Monday, May 27, 2013

Making an extension lead, (plug end)

I made a post last week about adding an extension lead socket to a length of wire.

Now I'm going to detail the plug end.

So start by looking at the pins, here you'll find two screw holes that secure the male plug pin part to the back cover that you hold whilst plugging or unplugging.

undo these screws and remove the back cover, then put the back cover onto the wire that you're using to make the extension lead, (or the flex for the equipment that you're attaching the plug to) so that you;ll be able to close the plug later once the wires are connectted.

Again, start by stripping your wire.
then cutting the phase wires slightly shorter than your earth wire, (so that if the cable is strained, your equipment would go dead before it became unearthed)

Now loosen the cable clamp and attach the wires to the plug terminals.

Finally clamp the cable in the cable clamp, push the back cover on, and screw it back into place with the screws that are next to the plugs inside the plug shroud.

Your extension lead is now complete.

Monday, May 20, 2013

Making an extension lead, (socket end)

So I dealt with mains electricity a couple of weeks ago.

Now this is a quick post on how to put together an extension lead.

At the end of the post on mains power I was pretty keen to stress that there were colour codes associated with mains power, well, as it happens the cable that I was able to buy for my 3phase extension lead does not conform to that colour scheme.

The cable has conductors that are Brown Blue and black with a green and yellow earth conductor.

So to start,
The cable I'm making will be a 16amp three phase 240 Volt cable.

 That means a 4 pin blue "commando" socket is needed. There are fairly uncommon in the UK (as our 3phase tends to have 415 volts. quite uncommon in the US (where the three phases are 120volts) but apparently is quite common in Sweeden. so you can get the plugs you want.

I found these plugs (and sockets) by searching Ebay for IP44, and IEC 60309.

You can find these at screw fix, (where they are £11 for each plug -I paid £1 each for five on eBay) sockets are also available at screw fix, but again I found them cheaper on line.
(screw fix is a nationwide UK distributor of all sorts of trade type building materials, it's open to the public, so if you can't wait for an item to ship they may be the best bet!

So I'm going to start with he socket end.

Take the socket apart such that the back cover is away from the connectors,slide the back cover over the wire (with the open side facing the bare end) so that you'll be ready to seal up your connector later!
To remove the back of the socket use the two cross head screws that are located inside the grip portions.

Now take your 4 core wire and removing some of the outer insulation.
Then cut the phase leads to be shorter than the earth lead -the reason for doing this is that if the cable were ever put under strain and connections were to come out of the plug then the equipment you;re using would stay earthed, the worst scenario for electricity would be using a piece of equipment that was unearthed, that malfunctioned and became live, then you're the path to earth! By leaving the earth lead with some slack in to you're able to know that safety can be maintained, even if the cable has been put under such strain that conductors have started being pulled from connecting plug pins!
Now open up the cable clamp on the blue half of the connector and attach the wires into the holes indicated, with the brown black and blue wires being the phase wires and the green and yellow being the earth wires.
Then close up the cable clamp.

Now slide the back of the lead into place.
you can see a large black rubber washer, (it's about a half inch thick).

This is what seals the unit from weather (that and the little black o-ring on the other end)

Once you've gotten the back in place and screwed down, slide the final part of the back into place.
 this screws down squashing the rubber washer forcing it to grip the cable and provide a waterproof seal.

Finally, you have a lead with a socket on the end.

Monday, May 13, 2013

Mass production, tooling, strategies and budgeting.

This blog could be titled, How to get it wrong.

I'll start with the story, then I'll point out the failings.

A few weeks ago I made a new heater for my solidoodle 3d printer, I was quite happy with the results, despite having broken a drill bit in my heater block, I got around that, and I decided that was my fault, I clearly wasn't drilling the hole straight, it was a small drill bit, and they often break anyway...

When I bought the aluminium bar to make the hot end I had decided that I would probably want to make something else anyway, so I got a 2 meter length.

After making that first hot end I decided that I was going to make and sell a whole load.
I had enough aluminium bar, I had bought a hundred heaters at the start of the project, (knowing that I could sell the heater elements on their own!)

So I started cutting up that long bar of aluminium into 100 small pieces.
by about the 3rd piece I gave up and went to ebay and bought a small hobby band saw. -this worked great for cutting the aluminium, right up until the blade broke -though this had come with the saw, (which only cost £30), and had made 99 cuts, -failing on the last)

After this I got my set square and scribe and marked out where I needed to drill holes on all 100 blocks that I had cut. then I centre punched them. -this is time consuming, that was 600 holes that I marked!

After this was done I decided that I'd start drilling, rather than drilling by hand I decided that I'd use my fathers pillar drill, a Draper tool, I dutifully loaded the drill bit into the chuck, and set about drilling holes, I started by drilling 2.5mm hole through all of the holes I'd marked, a lot of the holes needed to be 2.5mm, others would benefit from a pilot hole being drilled anyway.

However I found that on the point where the hole for holing the thermistor met the hole for the screw securing the thermistor, the drill bit would catch and break. this was the same problem I'd had with the hand drill, but now I was getting this with a machine drill, one that was square, level and had no lateral forces, clearly there was a problem with the way that the cut was being made, swarf from the hole was catching and causing the bits to break at an alarming rate.

Eventually I managed to get a few holes drilled carefully that did meet, (afterwards I bought some 2.5mm end mills that I would use in the drill to make these holes meet more successfully!

At the end of the time I had set aside that day I had 11 pieces half made, I had the holes for the thermistor set-up drilled successfully, and the long hole through the block pilot drilled. at this point I'd been at it around two hours, and decided that was enough... -and besides the drill had gotten quite warm and I thought it could use a rest!

One morning the following week I decided that I'd continue my project. however within ten minutes of starting the drill the motor had caught fire.

In the end I took the pieces home and finished the first batch with a hand drill.

I tapped them and installed the heater elements.

As it's a new month I've been paid and gotten some more money to spend on this project I've now ordered the thermistors, wire and heat shrink to finish these heaters up.

So... let's look at where I went wrong.
First, I'm hoping to sell these for around £12 - £14, this is in line with what others have sold for on Ebay.

the heaters were £130 + £15 import VAT for 100
Aluminium bar was £10
Thermistors are£70 for 100
heat shrink is £5 for the 6m of 1mm heat shrink I need
and £3 for the 5m of 3mm heat shrink I need.
wire is around £2 for 10 meters, (and I need 200meters) so £40
the grub screws cost around £15

So a quick sum up looks like I'm nearly £250 in the hole with materials.

Postage on each item is expected to be around £1. (so that's another £100)
Ebay will take ~£2 per item, (£200)
and pay pal will also want their 10% (£1.40 per item, times 100 = £140)

so that'll be around £700 of costs.
I'm hoping to sell these for a total of £1400

but here's where the problem starts....

now take roughly 25% of that away in taxation and national insurance that I'll need to declare. that's £175, leaving £525

Trying to do this cheaply has meant that I broke around £5 of drill bits whilst trying to make the blocks, and that £10 saw blade for the band saw.
(leaving £510)
I'd busted my dads pillar drill, because it's a hobby tool, not an industrial tool, it's meant to spend about 30 seconds being on, then have ten minutes to cool down, now spend nearly three hours in constant use, so that it over heats, and breaks down the insulation, (and then catches fire)
a complete replacement is around £300, second hand maybe £150, or a new motor will be around £100
My "profit" is now a pretty shabby £400...
then I spend a couple of hours cutting up the aluminium bar, a few more hours in front of the drill, a couple of hours sourcing materials, I'll conservatively spend probably 15 minutes per item with listing on ebay, talking to buyers, packaging and going to the post office to actually post the things.
(that's 1500 minutes, or about 30 more hours). I spend around an hour designing the thing in the first place.

Based on the initial ten I have that's 6 hours of machining and making,
So that 100 will be about 60 hours of machining, plus 30 hours of listing and posting.

So that £400 I've got remaining will need to pay for about 100 hours work. about 2/3rds minimum wage.

in other words.
I started out thinking, cool, the parts for this will make me loads of money, I'll spend about £2.50 on an item that I can sell for £14.

using hobby tools has increased costs due to breakages.
Using hobby tools has meant that I can't work for more than an hour at a time without significant machine downtime to cool off, increasing the amount of time take to produce parts.
Funding this venture myself has meant that I've had to wait until pay day to get more funding. - I could have taken this to a kikstart project, but them I'd have 100 angry customers breathing down my neck saying that my lack of planning or prep wasn't their fault, and where is their money etc.

The long and the short of it is:
before you decide that you want to give up your day job and live the dream of running a tech startup. do your sums first. be realistic.
I was wishfully thinking that I might get around £700 for what would be an easy day stood at a band saw and a drill. -actually I was thinking I could use an ordinary hack saw to do this work!

What I though would be around £100 per hour I'll retired a millionaire next week, has actually resulted in being a drain on time and resources. Maybe with a few thousand pounds of investment for industrial tooling I'd do better -but I doubt that also!

Monday, May 06, 2013

Electronics lessons: Mains Power -single phase and three phase

Whilst writing this blog I've stayed away from things that I would consider dangerous.

That is to say I've completed some projects that I've felt were either too big to document, (like when I put up my new storage shed in the garden and put electrics and lights etc in.) -at the time my thoughts were like this. it's OK to tell someone to stick bits of wood together to make a speaker, it's OK to say to people use this step down transformer and deal with the safe voltage that comes out the other side. I even thought it fine to tell people to stick electrodes into water to generate hydrogen/oxygen gases!

But big scary voltages have been something that I've stayed away from, the thing about mains utilities is that, you can smell gas, and know to shut off the supply and get out. you can see water and hopefully have the intelligence to get out before drowning. Electricity is completely invisible, it's not a substance, it's a force.

Anyway, that might give you an insight as to how I feel about mains electricity. it's dangerous to the point of deadly, and too much confidence can lead to mistakes that ultimately can kill you.

As a point of reference I live in the UK, this means that for me, voltages come in 120v for site tools, (where the 120v is considered safer due to lower voltages) this voltage is obtained by using those little yellow transformer boxes.

240v comes into every homes, (at least every connected home, I suppose off grid homes might make their own standards).

440V is considered industrial and is what most three phase power outlets are going to be using.

Voltages are measures with respect to neutral, live - neutral.

Single phase

Single phase power is an alternating waveform going from the positive extreme of the voltage swing to the negative extreme of the voltage swing in one wave form.

Single phase is what I've mostly dealt with, it's easy to visualise, easy to look at and easy to understand. remember that the positive is measured with respect to neutral, not with respect to ground.

Sometimes a single phase supply is actually a 2 phase supply, where instead of a virtual earth, or earthed neutral, there are two hot phases where the phases are 180 degrees apart.
the sum of the phases is zero, (e.g at 0 degrees phase 1 is 0v, phase two is at 180 degrees and is also 0v, at 90degrees, phase 1 is +120v and phase two is 270 degrees and -120, (+120 + -120 = 0v), the total potential difference between the two phases is 240 volts, (120 - -120 = 240)

Three phase

Here's where it starts to get a little more complicated.
Now there are three phases, each phase is 120 degrees behind the next, they are still sine waves, and they are still measured with respect to neutral, but there is no neutral in the transmission line, -when power enters your premises in a single phase set-up there is a live and neutral line. when you get three phase there is only 3 live wires, no neutral. (you can make a neutral by connecting all the phases together, because the sum of the phases is zero) -but I'll cover that in a later lesson.

You can see at 90 degrees now phase 1 (blue) is at at the top of it's rising cycle 240v, and phase 2 (green) is just coming up from the bottom (so during it's rising cycle) and is -120v, whilst phase 3 (red) is getting towards the bottom of it's falling part of the cycle, and is -120V
240 + -120 + -120 = 0

Colour Codes

Colour codes for wires are important, in that they will let you know what wire does what. everyone knows that green/yellow stripe is earth, and it's safe to touch. but what if I wired a plug so that the earth wire was used as a live conductor.
it's just a bit of copper, fundamentally there is nothing to stop me from doing that, provided I wire the other end the same way, where's the problem?

The problem is what happens when I'm out, and whatever appliance I've wired badly breaks, what if my wife/girlfriend/boyfriend/husband/friend/son/daughter/mother/father/grandparent etc decides that they just want to check the fuse on the plug, then they see the wires connected wrongly, so think that might be the problem. or something see's an earth wire, and decides that they can splice that wire to earth something else, -except it's not earth, it's live, and they are probably now dead.

Colour codes are set by the IEE.

for single phase systems.
Brown = Live, (the old colour was red)
Blue = Neutral, (the old colour was black)
Green and yellow stripe = Earth, (the old colour might be plain green)

for three phase systems,
Brown = Phase 1 (old colour was red)
Black = Phase 2 (old colour was yellow)
Grey = Phase 3 (old colour was Blue)
Blue = Neutral (old colour was black)

This means that if you are adding new wiring to an old system, don't just connect the new blue wire (N) to the old blue wire (P3), or the new black wire, (P2) to the old black wire (N)

you may also find three phase systems where the conductor colours are Brown, brown brown for P1, P2 and P3, with a blue for earth.

Earth (as always) is green yellow stripe.

earth may also be the bare wire in fixed installations, (where solid core wire is used rather than stranded wire).