DC Amperage Fluctuations?

Something to do with curves and straights? The drag is larger in curves and might cause extra amperage.

Regards

Fred

An interesting hypothesis. Did not consider that!

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

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.

THANK YOU, gentlemen!  ☺

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?

I suppose the throttle circuitry itself is drawing some current from the power supply even when set to zero?

Bottom line: the train runs smooth as the DC supply has a regulated and filtered output with very low ripple, so I guess I will have to live with the amperage fluctuations. The analog throttle has no pulse width modulation.

One of my power supplies also has an ammeter. I look at it when I see something irregular when running a train. When there is nothing irregular I look at the train and not at the ammeter; the train is much more interesting 

Regards

Fred 

Fred: Point well taken!

amperage will go up slightly on curves , and upward gradients ...

and it will go down slightly on downward gradients .. it's normal, no reason for concern ..

enjoy the train ...

THANKS, again!

Over-monitoring (my OCD?) is likely the culprit here, as the LCD screen on the power supply is right next to my office chair! I am now focused more on either my LGB 2085D or my PIKO BR 24 and their respective consists! ☺

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!  ☺

I know that the Suisse coaches, which have detailed power connections for an ELECTRIC loco, and running behind a Southwest German Eisenbahn narrow gauge dampflok (104) are incompatible, but HEY, it is MY railroad!  😁

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!

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!

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!  ☺

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! ☺

I should mention my Lab DC supply is a switching mode unit like the ones offered by both LGB and PIKO.