Multimeter/Ammeter Question

Discussion in 'DC Control' started by Wolseley, Jan 8, 2020.

  1. Wolseley

    Wolseley Full Member

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    Now that I have things up and running, I was looking at ensuring that my locomotives perform as well as they can. In order to monitor their performance, I was looking at some sort of meter that could tell me how many amps the motor is consuming. For those of you who may not be familiar with what I run, the bulk of my stock is three rail Hornby Dublo. If in good condition, it shouldn't draw much more than 0.65amps, maybe less. If it is badly in need of a service, it might draw 1amp or marginally over, which would cause problems. Needless to say, none of the stock is fitted for DCC.

    I would imagine that a panel mounted ammeter would be sufficient for the job, although probably a hand held multimeter would be a better buy, as it could be used for other purposes as well, not that I would be looking at that for the moment.

    I was looking for advice on how to connect one of these meters up (the internet is full of advice on how to use a multimeter to test for electrical conductivity, but there isn't much about measuring current draw - I hope I used the right term). There are some Youtube videos by Ronald Dodd on the subject but, unless I missed something, he tells you everything except how to connect the meter. In other words, I have a reasonable idea as to how to use the readings from the meter, but I'm not sure how to get the readings in the first place.
     
  2. Keith M

    Keith M Staff Member Moderator

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    A panel ammeter would need to be connected in series with whatever load current you might wish to measure, but a Multimeter would be a much more versatile tool which you could use to measure voltage, current, continuity, resistance etc depending on how much you are prepared to spend on one, and these days they are a fairly inexpensive tool, in the UK a reasonable quality multimeter suitable for the use you might put it to would cost around £15-£20, most if not all will be Chinese made (what isn't these days?). As a retired Electrician, I have a digital one which has served me well since the 1980's and should 'see me out' with no difficulty. The thing you will have to be most careful with is to ensure you don't attempt to measure voltage (particularly mains voltage) with the meter switched to resistance ranges, an easy mistake to make if not concentrating, otherwise it will go 'Pop' and become dustbin material. How do I know this? Simply because I've seen a number of guys using meters and not concentrating on what they're doing.....the result does tend to concentrate the mind somewhat!:giggle::giggle::giggle:
    Regarding connecting a Multimeter, current measurement is done by connecting the meter in series with the load, voltage by connecting in Parallel (ie, across the load terminals), resistance by connecting across the item to be tested (with no voltage applied and preferably out of circuit), continuity connected across the item being tested (again with no voltage applied and out of circuit), but many meters have separate input terminals for specific tests, so refer to the instruction manual, and stick to low voltage testing until you are more confident in using the meter. Hope this helps.

    Keith.
     
  3. paul_l

    paul_l Staff Member Administrator

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    If you have a couple of banana plugs and binding posts insert these into on leg of your power feed, then make up a pair of leads to go from the posts to the meter, and another short cable to just connect between the posts. If you did this for each circuit you could easily check any line.

    Paul
     
  4. Dr Tony

    Dr Tony Full Member

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  5. paul_l

    paul_l Staff Member Administrator

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    Careful, these will need connecting before the direction switches, as they are DC meters and have no mention of reverse voltage protection.
    Also they state they can measure 0-100V DC, but quote a operating voltage of 0-30V DC, with a danger of blowing the device up if you exceed 30V - not normally a problem for model railways smaller than O gauge.

    But if connected to the DC supply voltage to the controller, will work fine. And would also be great for monitoring power supplies for accessories etc.

    Paul
     
  6. bobcom52

    bobcom52 Full Member

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    One advantage of an analogue meter vs a digital one is how easy it is to see current fluctuations that are a sign of poor pickup when running.
    cheers
    Bob
     
  7. Graeme

    Graeme Full Member

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    Connection for the different meters. RL is the motor, I is the current.
    Paul I have used these as indicators on a power supply I built from a computer PSU.
    The 0-30V is the meter power supply voltage, they can measure up to 100V and 10A.
    The red and black is for meter supply and the 3 coloured wire is for measurement connection although I think the guage of the wiring shown is a bit wrong if you look at the terminals.
    I agree with the use banana plug method and I would use an analogue meter if I ever wanted to monitor my layout voltage .
     
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  8. Graeme

    Graeme Full Member

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    This diagram may explain meter connections a bit.

    https://www.bing.com/search?q=voltm...s=n&sk=&cvid=f8c2bcf2754e4811998705ac82e5afb0

    RL= motor I= current V = Voltage Orange symbol is power supply/battery.
    A is in series Ilne must be broken to insert meter, V is in parallel no break in line required.
     
  9. paul_l

    paul_l Staff Member Administrator

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    Thanks Graeme for the clarification, I will look into these for my workbench PSU (like yourself an old PC PSU).

    Paul
     
  10. Graeme

    Graeme Full Member

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    I love the old PC PSU I am using one to run 2 chargers, for the Li Po's and NiMh's I use for the G Gauge locos, at the same time heaps of current out of the 12V output.
     
  11. Wolseley

    Wolseley Full Member

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    I bought a cheap ($9.95) multimeter from Jaycar today and, after spending ages trying to figure out what the instructions meant, I gave up and ended up viewing one of Ronald Dodds' videos on Youtube (I'm not a huge fan of Youtube, but it can be useful at times). Ronald Dodds has produced quite a lot of Youtube videos on Hornby Dublo three rail layouts and maintenance. I had a recollection of one where he measured the amps drawn by a Dublo 0-6-2T and it wasn't too hard to find:



    I tested six locomotives and the results were interesting although, predictably, the two locomotives I tested that I had pulled apart, cleaned and renewed brushes and magnets, had the lowest readings. They were:

    Dublo Thomas the overweight 0-6-2T: .29 amps (!)
    Dublo Ringfield Castle: .37 amps
    Trix Flying Scotsman: .78 amps
    Dublo Silver Link: .47 amps
    Dublo Mallard: .89 amps, peaking at 1.09 amps
    Dublo Duchess of Atholl: .54 amps.

    It's beginning to look like I have a bit of maintenance to do.....
     
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  12. paul_l

    paul_l Staff Member Administrator

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    If you're doing a full strip down, may be worth getting g a few neodymium replacement magnets to replace the originals. I need to do this for my Wrenn City of Stoke on Trent,

    Paul
     
  13. Wolseley

    Wolseley Full Member

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    I know there are mixed opinions on whether or not the original magnets, where they have become weak with age, should be replaced with neodymium replacement magnets or be remagnetised, but I have replaced some of the weaker examples in my collection with neodymium ones, with a consequent increase in smoothness and power. Of the locomotives mentioned in my earlier post, Thomas and the Castle have been cleaned, lubricated and fitted with new brushes and neodymium magnets and the Duchess of Atholl has been fitted with a neodymium magnet, but the chassis and motor need a bit of a clean (I'm not sure what state the brushes are in). Silver Link is the odd one out - it scored well, but has the original magnet and the motor and chassis are badly in need of a strip down and clean.....
     
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