Category Archives: Uncategorized

Frigus Primore

Whew.  I was scared there for a bit.  For years now, I’ve frequented a website that has several online java-based thermal calculators.  I have used them to do quick evaluations of heat sinks and other thermal design challenges.  When I went to the site just now, I got an unpleasant surprise:

Luckily I was able to locate a mirror site (or maybe it was just moved).  You might find the tools handy sometime.  Give it a try: Frigus Primore

Source: Frigus Primore

Lock Washers

The lock washer is a contentious thing. Engineers tend to have their favorites and nothing else will do. Whether it is a split lock, conical, internal/external tooth, or maybe a nut with nylon insert, thread-locking compound, etc, there seems to be an endless list of mechanisms for securing fasteners. The ultimate goal is to prevent a fastener from loosening which can end in a catastrophic failure.

No matter which of these locking options you feel is best, this video from Nord-Lock will most likely cause you to pause and reconsider your die-hard stance.

Microsoft Mathematics

There are many free software downloads on the internet which are very useful alternatives to Microsoft tools. There are email clients, word processors, spreadsheets, and presentation tools all designed to give users a set of free productivity tools comparable to the King Kong of the PC world. Well who would have ever imagined Microsoft would get on the bandwagon and produce a free download. And to top it off, it appears to be a very handy tool for engineers. If you get a chance, take a look at Microsoft Mathematics 4.0.

Black Wire Syndrome

Everyone is familiar with the typical white corrosion found on lead acid battery terminals.  But there is another more aggressive corrosion to deal with when using Ni-Cad batteries.  It has been dubbed “Black Wire Disease” or “Black Wire Syndrome” because it has a tendency to creep up the wire attached to the negative terminal on the battery.  In typical DC applications, this is the black wire.

There are several theories on the causes of this corrosion.  In general, it is a chemistry issue that is enhanced by various contributing factors including lug and wire plating, insulation materials, environment, and shorted cells or cell reversal.  The problem is well documented in the remote control airplane community because they have been using Ni-Cad batteries for some time now.

In the telecom world, the “Black Wire Syndrome” becomes the “Red Wire Syndrome” because as discussed in the previous post, telecom uses a -48VDC power source.  The red wire is tied to the negative terminal of a battery string and the black wire is attached to the positive terminal.  The problem with this situation is circuit breakers are installed on the negative lead.  If the circuit breakers are a short distance (electrically speaking) from the batteries, there is a potential for the corrosion to creep up the wire and into the circuit breaker.  The corrosion then renders the circuit breaker non-functional.

For additional information see: “Black Wire Disease – What’s the Cause?” by “Red” Schoenfield published in the June 2001 issue of The Flightline by the Propstoppers RC Club

Why “Negative” 48VDC?

Why does the telecom industry use “negative” 48VDC for power? This is a common question that seems to come up. The answer is found in the electroplating process. When two materials are at different potentials in an electrically conductive environment, molecules migrate from the positive node to the negative node.

A telecom cabinet is electrically tied to an earth ground rod. If the negative terminal of the power system was connected to earth ground, and a wire with a positive potential is near the earth ground or cabinet, leakage currents would allow copper molecules from the wire to migrate to the earth ground rod or cabinet. This process is compounded by wet corrosive environments which are common for outdoor cabinets. In extreme environments the copper losses become significant and can cause the small wires (typically 24awg) and connections to fail.

The solution is to shift the earth ground to the positive terminal. This means all voltages in the cabinet are at a lower potential than earth so the direction of the molecular migration is reversed and deterioration of the phone lines is no longer a problem.

A much more definitive study of the issue can be found in this paper written by Professor Richard Levine of Southern Methodist University – Why Positive Power Ground in Telephone Subscriber Loops?”

Sheet Metal

Sheet metal is often used in the design of electronics products. It makes a great choice for enclosures, brackets, and many other components due to its formability.  Punching and bending sheet metal is a very economical manufacturing process relative to machining, die casting, etc.  It is an inexpensive media with many beneficial properties including thermal and electrical conductivity.  On the surface electrical conductivity may not sound desirable for an electronic product, however it is essential in the containment of electro-magnetic radiation.

Selection of sheet metal thickness is often based on structural strength.  There are standard material thicknesses for sheet metal typically referred to as ‘gauge’ in the United States.  Sheet metal gauges for steel are based on its weight.  Aluminum and other materials have different thicknesses for the same gauge (ie. 16ga steel is .0598″ thick while 16ga aluminum is .0508″ thick).  Rumor has it, the guy that established these gauges is the same guy that decided a yard will be 3 feet, a foot being 12 inches, and a portion of an inch being quoted as any fraction which has a denominator that is some power of 2.