one amp which allows testing things gradually by turning it right down at first then cranking it up.

I bought it when I was an apprentice at Mullards in the late 1960's - it was surplus / retired then and I paid 1 for it. Since then I've acquired a couple more as they are so useful.

Andrew.

I have several power supplies from 0-30v 1A up to a beastly (and dangerous) 0-70v 10A (or 0-35v 20A) and I binned an old Farnell 50V 1A only this weekend which didn't work properly and I couldn't be arsed trying to fix it.

I acquired all these surplus from work which by concidence was from Mullards (then Philips and latterly NXP). I did a student apprenticeship with Mullard at Hazel Grove (Stockport). I spent my first 7 months at Mullard Blackburn in the apprentice training school to get some workshop experience. They took apprentices from all the Northern Mullards as well as other engineering firms in the Blackburn area.

Which Mullard did you start at?

I visited Mitcham, Southampton, Blackburn, Simonstone and maybe some others in my time.

Cheers.

Phil.
Phil Fern
Location: Marple, Cheshire

Offline awemawson

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Re: Desk test DC voltage box.
« Reply #15 on: February 03, 2014, 08:44:36 AM »
Phil,

I was at Mullards in Southampton just by the Millbrook Roundabout a little before Philips got involved. I worked then as a TA (Technical Apprentice) in the EOD (Electron Optical) department. We were developing, making and testing multi-element infra red arrays used for satellite spying purposes so had armed guards on our 'bay' of the factory. Very interesting, I was able to get involved with the applications lab where I got a good electronics base. It was also my first introduction to computers. Apart from a programmable Hewlett Packard - (really a calculator) in the lab, we had an on line 110 baud Teletype link to the GEIS time-sharing bureaux, with which I was writing Fortran programs to calculate all the parameters of 1024 element arrays. These were amazing things cooled by liquid air which we produced in the lab using extreme pressure air from a diaphragm pump.

I remember Blackburn starting up, they were offering generous relocation packages, they were starting a new CRT line if I remember correctly.
Andrew Mawson
East Sussex

Offline philf

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Re: Desk test DC voltage box.
« Reply #16 on: February 03, 2014, 10:34:17 AM »
Hi Andrew,

I think that you would have to be at least a 100 to have worked for Mullard before Philips got involved as they bought the whole of the business from Captain Mullard in 1927!

Blackburn actually opened in the 1930s. When I was there (around 1970) they were still making valves by the million. The machinery to make them was amazing and nearly all designed and built in-house. They used to make gun parts for cathode ray tubes at Blackburn but the main manufacturing site for CRTs was at Simonstone near Burnley. The factory employed around 6,000 in 1970 and you had to make a very good mental note of where you parked your car in a morning because it could take an age to find it.

There's an interesting? video on valve making at Blackburn

<a href="http://www.youtube.com/watch?v=GDvF89Bh27Y" target="_blank">http://www.youtube.com/watch?v=GDvF89Bh27Y</a>

At our factory in Hazel Grove we made (still make!) power semiconductors but now the chips are shipped elsewhere for assembly.

I spent a few years working for our microwave section where they made parts ranging from traffic sensing modules for temporary traffic lights to guidance systems for missiles.

I used to play with a Hewlett Packard 9825 desktop calculator/computer.

The Southampton site was sold to a property developer in 2012.

Mullard/Philips were a good employer - I worked for them for 38+ years and now gratefully collect my pension from them.

Phil.
 
« Last Edit: February 03, 2014, 01:46:15 PM by philf »
Phil Fern
Location: Marple, Cheshire

Offline awemawson

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Re: Desk test DC voltage box.
« Reply #17 on: February 03, 2014, 11:54:40 AM »
No Phil Mullards at Southampton were owned by Philips but were largely left alone to their own devices until about 1970/71 when a change in Eindhoven management decreed closer control and things started to be more controlled :( Hence me saying 'got involved' !

I still have the only electric razor I've ever owned, a Philips Phillishave, bought at the staff shop, but having had a beard all these years it's hardly been used :)
Andrew Mawson
East Sussex

Offline John Swift

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Re: Desk test DC voltage box.
« Reply #18 on: February 03, 2014, 12:55:16 PM »
its a pity Blackburn didn't get the new version of the ECC81 into  production

new valves using the cathodes developed for cathode ray tubes !

http://rssconsultancy.co.uk/articleBMS.pdf

for those of a nervous disposition who don't want to open up a ATX psu

you could mount the sockets  or  terminal posts in a separate box
and either mount a chassis mounting plug or use a cable mounting plug as used on ATX extension cable

the  adaptor could also be used to test power supplies

    John


Offline chuckey

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Re: Desk test DC voltage box.
« Reply #19 on: October 16, 2014, 05:01:40 PM »
  Interesting tale about Mullards at Southampton:-  A friend of mine was  an apprenticed GLASS BLOWER, got at job at Southampton making very special  glass envelopes for valves. As this work closed down he transferred to semiconductors. Ended up designing analogue chips on a computer.  Long way from manipulating molten glass!!
      Frank

Offline John Swift

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Re: Desk test DC voltage box.
« Reply #20 on: October 16, 2014, 05:56:53 PM »
Hi Frank

welcome to mad modders

his glass working skills would have been used for mullards first transistors

the first Mullard transistors I have used was from the OC series germanium transistors 
the numbering being the same  used for Mullard  valves

 O indicated no heater !
 C indicated it is a triode device
 the numbers being the next available serial numbers

the OC transistors was in a glass encapsulation  that looked like a minature test tube !
{OC44 ,OC45 , OC71 and OC81 used in early transistor radios)

I think the nearest  NXP factory to me will be in Manchester
5 or 6 others in the northwest closed years ago

   John

Offline awemawson

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Re: Desk test DC voltage box.
« Reply #21 on: October 16, 2014, 05:58:51 PM »
I drove past a few months ago and was hard pressed to identify much !

I was in EOD (electro optical devices) but the OC71 line and the ORP12 lines were in the next bay outside the security barriers. An OCP71 was an OC71 without the paint used to exclude the light!
Andrew Mawson
East Sussex

Offline philf

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Re: Desk test DC voltage box.
« Reply #22 on: October 16, 2014, 11:05:32 PM »
I think the nearest  NXP factory to me will be in Manchester .

NXP Manchester is where I started and finished my working life. (It's actually in Hazel Grove about 10 miles from Manchester - they renamed it because Manchester is known throughout the world because of Man United. Not many outside the NW would know Hazel Grove.)

At the moment business is booming and previously abandoned parts of the factory are being filled with new equipment. One project they're involved with is the development of Gallium Nitride semiconductors as an alternative to silicon.

Oh how I wish I still had access to the rubbish skips which kept me busy most lunch times!

Phil
Phil Fern
Location: Marple, Cheshire

Offline Eugene

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Re: Desk test DC voltage box.
« Reply #23 on: October 17, 2014, 05:17:15 AM »
Andrew et al,

I never worked at Mullard Southampton, but I did make things for them.

They had a considerable requirement for photo etched / milled parts and I was the Tech Manager of their main sub contractor in Brum. One of the bigger efforts was a series of gold plated grids for X ray collimation in satellites, and there was other stuff which was security ticketed. I'd already signed "certain documents for certain organs of State" in my previous job so I was in the clear, but it was a limited number of people allowed access.

Back on topic, I used a computer supply to drive a foam cutter, and I have an outline plan for one to drive a DC motor based fine feed arrangement.

Eug

Offline Pete W.

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Re: Desk test DC voltage box.
« Reply #24 on: October 17, 2014, 05:48:44 AM »

SNIP

Oh how I wish I still had access to the rubbish skips which kept me busy most lunch times!

Phil

I'm with you there, Phil,

At my last job, the Chairman of the Model Engineering Section of the Company's Sports & Social Club was a fairly senior manager.  He was able to negotiate some fruitful skip-diving privileges for ME section members.  The company had three waste skips, one for copper & brass that was kept under lock & key, a second for aluminium alloy and a third for 'any old iron'.  The Company had to pay for that third skip to be emptied so the more stuff the ME section members took, the less it cost the Company!  All we had to do was get a note signed by an 'authorised person' to transfer legal title and act as a gate pass. 
The pickings were rich!   :thumbup:   :clap:   :thumbup:   :clap: 

I'm not sure whether it was when the Quality Department up-graded to granite surface plates or when the Company decided to out-source the machine shop but one lunchtime a 24" x 18" cast iron surface plate appeared at the skip.  It wasn't actually IN the skip because the labourers couldn't be bothered to lift it that high!  So they just leant it against the skip.  The 'authorised person' actually helped me lift it into my car - wow, did the suspension go down under the weight!!!  It now graces the bench beside my lathe.

The Company 'upgraded' secretarial chairs from four-arm base types to five-arm base types, they were supposed to be safer!  The four prong ones were made by Tan-Sad, a respected maker.  I was a member of the local Amateur Radio Club at that time and, before long, I and many of my fellow members were on the air seated on one of those chairs.  I never heard of any of them falling over!!   :lol:   :lol:   :lol: 

We could also pick from the aluminium skip but we had to get a price agreed & paid, the receipt for the payment then acted as the gate pass.  There was also a procedure for buying stuff that was a standard stores item in the Company stores and the Purchasing Department would place orders for non-stock materials and/or components including getting the sort of price discounts the Company would have enjoyed if the items had been for them.  The only limitation on that was that the employee would have to do the delivery progress chasing. 

Mind you, some employees did misuse the old iron skip - I saw an old lawn mower in there one lunchtime and it was too small for the gardening contractors! 
Best regards,

Pete W.

If you can keep your head when all about you are losing theirs, you haven't seen the latest change-note!