Not being very good at electrickery,how do I measure the amps a loco draws?
I ask because I want to be sure I get decoders rated for such as a Minitrix 9F and Flying Scotsman.
Allan
Brian Lambert's website shows how to do a stall current test.
http://www.brian-lambert.co.uk/DCC.htm#STALL%20CURRENT%20TEST (http://www.brian-lambert.co.uk/DCC.htm#STALL%20CURRENT%20TEST)
Not being good at electrickery myself I asked where the dials etc. on my multimeter had to be pointed. I was told, "You need the dial switch pointing to 10A and the leads , one in the common and the other in the 10A socket as most motors stall at half an amp on n gauge and 1 Amp on 00"
Murk Gurries suggests that the slip current is more important these days because of advances in decoder design.
https://sites.google.com/site/markgurries/home/decoders/decoder-motor-ratings (https://sites.google.com/site/markgurries/home/decoders/decoder-motor-ratings)
Of course Allan needs to know the current draw before fitting decoders the excellent links Poliss has posted will help tremendously.
If you have a NCE powercab you can set the handset (cab) to display the amp draw when using locos on DCC see here at the base of P59 of the manual (show track current)
http://www.ncedcc.com/images/stories/manuals/power_cab_manual_v1.28.pdf (http://www.ncedcc.com/images/stories/manuals/power_cab_manual_v1.28.pdf)
If you do any programming on the main you will need to reset the display to show the track current.
Hi Upnick,
I've got an NCE Powercab and I've added the Smart Booster to it which means the amp draw is no longer able to be displayed,only the clock.
I've got a multimeter thingy so I'll have a look at the links Poliss posted.
Allan
Quote from: Bikeracer on February 06, 2012, 06:55:54 AM
Hi Upnick,
I've got an NCE Powercab and I've added the Smart Booster to it which means the amp draw is no longer able to be displayed,only the clock.
I've got a multimeter thingy so I'll have a look at the links Poliss posted.
Allan
Hi Allan i didnt know you already where on DCC .. yes i have the Procab as well from NCE & that doesnt display track current either.
Pity really because the track current is more useful than the clock IMO.
Allan
Quote from: Bikeracer on February 06, 2012, 07:34:31 AM
Pity really because the track current is more useful than the clock IMO.
Allan
Yes i agree maybe you should mail NCE & ask if it become part of their systems.
You won't be able to measure the track current on DCC with a normal meter, as the AC setting is designed for a normal waveform at mains frequency and the DCC signal will just confuse it. Best to measure the current with the loco on DC or measure the resistance across the motor contacts (or just between the wheels either side if no decoder is fitted) and work out the maximum current from that (divide 15 volts by the resistance in ohms and multiply the result by 1000 for milliamps).
Quote from: edwin_m on February 06, 2012, 09:01:08 AM
Best to measure the current with the loco on DC or measure the resistance across the motor contacts (or just between the wheels either side if no decoder is fitted) and work out the maximum current from that (divide 15 volts by the resistance in ohms and multiply the result by 1000 for milliamps).
This is not a good way of finding out the current a motor draws. The motor experiences a much greater effective resistance when running, or a much lower voltage as the armature generates its own opposing voltage when turning (i.e. it acts like a generator). This 'back emf' cuts down the net voltage and hence the actual current drawn.
Take this example:
Farish 5 pole armature has coils that generally measure around 15 Ohms in resistance. For a 12V DC supply this then equates to a current draw of 800mA (0.8A). Measuring the same motor actually running and it draws maximum 125 mA. At no point through any of the speed range does it ever come anywhere near 800mA.
As such direct measurement of the drawn current is the way to go.
Cheers,
Alan
Alan
Beat me to it. The calculated current is the stall current.
For DCC, there is a simple way to tell, as long as your unit uses an external power supply that is a similar voltage to the track (C12-18V) and DC.
If you measure the current on this when there are no locos (or even better reset to 0A) then this can be subtracted from any future measurements, to give an indication of loco draw.
You do have a DC controller to test the stall current of your locos before you fit decoders Allan?
If you avoid basic decoders, such as the Hornby R8249, and go for decoders with a 2 amp peak then they should be powerful enough to run any N scale locos.
Quote from: poliss on February 06, 2012, 02:25:47 PM
You do have a DC controller to test the stall current of your locos before you fit decoders Allan?
If you avoid basic decoders, such as the Hornby R8249, and go for decoders with a 2 amp peak then they should be powerful enough to run any N scale locos.
I've got the basic Bachmann DC controller that came with a starter set.
I'll see what these Minitrix locos stall at and see what decoders to get,I got a small TCS Z2 which was going in a Jinty,but it's only rated at 1 amp which is why I wanted to know how to measure track power,I want to use it but I don't want to let the smoke out.
I've got a spare Bachmann six pin decoder which I'm considering wiring in to try if the Z2 can't be used,but of course I'll have to check what it's rated for first.
All this will be academic if the Minitrix locos draw less than 1 amp stalled
Never having done this before I suppose I could end up letting the smoke out of both locos and decoders. ;D
Allan
The small TCS Z2 decoder seems to work fine,it's rated at 2 amp peak current.
Checked the stall current on DC and it was around 0.6 amps but it was a bit of an inconclusive reading the way I did it using a multi meter,really needed three hands.
Anyway I've set the loco up and used my NCE Powercab without the booster and the current draw is about 0.4 amps on average,maybe the old 3 pole motors draw more current ? I also get the impression that the motor is not as smooth as the current day motors,I'll know better after I've settled down to running it.
Next is a 9F to chip and then a Minitrix Hall class.The Flying Scotsman took most of the day to do,but it was my first attempt and a lot of pondering happened before I made each move,the next conversion should be a bit quicker I think.
I lost a good two hours making a puller to get the tender wheels off so I could clean and adjust the wipers,the puller was a complete disaster and was made wrong,but I did end up cutting a slot in the end of a six inch rule,held the rule in the vice,slide the wheel over the slot and tapped the axle through using an old scriber with the point ground off.
Allan