Trolley technical question (slightly ot)

Hi,This might be a little off topic and out of the scope of this forum, so if it is, I apologize for that. But since we were talking about a few technical things in the PCC and light rail discussion earlier (poles vs. pantographs, etc.), I thought maybe you guys could help with something I've been curious about. I had bought an HO scale trolley car from ebay a little while back and I've been wanting to build a little trolley car town layout with it. One of my other hobbies is electronics, although I like to work with AC mostly and I don't do a whole lot with DC. Anyway, I wanted to build my own controller for the layout, since the ones you get from the hobby shop are pretty weak (ever notice when you throttle up the trains, sometimes the lights in your buildings would dim or flicker? That's from the voltage drop) and they're too expensive. I could build a much better controller at a fraction of the cost. Well, since I don't work with DC normally, I was asking a friend what would be the best way to convert the AC from the transformer into DC that the trolley cars could run on. Well, he told me about a rectifier circuit I could build. Then I had asked if I would neccessarily have to have a variable transformer to control the speed of the trains, or if I could just do it by varying the current. Apparently, the only way I could vary the speed would be with voltage or frequency...and of course the easiest way in this case would be with voltage. Now here's the thing I'm wondering about. If that's the case, then how did they control the speed on the early trolley cars?? I've had a chance to take a pit tour and I've seen underneath one of them before and as far as I know they just use resistors, which are switched in an out of the circuit to the traction motors with the motorman's controller. So how did that work to control speed? Sorry about my technical ramblings here, but I've always been curious about that. The other interesting thing I found out one time is that driving a trolley car is a lot different than I thought it would be. I had a chance to operate one at the Orange Empire Railway museum in Perris, CA (Los Angeles Railway car 1201) and it's weird how the controller is set up. To increase speed, you'd notch the controller up like you do in the cars in MSTS, but when you want to slow down, you can't "back notch." You actually have to pull the handle all the way back to turn off the controller, coasting the trolley down the track. When you want to accellerate again, you move the handle back up to the notch you were at. I was told that it was wired this way to save the resistor elements and contactor drum from damage by arcing. It's pretty weird!

Chris T.
San Bernardino, California

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RE: trolley technical question (slightly ot), davidbeach, Apr-07-03, 02:24 PM, (1) RE: trolley technical question (slightly ot), chuckzeiler, Apr-07-03, 06:38 PM, (2) RE: trolley technical question (slightly ot), smallspy, Apr-07-03, 06:52 PM, (3) RE: trolley technical question (slightly ot), davidbeach, Apr-07-03, 07:06 PM, (4) RE: trolley technical question (slightly ot), davidbeach, Apr-07-03, 07:11 PM, (5) RE: trolley technical question (slightly ot), gatecityca, Apr-08-03, 00:43 AM, (6) RE: trolley technical question (slightly ot), chuckzeiler, Apr-08-03, 11:04 AM, (7) RE: trolley technical question (slightly ot), davidbeach, Apr-08-03, 03:06 PM, (8) RE: trolley technical question (slightly ot), davidbeach, Apr-08-03, 03:17 PM, (9) RE: trolley technical question (slightly ot), John 136 6000 GO, Apr-23-03, 01:52 AM, (10) RE: trolley technical question (slightly ot), tryagin, May-06-03, 11:44 AM, (13) RE: trolley technical question (slightly ot), davidbeach, May-06-03, 03:10 PM, (14) RE: trolley technical question (slightly ot), Overkill211, Apr-27-03, 11:35 PM, (11) RE: trolley technical question (slightly ot), sniper297, May-04-03, 11:27 AM, (12)

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DC motor speed is a function of field strength and armiture voltage. Using a permanent magnet universal motor, your HO trolley can only be controlled by voltage. Plus you will want to filter the output of your rectifier as the pulsed voltage (and therefore) current is not good for the motor at voltages approaching rated voltage.Real trolley controller could do a number of things. The generic control sequence for a four motor car would be:1. All four motors in series, all field resistors for each motor in, and in series. When voltage is applied, this gives the slowest operation. Armiture voltages on each motor are 1/4 of line voltage.2. Depending on the number of resistor steps, resistors are consecutively cut out of the field circuit, reducing the resistance of the circuit and thereby increasing the field voltage.3. Transition time. The motor armiture circuits are reconfigured so that the motors are in groups of two, in each group the motors are paralleled, but the two groups are in series, giving an armiture voltage of 1/2 line voltage. Field resistors are cut back in, to an appropriate amout, may not be all.4. Resistors cut out again for increasing speed.5. Transition again. This time all four motors are in parallel, each seeing full line voltage. Field resistors again to their thing.Two motor cars would obviously go from all series to all parallel without the first transition. Other variations are possible.The reason you can't trottle down, is that the system was not designed to deal with the regenerated voltage. The only difference between a motor and a generator is what applies the torque to the shaft. If the electrical machine applies torque to the shaft and what ever is connected to the other end of the shaft absorbs the torque, the electrical machine is a motor. On the other hand, if what is connected to the shaft is applying torque, the electrical machine will absorb it, producing voltage and current as a generator. Generators need voltage regulators, which were not easily implimented in the earlier trolley days. If you are going to be doing dynamic braking, the regulator can be more reduimentary as long as the voltage rating of the braking resistors is not exceeded, and you do have to have the dynamic braking resistor grids. Regenerative braking is the next step up, where the power produced by the traction motors acting as generators is returned to the overhead supply lines, but that requires better voltage regulation at the source, and then the whole supply system needs to be designed to absorb power from the load.David Beach.Palouse & LewistonRoute Building 1% Completed
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David, thank you for the explanation. Perhaps you can explain one more item about electrical power on trolley systems.One of the MSTS objects available to me is a pole called an Equalizer. It has three transformers on it. It appears to me to be connected to the high voltage lines, but I'm wondering about its purpose, and how often an Equalizer pole should appear on an average trolley system?

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Chuck, that looks like a pole with a trio of transformers on it...likely to drop the higher voltage of the tranmission wires to the line voltage of the trolley system, whatever it may be.Toronto doesn't have anything like these, but we do have obvious power supply cables from the power buses that run along the lines...guessing that all things being equal, I'd guess that they could be put every mile and a half to two miles, depending on the line voltage. The higher the line voltage, the further apart they can be: i.e. Toronto runs 600V DC.Dan

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Transformers don't work on DC. In the good ol' days of street railways the only way to convert DC from one voltage to another was the use of a rotory converter, otherwise known as a motor-generator or MG set.David Beach.Palouse & LewistonRoute Building 1% Completed
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Chuck,I really don't know what the "Equalizer" might be, too many possibilties. In the picture you have there, they might well be a three phase bank of transformers providing power to the substation to power the MG set in the substation. With a power system diagram showing how the Equalizer relates to the rest of the system, or a decent technical description, I could probably figure it out, but the name alone is not enough.David Beach.Palouse & LewistonRoute Building 1% Completed
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Chuck,To me, the term "equalizer" suggests that it is a device to compensate for voltage drops - whether this is caused by the load of a passing electric locomotive (sometimes called a "juice jack" for that very reason) or simply due to voltage drop over distance...resistance losses. If it is for the latter, then you could calculate what a fixed voltage drop would be over distance and in theory wind a transformer to compensate for that. The problem of course is transformers can only work with alternating current. So we'd have to assume that a trolley line using that system would have feeder lines running on AC, with some kind of rectifier after those transformers to supply the trolley wire itself. But as far as I know early trolley lines were almost universally DC (600 volts typically). There would be no use for them to have any AC on the trolley circuit. I did remember reading that one way they compensated for voltage drops was to have batteries in parallel with the trolley line. Normally, the batteries would be at the same voltage as the trolley line. But if a passing locomotive or big interurban car put a big load on the line and the voltage dropped, the batteries would boost the line voltage back up. As the batteries drained, the voltage difference would cause the current from the trolley line to recharge them. So, the "equalizer" you have for your route might just be that kind of system.

Chris T.
San Bernardino, California

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LAST EDITED ON Apr-08-03 AT 11:05 AM (EDT)

I'll share this with you, the only time (so far) that I found the word “Equalize”. This is from the book, "Electrification By GE", first published in 1927 (GE Bulletin GEA-150A):A brief summary of the duties performed by the power-limiting and indicating system as installed on the Rocky Mountain and Missoula Divisions of the Chicago Milwaukee & St. Paul Railway follows:
1. Indicates total net amount of energy being delivered at all times and makes permanent record for future study and for a power bill basis.
2. Automatically deducts regenerated power, if returned to the company’s lines, or power transferred from one line to another over the railway company’s transmission line.
3. Automatically limits the amount of power supplied to a division by lowering the trolley voltage and slowing down the trains, thus limiting the maximum peak load on the system to a predetermined amount.
4. If desired, the equipment can be adjusted so that the lightly loaded substations will not be affected while the heaviest-loaded substations will have their voltage reduced slightly in advance of the other stations, thereby equalizing to some extent the load on all stations.
5. If an excessive demand on power occurs near any one substation, the voltage is automatically reduced on this station, without affecting the regulation of stations on either side. A portion of the load is thus shared by the other stations.

If the above is relevant, then maybe those transformers act as load regulators?

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Chuck,What is described in your post is something that would have been done with the controls of the MG sets which were providing the DC power to the trolley from the AC power supplied to the substation. A black box in the field controls of the generator, not something hanging on a pole.David Beach.Palouse & LewistonRoute Building 1% Completed
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Chris,What you describe, which as you state works on AC but not DC, is certainly one possibility as to what an "equalizer" might be. In modern parlance the equipment performing that function would be referred to as a voltage regulator.If you drive out in the country, along some long utility distribution circuits you will occasionally see voltage regulators. Typically there will be three transformer looking things on a platform between two poles. Each of the regulators will have two or three leads with two leads connected to different points of the three phase conductors, and you will see an insulator in the phase conductors between the two connections of the voltage regulators. Different utilities will construct and wire these things somewhat differently so my description my not exactly match what you might see. The basic voltage regulator is an autotransformer with an automatic tap changer, used to boost voltage to counter the voltage drop in long lines. Specific line drop can not be calculated in advance and a fixed ratio transformer used, at least not in practical terms, because voltage drop is a function of load, which can be highly variable.David Beach.Palouse & LewistonRoute Building 1% Completed
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Just picking up on the batteries, and perhaps slightly deviating from the main thread of discussion.The London trolley busses that I can remember from my youth (lovely double-decker vehicles with a very smooth ride) were equiped with batteries which could be used to move the vehicles a short distance in an emergency (power failure, pole off in the middle of a busy road, etc). I don't know if they also served an additional purpose such as absorbing regenerative braking current, or stabilising supply variations.CheersJohn

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LAST EDITED ON May-06-03 AT 11:47 AM (EDT)

Chuck, Here is the picture out of the 1911 Electric Railway Journal's "Great 1911 Convention Issue" which featured the Public Service Railway of New Jersey. Unfortunately, there was no mention of the EQ Feeder boxes in the text, just this Picture. I made the model from this pic, because I thought it was an interesting piece of equipment.
I also researched the Equilizers in a 1915 volume I have of Electric Railway Engineering, which only makes mention of equilizers at the substation as the final piece of equipment between the substation, or "boosters", to the negative buss-bar, then to the rail. So, they're not transformers, nor circuit-breakers. The reason for three boxes is there are three MG sets powering the 600vdc trolley. Now why they are shown mounted on a pole at streetside is a mystery to me. I'm incuding the illustration from the 1915 book, to give you another perpective. I'm no electrical engineer, and all this is over me head. Tim

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As best as I can tell from the diagram, the equalizer switch would allow some of the MG sets to operate without the series field coils. The machines could have been set so that with just the shunt field the generator produced 550VDC and with the series field added in it produced 650VDC. The equilizer switch in that case would need to be interlocked with the feeder switch on the positive side of the circuit. What I can't explain is the separate equilizer bus on the bottom, but DC machines remain rather theoretical for me, having not had to deal with them since electrical machines class 20+ years ago.David Beach.Palouse & LewistonRoute Building 1% Completed
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Having been a member at OERM for many years, and riding along with my father on training, I don't think the 3-transition layout was ever used on streetcars (at least in California ). LARy cars, for instance, had nearly identical controllers at the Motorman's station across the board; which only had series and parallel runs. So the main difference was in the relay and resistor box under the carbody. A two-axle car runs its motors through series and parallel; no fuss. Four-motor cars were a bit different, though. Most were set up so that each truck was one branch in a parallel circuit. So, in the series run, each truck acts as a series circuit. Once you transition to the parallel run, each motor is being applied full line voltage.
I seem to recall Pacific Electric's "Blimps" and "Hollywood Cars" following this layout, as well.

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"ever notice when you throttle up the trains, sometimes the lights in your buildings would dim or flicker? That's from the voltage drop"On the last few model layouts I wired, I took a few power packs and wired all building lights, block signals, and switch machines into them. The power packs that controlled the track voltage (and therefore the trains) never had anything else tapped into them, so when trains were running there was never any voltage loss to anything else.Last layout my Dad and I had used a Keller command & control setup, the track got a steady 14 volts DC, and the control pads sent an AC signal to the circuit card in the loco or tender (shoehorning them in with the sagami can motors was fun!) to control the speed of the engine(s). I think Keller is out of business these days (that was early 80s), but there are probably others like that. Big advantage is it does away with having to chop the layout up into control blocks, you can independently operate two or more engines on the same track for switching ops (switcher comes out of the yard and grabs the last 5 cars and pulls them off, train moves on, or add and subtract helper engines operated by two different people), and the slow speed control is smoo-oo-ooth, since the track voltage always stays at a steady 14 VDC, with the circuit board in the loco drawing what it needs according to command input.

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