Fitting ammeter/multimeter to 'rolling road'

[Fat Controller]

During my Sunday visit to Ally Pally, I purchased a 'rolling road' to enable me to test and run in my locos. One thing that very quickly became evident was that the performance of locos (even of the same type, and from the same manufacturer), varies greatly for a given setting of the controller. I was wondering how easy it would be to fit some sort of voltage/ current measuring device into the set up to enable me to check the relative power consumption of different locos? Does anyone here have any experience of such a set-up?

Thanks in anticipation.

Brian

[Brian]

Hi

As you have posted in the non DCC are I assume you're a dc (Analogue) user.

All you need is a basic multimeter. Any that reads dc volts and dc Amps should be fine.

Set it to read 20 volts dc for voltage testing and connect the two leads across the two feed wires from the controller.

Set its switch to the 10Amp dc current range - plus often moving the red test lead to the 10A socket on the meter. Connect the meter in series with one lead from the controller. I.e. Remove one lead coming from the controller on the rolling road and connect this to the red lead of the multimeter, connect the black lead of the multimeter to the terminal on the RR where you removed the wire from.

This will then read the current taken by the loco as you increase the power via the controller.

Once finished disconnect the two meter leads and after read current return the lead to the other red socket on the meter and turn the dial to Off.

Example.... http://www.maplin.co.uk/p/precision-gold-wg020-digital-multimeter-gw26d

Even cheaper from ebay....http://www.ebay.co.uk/itm/Digital-LCD-Voltmeter-Multimeter-Ammeter-Volt-OHM-AC-DC-Voltage-Circuit-Tester/351158829768?_trksid=p2047675.c100005.m1851&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D29952%26meid%3D3aa5a4db7b8d4bb88f173999bb69aef3%26pid%3D100005%26rk%3D1%26rkt%3D6%26mehot%3Dpp%26sd%3D181699898858&rt=nc

 

Edit to add ebay URL.

[Fat Controller]

Hi

As you have posted in the non DCC are I assume you're a dc (Analogue) user.

All you need is a basic multimeter. Any that reads dc volts and dc Amps should be fine.

Set it to read 20 volts dc for voltage testing and connect the two leads across the two feed wires from the controller.

Set its switch to the 10Amp dc current range - plus often moving the red test lead to the 10A socket on the meter. Connect the meter in series with one lead from the controller. I.e. Remove one lead coming from the controller on the rolling road and connect this to the red lead of the multimeter, connect the black lead of the multimeter to the terminal on the RR where you removed the wire from.

This will then read the current taken by the loco as you increase the power via the controller.

Once finished disconnect the two meter leads and after read current return the lead to the other red socket on the meter and turn the dial to Off.

Example.... http://www.maplin.co.uk/p/precision-gold-wg020-digital-multimeter-gw26d

Even cheaper from ebay....http://www.ebay.co.uk/itm/Digital-LCD-Voltmeter-Multimeter-Ammeter-Volt-OHM-AC-DC-Voltage-Circuit-Tester/351158829768?_trksid=p2047675.c100005.m1851&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D29952%26meid%3D3aa5a4db7b8d4bb88f173999bb69aef3%26pid%3D100005%26rk%3D1%26rkt%3D6%26mehot%3Dpp%26sd%3D181699898858&rt=nc

 

Edit to add ebay URL.

Thanks for that- I shall give it a try with my found-in-a-skip BT multimeter...

[Huw Griffiths]

I hope you don't mind me checking - your multimeter is digital, isn't it?

 

The reason I'm asking is that moving coil meters can be destroyed if they're overloaded, or connected the wrong way round.

 

Digital meters are less likely to be damaged in this way - to be honest, they usually seem to be pretty tough, full stop. This might explain why I still use mine - despite it being more than 30 years old.

 

(In fact, I've actually got a couple of DMMs - and a moving coil meter - and I'm sure that a lot of electrical / electronic engineers are in a similar position. It's sometimes useful to be able to take readings at a number of points on the same circuit, at the same time. It can also be useful to keep meters in different places, for different purposes - well, at least that's what I tell people ... .)

 

When it comes to taking measurements, DMMs have usually got reasonably effective overload protection - a higher current or voltage than the range will usually result in the last few digits of the display going blank - occasionally, you might also get a fuse blowing (though I've never had this happen). If you get their terminals the wrong way round, you'll just see a "minus" sign in front of the reading.

 

 

I don't know what make your meter is - though, if it had previously been used by an outfit like BT, I'd imagine it's probably a good one - Fluke, perhaps?

 

As for why it had been discarded, I'd guess that the reading accuracy might no longer be within spec (so readings might be a few percent out) - either that, or it was rather old or had been damaged in some way. Probably not an enormous problem for you - probably wouldn't be for a lot of people, as long as they don't need "lab grade" measurements - but just be aware that you might get some errors.

 

 

In case anyone's wondering, I'm not writing off moving coil meters. They certainly have their uses - but, for your purposes, I'd definitely recommend digital.

 

 

Regards,

 

Huw.

[Fat Controller]

We've had the meter for about 25 years; the person who found it was an electronic engineer, who checked it out thoroughly before passing it on. It is digital; presumably dating from the early days of such devices. These days, the main use it sees is checking battery outputs and suchlike, so not really heavy-duty work. I was just a bit wary of connecting it in series without checking for potential (sorry..) problems. If it does work as it should, then I'll look at getting a panel-mounting type, to fix permanently on the same board as the rolling road.

Thanks again for your help.

[merlinb]

 I'll look at getting a panel-mounting type, to fix permanently on the same board as the rolling road.

 

You can get some rather nice panel-mounted volt/ammeters from eBay China for next to nothing:

http://www.ebay.co.uk/itm/DC-0-100V-Voltmeter-Ammeter-10A-Red-LED-Panel-Amp-Digital-Volt-Gauge-Display-VM-/221665874438?pt=LH_DefaultDomain_3&var=&hash=item339c50d206

[chaz]

While I agree that digital meters are better protected I do prefer moving coil types for this sort of work. If there is some binding in a chassis this can often be detected and investigated by watching the current drawn changing - in my experience a digital meter will have too slow a response time to show this. Brake the wheels with a thumb and watch the current draw increase!

 

I use a bench PSU (which I bought for electronics work) to power my rolling road. This has both a voltmeter and an ammeter. Watching the ammeter with a loco running on the rolling road is very revealing; even with a very free running chassis the current level usually flutters a little.

 

 

However I must say that this would be an expensive option if you bought one just for this job.

 

Chaz

[Nile_Griffith]

So what are people recommendations if you have a DCC layout?

 

The only time I've used a DMM on a Chipped loco meant doing some fudging around with the wiring on the supply side of the DCC board. I had promised myself that one day I'd make up a jumper cable. As most of my DCC loco's use either 8 or 21 pin sockets I was going to try and make a lead set up with an NEM socket at one end and NEM plug at the other tapping of the wiring look as required for measuring the current draw.

 

Be interested to know if anyone out there has a more elegant solution.

 

Should add, that I was trying to measure the current draw of the Loco's motor and realise that by measuring across the supply to the motor itself I wouldn't get a measurement of any current draw from the loco's lighting.

[Crosland]

Remember not all DC controllers are pure DC and the readings you get with a basic multimeter could be just as misleading as you get trying to measure DCC.