Something not quite right.....

As you will have seen in my Eastwood Town thread, I have at last managed to get a circle of track up and running, but the loco's themselves are running about half speed.  I'm only using the basic NCE Powercab, which from memory is rated at 2A.  I have the full ProCab set up upstairs, but that's still wired into the layout.

I've measured the voltage with my meter and I'm getting a steady 12.4v at all points around the circuit, but I'm unable to measure the current available when a loco is running.

I've connected the meter in series with one of the DCC supply leads to the track and am getting zero reading in both mA DC and AC modes.  A search on the web suggested setting the meter on ohms and shorting the test leads together to see if the fuse has blown.  The reading here was 0.0 ohms so I assume the fuse is OK.  I've just noticed the meter has a 600v, 400mA fuse, so perhaps the current consumtion is outside the meter range (Wavetek DM9).

Can anyone give some guidance on this one?  How to measure the current and why loco's are running slow?

I've yet to fit the main bus, so am just using the copper tape mini bus and 24swg droppers for power supply.  Could this be limiting the current?

Gordon, have a read of this & see if it helps.
http://www.members.optusnet.com.au/nswmn2/DCC_Meters.htm

That voltage looks a bit low - I'd expect to see something around 14 - 16 if you want to belt locos around in a circle at top speed.

Just a thought, can you measure the DC voltage output from your NCE power supply. The voltage supplied to your handset may be lower than that supplied by the power supply on your "big" NCE set up.

Thanks guys.  That RRampmeter looks interesting Sol and may be worth investment to build it into Eastwood's test rig/main control panel.

You could be right Ian as the Powercab manual says the output from the powerpack should be 13.5v regulated.  'Scuse my ignorance though but I seem to recall that the track voltage measured across the track will be lower that than the powerpack output.

Just checked that out and it's 13.32v, so that's a little below the spec.  Problem?

Don't forget that normal AC meters do not read DCC volatge correctly - a bit on the low side I think.

[user=396]gordons19[/user] wrote:

 … the powerpack output.

Just checked that out and it's 13.32v, so that's a little below the spec.  Problem?

If this is significantly lower than the voltage from the power pack that supplies the main layout it could be a reason but half the normal speed sounds odd. Is the auto-reverser wired in yet? Does the NCE handset have a switching/shunting function that is accidentally on? Can't think of anything else. In my case I'd be looking at dodgy soldering but I suspect that isn't likely as you can see everything. Have just thought of something unlikely though. I assume eventually this is going to be wired as the normal DCC supply to the track between the turnouts and the rest of the circle from the auto reverser? What I'm getting at is while it it is a simple circle, would this cause a problem, does it need to be temporarily turned into a circle with a break with snubbers terminating it. I've had various DCC systems feeding into train set sized ovals (but not the size of Gordon's track)without any problem.

Power Cab manual has voltage input 10-15v Regulated DC & the output is that volatge minus 0.5 - page 22.
Page 57 also indicates how to set it up to show track current.

Don't forget, reading voltage without a load is a mistake, what does your meter show with a loco running around, it should be the same as no load with DCC but if it is lower, then resistance is in the leads.

As Sol says, Gordon, you need to measure under load. If you get the same voltage reading around the tape while a loco is running, as you do when there is no loco on the track, then you are not having a problem with current supply.

As Dave said on your layout thread, we did see you having a similar problem on your main layout before. I have just checked voltages on mine. I know meters will be different, but on the 200v ac setting on my meter, I get 15.4v across the track.

A better way would be to measure the DC voltage following a bridge rectifier as this is what happens inside the loco decoders. I already have bridge rectifiers for my frog detectors. These reveal a DC voltage of 10.5v. (Sounds about right as I would expect to lose about 1.5v across the diodes in the bridge)

If you have a bridge rectifier available, you might want to try doing the same thing. Otherwise, if you have a decoder with function outputs, then connect it across the track, turn on aux output 1, which will take the yellow (or is it white??) lead to 0v. Then measure the voltage between the blue and this grounded output. That will give you the DC voltage available to the motor. Clearly the decoder actually chops up this voltage to control the motor speed, but if this DC level is not close to 12v, then the motor will never be able to run at top speed.

I've got the RRampMeter 2 and it is well worth the money in my opinion.

Spec is :
DCC : 23 volts, 9 Amps
DC : 23 volts, 9 Amps
AC : 16 volts, 6 Amps

I guess that you pays your money and takes your choice - as my granny used to say. But £76 is a bit steep for a meter for me. Anyway, I realise that my ZTC controller will display DCC voltage, and AC input voltage at no extra charge. ;-)

So does my ECoS Geoff but it makes the measurement internally so no good to find faults on the layout.

A Version 1 for fitting in a panel or make your own case is £46.21 at Digitrains
v2 is £70.53

[user=523]chrish[/user] wrote:

So does my ECoS Geoff but it makes the measurement internally so no good to find faults on the layout.

A Version 1 for fitting in a panel or make your own case is £46.21 at Digitrains
v2 is £70.53

Or even cheaper elsewhere!

Gordon - how have you plugged the PowerCab into the mains?  With a fused adapter?  If so, what is the rating of the fuse?

Hi John

The Powerpack is plugged into one of those 2 pin US adaptors, which is rated at 13A and has a 13A fuse fitted.  Will that impact the output?  Thinking about it, would a 3A or 5A be more suitable?

Hi Gordon

When we supplied PowerCabs with adapters we always fitted 2 amp fuses to protect the PowerCab from any current overload.  Now the PowerCabs for the EU come with a powerpack that has a range of plug fittings.