Does Series Wiring Cut the Volts but not Amps?

Current (amps) stays the same. All the current drawn by the locomotive goes through both motors.

The voltage is divided between two motors when wired in series, which is why it runs better at slow speeds.

I think I get it. so for any given speed I'm now using about twice the throttle post series mod vs. parallel, and each engine is experiencing twice the amps but just the same voltage? 

Arlo-

The speed and torque of a motor depends on the supply voltage; higher voltages result in faster speeds and less torque. Wiring two (or more) motors in series fractionally reduces the voltage to each motor, which in turn reduces the motor's speed and increases the motor's torque.

Your modification simply reduced the amount of voltage each motor receives without increasing the current (amperage) drawn from the transformer. If the motors were wired in parallel (factory wiring), each would receive the same voltage but draw more current from the transformer.

-John

Thank You, that's exactly what I was thinking.  So now I'm sort of fascinated by how you can get such different characteristics out of the same motor, at the same RPM, based on volts and amps.  Since nothing in physics is free, do I also get more heat when operating in Series and doubling the ZW80 throttle? 

Arlo-

You do not generate more heat when the motors are in series or parallel, but I think there might still be a little confusion between motor speed, voltages, currents (amperage), and the relation of the three to the CW80 transformer. I'll try to clear things up a bit.

The CW-80 transformer is rated to supply a maximum of 80 watts of power; power is always the product of the voltage and current (P = VI in physics terms). Voltage and current (amperage) are inversely proportional to each other - the higher the voltage, the less current. On the bottom of the transformer you'll see a sticker that says "O/P 18VAC", which means the maximum voltage the transformer can put out to the tracks is 18 V(olts), AC current. Since the transformer has a throttle to adjust the voltage, we refer to this as a variable voltage, meaning the transformer can supply anywhere from 0-18 volts to the track, depending on what the throttle is set to. Pushing the throttle away from you increases the voltage; pulling the throttle towards you reduces the voltage. Since we know the transformer is rated at 80 watts, and the maximum voltage is 18, we can find the maximum current by dividing the power by voltage, which in this case is about 4.4amps (at 18 volts). However, the transformer will only current based on what the load (motors and lights) is drawing - the transformer NEVER supplies its maximum current without a load attached.

Now let's talk about the locomotive. The locomotive has a motor which converts the electrical energy supplied by the transformer into mechanical energy to move the train. The motor consumes energy - it needs voltage and current to work. The more voltage the motor receives (at whatever current the motor draws from the transformer), the faster it will spin. Your locomotive has two motors, originally wired in parallel. When wired in parallel, both motors receive the same amount of voltage as what is supplied on the track (if track voltage is 12 volts, the motors receive 12 volts), but the current needed to turn the motors doubles (1 amp per motor x 2 motors = 2 amps total current needed from the transformer). Now your modification changed the way the motors were wired; instead of each motor receiving full track voltage (parallel), you connected the motors together in series. By doing this, each motor now receives 1/2 of the supplied track voltage (so keeping with the example before, if the track voltage is 12 volts, each motor is now receiving 6 volts). Since the voltage decreased, so did the amount of current needed to drive the motor. Going back to the example, if the motor is now running at 1/2 the voltage as it was in parallel, it is also drawing 1/2 the current too, so both motors consume a total of 1 amp of current (0.5 amps x 2) instead of 2 amps when wired in parallel.

Earlier I mentioned that the motor's speed is based on the voltage supplied to it. Regardless if the motors are wired in series or in parallel, raising the throttle will make the motors turn faster simply because you are supplying more voltage to the tracks. So let's say at 18 volts (maximum voltage) each motor turns at 1000rpm. When both motors are connected in parallel, each motor spins at 1000rpm at 18 volts; if the motors are wired in series they will spin at 1/2 the speed, or 500rpm (remember: two motors in series receive 1/2 the voltage). Thus, if you wanted two motors in series to turn at 1000rpm at 18 volts, you would need to supply 36 volts to the track (which is beyond what model train transformers can supply!).

So now we have the relationships between the transformer and the locomotive, and the relationships between all the different voltages and currents and what that means for the locomotive's speed.

Hope this all helps!

-John

it's helping, thank you.   What I'm trying to understand is why the train seems to maintain it's speed through corners better now than before, and I thought increased torque was the answer, but now I'm not so sure.

In my application I'm dragging 12 cars at what I'll call 30 scale MPH (i'm guessing here) around a 14 x 5 layout with O36 and O48 curves.  before, at 30 scale MPH the train would slow somewhat in the curves, but after switching the wiring to series and doubling the throttle, the train still is at my desired speed of 30MPH but maintains it right through the curves.  so the motor is at the same speed now, and each motor is getting the same voltage as before because I doubled the throttle, so why is the behavior when the increased friction of the corners drags on the motors different now?  Why do they respond to the load of the corner friction better with the ZW80 throttle opened up more even though they still are getting the same voltage per motor?    Thanks for your patience.  I'm new at understanding current. 

Hi Arlo,

I live in Oregon also.  My email is in profile.  Drop me a line sometime.

TEX

Steve

I think the dynamics of this situation are not as simple as computing series vs. parallel currents in two equal loads. 

• When you have twice the voltage (roughly) going to the track, but about half the current (roughly). the effects of voltage drops in the wiring and tracks is not nearly as great.  You have half the voltage drop because of half the current, and you have twice the voltage to work with.  The effect is that the overall loss in power from the transformer due to voltage drops is a lot less than the parallel motor connection.
• When the motors are in series, the dynamics of one being more loaded than the other will also change vs. the parallel connection.  The heavily loaded motor will attempt to draw more current, and the only way it's going to get it is through the other motor, thus adding power to that motor in the process.  When motors are in parallel, the heavily loaded motor will actually sap the power of the other motor.  I see this all the time with dual-motored locomotive with speed control, if the motor with the speed control starts slipping, the other motor that you'd normally like to take up the slack and keep you going, loses power because the no-load current and voltage to the motor with speed is far less than if it was actually working into a load.

If this wiring setup is so much better for performance (which it is),

then WHY don't they do it at the factory to begin with??  Seems to be

a no-brainer.

     Hoppy

The fact a dog has a layout and can rewire a loco alone is very impressive!

You'll have to ask the factory folks about that.

I think one reason is, depending on the layout, you may not achieve the maximum pulling power with the series connection, as it does take twice the voltage to deliver roughly the same pulling power.  You may run out of throttle before you run out of desire.  

For the reasons stated above, I think in some ways the series connections works a bit better, at least under some conditions.

The fact a dog has a layout and can rewire a loco alone is very impressive!

Australian Shepherd, very smart!  I once saw 2 of them running a filling station in rural Oregon with no humans to help.

K-Line did this with a series/parrallel switch. The only problem the switch is the weak link. Come off the track and cause a dead short and the contacts in the switch fry.

Yes you will run out of throttle when pulling longer train. My K-line does. switching back to parallel gives it back it's pulling power

Just think as the motors as 2 resistors. In series resistance doubles, parallel, resistance is cut in half. In parallel voltage is basicly supplied equally to each motor. In series voltage is supplied through one motor to get to the next.

My experience in trying this was the transformer I was using only could muster 17 volts tops and the engines ran too slow. If your transformer can put out at least 19-20 volts then it may work out ok. I changed mine back to factory for this reason.

Rob

You'll have to get rid of the dog and put your own face up there.  That's the rules.

.....

Dennis

Are you saying Arlo is NOT a dog?!?!?!?! I was so impressed too!!

I like GRJ's explanations.

For starting a heavy consist, it's all about available starting torque.  That's the "drawbar pull" spec which the HO guys fixate on when a new engine comes out.  Parallel motors provide twice the available drawbar pull than series motors for reasons given.  Obviously you can double the transformer voltage to the series motors but our transformers max out at, say, 20V.   If you can't get the consist started, then game over.

So now the consist is running.  As GRJ points out, for the same speed and load, each motor sees the same voltage and current in either parallel or series configuration.  But if the voltage at the engine drops (due to voltage drop from the transformer when approaching a curve or grade) each parallel motor sees the full drop, while each series motors only sees half the drop.  As pointed out, the track current is 1/2 in the series configuration; so while the track voltage itself is higher, the voltage variation from track/wiring resistance is smaller so there's a smaller speed variation. 

I wouldn't be surprised if someone pops in with an electronic "transmission" that senses speed and activates a DPDT relay that swap the motor leads between parallel and series.  That way you'd get full drawbar pull to get things rolling, and then better speed control at mainline speeds.

My dogs are people.

TEX

Steve

I have some locos wired in series.    I also experienced much better performance with conventional DC power.   However, there is one anomoly with this wiring.   My experience was that if one motor completely stalled, the other would go to full speed and slip.    This would occur if the train were too heavy and stalled the whole locomotive.   In a stall situation, one motor would spin the wheels, while the other did not move.

In a second thought, with most of these motors, I think they have the most torque at some speed closer to high speed.    Hence, they tend to stall at low speed with the gearing we see in some models.   At higher speed the motor torque, is sufficient, but at very low speeds, the torque is very low.   This is why in my opinion, engines with some reduction gearing that allows the motor to turn at higher RPMs for lower speeds, run much better.    This may be related to series wiring putting more current into the motors, which I had not heard before.

As for why the factories do not wire this way, I also have an opinion.   I think there are 2 reasons.   The first is that many 3-railers like "fast" speeds, and with the type motors used, this is easy to do with parallel wiring.   And related to that is the stall situation I described, which might tend to frustrate some customers who want to pull, or try to pull long strings of boat anchor diecast cars.

I'm do not believe that this was touched upon above, so I'll add it as a little FYI:

This parallell-to-series change can be done on any 2-motored (more-motored) loco, natch, so don't forget the PS-1 RailKing articulated steamers, and/or also

those that have an early non-cruise TMCC conversion. I have both. It slows them down nicely - no crawling, but much better, and worth the 15 minutes it takes to do it.

Mechanically/electrically a RK (or Lionmaster) articulated is really built just like

a typical diesel: two swiveling trucks with a vertical can motor each. They just -look-

like steamers.

There are some early 2-motored, non-cruise electrics that can benefit, too.

There is no magic here.  You do not get free work wiring motors in series.  Motors wired in series drawing half X voltage and half Y current are producing one quarter the torque of a motor drawing X voltage and Y current.  To get the same amount of mechanical work requires the same number of watts; XtimesY.  Series wiring can provide a finer level of work management at lower speeds but to provide a pull at a certain speed still requires the same number of watts.  If it requires 6 watts to pull a train 10 MPH then at 12 volts thats .5 amp.  At 6 volts it's 1 amp.  

Note, amps also equals heat, so motors wired in series will run a little warmer.

Apples and oranges.  If pulling the same load at the same speed, it doesn't matter which configuration for the same pair of motors.  In your example, each motor has 6V across it and has 0.5 Amps running thru it.  Each motor will dissipate the same power and deliver the same mechanical work no matter the configuration.  OTOH the motor electronics is a different matter.  In the series configuration it must deliver double the voltage, albeit at half the current.  The semiconductors that drive DC motors have current and voltage relationships/constraints which don't trade off one-for-one but that's a different matter.

If you're talking about special cases where one truck/motor starts slipping and how the other motor responds to it, then indeed you get a different power dynamics depending on configuration as was described earlier.

Wiring in series will divide the voltage, not always equally to each motor and the wattage (watts are a smaller measurement [than amps]of current flow)to move will go up slightly to compensate for the new motor draw.

Also each motor will draw what it wants because the of resistance factor in each motor. There is a much greater chance for slippage of the wheels with series wiring! When the one motor slips it takes almost all the power to overcome the problem and can burn out if not noticed.

A common problem with series wiring; if one motor goes out they both quit!

Series wiring was common during the early 1900's when electricity was somewhat new and is not that popular today because of it's drawbacks or problems.

The best way would be to reduce the voltage to the motors in your engine by using DCS or TMCC or a TPC 300 and track voltage setting.

Lee Fritz

Isn't this just P = V^2/R? Two motors in series will have a resistance of 2R and two in parallel will be R/2. So for the same voltage, the motors in series will draw 1/4 the current that the motors would draw in parallel. And since P = IV, the overall power into the series wired engine will be 1/4 of the power into the parallel wired engine at the same voltage setting.

All that said, it would be great if the WBB engines had a simple switch that would allow you to select series or parallel. All of my WBB engines are series wired. Smoother, quieter and more fun.

Resistors are passive devices and follow the rules above. Motors are not passive devices. Once they start turning they become generators developing a voltage opposite (counter Electro Motive Force) to the applied voltage. The stall current rating motor is the maximum current the motor will draw for a given voltage. As the motor turns the counter EMF reduces the voltage drop across the motor and therefore the current that the motor draws. Say you apply 12 volts to the motor. If is spinning freely, no load, it may develop 10-11 volts so the net voltage is only 1 or 2 volts. Under load the motor slows down and develops even less voltage, say 7-8 volts. Now you have a net applied voltage of 4-5 volts and a subsequent increase in current through the armature.

Others have hinted at it but the problem with series wiring occurs when you have wheel slip and the voltage drops across each motor differs.

Pete

Which is what K-Line eventually did toward the end of their production on dual-motored diesels.  All it takes is a DPDT switch.

Thanks for all of the good responses.  My train still runs great today and no slippage problems.  Later tonight when I have time I will research the rules re the Dog picture.  He can operate a Lion Chief remote and is interested in the trains, so I'm not sure why he would not be allowed on the forum.  

actually a 4PDT switch.

http://www.alltronics.com/cgi-...ch/4PDT-Slide-Switch

I don't know what K-Line used, but it only requires a DPDT.

Are you saying K-line used a 4PDT?  And if so why not a DPDT?