My power setup: a lab quality DC switching mode power supply rated at 0-30 volts and 0-3 amps. This powers a PIKO 5 amp analog throttle, which in turn is securely connected via a 14 gauge power cable to a small oval of LGB R2 radius track. The DC supply has an LCD screen which reads out volts and amps. The voltage output is finely set at a constant 22 volts feeding into the analog throttle. With the PIKO analog throttle at zero, the amp display on the power supply reads 0.13 amps. When my train headed by a new BR 24 analog loco pulling three PIKO two-axle beer reefers plus an LGB 3019 postal/baggage van is energized, the train accelerates smoothly to running speed. The DC amperage display then fluctuates between 0.71 and 0.85 amps as the train negotiates the oval, the difference being as much as 0.14 amps, yet the train runs smoothly. The brass LGB track is clean and this is an indoor layout. My question is why the fluctuation in amperage of 0.14 amps? What am I missing here? Explanations welcome!

vita sine litteris mors est  (Seneca)

Original Post

Agreed, that it has to be the increased load when negotiating curves. When the load is increased on a DC Permag motor the motor slows, which reduces the counter-EMF in the armature windings, which in turn allows a higher current flow, which increases motor torque to offset the increased load.

When I took a DC motor lab course dinosaurs still roamed the Earth and we didn't have permanent-magnet motors.  A shunt-field motor does simulate a Permag motor in this regard and I remember demonstrating the above speed regulation principle.

Lew

Lew

 

Operator of the Plywood Empire Route in the Beautiful Berkshires

Growing old is so much more fun than the only alternative.

Sounds reasonable, especially since there is only a single 12" straight between each quarter section of the track circle. The fluctuation sometimes is as great as 0.19 amps. Also, the six drive wheels on my BR 24 are about 1 3/4" in diameter, which might add to the increased friction on the curves.

vita sine litteris mors est  (Seneca)

I’m surprised at the amperage draw when the throttle is set at zero. That’s a pretty high percent of the current draw when the train is running. Is the throttle circuitry drawing that much current by itself, or are there incandescent pilot lights that are on even if the throttle is not?

Bill in FtL

There is a power monitor green LED on the analog throttle that remains lit while the 22 volts is fed in from the power supply. Whenever the throttle handle is moved, there is also a yellow LED that indicates the relative voltage being applied to the track. I guess the green pilot LED could account for the static 0.13 amp reading?

vita sine litteris mors est  (Seneca)

I currently have two beautiful 26" LGB RhB 2nd Class beige/green coaches with factory lighting and metal wheelsets behind my equally beautiful 2085D mallet, with its pleasing valve gear motion on two sets of drivers, and it smokes well - a true visual delight!  ☺

vita sine litteris mors est  (Seneca)

One consolation is that the prototype for the LGB 2085D actually resides in the Blonay-Chamby museum in Laussane, Switzerland as a static display. This is their oldest operating railroad museum with several restored steam engines plus rolling stock. Worth a visit if you are ever in Der Schweiz!

vita sine litteris mors est  (Seneca)

Regarding your original question, I agree with everything that's been posted.  With a 12V motor of the same torque capacity, the increase in current draw would be even greater.  O scale manufacturers, in their slavish devotion to outdated NMRA standards, are throwing away the better performance that's potentially available by using 24V motors and power supplies.  Of course most folks use some type of command control, so maybe it's a moot point.

You could test our collective hypothesis by switching to wider curves.  I guess that adding more cars to the train would tend to even out the current draw.  Running the loco "light" without a consist would cause average current draw to decrease, but I would guess that the variation as a PERCENT would increase, since the added friction from the loco's rigid wheelbase (flanges, and rubber tire, if your loco has one) would be noticeable as it abruptly transitions from the tangent to a circular curve.  Good topic!

Creep, coast, and pull.  We're not talking about cold fusion here.

Based on the original descritpion   I wonder about a 3 amp power supply supporting a 5 amp capable throttle.    It seems like that may create a possibility that the throttle could overload the power supply.    I guess if the power supply has its own breaker it is protected.

prrjim posted:

Based on the original descritpion   I wonder about a 3 amp power supply supporting a 5 amp capable throttle.    It seems like that may create a possibility that the throttle could overload the power supply.    I guess if the power supply has its own breaker it is protected.

No, that is not what is happening. The throttle capacity has nothing to do with the load. The load comes from the motor and any lighted cars on the track. Even though the throttle is rated at 5 amps, it will never draw more than the supply is capable and will not in itself create an overload. An overload would be caused only by too large of a “load” or a short circuit.

George

BOTH my PIKO BR 24 (2019) and my older LGB 2085D DO have 24 volt, seven-pole motors. Current draw with my four lights, smoke unit and two motors on the 2085D plus those two heavy, and factory-lighted 26" coaches with metal wheelsets is ONLY 1.18 amps. I would likely never even reach 2 amps with the equipment I run, including my 2015D with a motorized tender. The PIKO 5 amp Farreglar throttle will NEVER see even 2 amps. Furthermore, the auto cooling fan on my 3 amp supply has NEVER come on, and the unit is cool to the touch. NO overloads here!  ☺

vita sine litteris mors est  (Seneca)

Oh, and for the record, the 5 amp PIKO throttle does have a circuit breaker. The 3 amp supply as well. I am very pleased with the "marriage" between my lab quality DC supply and the PIKO throttle, which has NO PWM (confirmed by PIKO technician). Both units are also plugged into a high quality Monster surge protector. ALL my electronics are surge protected, including my Samsung home theater system with a vacuum tube sound bar, protected by a large capacity Monster home theater unit. You can NEVER be too careful. My MTH Z-4000 AC power supply is also plugged into the Monster unit. Some folks may consider it "overkill", but ALL my HDMI and optical sound cables are high-end Monster products! Works for me! ☺

vita sine litteris mors est  (Seneca)

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