TT8027 and TT8028 power clips

[Kenneth-365689]

I have a number of TT8027 Power connecting clips (which are designed for Analogue running) and would like to use them to supply power to my DCC layout. I was told that this can be done by removing the component (diode.?) that is soldered across the two copper strips. Has anyone done this, and if yes, does it work? Or is it more complicated than that? Thanks in advance for any information. 

[ntpntpntp]

The component is a capacitor, it's there to reduce RF interference for TVs etc.  For DCC use, just remove it as has been suggested.   If not removed it can upset the DCC signal in the track.  DCC decoders have their own interference suppression built-in.

Edited March 19 by ntpntpntp

[Rog RJ]

Just cut it out.

[Kenneth-365689]

Thanks ndpndpndp, I will start snipping the capacitors out.. ✂️.. Just needed a little reassurance before committing snippers to wire. 🙂

[marcus28]

Begs the question though, if the TT8027 is the same as the TT8028 but, with the addition of a capacitor......how come it's £2 cheaper.

I cut the capacitor out on a TT8001 and one of my locos started stuttering down the track with the throttle on the DCC controller set to 0. Replaced it with a TT8029 and had no issues at all. Could be me.

[96RAF]

21 minutes ago, marcus28 said:

Begs the question though, if the TT8027 is the same as the TT8028 but, with the addition of a capacitor......how come it's £2 cheaper.

I cut the capacitor out on a TT8001 and one of my locos started stuttering down the track with the throttle on the DCC controller set to 0. Replaced it with a TT8029 and had no issues at all. Could be me.

It all depends what power source you are using. If you are applying DC to the track to power normal analogue locos or HM7000 locos then it can be left in. If you are applying a DCC sign al to the track from a DCC controller to the track to power normal digital locos or HM7000 locos then cut it out. Note that HM7000 locos can use either DC or DCC track oower.

[Rallymatt]

Cost can be less even with additional components due to the economy of scale, ie a lot more being made and the individual component costs are tiny. 

[ateshci]

The capacity as indicated is 100nF which will result in a capacitve resistance (reactance) of ~80 Ohms, because the DCC signal is rectangular with two nominal frequencies of 4,5 and 9kHz. This results in a constant current draw of ~200mA per clip additional to what the loco(s) may use. I've seen people being puzzled by 'unexplicable' cutouts or sudden stop of all vehicles  after half an hour of operation due to the CU's built-in thermal protection.

 

[Fishmanoz]

Haven’t dug out my slide rule to check your calculations at the fundamental frequency ateshci but this I do know - we are talking about square waves here, not sinusoidal, and that means that, as well as the fundamental, Mr Fourier will tell you there is a whole series of harmonics present as well. At each increasing harmonic, the reactance drops and the signal is degraded from square towards sinusoidal and outside the DCC spec.  This is what causes the running problems with the decoders and why the capacitor must be removed. Also, some decoders are more sensitive to this than others meaning some locos will work fine, others not. 

[Fishmanoz]

Marcus, I’m not doubting what you saw between an 8001 with capacitor removed and an 8029 but there is no logic to it. The 8001 without capacitor and 8029 should be electrically and physically exactly the same as each other. So different behaviour of a loco on one v the other is a mystery. 

[ateshci]

The value I have is an educated guess for rectangular waves, because the resistance for sinusoidal voltage would be twice as much. With the exception of Lenz, almost all decoders sample at half the 'on' time of the half-wave in order to avoid ( within a certain range ) signal degradation problems due to parasitic capacity/inductivity effects. To sum it up -capacitors will  overload the system and degrade the signal.