Will this wiring work please: rolling road, voltmeter, ammeter, additional tracks?

[AndyID]

12 hours ago, kevinlms said:

It is a bit complicated,  because the task of accurately measuring voltage and current on a varying DC circuit isn't really simple.

 

 

And adding diodes and rectifiers destroys any calibration the meters might have had which makes the values they present fairly useless.

[flockandroll]

On 01/05/2022 at 22:40, AndyID said:

Another way to do it is to always set the controller in one direction when you are using the rolling road. Put the voltmeter across the controller output and the ammeter in series with one feed then connect that to a two pole switch wired to be able to reverse the polarity to the rolling road. It might be useful if it also has a center off position.

 

You would still need to be able to disconnect the voltmeter when the controller is running in normal mode but you only need a single-pole off-on switch to do that.

 

Thinking about this some more, at the moment this seems the best idea, because you are using the switch to change the direction of the rolling road, which is more simple to use than my idea, and perhaps makes more sense for the meters than does the bridge rectifier (I kind of get the basic idea of what one is now)

[AndyID]

1 hour ago, flockandroll said:

Thinking about this some more, at the moment this seems the best idea, because you are using the switch to change the direction of the rolling road, which is more simple to use than my idea, and perhaps makes more sense for the meters than does the bridge rectifier (I kind of get the basic idea of what one is now)

 

You could add a diode across the voltmeter terminals. It would limit the meter voltage in the event that the switch was closed when the controller was turned the wrong way. That should prevent bajaxization of the meter.

[Crosland]

16 hours ago, AndyID said:

 

And adding diodes and rectifiers destroys any calibration the meters might have had which makes the values they present fairly useless.

 

If the meters are calibrated, they are calibrated. The diodes more or less cancel out. Perhaps a drawing will help.

 

 

The voltage applied to the RR will be two diode drops less than the supply. The voltmeter will read two diode drops less than the supply, i.e. the voltage applied to the RR.

 

There will be some inaccuracy due to the much lower current flowing through the voltmeter but it wouldn't be hard to bias the current through the lower bridge to even things out.

 

 

 

 

Edited May 6, 2022 by Crosland
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[Compound2632]

The OP says they've got analogue meters, which they like, for the look of the thing. I don't think these are going to come to any real harm if connected the wrong way round.

Edited May 6, 2022 by Compound2632

[Brian]

One of these in 1.0 or the 5.0 Amp range would be ok for direct current reading Amp Meter link

 

Can't so far find a centre zero voltmeter, but will continue searching!

[AndyID]

7 hours ago, Crosland said:

 

If the meters are calibrated, they are calibrated. The diodes more or less cancel out. Perhaps a drawing will help.

 

 

The voltage applied to the RR will be two diode drops less than the supply. The voltmeter will read two diode drops less than the supply, i.e. the voltage applied to the RR.

 

There will be some inaccuracy due to the much lower current flowing through the voltmeter but it wouldn't be hard to bias the current through the lower bridge to even things out.

 

 

 

 

 

That would work although the voltage drop at the diodes for the ammeter will increase a bit with increasing current. Positions of the controller knob will produce different results on the rolling-road from layout track. Don't know to what extent that's really a problem.

[flockandroll]

As I am planning to use Wago 221 connectors for the wire to wire joins, I might actually try both methods in the end.

 

Would this be a suitable bridge rectifier?https://cpc.farnell.com/multicomp/mp606g/diode-bridge-rect-1-ph-600v-th/dp/SC14910   AIUI the power it loses as heat will be 2 x 1.1volts x the current, which will be less than an amp, so about 2 watts max, so no need for a heat sink. So I can use the screw hole to fix it to the baseboard.

 

But I will go for the switch to reverse the rolling road method first. 

 

[AndyID]

2 hours ago, flockandroll said:

As I am planning to use Wago 221 connectors for the wire to wire joins, I might actually try both methods in the end.

 

Would this be a suitable bridge rectifier?https://cpc.farnell.com/multicomp/mp606g/diode-bridge-rect-1-ph-600v-th/dp/SC14910   AIUI the power it loses as heat will be 2 x 1.1volts x the current, which will be less than an amp, so about 2 watts max, so no need for a heat sink. So I can use the screw hole to fix it to the baseboard.

 

But I will go for the switch to reverse the rolling road method first. 

 

 

Yes, that will work with plenty of margin. At the sort of currents you'll be seeing the voltage drop per diode will be less than 0.9 volts. You could even make your own bridge for the voltmeter using cheap diodes but it's probably simpler just to use a second bridge.

 

(BTW, that data sheet has more than a few errors but I don't think that should be a problem 😀).

[flockandroll]

I was hoping to get some of this working over the long weekend, but I have discovered I failed to realise that the 9mm plywood I have used is too thick for the toggle switches to easily fix through, so it will take me even longer! 

Thank you for your help so far

[WIMorrison]

Just countersink the holes with a larger drill 9e.g. 12mm) from the underside sufficiently to allow you to get the nut on the switches.

[flockandroll]

Yes, it works!

Forwards and reverse. So starting to get there! Thank you all