The Power Cord Dilemma.

[Hugo Holden]

One thing that really bothers me is when some piece of apparatus has a line power cord dangling out of it. Both my AIM-65 and my PET has this. The cord is always dangling down and trailing behind like the Tail on an Alien moving them around.

I much prefer standard IEC panel line power connectors. On many of my machines I have fitted these and eliminated the power cord. Then I just need a few IEC power cords.

I had been meaning to convert my AIM to 230v, it just requires changing the transformer's primary connections.

The power cord on the AIM is a thick ( 9mm diameter ) heavy duty affair that looks suited to running a concrete mixer.

So I looked at fitting an IEC Connector to the AIM-65:

It was complicated by the fact the original panel work, in the region where the power cord entered and original fuse holder was, is quite narrow on each side, only about 6.6mm. Photos attached.

The square hole there (where the fuse-holder was) is 16mm wide, and I did not want to widen it and possibly weaken the panel, which would have happened if I made the usual cut-out for the IEC connector which is about 20mm wide. It would have required 2mm cut of each side, thinning the the width to 4.6mm on each side. But there was another complication; if the connector was mounted there, on the front panel surface as usual, the upper flange of it would interfere with the case cover, and then I would have to cut some plastic out of the case. I decided therefore to go down the road of removing as little material as possible. And again if it was mounted on the front it could not easily be moved down, to avoid the case interference, because the pcb sits just under the rear of it too.

I noticed a couple of things though, one is the width of the internal socket was 16.1mm, and the panel hole already 16mm. So I figured I could mount the IEC Connector on the rear of the panel with some small rectangular washers which are about 1.2mm thick, this to allow for the flange on the front face of the IEC connector.

Also I measured the length of the IEC plug, they are a little different on different brands and some have a flange around the base and some don't. I found the depth of the IEC connector when mounted on the rear of the panel was 19mm from the panel exterior surface. The plugs ranged from 18mm to 20mm for the versions with flanges, so in the worse case there was only a 1mm loss of projection of the plug into the socket mounting it this way, but for most plugs without flanges no effect at all. So again, but for a different reason, I decided not to file away the aluminium to allow for flanged plugs.

Of course a different primary fuse had to be added, I placed it beside the power switch and its upper surface , the added insulators sit just a little lower than the top of that original switch. The surface is actually flush nearly with the lower surface of the pcb. I threaded a hole in the side wall using a Roll tap (these create incredibly strong threads by compressing the aluminium, rather than but cutting it away. (To do it on a thick panel like this, start with a cutting taper tap for a couple of turns then change to the Roll tap). The screw is a 4-40 UNC, 1/4 inch length with a lock washer too. It it important to put insulation around the fuse holder.

I also tied the line wiring down under the board to make it more tidy and so it wasn't rubbing on the lower pcb surface. In the orginal design, the wires were just loose, and touching the lower pcb surface in places. That could be awkward if the insulation failed on a sharp spike from a pcb component and injecting line voltages into the pcb ! The hookup wire I used is very good silicone rubber covered made by Permanoid in the UK (shame they stopped making it, it is a harsh environment wire), it has normal strands unlike the fine multi-stranded type and has thick insulation. It is great because it is not melted, even by high soldering iron temperatures. The original wire wasn't bad either it was small OD white Teflon coated, I kept a piece of it that connects from the fuse to the switch, because it already had a spade terminal fitted.

Now I think I might have a look at the PET.

 

[Hugo Holden]

So I did the same thing to my PET, but it was a lot easier. Though working with Steel is always just a little more difficult than Aluminium.

One important thing is, if you are cutting holes, that the surrounding surfaces should be masked. You don't want to scratch or mark them. I use blue painter's paper masking tape, often a few layers, it has a weak adhesive and doesn't pull off paint.

I found that the easiest thing to do was to make the rectangular hole conform to one edge of the existing hole where the cord clamp preciously entered. Then drill an array of 3mm holes to remove most of the material. I added some long 6-32 screws to help support the panel while drilling.

Once that most of the steel was removed, I filed out the hole to suit the snap in IEC connector which was 20 x 27 mm with a radius of close to 3mm in the corners. The panel is just over 1mm thick which was perfect for the snap in IEC connector I had on hand, rated for a 1mm panel. It snaps into place very well.

Once the hole was filed to the correct geometry, I smoothed it with a diamond file and then 600 and then 1000 grade paper and removed the burs from the hole edges with the diamond file. After that I painted the cut surfaces with black paint (I'm afraid if you leave bare steel it will rust).

Then I fitted the new connector and re-wired it. Originally there was a paucity of insulation on the switch & fuse contacts, so I added some heatshrink sleeve and some Scotch 27 Electrical fiberglass tape too (this is wonderful electrical tape, highly heat resistant with an amazingly good adhesive).

There was one of those ridiculous screw on connectors (the orange one) to join the Neutral wire to the transformer, but I got rid of that and joined the wires by twisting and soldering and added three layers of heatshrink sleeving. I always seem to be adding insulation to line wiring, but it is just me.

My pet did not have the diabolical line filter capacitors and I don't plan on adding them. In the case of an analog supply the inductance of the transformer does the RF filtering for you.

The wiring sequence is always: Line (phase) passes to the fuse first, then to the switch, and then to the transformer.

Now my PET is free from a power cord dangling out of it.

 

[daver2]

Hugo,

What I find over time (and this is with way more modern equipment also) is that the weak point with the permanently fixed cable solution is where it goes through the panel into the equipment itself - especially for equipment that is moved on a regular basis.

Hence the logic behind the Portable Appliance Testing (PAT) within the UK.

Dave

 

[Hugo Holden]

Hugo,

What I find over time (and this is with way more modern equipment also) is that the weak point with the permanently fixed cable solution is where it goes through the panel into the equipment itself - especially for equipment that is moved on a regular basis.

Hence the logic behind the Portable Appliance Testing (PAT) within the UK.

Dave

Yes, the plastic cable clamps crush the cord in the interests of it not being pulled out of the unit, but with some flexing at that point, the cables can fracture over time.

It happened to a slow cooker we had taken in and out of the pantry. It was bad news because this particular slow cooker, which just had a couple of temperature switches and no electronics at all , freakishly had a temperature cycle that was perfect for twice slow cooked Duck.

When the cord failed at the entry point, my wife threw it in the trash, and got a precision controlled temperature slow cooker.

But the new cooker was hopeless for the Duck. It was something about the temperature cycling of the thermostat control one that somehow was helpful cooking Duck. Luckily the rubbish collectors hadn't come yet, so I retrieved it from the bin and cut out the few inches of cable around the plastic cable clamp the cord fracture and repaired it. Now we are back to tender twice slow cooked Duck and of course my wife's patented Duck sauce (you might be in for a treat if you visit).

The PAT testers make me laugh though.

Some people came to work and started testing everything with them and slapping stickers on power cords. They tested a double insulated wall wart adapter that had no earth pin on it and certified it safe (Doh). They then went on to check the microwave oven in the Tea room for "radiation Leakage", and stuck a sticker on it. I tried to explain that with the microwave wavelength being what it is, the door would have to be open a centimeter or two, and by then the switch on the door would have deactivated it.

Then I suggested, that for their services to be of great safety value, Elves or wayward Garden Gnomes would have to be visiting in the middle of the night and re-wiring all the power cords and swapping the Phase for Earth, and that they would also have disabled the residual current devices on the breaker boxes. They were not amused especially when I suggested that if we spotted any frayed power cords we would discard them ourselves. Very few commercial/professional equipments now have fixed power cords, they are all IEC connectors.

 

[Chuck(G)]

If space is tight, you may want to consider using C5/C6 "mickey mouse" plugs and receptacles.
As far as making accurate holes in sheet metal, I employ a sheet-metal nibbler. You can also sometimes find Greenlee punches for sale, if there's room for one.

 

[Hugo Holden]

If space is tight, you may want to consider using C5/C6 "mickey mouse" plugs and receptacles.
As far as making accurate holes in sheet metal, I employ a sheet-metal nibbler. You can also sometimes find Greenlee punches for sale, if there's room for one.

Yes the punches are good, especially if new and sharp and lubricated.

I've never been that keen on nibblers because they distort the edges of the material and produce an irregular look, but if it filed afterwards as well its ok, so a nibbler is good for bulk material removal.

When the hole is filed out by hand (or cut with a router) the material is completely free from distortions at the edges of the hole because there is no bending of the material.

Punches create some distortions. It is like a cookie cutter, at the edge of the hole one face is left rounded the other a little sharp with an inward facing distortion at the hole perimeter. I have plenty of round punches for tube sockets etc, but no square ones so I usually do the square holes by hand. Of course these issues produced by punches get worse as the punch gets worn, especially if used on a lot of steel and not just aluminium.

However doing it by hand is time consuming and the surrounding surfaces must be protected with liberal amounts of tape.

The attached photo shows one panel I did by hand, the other was done by a rectangular punch in Japan. There were some visible distortions in the plate as a result of it being punched, the edges were pretty good, but there was a generalized small distortion of the panel away from the punched surface and it wouldn't perfectly sit on a flat surface that I had to fix, that you don't get with a file or machine routed out hole.

Also I finish the edges of holes with fine files and then 600 and 1000 paper. And in the case of steel, I always paint the cut edges.

 

[Chuck(G)]

A (manual) nibbler, followed by a light filing is good enough for my purposes. I'm mostly interested in getting something to work, not in fine cosmetics.
I remember in the bad old days, cutting holes for transformer mounts in steel chassis using a hammer and cold chisel against an anvil. Basically, the can-opener method. The alternative was drilling corner holes and working a fine-pitch keyhole saw between the holes. No saber saws then.
In 50 years, there will probably be a plasma cutter in every workshop...

 

[radventure]

I'll have to add this thread to my ever increasing list of "todo" bookmarks. Never been a fan of attached cables.

 

[1944GPW]

This is a great thread Hugo (perhaps it could go to the Tools forum?), I completely agree with the notion of changing out power cords for IEC320 sockets.
Here are some that I've done.
A laboratory Variac I picked up at a swap meet for $20 which had 2 input and 2 output thumb screw terminals on the phenolic front panel. One of them had the cap broken so it was not terribly safe. I removed them and put an IEC320 C13 on the front for output, put an IEC320 C14 on the back. The scrap of cut-out phenolic was drilled with a piece of sharpened brass tubing to make the circular plugs to fill the terminal post holes. I also added a on/off rocker switch. I have a collection of flyleads to australian, US, NEMA flat pin plugs for it.


My trusty paint sprayer had a fixed cord that had solidified and cracked from solvent vapor. There wasn't enough room in the back of the shell for a IEC320 C14 so I put a IEC320 C8 in.


A small isolation transformer that had a very ratty cord so fitted a C14 to lower back shell and blanked off the upper.


My octopus curve tracer in a electrical conduit box with switched C14:


I keep a good variety of IEC320 sockets switched and unswitched on hand as they are so good to use in equipment. For cutting the receptacle holes I use a Dremel clone with cutoff wheel and rotary cutting bits, nibbler, drilled line of holes, coping saw or hacksaw blade, chisels, scrapers, sanding blocks, files, X-acto #11 blade, and so on, really whatever seems to be suited best to the task at hand.