Loco slowing down when another loco starts

[WIMorrison]

It points to your power supply not being ‘man enough’ for the locos you are running 

[NIK]

1 hour ago, Clagsniffer said:

So, I’ve finally got round to do some testing with the decent Fluke 179 multimeter and this is what I’ve found:

 

voltage on the UTP panel going to the track is 12.87v

 

resistance from UTP panel to the rails is 0.3ohms on each cable.

 

resistance from the UTP track connections to the furthest point on the layout was 0.4-0.6ohms

 

when running the Heljan 47 on its own, the track voltage reduced to 11.7volts

 

when running the Heljan 47 with a Bachmann 37 track voltage reduced even further to 11.1volts.

 

Does this point to the Heljan dragging voltage/power down?

 

Hi,

 

Yes it does point a bit to the locos mentioned dragging down the output.

 

Its not actually a UTP panel but its looks similar.

 

I found with the DMM I used that I got 0.4ohms when test probes touched together so you may find the resistance of the cables is less. 0.4 to 0.6 ohms from the track output to the farthest bit of track seems a bit high to me.

 

If you measure the DC voltage at the PCB marking + and - before and when running the Heljan 47 with the Bachmann 37 you can see if its the DC power supply causing the problem.

 

Regards

 

Nick

[melmerby]

I've measured the output from my Z21 which is also rated at 3A max

The DCC output voltage is 15.5v on my Fluke and hardly varies with differing loads. Just a couple of hundred millivolts.

 

EDIT

The input can be between 18 & 24v DC and at 24v DC it can be adjusted to between 12 & 24v DCC output.

They supply a 19v PSU

 

 

Edited March 28, 2021 by melmerby

[NIK]

Hi,

 

The Power Cab requires a regulated power supply with a maximum of 15V DC.

 

To provide 12V DC to a typical OO loco motor it needs to output 12V + 2*0.7 Volts (to allow for the two silicon diode voltage drops in a typical DCC decoders internal bridge rectifier).

 

If the OP now has a DMM then any voltage drop due to the DC power supply can be checked.

 

It is easier to check a drop in a medium voltage with a DMM than a low resistance.

 

Regards

 

Nick

[melmerby]

9 hours ago, NIK said:

Hi,

To provide 12V DC to a typical OO loco motor it needs to output 12V + 2*0.7 Volts (to allow for the two silicon diode voltage drops in a typical DCC decoders internal bridge rectifier).

Regards

 

Nick

Motors don't actually get 12v DC but a PWM waveform and the actual "voltage" is not overly important in most cases.

How many locos are run at max speed?

 

The output from DCC systems however should be capable of ouputing a DCC level that does not vary significantly  between no load and tripping current.

you should not see a drop with just one extra loco operating