Wiring quality
 

This thread is intended to discus the points that determine the "quality" of a control box....

To kick off, the following pics show a poor quality of connection:
The copper shouldn't be exposed outside the terminal by that much. A slip of a measuring probe could cause a short.

Good terminal blocks have deep separators:

Here is another terminal block that has good separation between the wires:

But the Gecko terminals are a bit too shallow and close for 80V 7Amp applications and I feel that the terminals shown below are needed:

These terminals are crimped with the following tool:

If you touch the exposed heads of the lock down screws on the terminal block, you also cause a short.

Steve, have you noticed the big bare leads on the other side of that terminal block? They are the legs of the G202's internal capacitor.

The exposed copper I showed above is not serious, but it can get worse. For us guys with poor eye-sight, we can't easily tell when one copper strand has not entered the terminal properly and is threatening to visit its neighbour.

Some guys would "tin" the strands together with solder, but that practice is frowned upon by others. The crimped lugs are just so darned easy, but they take up space.

Here are some more arguments for the crimped end terminations. At first glance, the wire on the left is fine, but on closer inspection it has a stray. When it is removed, it looks like a birdnest:




A basic problem is that the strands of the wire are too fine - this happens when very flexible wires are used in panels


Another problem is that the stripping process easily cuts some copper away:




When a wire is removed from a terminal, it should look as on the left. The right side version is messy and dangerous because the little broken strands fall into other circuits and cause shorts:



Broken strands after tightening is often caused by the type of terminal where the rotating screw rubs directly on the strands. Use better terminals of the "cage-clamp" type.

Twisting wires together before clamping in a terminal can work, but it mostly gets messy:




The insulated crimp lugs solve a lot of these issues:




A basic rule is that a maximum of 2 wires may be fitted to a terminal. And most times a pair of wires will only be properly clamped if:
- they are twisted together first, or
- they are exactly the same size and lie side by side.

The crimped pins in the last pic show that the pins are the same size even though the wires are completely different sizes. (The colour on the crimped pins give the wire size only).

Good wired joints can be disconnected and re-connected a good number of times without degrading the connection. An inspector will tug quite hard on a couple of joints and he will undo a few suspicious ones to see what is happening inside - any single failure and whole panel must be redone.

As someone who has worked on a lot of machines during the past thirty years, I can vouch for everything that you've posted, Gerald. Much of my work has been with Kodak design and built photo printers (S-series mainly). Kodak was famous for connecting everything via open terminal strips. At least they used crimped ring-style connectors; but, because the terminal strips were open, anything falling onto them, including dropped multimeter probes, destroyed things. When I started servicing European machines, particularly Durst and Gretag from Germany (at the time - both companies have changed hands and countries multiple times), I was amazed at the difference in wiring. The Durst and Gretag used the same practices that you've shown. They were neatly laid out. The 2.5mm DIN connection blocks were numbered. Scope and meter probes could be used without worry. Years ago, I copied them, except for the crimped lugs - which I'll start using immediately. After all, it's faster and easier to crimp something than it is to solder the exposed wires. (Maybe the lead in the solder is the real reason for my approaching insanity.}

The first check by an inspector is often the floor of the box. Any signs of copper lying there and the box is condemned on the spot.

Posed photos:

Screened flexible cables
 

How to "strain relieve" the fine "drain" wire of "Mylar screen":

Mylar screen used inside the control box only, where the cables don't flex.

what do you call the connectors used to wire into the gecko drives? Where would one find these?

BlockMaster DGPBP111 from www.blockmaster.com are the ones that Gecko now use (and supplied with each drive). Beware, there are also many generic equivalents, but you must ensure that they connect positively - a bad connection can blow the drive.

Why would the practice of tinning be frowned upon?.

The size of the crimped lugs makes it very difficult to insert two wires into one terminal block, with the result that in those instances I find I have to leave the lugs off and just insert the stripped wire straight into the terminal, I am less than happy with this approach and would rather tin the wires first.

Alan, from personal experience, solder tinned wires come loose because solder (lead) always relaxes under load. Also the rosin/acid seems to attract moisture and fuzzy growths. Some people will object to the lead content.

The DIN-rail terminal blocks can happily take 2 or 3 wire ends without pre-crimped lugs. Their entries are deep and they give good separation from one terminal to the next. See photo near top of thread.

Gerald and / or Mike Richards,

I have never had any faith in my crimped connections. Now I know why. My crimper, although a decent quality Thomas & Betts tool, is a combination strip, cut, and crimp tool. When I look at the picture of your crimp tool, I see that it is a nice looking dedicated crimper. Made to just crimp. Combination tools are usually not very good at any one thing.

Therefore, I am looking at the McMaster catalog to buy one. (I am fortunate that I have a McMaster distribution center near my house. Very handy!) They have many different models.

Models for insulated and non-insulated (that one I can figure out)

But they have models for:

• Ring and spade lugs
• Quick disconnect connectors
• Open barrel.

I figured out that open barrel are the types found in automobile wiring harnesses. Are the quick disconnects the pin lugs that are shown in your pictures? If they are, what is the differences between the crimp portion of the terminal between quick disconnect connectors and the ring and spade lugs. I can't see why the crimper would 'care' between those. Therefore, I bet that the quick disconnect terminals are something else and I want the one for ring and spade lugs.

Please straighten me out!

To boil it down, could you tell me which tool I want??

Thanks,

Marc

Marc,
I use a tool similar to the 5722K12 found on page 723 of the McMaster-Carr catalog. The tool that I use only handles three wire sizes, but it is a ratcheting type tool that has always made a 'proper' crimp.

Marc, see last post in this thread "Tools needed to build and operate the MechMate - gift ideas". I have used expensive and cheap versions of the same tool and they all crimped very well.

Thanks gentlemen.

Although I have done a lot of wiring (rewired the last three houses I have owned) that is more like doing plumbing. This is a bit differrent. In any case where I rewired something in my woodshop where terminal connectors were required, my tool never made a single crimp on an insulated connector that I trusted. I finally quit using insulated connectors and started insulating them myself with shrink tubing. I should have just taken the time to find a real crimper.

I'm old but I can still learn!

Last night there was a discussion on soldered wire ends on the Gecko Yahoo forum. What follows is an extract from http://finance.groups.yahoo.com/grou.../message/12638 , a post by Mariss of Geckodrives:

"1) Never solder tin stranded wire that goes into a compression type
connector. The connector relies on stranded wire to conform to the
shape of the connector when compressed to create a reliable, gas-tight
connection.

1a) Solder tinning prevents this and contact is made at only a few
microscopic contact points. This degrades the contact resistance.

1b) Solder has a tendency to flake like graphite when wire flexes in a
compression connector. It's what leaves the black stains on your
fingers if you wipe a wire when used like that. These flakes oxidize
and further degrade the wire to connector contact resistance.

1c) The solder to no solder transition on the stranded wire is a
stress concentrator and invites fatigue failure and separation of the
wire at that junction after a very few flexure cycles. Unsoldered
stranded wire endures far more flexure cycles.

1d) NASA workmanship guidelines expressly forbid solder tinning of
stranded wires for use with compression type connectors. It's that bad."

Gerald,

I did go buy that Harbor Freight crimper that you suggested and it works great. Very professional crimps that were NOTHING like what my last tool would do. Thanks.

http://www.harborfreight.com/cpi/cta...emnumber=93977

Gerald,

I want to use those plastic connectors you used to plug your stepper motors to the flexible cable. I surfed the web and Molex has a good selection. Is there any reason I shouldn't buy and use the type that computer manufactures have on the power supply for hard drives? The data sheet I found shows 4 circuit connectors that handle 18-22 gauge wire and they are shaped so that they can only be plugged together in the correct orientation.

I wouldn't have asked this simple stupid question but I've been surprised several times already by what we should and shouldn't do during the building process.

Thanks.

The ShopBots used connectors type Wago 231-604 on the motor and 231-104/037-00 on the cable, and what you see in our pics is a legacy from ShopBot. Those connectors are not a good idea - too many chances of things going wrong and coming loose. We now crimp the cables together with a "butt-splice" similar to McMaster-Carr 7227K12.

Generally, motors do not go bad. There is seldom a reason to swop one motor with another. (We have swopped to find faulty connectors - the swop-ability was useful to test the swop-ability devices, duh!)

Gerald,
Wouldnt the above statement also hold true for the crimped pins that you are using? The hard pins would not compress much I think and cause similar problems? I know in systems that we produce at work, we never use crimp on pins in compression type connectors, just bare copper. We DO twist the stranded coppper before we insert it though. Have you inspected used pins to see if they compress at all in the compression connectors?

Also if you still want to use the crimp pins and need two wires, then you could always crimp the two wires into one larger crimp pin. This practice of crimping 2 or more wires is allowed in military electronics. There is a table for the number and type of wires allowed into specific sized crimp terminals. I could provide you a copy if you are interested.

Gerald,
I just ordered a really nice assortment of single and double wire ferrules on Friday. The link is here :http://www.ferrulesdirect.com/
Great pricing on their sample kit which has about 50-100 of each wire gauge size one should need for the control box.
Sean

Heath, I would be interested in that table if you don't mind. Thanks.

Heath, I was quoting somebody else there - I don't personally believe in the "gas-tight" theory. I just don't see how a crimp can ever be truly gas-tight or why that should be so desirable. The "hard" pins have always worked well for us. (We can get flat or round hard pins, but I generally only use the round ones.) DIN 46231

Sean, I have no experience of the type of ferrule you are talking of. They are quite different in that the crimped part goes under the terminal screw. I think these are called "bootlace" ferrules? They are only an "anti-fray" and colour coding system? DIN 46228, part 4

The colours means something completely different for the two different systems.

I have used the bootlace ferrules in most of my control panel and found them to be quite "soft". They crimp nicely onto the wire strands and do deform slightly under the screw to conform to the inside of the terminal block.

The only problem I experienced was when trying to get two wires into the relatively small DIN terminal blocks, the plastic shrouds at the back of the ferrules interfered with each other so I ended up not using them on double connections. OK I was using a fairly large wire guage (1.5mm), another reason I want to use smaller guage wire in the final assembly as the bootlace ferrules for the smaller guage is physically smaller too.

Alan, the original bootlace ferrule I remember had no plastic shroud at the back - the whole thing crimped smaller than the OD of the wire.

With those rail mounted terminals, it would be unusual for me to use any crimp sleeve at all. Those terminals have an excellent "cage-clamp" action on the wire conductors and the insulation dividers are nice and deep. See second pic from top of this thread.

Gerald,
I don't subscribe to the Gas-Tight theory either, but the compression and deformation of the stranded copper is what makes any crimp type connection work. By compressing the copper strands, the surface area being contacted increases greatly. With any type of hard surface, soldered leads or possibly hard pins, this compression doesn't happen and contact surface area is decreased. This doesn't mean that it wont work, but that it might not be optimal.

The "hard" pins are not getting hot, nor are they working loose with time, nor are they picking up corrosion - so I believe they are good. (Those pins are not really "hard" - they do conform to the mating surface to some extent. Almost like a solid strand of copper)

If you look at what is happening, one is putting 2-3 amps of 35-70 volts so, 140 watts (theoretical) would be maximum, but since it is PWM, figure 1/3 of that.

That means there is so little power, there would have to be a pretty sloppy connection to generate any heat.

The Gecko at maximum power only generates about 17 watts of heat.



Dave

Dave, we use that style of terminal for many other things besides Geckos. Lots of industrial machinery, mines, ships, automotive, railways, etc. We know them as a trouble-free, long-term reliable, terminal that can even be installed by unskilled labour.

Here is the table we use at work for the number of allowed wires in a certain size crimp terminal. We do a lot of military electronics work. I dont recall where the chart came from initially, probably some mil spec.