Power Consumption of modern locos

Modern Hornby and Bachmann motors generally consume no more than about 200mA. I did measure the current consumption for a couple of the reviews I did for the Forum as I think this is something that DCC users have more than a passing interest in as you have explained in your post.

Heljan have a reputation for using "hungrier" motors, up to an amp or so but I don't own any, so I can't confirm these figures.

For a collection of Hornby and Bachmann models, you could conservatively estimate 250mA per loco, or 4 per amp. In theory that would max out your Prodigy at 14 locos running simultaneously but would you be able to keep up with them all? Personally I wouldn't want to run at more than 75% of full capacity on a continuous basis which knocks that 14 back to about 9 or 10. Still plenty for one person to handle?

I am sure there will be other thoughts along soon.

David

Many thanks everyone for your constructive advise. I appreciate sometimes questions do seem funny to the initiated but I was looking back to the days when Hornby Dublo supplied a 1 amp transformer and the locos were drawing around 1 amp !. I have not really seen anything in print to change my mind other than common sense thinking that progress has been made in motor design since then. As I said I really have struggled to get anything from manufacturers specifications.
Its a bit like a quiz if you know the answer its easy if you don't , well its not.
As regards running locos I have been forced to build a 2 level layout in my "dining room " (now christened the train room by my grandchildren) and due to the smaller size ( previously in loft in my old house) It is quite complicated and quite a lot of auto systems are going in so I can actually run around 6 or 7 trains comfortably with some double heading to pull up the inclines.
Being a newbie to the site its nice to have some real assistance instead of sarcasm that seems to be prevalent on many sites.
Thanks again

*** Hi

I have an interactive ammeter on my DCC system and install and test may locos.

(1) it is rare for any Bachmann or Hornby loco made since can motors to draw more than 100mA when simply running with a reasonable train. Say 150mA when heavily loaded

(2) the important spec for layout use is probably slip current - in other words, what current will the loco draw when placed against a solid object and the power applied so that the wheels slip. This rarely exceeds 200mA

(3) Sound generally adds about 50mA, max 70mA.

LEDs add very little (lighting) for example a ten coach train I did recently was only just over 300mA with aound loco as well - and that was 10x 8 LED per coach + loco lights + sound decoder + loco.

Incandescent bulbs are current hogs (you can tell jsut by touching one - they get HOT!!! - avoid them - allow 50Ma per bulb - for example, that same train with only 2 bulbs per coach + 1 in the loco would have been about 1.5 amps!!

(4) There are exeptions to low current for locs
older Hornby Dublo locos unless the magnets are replaced with neodymium in which case the current will drop from 500~700mA to about 200~250mA (and will run better)
heljan which is a little higher
older models of every source (+15 years or so)
Older Athaern
loco's with open frame motors.

(5) You can calculate potential max current easily. take the wires off the motor brushes and put a meter set to ohms on each terminal. this will give you the static resistance. Use ohms law to work out current draw. Use say 10v as the calculation point for this, its rare to ever run with 100% power on a layout. This applies to DCC too by the way - the voltage is always high but its only "on" part of the time, so the same rule of thumb applies.

(6) Current draw can be managed. Keep motors clean and free of oil. Do not over oil motors ever, and never use sewing machine type oils on them as they creep - this means oil migrates to armatures, softens brushes, which means lower impedance which means high current/heat/damage to motor.

(7) If you have over oiled don't be afraid to take the motor out and literally wash it clean - probably in a gentle solvent to kill the oil, followed by an alcohol bath.

(8) It is better to NOT oil a motor if you cannot be sparing in applying it - enough for the head of a pin is enough for a motor bearing!

For layout power handling I would calculate at 5 loco's per amp, but be relaxed about it - that would allow the odd current hog or several consists plus several loco's to operate as it has lots of lattitude.

Kind regards

Richard

Very specifically regarding Heljan, the mech is a very sweet running unit with a high grade Buhler motor, that is considerably more current hungry than anything else in current OO production. Following a friend's experience of a burned out decoder in one, I measured it on a Fluke meter with an instantaneous maximum current recording capability, and that particular example peaked at 1.4A when starting light engine. A subsequent test on a second Heljan model went just over 1.3A (motor looked to be the same unit). When running, somewhere around the 0.4A mark was typical with a full size train on. Really load it up (a train much larger than the prototype would haul) a peak consumption around 0.7 - 0.8A was observed. This suggests to me that a decoder spec of 1A continuous/ 1.5A peak is the bare minimum, something closer to 1.5 A continuous / 2A peak would be better.

*** Peaks are deceptive - and not really a concern. The issue with current draw is heat generation, and a fast transient current peak will not create heat, whereas a constant high current will. In reality for current draw to get a usable spec you should be testing with slower sampling or averages, especially with a fast, high quality meter like the fluke.... For example,the momentary peak voltage during recovery / after a short at the track is far in excess of all decoders parts specifications but it is a very fast transient, so they cope.

I have done lots of Heljan... Usually either the small TCS MC series, the larger TCS T Series and of course ESU Loksound and found nothing excessive or overly concerning in current draw.... certainly they are higher than some other brands, but not over the top or concerning.

The Hornby 1/2 amp decoders and lokpilot micro/ Lenz gold mini would be very marginal, but the majority of the current ranges of Bachmann, TCS and other brands will all be fine.

Richard

QUOTE (Lancashire Fusilier @ 18 Nov 2008, 01:37) <{POST_SNAPBACK}>Conservative approach has been to look at the stall current of the motor and not the running current consumption. Maximum draw is at maximum load which is when the mototr is trying to turn but just can't. It is suggested in some texts that this can be replicated by holding a loco down firmly on the rails and measuring the current draw which on some locos H0 / 00 size can be as high as 1 amp,
This method is deprecated due to the risk of damage to some motors. Do what Richard suggests and calculate the stall current from the track voltage and motor resistance.

Stall current is used for determining the maximum current required from a decoder, rather than overall system power budget.

You can also apply "diversity", roughly meaning that the system can be sized a lot lower than the theoretical maximum requirement, since you will not normally run all locos at maximum current at the same time.

Andrew