Track Voltage for Z in DCC?

Hi all

I'm new here and just having my locos converted to DCC, which is of course exciting.

I'm confused about the voltage required to the tracks due to differing advice:

A Lenz person has advised that the Lenz system can be adjusted to output 10v to the track and I should choose that system on those grounds.

The UK distributor of MRC Prodigy Advance has said that their signal output of 14.5v at 3.5amps is fine because the chips in the loco will limit voltage to the motors and the Prodigy Advance can limit top speed by limiting voltage. I"v had a demo of this system on HO/OO and found it easy to follow so would be pleased if it were safe for Z

I'd be very greatful for the advice from experienced users here please.

Many thanks in advance

Simon

In theory the MRC chap is correct but in practice it has proven to be dangerous to Z-scale locomotives. The problem comes when you develop a short and the 14.5vac at 3.5 amps will literally fry the Z-scale engine.

Both Lenz and Atlas suggest support lower track voltage in range of 10 to 12vac. There is a problem with some decoders in that they will not program properly at 10vac track voltage, but most seem to be happy at 12vac when it comes to programming the decoder. I have not seen anyone using the Lenz at 10vac so can not comment on how it is for operation. I also like to see the amperage reduced to 1 amp but this is not always easy to do but you can introduce a car brake light bulb into one leg of the feed to the track.
With the track power passing through the filament as soon as a short develops the bulb will light limiting the current to the track and usually preventing a burn out of the decoder and loco motor.

cheerz Garth

In my experience, no problem with 13.0 to 13.5 V.
All my Märklin locomotives are 5-pole motor.
Decoders: Uhlenbrock, Digitrax, CT Elektronik, Kühn, Hornby, Velmo ....



Greetings from Spain

Hi Simon. First, make sure you measure the DCC voltage with a True RMS voltmeter, not an ordinary "AC" voltmeter. The DCC signal is a squarewave, changing between 8 kilohertz and 10 kilohertz. An ordinary meter can be 2-5 volts higher or lower, depending on the internals or digital or analog display.
More info: members.optusnet.com.au/nswmn2/DCC_Meters.htm

It is best if you can reduce the voltage. Running at 14 volts is not a good idea, but, the motors will typically survive. Garth is right about the current though. If a short occurs, there is a LOT of power place thru that metal wheel, even if the DCC system protects in the typical 1/4 or 1/2 second. But most turn on again in a 1/4 or 1/2 second and repeat, pulsing this full power ! ALWAYS WATCH YOUR TRAINS ! If you use a light bulb, it should be rated at 1/2 or 1 Amp, max. NCE also sells a 6 bulb board (CP6). However, this technique does not give good voltage regulation. An electronic circuit breaker is better (DCC Specialities has the best function and can be set as low as 1/4A)

The UK distributor's comments are NOT correct ! The decoder will NOT limit the voltage! All decoders use Pulse Width Modulation (PWM) to control the speed. To make and effective speed change, the amount of on and off time is changed. When the motor controller turns on, it is almost the track volage. Off is zero volts. So even at the slowest Speed (1 Speed Step), the near full track voltage goes on for 1/28 or 1/128 of the time. If you change CV5, the Max Speed Step, it only sets how much duty cycle is so it would appear that there is less voltage but in reality, the same near full track voltge is applied to the motor, just not all the time.

One way you can make lower track voltage is use a diode (rectifier) drop string. Each diode will drop about 0.5 to 0.7V if using Silicon diodes. Place diodes back-to back. See: members.optusnet.com.au/nswmn/excess_voltage.htm

While have a circuit breaker of a lower value is a good idea they do not react fast enough for our small motors.

Use of an 1156 standard 12vdc (13.8vdc rated) automotive brake light bulb in series with your track feed is a smart thing first is limits the amperage and converts the short to a switch closing the loop to power the bulb and it is instantaneous when compared to a circuit breaker's response time to trip. Many DCC systems are 5 amp jobs at about 15vac and it takes but a fraction of a second to fry something. At least one DCC manufacturer supplies a board with these lamps on it for providing protection for each booster or block on your railroad. Atlas also makes a Diode block for dropping the track voltage.

Typical problem that may not cause a burnt motor but can still destroy a locomotive is a short between the two rails and it starts with a partial derailment when the engine has not fully left the track and one of the wheels shorts out between the two sides of the track power at a switch if not using the protection of a brake light the wheels becomes a resistor of shorts and the current heats the wheel up and in the process the delrin axle and the wheel slumps and after you have removed the engine from the track the delrin plastic cools and now is set at an angle to the inline position it originally had and the engine jams. I have seen the valve gear hangers etc melted on a steam engine with metal side rods. I have seen truck side frames melted and axles warped from shorts like this. It can even happed on your DC system as well but in most of those cases the voltage a current are less and so the time interval to damage can be several seconds while with DCC it is measured in micro seconds.

So for my money reducing the track voltage to 10vac and using a brake light in series with one of the track feeds are the two most important factors to creating an environment where the risk factors have been calculated and addressed to minimize the risk to you equipment when operating on a DCC system. In the case of multiple blocks a brake light bulb for each block is useful tool in diagnosing where on your system the fault has occurred.

Saw the effectiveness of the brake light on several layouts over the weekend and at least one disaster on a layout with no protection and this was in N-scale.

cheerz Garth

Many thanks for the detailed help. Very much appreciated. I'll see what I can piece together. Any specifications for the break light components please? Thanks . Simon

Hi Simon;

The lamp that has been used for years in NA is the 1156 which is a generic automotive brake light bulb with a bayonet base. This lamp is good for 5amp systems as it is rated at 35 watts or 3 amps. NCE offers 6 lamps with 1 amp capacity for protection of DCC locos. They also offer those with a 1.75 amp rating.

For Z you can use any lamp with a 1 amp rating at 12v or 12watts at 12v. Remember the lamp does not care it the power is AC or DC and the formula is I=P/V I=amps P=watts and V=volts.

There are several systems that offer the possibility of reducing the voltage to the track NCE is one such on their Power Pro series. It can be adjusted from 9.5 to 13.5 vac to the track.

Atlas also published a sheet on how to use bridge rectifiers to reduce the track voltage. They have to be used in pairs one in each leg going to your track. Each pair will drop the voltage 4 x .7 or 2.8 volts. Using the bridge rectifier handles the AC and in this application does not turn it into DC due to the way the rectifiers are connected in parallel and in series for drops of 5.6 volts using their system for Z.

members.optusnet.com.au/nswmn/excess_voltage.htm this web page talks further about this subject and uses diodes instead of a bridge. The bridge is just a quick way of getting 2 diodes in each direction in one device.

www.atlasrr.com/voltage.htm this is the solution from Atlas for voltage drop to the track.

cheerz Garth

I've been using Lenz at 10v for several years. No problems that I am aware of. If you want to increase the voltage, it is easy on the Lenz as it is just a software program change - much like programming a decoder. I use a TONY'S Rampmeter which is specifically designed for DCC. All the Marklin engines draw more amperage than the Micro Trains. OTOH with about about 10 engines sitting on the track I see very little amperage [expected]. Running up to three to four [some mued engines] I never see amperage over 1 amp except at startup.

...don a