Miscellaneous electronics, parts, components, etc.

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How to use a multimeter https://learn.sparkfun.com/tutorials/how-to-use-a-multimeter

http://ringengineering.com/index.html

This section is for miscellaneous electronic items, that span all power systems, or do not fit anywhere else.

 

Automated control:

There are a number of places that sell nice little automated controls to use on DC. Here's one that has stood the test of time: http://www.rr-concepts.com/

Getting components/parts:

I try to use circuits that have parts carried by Radio Shack, but they are slowly phasing out parts, and when you used to be able to buy a resistors in different values, often all you can get is an "assortment".

Internet ordering is probably where you will need to go, try DigiKey or Mouser or All Electronics

Reed switches:

I recently found what seems to be identical to the reed switches that come with the QSI boards, these are nice general purpose reed switches. Look up part number 59025-010-nd on the Digikey site

Some commonly requested/misunderstood items/circuits

Full wave bridge rectifier:

Here is a picture of the most requested item, a full wave bridge. Normally, it is used to convert AC into DC, but you can feed it DC that changes in polarity to get DC on the output that is of known polarity.You can buy these from Radio shack made up, they are all in one unit with 4 leads. The leads show + and - output, and two, the inputs have a "~" on them (Means AC input). The use that many people do not consider is taking DC of any polarity and outputting DC of a "known" polarity.

Add a capacitor for uninterrupted  power:

For lighting circuits, people often add an electrolytic capacitor to keep lights lit:

Notice the full wave bridge rectifier from the track? This way you make sure you have a known polarity to your capacitor.

The capacitor is a storage device, often like 3,000 to 50,000 mfd (microfarads). The bigger it is, the longer it can supply power, but the downside of bigger, is more size and longer to charge. Be SURE you select a voltage rating WELL ABOVE your track voltage, these devices are NOT tolerant of overvoltage. If in doubt, pick the next voltage higher.

The resistor is there to limit excessive "inrush current" when the unit is first connected to the rails. The capacitor charges up, but it looks like a dead short for a brief time as it is charging. Use ohms law to set the resistor value. For 18 volts track power (max) a dead short simulates a discharged capacitor, the worst case. So with V=IR, an 18 ohm resistor would limit the inrush current to one amp. Note that you should use a resistor of high enough wattage, again if you use the worst case, W= I2 R, then you have 18 watts! Better choose a resistor to about 1/4 amp, so for 18 volts, you want a 72 ohm resistor, and then the wattage would be 4.5 watts. Since you would not be doing this all the time, try a 2 watt resistor.

 

How to use a full wave bridge to make a voltage "dropper".

There are 2 pictures below.

The picture on the left is a normal full wave bridge. Apply AC to the two tilde ("~") terminals, and DC appears at the + and -.

The picture on the right shows how to make a compact and efficient voltage dropper from a full wave bridge:

  • connect a string of diodes from the plus to the minus terminals as shown
  • then put the device in line with one leg of a circuit (like from the track or the motor), you wire this in in like a resistor.
  • Notice that no matter what the polarity, the current goes through 6 diodes, or 0.7 volts times 6, or 4.2 volts constant drop.
  • Vary the number of diodes to suit the amount of voltage you wish to reduce or "drop"

This is good for reducing voltage to a dcc decoder that does not meet nmra specs on max voltage. It allows you to slow down a loco that is much faster than others. The use of diodes avoids the nonlinearity of resistors and also the heat they generate.

 

FULL WAVE                                                                                                           VOLTAGE DROPPER

BRIDGE                                                                                                                  FROM FW BRIDGE

 

 

Below is the dropping circuit as above right, you can see the full wave bridge and the diodes....


More on rectifying AC (to DC):

 


Filtering AC:

When you feed normal AC into a bridge rectifier, you get a series of "humps". To smooth that out, you add a filter capacitor. What you get out is DC, but with some "ripple". The less the load, or the bigger the capacitor, the less ripple.


LEDs

Calculating LED dropping resistors

  http://led.linear1.org/1led.wiz

 

Using a 3 terminal bicolor led where you have DC of "reversing polarity"

http://www.neufeld.newton.ks.us/electronics/?p=151

http://www.scienceprog.com/bi-color-led-indication/


 How to drive a bipolar LED from 2 DCC functions:

Sub-Pages

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