At 1:16 AM -0700 5/7/07, Gary Lane wrote:
I have used Ingram and LGB EPL diagrams to make a number of automatic public displays.
Why do I like latching relays over LGB switch motor with 1203/DPDT (double pole double throw switch)?
- Since I installed restaurant LGB train displays using EPL components, I soon discovered that the system kept jamming due to engines parking on top of 1700 reed switches or due to LGB switch motors not fully moving to throw the 1203 DPDT switches. This led to train crashes or simply a lock up of the system until I could drive 120 miles or 155 miles to the restaurants to make adjustments.
When I switched to RR Concepts latching relays the number of layout failures dropped dramatically and the reasons changed to staff idiotic “adjustments” or customers tossing jelly containers or peanuts or silverware onto track. Incidentally, since LGB’s Jumbo transformer has an automatically resetting circuit breaker, I had to install a manually reset circuit breaker to the track wires so that short circuits were not constantly being reset. The manual reset circuit breaker forced staff to remove the silverware or other metal item that was shorting the track power. - A latching relay has a motor like LGB’s turnout/switch motor that moves several on/off switches (contacts or relays that often offer more options than the LGB 1203 switches). Latching relays are much more reliable than LGB’s system. Latching relays vary in specs for the motor and the switch. For example one relay might only need 3 VDC to throw the relay, yet the contacts can handle 100 amps. Another unit might require 6 VDC to move the contacts, yet the contacts can handle less than .25 amps. This is initially a bit daunting for a person who is familiar only with LGB components.
- LGB components are prone to not moving completely and therefore may not throw the DPDT switch completely. LGB switch machine and the old 1203 have to overcome a lot of friction and spring tension to move the two mated components that LGB used as a latching relay. LGB’s switch motor can also jump gears and end up not being able to move equally in both directions. A dedicated latching relay requires very little energy to move the contacts, therefore the latching relay virtually never misfires. Telephone companies used latching relays for many decades and may still for all I know. Phone companies had to have reliable equipment. Bottom Line: A latching relay is a more reliable and more compact option than LGB’s expensive two part system.
- The problem with a latching relay is the more complex circuitry options. Only two leads are for the motor to move the contacts. Contacts available may include normally open and normally closed contacts. The normally open type is what train nuts would usually wish to use. Normally Open means the default position of the relay is for No Electricity to flow.
Only when an electric impulse from a reed switch activated by a magnet under an engine (or if you wish an optical or motion sensor) forces the switch motor to move the contact to a Closed or On position is the Normally Open contact/switch Closed or completing a circuit. Usually a second reed switch will then open the circuit or turn it off when the engine passes over a second reed switch. A reed switch can be one of the two varieties LGB made or a simple cheap reed switch taped to a track tie. - I like the much smaller size latching relays than the LGB switch motor with attached ON/OFF set of two switches (1203 or newer version).
- There are surplus latching relays I have set up inside the operating Pola Crossing Keeper hut. Those units are the size of two 35mm film cans end to end. Still pretty large, but the relays were only $3 each at an electronic salvage shop (now out of business). Relays the size of half a wine cork easily handle the amp and voltage loads common on our layouts (< 25 VDC or AC and < 25 amps). ( < = less than, < = less than or equal to) Just specify the volt and amp limits to a sales clerk at Radio Shack or a real electronics parts store. Tell them you want at least two normally open contacts and you want clear instructions so you know how to wire it.
- Short article comparing relay vs latching relay:
geofex.com/Article_Folders/relays/relays_for_switching_audio_signa.htm - Radio Shack page of relays:
http://www.radioshack.com/search/index.jsp?kwCatId=&kw=relay&origkw=relay&sr=1
Scroll down to see several latching relays that only require 12 VDC to “throw the equivalent of the LGB switch motor, and the relay handles 3-10 amps. Note prices are usually about $9. Instead of buying an $18 LGB switch motor and another $12 or more for the DPDT switch, pay $9 or 30% of the LGB tab that is also much less reliable and takes far more room. If your power pack puts out 25 VAC you will need to reduce the voltage that arrives with resistors or a zener diode or simply use a 12 VAC transformer for your latching relays. - Like Jim Ingram, I am not a trained electrician. I can apply logic and follow simple diagrams. I also ask for help or information if I am not sure. Curtis Roecks of RR Concepts is an electrical engineer who knows subminiature components and circuits. His latching relay is larger, but is specifically set up for model train use and is very difficult to burn out.
All terminals accept 18 gauge wire easily and clamp with a small screwdriver. His drawings are very easy to read. His units have well labeled terminals and adjustment pots. RR-concepts.com
