PRR H10 Remotor

[victor miranda]

I spent a little time hunting in my basement/shop/laboratory this evening.

I found one of the motors that looks like the one in nscaleSPF2's photos

I turned the power supply up and ran the motor to where my meters
said 12 volts and the current draw there was 50 to 60 ma.

without touching the throttle,
I stalled the motor.

the meters read 180 ma and 9.5volts.
the motor got noticeably warmer...

my conclusion is that 200 ma is the stall current at 12 volts.

max possible power from this motor is
200ma times 12 volts --> 2400mW
my rule of thumb for motors is that half of stall power is a reasonable limit.

victor

[nscaleSPF2]

So the consensus seems to be that we are good to proceed with the build.

I am still trying to make a little more sense out of the data that I recorded a couple of days ago:

I put the loco on the track and powered the decoder with dc.  I measured the loco by itself, and with it pulling 20 cars on level track.

LOCO ON TRACK, WITH DECODER                        
                        
      LOCO ONLY           LOCO + 20 CARS   
Volt      mA      mph      mA      mph
5      86                      94      
6      104                    106      
7      113                    120      
8      119                    132      
9      124                    139      
10      130                    142      
11      132                    145      
12      137                    151      
13      140      46.8      151      36.4

It occurred to me that the current measured includes the current that flows thru the decoder.  I don't know how much that is.  Neither did the technician I asked at TCS.  No one had ever asked them that question before.  I suppose that I could measure how much current the decoder draws, by disconnecting the motor and applying dc to the decoder.  Are there any decoder experts out there who would care to offer an opinion, or better, data?

Next step is to re-gage the new drivers that I just installed.  Should have measured them before they were installed.  Silly me.  Two steps forward, one step back.  Man, this build seems to be taking forever.

[peteski]

It occurred to me that the current measured includes the current that flows thru the decoder.  I don't know how much that is.  Neither did the technician I asked at TCS.  No one had ever asked them that question before.  I suppose that I could measure how much current the decoder draws, by disconnecting the motor and applying dc to the decoder.  Are there any decoder experts out there who would care to offer an opinion, or better, data?

The additional (10-15mA) current while DCC decoder is in the circuit seems reasonable for what a DCC decoder circuitry would draw (with the function outputs off).  I'm surprised that the manufacturer's support personnel would not know this type of info. 

[nscaleSPF2]

Thanks for the info, Pete.  I won't need to desolder the motor lead, at this point.

[victor miranda]

The additional (10-15mA) current while DCC decoder is in the circuit seems reasonable for what a DCC decoder circuitry would draw (with the function outputs off).  I'm surprised that the manufacturer's support personnel would not know this type of info. 

Hi nscaleSPF2,
I am quoting peteski because I both think the miliamps for the decoder is in the ballpark
and it needs a little more information.

If you had asked me how much power the decoder uses I'd have said about 100mW.
or about 20ma and 5 volts.
this is chainsaw carpentry, it leaves some to be desired....

If you run your loco with the decoder the first 4 to 5 volts and 10 to 20 ma will 'light' the decoder
then the decoder will attempt to spin the motor.

you can subtract the power in mW.
for what you are doing it may be the better way to keep an eye on the motor.
use mili-Watts.

victor

[nscaleSPF2]

Hi Victor,

At 3V, current drawn by decoder + motor = 60ma.  Speed = 0.
At 4V, current drawn by decoder + motor = 70ma.  Speed = 0.

Had difficulty getting consistent readings at less than 3V.

So much for the chainsaw science.
I have to get back to installing some air lines.

Regards

[victor miranda]

the numbers are good.

It is a little hard to guess how hard the decoder is trying to move the motor.
the lower end at 3 volts is a good set to use.
we are guessing here because we do not want to desolder to put test meters in the circuit.

at 3 volts the decoder begins to operate AND tries to spin the motor.

that is 60 miliamps  times 3 volts  --> 180 mW

it is possible that the decoder is using all of that power and is sending none to the motor.
and on the other extreme: the motor's static resistance is 50 ohms
at 3 volts divided by 50 ohms --> 60 miliamps
This does imply the decoder is using no power.

Off we go. on to another possibility.
from the free motor part earlier...
you wrote this

MOTOR ONLY, ON BENCH, NO LOAD
V, dc      mA
...
3.7      34
...

my thinking is that  at 4 ish volts
you know the motor can absorb about 34 miliamps.
this is within reason.
34ma * 3.7v --> 125 mW

180 minus 125 is 55...
that leaves 55 mW to run the decoder.

so we have a number to subtract from the overall power.

I suspect that figure is on the low side.
in that we do not know how much of the 180mw the decoder is sending to the motor.

from my tinkering with PIC processors, they can run at 3 volts
and I do not remember specific power consumption figures.
the way one uses pheripherials has a lot of affect on the number.

so, your choice, subtract 50 to 180 mW for power to the decoder.

I'd use 100mw 'cause it is easy to calculate.

edited to change an ma to a mW.
context makes it pretty clear and I decided to change it anyway

[nscaleSPF2]

OK, Victor.  I think I understand what you are saying.  The numbers seem to say that we are good to go with this combination of motor/decoder/chassis.

But the real test is keeping the the maximum motor temperature below a certain threshold, is it not?  The armature windings need to say below the temperature that will melt the insulation, no?

Any idea what this temperature is?  And how to measure it?  Maybe an infrared thermometer?  There are several of these for less than $20, but I don't know if they would work.

Pardon me if I seem a little anal here, but I'm just curious.

[peteski]

Measuring the motor armature with an IR non-contact thermometer: you are taking modeling to the next level here!   

The non-contact thermometers work quite well but they sense the average temperature in their cone of measurement - you will have to get very close to the armature to accurately measure its temperature.

[victor miranda]

!!!
things I did not expect....

Hi nscaleSPF2,
the commercial motor I have met _LOOK_ like they are insulated
with high temp coatings. it is the color of gold kapton tape.
that stuff is supposed to hold up to 450 degrees
(assuming my memory from slotcar wrapping and wire specifications is accurate)
I think the nylon insulation is good to 250. I know no easy way to tell the difference.
I would state if you are driving the motor to 250 degrees you are overrunning it.
If you can't keep a finger on it, you are too hot.

at this point I can only share what I do.
I run the loco by itself at 8 volts for a minute at what ever speed it does.
and I set a finger on it. If it heats up enough to make me uncomfortable...
something has to change. motor, gears, bearing alignments, anything.

If the motor is only warm then I assume all is good and run it
and check it every ten minutes for a half hour.
it should level off to a friendly warm.

what you want to avoid is what ever heats the motor quickly.
heavy loads and high voltage will get heat fast.

use your finger tip as your temperature sensor.

my opinion about your motor/chassis/decoder combo...
you are at about the limit of the motor's power output.
12 volts and 20 cars is likely to over heat the motor.
the 8 volts 132ma and 20 cars is about all the numbers state you should do.
if you use the finger test, you will get a sense of the limits fairly easily.

If you run the loco for a few hours, it may loosen up and your current draw numbers will drop.
or install a bigger motor and run the chassis for a week straight to loosen it.

victor
 

[SkipGear]

The color and texture of the material being measured also has a large effect on the measurements, especially with the cheaper units. I have one that I use for RC racing that can be calibrated to compensate for this.

[peteski]

the commercial motor I have met _LOOK_ like they are insulated
with high temp coatings. it is the color of gold kapton tape.
that stuff is supposed to hold up to 450 degrees
(assuming my memory from slotcar wrapping and wire specifications is accurate)
I think the nylon insulation is good to 250. I know no easy way to tell the difference.

In my experience all the enameled magnet wire I have dealt with (from back in the 70s winding transformers and chokes while attending telecommunication school in Poland to dealing with N scale motors and also using it for hooking up SMD LEDs) was not coated Kapton or Nylon. the insulation can easily withstand couple of hundred degrees Celsius (quite a bit more than 200 F).  Good insight of what the "enamel" is made of is here

[victor miranda]

color of gold kapton tape....

and one of the possible coatings is polyamide

which is the magic ingredients in kapton tape...

and thanks for the wiki link.

[nscaleSPF2]

OK, Verne, it's time for another public service announcement, so brace yourself.

Do you remember, Verne, when I told you that the pilot wheels didn't look right?  I didn't think so.  So I took a picture:



What problem can this possibly cause, you say?  Well, there is no problem when the engine is on a straight track.  But don't you remember, Verne, when she was going thru the Waynesboro tunnel?  The front outside driver was trying to climb the outside rail, while the inside pilot wheel was gently rubbing the cylinder and trying to lift the inside.  Presto, derail.  Every time.

Verne gives himself a dope slap.

Now take the part on the left back to the shop, Verne, and make it about .03in longer.



Verne returns, several days later, with this:



Now, I can think of 3 or 4 simpler ways to do the same thing, but what can you do?  Feel sorry for Verne, he's only an engineer.  At least the end result looks a lot better:



Ok, Verne, now go grab a cold one while I try to get some temperature measurements.

[Chris333]

I'm pretty sure I just moved the pilot back on mine, but it was long ago. Knowwhatimean?