Slug Observations

[refshop]

" The slug can only assist a single locomotive, the one that was MU’d first "

That's a shame as topping and tailing a slug with a pair of DE2s would have made quite an interesting loco setup ?

"The back EMF from its 6 TMs may drastically reduce locomotive’s top speed"

If the motors in the slug are the same type as those in the DE6, then won't their back EMFs be roughly the same too ? ..... One way around this is to use the slug on inclines only and disconnect the blue MCU connectors when on the flat? Just a thought.

Do we know the mass of the slug ? ( The same as the DE6 perhaps?)

[maxine]

There are more motors connected, therefore the total back EMF is higher, since it adds up.

I haven't played the new update yet, but it should tell its mass on its side, just like any other rolling stock.

[refshop]

Originally posted by maxine:

There are more motors connected, therefore the total back EMF is higher, since it adds up.

I haven't played the new update yet, but it should tell its mass on its side, just like any other rolling stock.

Good point.. I'll spawn a Slug in Sandbox Mode and take a shuftie.

The EMFs would add up only if the motors are connected in series.
As the current per motor is reduced, that suggests the motors are connected in parallel. If that's the case then the back EMFs would not be added, but more like averaged?

[Sparka🎄❄🐉]

Originally posted by maxine:

There are more motors connected, therefore the total back EMF is higher, since it adds up.

I haven't played the new update yet, but it should tell its mass on its side, just like any other rolling stock.

That's not how back EMF works, since the motors would be in parallel. If they weren't parallel, adding more motors wouldn't reduce the amperage (or it would, but it would be also reducing the force and making the slug pointless). EMF increases with motor speed until it equals the applied voltage, which is how a motor's kV is determined, but motors in parallel wouldn't induce more EMF, they would simply all have equal EMF applied against the shared current.

I'm hoping that these statements are just from someone who doesn't understand it though, and the simulation is modelled correctly regardless. Certainly with the de2 comfortably breaking 40 I've not come across a huge speed reduction yet.

[refshop]

I like to run multi job consists which are of course pretty heavy. To me it makes no sense to try and chase track speed limits with 2000T+ on the drawbar. Speeding that mass up and down is very energy inefficient. Normally I try and stick to 40 Kph max as there are many 40 limits but not many 30s. So for me, the ultimate speed is not the point. What is more significant, I would suggest, is the ability to maintain a decent speed up a long incline and not be reduced to a 10kph crawl after the first half of the climb!
The mass of the Slug turns out to be 125T, so just a bit less than a DE6 as expected.
It will be interesting to see a comparison of DE6 + Slug Vs 2 x DE6

[maxine]

If the mass is less than a normal DE6 then what is the point? I can just use another DE6 to get more traction out of it and still have more power at the same time.
I thought the point of the slug was to be heavy to get more traction, therefore it is filled with concrete.

[refshop]

Originally posted by maxine:

If the mass is less than a normal DE6 then what is the point? I can just use another DE6 to get more traction out of it and still have more power at the same time.
I thought the point of the slug was to be heavy to get more traction, therefore it is filled with concrete.

The difference in mass is only 7T in 132 so that's only around 5%, plus there are no overheating issues when using a slug. Is that true of 2 x DE6 ?

[GizmoXomziG]

- DE6 costs money to operate
- DE6 needs repairing (when crashing/derailing)

[TruePikachu]

Originally posted by refshop:

" The slug can only assist a single locomotive, the one that was MU’d first "

That's a shame as topping and tailing a slug with a pair of DE2s would have made quite an interesting loco setup ?

I haven't looked to see if the code was changed in the latest build (it probably has, since I don't think slug back-EMF was a thing), but the support for slugs that was present in the previous build (before the slug itself was released) leads me to believe it's a technical issue. It might be possible to have it changed in the future (either via mod or patch) to support multiple locomotives powering it, but I think it would require quite a bit of work that might be better spent elsewhere right now.

[refshop]

I was musing that the front MCU connection could drive the front bogie of 3 motors, likewise the rear. That would keep the two systems separate except for the control signals via the MCUs as per normal. Just needs a selector breaker to select 2 x3 mode or 1 x6 mode.

[Knsgf]

Originally posted by Sparka🎄❄🐉:

Originally posted by maxine:

There are more motors connected, therefore the total back EMF is higher, since it adds up.

I haven't played the new update yet, but it should tell its mass on its side, just like any other rolling stock.

That's not how back EMF works, since the motors would be in parallel.

When motors are in parallel, their currents add up at generator side. If you're pouring 600 A into each motor in a six-axle locomotive + six-axle slug to maximise tractive effort - the very reason to use a slug in the first place - the combined current the generator has to withstand will be no less than 12 * 600 = 7200 A. This is more than enough to trip a circuit breaker at best and fry a typical locomotive generator at worst. So the slug has to be connected to host locomotive in series and not in parallel.

There is another advantage of series connection - it ensures that amperage in the host and the slug is the same. Parallel doesn't guarantee this if motors in the host and slug are of different design.

Originally posted by Sparka🎄❄🐉:

If they weren't parallel, adding more motors wouldn't reduce the amperage (or it would, but it would be also reducing the force and making the slug pointless).

First, motor windings have innate resistance, so they will reduce current even at standstill. Secondly, the only purpose of a slug is to provide additional traction at very low speeds when combined counter EMF is small and generator is able produce enough voltage to maximise amps. At around 10-15 mph back EMF will indeed grow big enough to reduce the force and make the slug pointless. So real locomotives that operate with slugs routinely disconnect them from the host upon reaching sufficient speed.

Originally posted by Sparka🎄❄🐉:

EMF increases with motor speed until it equals the applied voltage

In a series-wound traction motor, EMF can never reach and equal applied voltage, as the strength of motor's magnetic field is tied to current. When motor speeds up, the current drops and magnetic field is weakened. This arrests further increase of counter EMF.

Originally posted by refshop:

Originally posted by maxine:

There are more motors connected, therefore the total back EMF is higher, since it adds up.

I haven't played the new update yet, but it should tell its mass on its side, just like any other rolling stock.

Good point.. I'll spawn a Slug in Sandbox Mode and take a shuftie.

The EMFs would add up only if the motors are connected in series.
As the current per motor is reduced, that suggests the motors are connected in parallel. If that's the case then the back EMFs would not be added, but more like averaged?

For those who're curious, the combined EMF of TMs in parallel is determined by the following formula:
E = (E1 / R1 + E2 / R2 + ... + En / Rn) / (1 / R1 + 1 / R2 + ... + 1 / Rn).

[GHKtruc]

DE2+slug, failed to carry 661 tons up the harbor in comfort mode. So the slug doesn't quite double the pulling power. Anyone have updated numbers ?

[Knsgf]

The maximum tonnage that DE2 + slug combo can pull on a 2 % slope seems to be in 350-400 ton range.

[refshop]

"For those who're curious, the combined EMF of TMs in parallel is determined by the following formula:
E = (E1 / R1 + E2 / R2 + ... + En / Rn) / (1 / R1 + 1 / R2 + ... + 1 / Rn)." / quote

Can you explain the derivation of that formula please,
I'm not much of a mathematician.

My thinking is you will have 12 circuits as shown below.....

For the Loco:-
Vtl = EL1 + IL1 x RL1 where Vtl = Loco motor terminal voltage.
Vtl = EL2 + IL2 x RL2
-------------------
-------------------
Vtl = EL6 + IL6 x RL6

For the Slug:-
Vts = ES1 + IS1 x RS1 where Vts = Slug motor terminal voltage.
Vts = ES2 + IS2 x RS2
-------------------
-------------------
Vts = ES6 + IS6 x RS6

I presume what we want is Vt = Eav + Iav x Rav to give 1 normalised motor ?

[GHKtruc]

Originally posted by Knsgf:

The maximum tonnage that DE2 + slug combo can pull on a 2 % slope seems to be in 350-400 ton range.

So it's barely more powerfull ?

[refshop]

Originally posted by GHKtruc:

Originally posted by Knsgf:

The maximum tonnage that DE2 + slug combo can pull on a 2 % slope seems to be in 350-400 ton range.

So it's barely more powerfull ?

How much does a DE2 pull on a 2% slope on it's own ?
P.S the slug on it's own weighs 125T