I'm new to DCC and have many older Proto 2000 locos (Alco PAs and EMD E-8s).
Is there more than one way to test the draw and what are the limits?
Thanks, like I said, I'm new to this but have committed to converting my vast fleet over to DCC, one engine at a time.
L
will not tell you anything aboaut DCC, but the STALL amperage is what you measure when the locomotive is at full power and held in place (by brakes or by hand) with no wheel slippage.
ROAR
The Route of the Broadway Lion The Largest Subway Layout in North Dakota.
Here there be cats. LIONS with CAMERAS
The point of the test is to find out the maximum amperage the motor will draw, to compare to the maximum amperage a DCC decoder can handle. It's not all that relevant these days, because both motors and decoders are getting more efficient, and because that particular situation of a motor being completely stalled would almost never happen in real life. That's why we don't list it in our product reviews any more.
--Steven Otte, Model Railroader senior associate editorsotte@kalmbach.com
"Draw" equals the amount of current which is measured in amps. Newer locomotives with sound decoders and passenger cars equipped with lighting draw a lot of current when power is first applied. The reason for this is due to capacitors which charge up when voltage (aka: potential) is present. Once a capacitor is charged, the current draw will drop. Your limits are determined by the current rating of the power supply. When shopping for supplies you shoud always choose to overbuild, especially if you plan on adding sound to your locomotives.
Steven Otte The point of the test is to find out the maximum amperage the motor will draw, to compare to the maximum amperage a DCC decoder can handle. It's not all that relevant these days, because both motors and decoders are getting more efficient, and because that particular situation of a motor being completely stalled would almost never happen in real life. That's why we don't list it in our product reviews any more.
Thank you Steven, you are right at my point of concern.
When doing this test, I'm getting from .7 - 1.3 amp draw, wheels spinning, depending on which loco is being tested.
To totally stop the wheels while at full power can produce numbers over 2.0 to 3.0.
But I see most decoders are rated at 1.5 continuous to 2.0 stall. I just don't see how stalling a loco out has much bearing on typical operation on a lay out with little to no grade present.
My whole point of this is to determine if I'm looking at remotoring my fleet, or just installing decoders and getting on with the business at hand.
Thank you all for your feedback.
Tinindian I'm new to DCC and have many older Proto 2000 locos (Alco PAs and EMD E-8s). Is there more than one way to test the draw and what are the limits? Thanks, like I said, I'm new to this but have committed to converting my vast fleet over to DCC, one engine at a time. L
The proper way to do the test is to put a DC ampmeter in series with the motor, lock the rotation of the motor, and apply an operating voltage. The meter reading is the stall amperage.
Another way you can do it is to put an appropriate ampmeter ahead of the motor (electrically) and use that measurement LESS the various electrical losses previous to the motor. Not as accurate, but you don't have to get at the motor.
These measurements should be done very quickly, as there is a possibility of damaging the motor. Very quickly.
The reason anyone would use this test is to determine the maximum load for the motor. You can use this number to determine the largest size of power supply you will need. You can add up the numbers for multiple motors to get the size of supply for all of them.
This number is pretty much the maximum current a motor can ever draw.
As has been said, it's not a number that is used much. One reason is that, in real (model railroading) life, we never let our motors get to a locked rotor state. Or, if we do, we may be replacing the motor soon.
There is another more useful number. That would be the maximum full-load amperage. In this case, the motor still turns. It will be lower than the stalled rotor amperage.
Ed
This sounds like the question I asked in November:
http://cs.trains.com/mrr/f/744/p/266322/3011397.aspx#3011397
Mike.
My You Tube
On a model railroad, it is almost impossible to get the drive wheels to stop turning by pulling some load. Even on the steepest grade, the engine and cars might come to a complete stop, but the drive wheels will continue to spin.
With a RailPro control system, one of the first things you do after installing a decoder is do a load test. You attach a car to the rear of the locomotive and hold it from moving with your hand. Then press the test button on the handheld controller. The controller ramps the engine up to full speed with the wheels spinning and measures the current. Takes about 10 seconds. Most of my engines are in the 4-5ma range.
The decoder now has that information stored inside. On one of the pages of the handheld controller, you can see a real-time current draw as a percent of the max current from the test. The handheld controller and decoder use the max current to speed match engines in a consist, automatically! Even different brands and types of engines. ( trying to speed match 4 engines for a consist with DCC is an exercise in futility. )
Also keep in mind that the current rating on a decoder is for everything, not just the motor. Like the lights.
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The first part, about different methods, has been answered. The second, about the limits, I interpret thusly:
There are two limits:
a. the stall current of the motor: and
b. the engineered maximum amperage rating of the decoder.
If the first number is less than the second, you're good to go.
As has been explained, modern drives don't really need this kind of figuring because they draw so little amperage and can still keep spinning the wheels under the locomotive when it stalls on the rails. They aren't heavy enough; they'd have to weigh maybe 10-15 pounds.
In your case, converting older drives, you WOULD want to know if the decoders you intend to use are safe to install because your drives are less efficient and may overdrive the decoders.
Below is a link I have used for some years. I have four of those meters.
http://www.trainelectronics.com/Meter_HF/index.htm
The only decoder issue I had was the SoundTraxx Micro, 750 ma max which had a tendancy to over heat even if not near that amount of current.
Rich
If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.
Older locomotives could draw 1-2 amps when running. If you have one of these, it is best to replace the motor while you are installing the DCC.
LION is replacing the motors of him even while not adding DCC.
DCC serves no point on railroad of LION. Him runs ten trains at once and is only one LION. Him cannot run ten trains by operating trains. Him does it by operataing the railroad, and lets the little plastic people in the cabs operate the trains on their own.