NCE EB1 DCC Circuit Breaker

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The EB1 is NCE's 2nd generation advanced DCC Circuit Breaker.  It replaces the obsolete EB3 which was not compatible with Sound Decoders with high Inrush current issues.  
If you do not understand what the problem is, go here: Inrush Current (Sound Decoders)

The EB1 is only available as a single Circuit Breaker.  To replace a NCE EB3, you would have to buy 3 EB1.  However it has two big feature over the EB3 or any other brand of DCC circuit breaker that is not compatible with Sound Decoder high inrush current issues.

1) Support Booster Currents up to 8 Amps.

2) Controlled current recovery to address high inrush current loads.

The current version is V1.0.  (The RevB notation on the PCB has nothing to do with the version of the product.) The product was introduced in 2005 which set by the date of the manual.  Production has varied over time causing some stores to go out of stock.  The EB1 directly competes with the DCC specialties PSX1.

The EB1 uses current sensing resistor to detect the current flow.  It is the big cylinder item on the far left side of picture above closest to the blue connector.  The switches that turn on and off DCC power are on the far right closest to the blue connector.


There are two problems with the EB1:

1) The EB1, right out of the box, has the sound decoder inrush current option turned OFF!!!!!!   CV135 Default value = 0 which turns it off.   If you program the EB1's CV135 = 4, the function will now be turned on.

(Note: On the other hand the PSX circuit breaker, right out of the box, has this function turned on!  Instant Plug, Play and gratification solution!  There is a marketing clue here NCE!!)

2) The manual fails to describe what the problem is with sound locomotives followed by a solution using the programming options offered.  I suspect a timing diagram is worth a lot of words.  Part of the problem here is that to understand what going on means getting into the nuts and bolts of this technical topic.  Something that most DCC vendors try to avoid.


One way to limit the current is to TIME AVERAGE IT.  Stated another way, apply small pulses of power that are NOT long enough to shutdown the booster but still allow the capacitor to recharge.  This is exactly what decoders do to drive the motor.  Pulse Width Modulation (PWM) is time averaging of full power.  

For example, if the power is on for same amount of time as it is off, 50% on and 50% off, then you cut the total power in half.  We call this 50% duty cycle for the number refers to the % of time the pulse is off relative to it matching off time.  So by managing the time the circuit breaker is on relative to the time the circuit breaker is off or "Pulse Duty Cycle", we can control the average current to be something less than the boosters full rating.

If the circuit breaker is off due to a short circuit, how can it be on again?

The DCC circuit breaker is doing two things at once.  The small pulses of power are being performed BETWEEN the DCC circuit breaker's shutdown times.  In this case during the period of time set by CV130 which is normally two seconds long by default.

When the circuit breaker is turned back on for any amount of time, is there not still a short circuit due to the capacitors being discharged?   

Yes.  However this solution relies on the booster unique property of current limiting track power to the booster current rating.  The booster only shuts down if the current limiting mode last to long.  In other words there is a "watchdog" timer built into every booster that says after it has timed out that "enough is enough" and shuts down the booster.  So the trick is to keep the power pulses to be LESS THAN the booster watchdog timer timeout period.  Stated another way, small and fast power pulses relative to the booster response timing.


The EB1 allows you to "custom define" the "power profile" of these small and fast pulses of power by programming timing values into the  "Custom Startup Table" consisting of CV135 through CV146.  The "Custom Startup Table" allows up to 6 different small pulse cycles to be performed back to back where you set the timing of each pulse.

The default values show a increasing pulse power profile.  All the "Off times" are set at the same 4mS.  The on times are doubling with each pulse.

Pulse# On        Duty  CV#    Notes
          Time     Cycle
-------- ------    -----  -------  ----------------------------------------------------
Pulse 1 4ms      50%  CV135 
Pulse 2 8ms      66%  CV137
Pulse 3 16mS    80%  CV139
Pulse 4 32mS    89%  CV141
Pulse 5 80mS    96%  CV143
Pulse 6 0ms        0%  CV145 (No 6th Pulse provided.  It is off)

Article Revision Dates:  
V1.1 12/27/2011
V1.2 10/21/2015