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Senior Dish Washer
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Discussion Starter #1
Last year I had a 14.8 volt battery in my Aristo Craft Dash 9.

It didn't have the power needed to pull a string of grain hoppers up the highline.

When I say it didn't have the power, i mean it just stalled out.

If it had enough power but the load was too great, it should have spun the wheels, but it didn't.

This year I brought a 18.5 volt battery and while I only pulled 4 USAT streamline passenger coaches, it didn't seem to have the increased speed I felt the 18.5 vold battery should have provided.

Before I changed to battery I was powering the Dash 9 with a MRC Power G transformer putting out 22 volts DC.

With the Power G the Dash 9 ran faster and to me had more power to haul a bigger load.

With 4 motors powering the two trucks in the Dash 9, maybe I should have bought a 22 volt battery.

With both purchases, I was told the battery would provide plenty of speed which might be true as far as scale speed, but I don't think either provides enough power to pull greater loads.

Am I wrong, doesn't more volts means greater power, not just greater speed?

Maybe I've over looked an available chart, but we really need a chart that gives specific battery voltage required for specific locos.

It needs to specify the speed and loading the specific voltage will provide per the number of motors the loco has.

Also, I'm wondering if my problem might be a dead motor. How can I tell if one motor in one of the trucks is either dead or not running as it should?

If the truck was dead all together, I assume the Dash 9 would not run at all as the bad truck would not free wheel.

Any ideas?
 

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Super Modulator
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Given enough "capacity" (the ability to deliver amperage) the voltage should not drop under load.

Thus the higher voltage should result in higher speeds.

One thing to remember is the last few volts to a motor make the largest difference in speed.

An example, on my layout, 20 volts to the rails only ran my E8 at 62 smph... now I run 23.8 volts and get 95 smph... notice 50% faster for only a slight increase in voltage.

Conversely, "losing" a few volts will markedly affect top speed.

If there is anything in your installation causing excessive voltage drop this could be an issue.

All of that aside, you should measure your scale miles per hour, you might be surprised how fast you are actually going.

The 3 axle Aristo trucks are not really speed demons, but I'd have mine set up so they could hit 75 smph...

To debug a dead motor, you would have to get into the electrics and power each one individually and check current draw under load.

Yes, if the entire truck was dead, you would know right off.

Greg
 

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Randy I agree with the free wheeling line ..One dead motor should be dragging around one limp leg...ha

Think of an air compressor and air tank here for a moment...

They have air pressure and a tank size... volume & psi
volume = battery capacity
air pressure = voltage

increasing either one will increase your useful tool run time, hence increasing battery cap ( in amp hours ) or increasing the voltage will increase the run time. the duration & the pressure to be applied to the motors..
to me each company's motors are different, and counting motors alone does not give a complete picture. so it is really up to each motor group.

I would ask what volt range your decoder system can transfer to the motors? Can you test and read the voltages at the batteries while under some load? Can you then read the voltage at the motors to see what they actually get!??

And check each motor anyway just to be sure, do the wheels turn all of 'em...! what voltage or current applies to each motor...

Time spent getting to know your loco would reveal a lot.

Dirk - DMS Ry.
 

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Super Modulator
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Since both motors are physically connected, it's VERY possible that having a dead motor would just make the pulling power less... maybe only slightly...

And it would double the load on the working motor, it would probably be very warm to the touch, and the other stone cold.... something you could try... but under load...

run it hard for a while, like running on a test track against a backstop with the wheels slipping...

Greg
 

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Discussion Starter #5
ok, so more voltage will increase run time and speed but what about pulling power?

If a train can pull a max 20 cars with 18.5 volt, will it pull more cars with 22 volts

By the way, I'm using a revolution decoder.
 

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Randy,
I had no trouble pulling 48 coal cars or 110 feet of intermodal with 3 Gp38s all on 14.8 volts....around curves and up and down hills....using Airwire. Each engine had it's own Rx and battery. Seems to me that 18V ought to be more than enough.
Yes...you can pull more weight with 22V than with 20V.
 

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Super Modulator
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More voltage will increase speed.

More amp hours will increase run time GIVEN same speed.

"If a train can pull a max 20 cars with 18.5 volt, will it pull more cars with 22 volts "

Sorry, that cannot be answered on it's own very well, but if the wheels are not slipping, and the amp hours of the 2 packs being compared are the same, then it's a qualified "yes"...

POWER in watts is basically a combination of amps AND volts.... WATTS / POWER is what moves a train.

Speed, given enough power, is solely dependent on VOLTAGE... given enough power...

Sorry for the complicated answers, but I'm giving you the correct answers...

Regards, Greg
 

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Just curious here... seems like You are referring to Marty's layout. What are the grades on the Hi-line..?

I know of dash-9's pulling long trains without difficulty....
I know of My own SD70 pulling 70 intermodal cars on grades of 2.5 - 2.8 percent , and very long! I run a 18 volt pack / 4.5 amp hour. ( I have not a clue as to the scale speed tho )

It just seems there may be some other issues here,... in between the lines....


Dirk
 

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Increasing voltage does not increase run time, in theory perhaps it should but in the real world of trains and electric motors NOT! Higher voltage can deliver like power at lower current levels, but the required power to drive a fixed load to a named speed is unchanged in either circumstance. Our trains generally do not represent fixed loads. Motors are complicated, since magnetic fields are proportional to the current being absorbed.

There is no free lunch; all things equal the most basic method of increasing run time is with higher capacity batteries.

Speed is proportional to the power available, i.e., if it can be sustained under load.


Calculating power using current and voltage:
There are three ways of writing an equation for power, current and voltage:
Power = Current × Voltage so P = I × V
or
I =
P
V
or
V =
P
I


where:
P = power in watts (W)
V = voltage in volts (V)
I = current in amps (A)
or:
P = power in milliwatts (mW)
V = voltage in volts (V)
I = current in milliamps (mA)

Calculating power using resistance and current or voltage Using Ohm's Law V = I × R we can convert P = I × V to:

P = I² × R
or
P = V² / R
where:
P = power in watts (W)
I = current in amps (A)
R = resistance in ohms ( )
V = voltage in volts (V)
 

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Sorry
but the amp hour capacity of the battery won't make a difference in the answer to "will it pull more at 22V" The ability to deliver/use the watts is a function of what the train will draw in amps. So if the cicuit hasn't changed then yes 22 will allow it to pull more. It ought to be safe to assume that the packs have a wire size that's useful and not some theoreticle size like 30 gauge. And yes I'll conceed the wheel slip issue, and leaves, rain,snow, sleet, burned out motors, frozen wheelsetc.
 

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I agree with Dirk. Something is missing. I believe the grain hoppers like the USA long tank car can get heavy. But... as I said I could pull 110 feet of intermodal with 3 Gp38s all on 14.4V up hills with 180degree curves with no trouble. 2 -9s ought to do the same.
 

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I don't disagree with the laws of 'tricity here, but again - like a air tank - if it runs well on a thresh hold of 16 volts, then the buffer above that voltage will make a loco run longer. If you use a 18 volt pack a 2 volt buffer would be present, but if a 22 volt buffer was used, then there would be a longer period of time of use before that will drop down to the 16 volt thresh hold before you have a less active loco...

I realize this is a function of the amp hour capacity, but still holds true in use....

Dirk
 

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Larry - 110 feet of Inter-modal is about 48 cars!! for a better idea here..

I would think a Dash-9 should be able to do the work of 2 GP-38's , not 2 for 2 ...

My SD70 can do about the same amount of work of 2 GP-30 locos in the same setting...

Dirk
 

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Voltage depression under load is a BIG problem, more likely than not the issue here is related to same.

There is concern in my experience to more closely monitor your batteries when they are constructed of series-parallel construction. When, not if a single cell fails or drops out, the voltage appears to be normal, however under load it falls off. Accordingly the batteries combined mAh capacity is reduced by any single failed cells capacity. For instance an 18.5V, 5600mAh battery is comprised of ten 2800mAh capacity cells wired in 5S2P configuration, half the 5600 mAh batteries capacity is availble when a single cell is weak and or defective. That said batteries with a single series cell configuration (no cells in parallel) suffer from the same problem, BUT it’s more readily realized IMO. Remember a battery is only as good as the weakest cell; a weak and or defective single cell will bring down the power or potential of the entire battery.

I’ve found many batteries with failed cells by simply placing a variable one amp load on the battery and watching the voltage dance about, I retire these batteries from flight service. Perhaps trains are more forgiving than aircraft… (I used to use Li-Ion batteries to power gas powered Giant Scale Aircraft flight systems; not electric propulsion motors)

Michael
 

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Discussion Starter #15
ok, the Highline does refer to Marty's layout.

While the loco wouldn't pull the grain hoppers (about 15) up the highline which does have a steep grade with the 14.8 volt battery, it did pull the 4 USAT passenger cars up the same grade.
It wasn't that it wouldn't pull the 15 hoppers up the grade but that it stalled out instead of spinning the wheels. It has just the one small weight from the factory

Before changing to battery, the Dash 9 would easily pull 50 coal hoppers on level track.
 

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you guys are asuming that the battery voltage is what it is while running under a load ... it may not be .... and that there is no loss in the system to move and control that power ..... the only way to know for sure is to hook a volt meter to the motor leads that you can see while the loco is running and under load
 

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Yep Michael - as you a very aware of when batteries in a train rundown the trains reaches the station stop early tho maybe not the station itself...

When a plane runs low on batteries it stops early also, but you have to get a bag and pick up the parts ....

:~}

Dirk
 

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Randy, If you were not spinning the wheels then the added weight should not matter here... sounds like you powered out or the batteries simply may have run down at that point in time, and the loco could not pull any further,.. possibly yet may have run on level track later...

This is one reason why I enjoy having a set of panel meters in at least one loco to have definitive knowledge of what is going on when it happens...I continue to collect data anytime I run My SD70 Mac, which provides me with more accurate info to base choices and changes on later.

This is also the basic reason I suggested measuring the voltage before and after your control board...to see if their is a board issue .. a wiring issue (to light for current passage ) and to eliminate what is working and help discover what is not working, or at best to verify that it is all working as it should..

Dirk
 

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Randy, when you say the Dash 9 with the 14.8 V battery stalled out, was this a Li-ion battery? I've had a Li-ion battery shut down due to excessive current draw.
 

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Discussion Starter #20
Yes Jim it was a Li-ion battery. It shut off for a few seconds and then would try again. But the wheels never tried to break loose. As for excessive current draw, it only had excessive current draw because it didn't have the power to break the wheels loose and spin.
 
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