I have an Atlas C-424 Phase 3 locomotive operating on a DC system. I want to make sure I'm not overloading the locomotive. What is the maximum current I can draw before I expect damage? The motor/flywheel assembly is Atlas part #920100
I am not an expert in this, but I believe the manufacturers of the various HO scale decoders design them so that they take just over 2 amps continuous power. Presumably, that is what the can motors can stand, and I would guess the older, less efficient open framed motors could draw more, up to three and a bit amps.
That's current. As for voltage, the typical DCC system limits voltage output near 15 volts. I don't know what your typical DC system does in that respect, but it should state the maximum output on a description panel on the side of the cover.
-Crandell
Most locomotives with metal wheels will spin their drivers before the motor overloads, but it's always a good idea to check.
If your locomotive has a traction tire, or has been treated with Bullfrog Snot, all bets are off.
Chuck (Modeling Central Japan in September, 1964.)
Take your multimeter and set it to measure DC currnet. Use the 10 amp scale and set power pack at 12 volts DC. I expect you will see less than 1 amp, probably around 0.5 amp. Many decoders for HO size are rated for 1 amp.
Hold the loco so the drivers are slipping. That is what I do with my HO scale locos to measure 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.
DutchEngineerWhat is the maximum current I can draw before I expect damage?
Are you asking this because of a concern in DC operation, or are you asking to help determine which DCC decoder to install? As already mentioned above, most if not all model locomotives will slip their wheels before the motor gets to the point where the current is great enough to cause any damage to the motor. This assumes of course that you have not done any modifications that would limit the wheels ability to slip, such as adding additional weight.
On the other hand, if you are trying to determine what the maximum current draw would be so that you can pick an appropriate DCC decoder, most of the recommendations I've seen suggest that you need to determine the stall current. To do this you need the same meter arrangement that you'd use to determine slipping current, except that you would hold the engine down on the track with enough force to keep the wheels from slipping. This would tell you the maximum current the engine would draw if there were a problem in operation. For example, should the gears lock up and stall the motor.
By the way, if you do check for stall current, you want to only apply the force to the engine momentarily, as in just long enough to get your reading.
I just tried my new HO scale Atlas GP40 with QSI sound decoder on board and I see 0.310 amps at twelve volts DC with drivers slipping. The decoder is a dual more decoder.
The motor will only draw what it requires, and unless you've added a significant amount of weight and/or traction tires, that loco will slip its wheels when the resistance of the trailing cars exceeds its pulling power.
Wayne
DutchEngineerI have an Atlas C-424 Phase 3 locomotive operating on a DC system. I want to make sure I'm not overloading the locomotive. What is the maximum current I can draw before I expect damage? The motor/flywheel assembly is Atlas part #920100
Since you have a modern can motor, you should see 0.5 amps or less when the wheels start slipping. More than 0.5 amps continuous, and the motor is likely to get very hot. When the motor gets too hot, it begins to break down permanent damage. Having the wheels slip before max continuous current is reached is a "safety" valve.
The second key is how much current the locomotive is drawing in normal operation (10 car train on level track for example). This should be 0.3 amps or less. More indicates there is excessive friction somewhere with an unlikely possibility of weakened magnets as another cause.
You might ask Atlas what the maximum continuous current rating for the particular motor is - what I gave you are generic guidelines.
Fred W
My Atlas GO40 uses motor/flywheel 891100 which is probably a little smaller than the one you have but I would expect no more than 0.5 amps as mine uses under that for the motor, decoder power and lights with drivers slipping.
Again, drag out your multimeter and you will find exactly what your loco uses for current.
I am pulling up to eight railcars of varying weights and drag. I have a short incline in my layout (3% slope, 1.5 inch rise) and the locomotive doesn't seem to have any trouble with it. I want to add an ammeter to the dc circuit to monitor the loading to see if I can add railcars without problems. The trouble is that I don't know what the maximum current is. Based on the the posts here is seems that 500mA is a good 'rule of thumb' but I'd rather not find out the hard way.
Thanks for responding so quickly to my post
DutchEngineerI am pulling up to eight railcars of varying weights and drag. I have a short incline in my layout (3% slope, 1.5 inch rise) and the locomotive doesn't seem to have any trouble with it. I want to add an ammeter to the dc circuit to monitor the loading to see if I can add railcars without problems. The trouble is that I don't know what the maximum current is. Based on the the posts here is seems that 500mA is a good 'rule of thumb' but I'd rather not find out the hard way. Thanks for responding so quickly to my post
Ok, I will try to answer again. I used twelve volts DC and put my hand in front of the loco so it could not move.
The wheels were slipping and the current was about 0.310 amps. That is quite a few cars. No problem.
Probably the current would be a little higher if I held the wheels but I see no need to do that.
I have some Spectrum locos that I used the stopped condition and nothing higher than 0.630 amps.
I have a new Walther's H12-44 diesel that is not DCC ready with the old horn hooks and it draws about 0.700 amps which I would expect with an older generation diesel. It does have a can motor. I have yet to open the gear towers and check for old grease.
I can't comment with regards to DCC-equipped locos, but for a DC-powered loco, the current draw under wheelslip conditions is unimportant. As you add cars to the train, the loco should require more and more current. As soon as the wheels begin to slip, the current draw should drop down to next to nothing - almost similar to what it would be if the loco were up on blocks, with the wheels turning freely. For a reasonably well maintained loco with a can motor and no obvious mechanical binds, simply run the loco and train up the hill, then add a car or two, repeating as necessary until you reach a point where the wheels begin to slip. Remove a car at a time until the loco will go up the hill without slipping. Make a note of the number of cars, then select the same number of different cars, and see if the loco can take them up the grade without slipping. If you can repeat this, trouble-free, with three or four different trains, you'll then know what the maximum number of cars you should be able to move up that particular grade with that particular locomotive. If any of your three or four test trains won't make it with the designated number of cars, remove cars, one-at-a-time, until it will. This total number of cars should then become the maximum number which that particular loco can move up that particular grade.
Like the prototypes we model, you can throw around figures 'til you're blue in the face, but the real test is in the doing. I test all of my locos, singly and in combinations, to determine which of them and in what possible combinations are best suited to move any train over any part of the layout. If you're not testing the rolling resistance of your freight cars, and/or don't know the precise effect of grades or curves or grades combined with curves on train dynamics, and quantifying the results, then knowing the motor's capacity is not especially useful.
Have some fun. Run some trains. Gain some first-hand knowledge.
You will not overload the engine unless you have found a way to stall it, that is to stop the wheels from turning while applying power. As long as the wheels can slip it will be fine.
A mechanical problem like a broken or jammed gear or anything that keeps the wheels from slipping is a different story.
Dave
Lackawanna Route of the Phoebe Snow
Current drawn by an electric motor is proportional to load. An engine running on the flat with no cars coupled to it will draw perhaps a few tenths of an amp. As the load increases, the motor will draw more and more current. As the motor draws more current it runs hotter. Heat is generated proportional to the square of the current times the resistance of the armature. When the motor gets too hot either the insulation fails or the solder holding the windings to the commutator melts and the motor is toast.
To check for over heating, lay the back of a finger on the motor case. If you can keep the back of the finger on the motor for the count of ten, it's not too hot.
Should a motor be prevented from rotating, current flow can get so high as to damage it. Locomotives should be and nearly all HO locomotives are) designed so the the drivers will slip if the locomotive is prevented from moving to prevent this.
Older open frame motors for HO could draw as much as an amp or even an amp and a half with drivers slipping. The newer can motors seldom draw more then 0.5 amps, drivers slipping. The can motors have a stronger permanent magnetic field and so require much less current. Torque in electric motors is proportional to the product of armature ampere-turns and magnetic field strength.
That's the long answer. Short answer, if a can motor, 0.5 amps. Open frame motor 1 to 1.5 amps.
David Starr www.newsnorthwoods.blogspot.com
Thank you to everyone for your responses. I will post my findings when I get a chance to try it.
Hi,
I tried to find out the same info, here is my post, you might find it interesting: http://cs.trains.com/trccs/forums/p/168555/1851260.aspx#1851260 .
Hope it helps
Frank
"If you need a helping hand, you'll find one at the end of your arm."
The following are my current measurements. I took them with 10VDC applied to the tracks. Thanks again for your replies to my question.
Locomotive unloaded with 8 railcars (approx 25 oz)
Straight 130mA 165mA
18" curve 140mA 175mA
Up 3% incline 155mA 185mA
Down 3% incline 125mA 130mA
Stopped, wheels spinning 230mA
Stalled 460mA