newbie needing help. set up my trains after 45 years in storage. (grandson loves trains) I have a TW and KW transformers.
Have 2 loop layout, cross over switches are totaly insulated between inner and outer loops. all switches are running isolated power from 14v side of a TW.
my question is: can I wire one loop to one handle and the other loop to the handle of my KW transformer, and drive the trains from loop to loop, without damaging anything?
Yes. Voltages need to be close to the same on each “handle”. I think you have indicated the loops are insulted from each other. I still have the commons [outside rails] connected to each other. I run trains from one loop, sidings and to another loop using three different post war ZW’s. Never had a problem.
+1 to what Chief says. Yes you can wire each loop to a separate throttle.
The “A” post (adjusts voltage) goes to the middle rail of the first loop.
The “B” post (adjusts voltage) goes to the middle rail of the second loop.
The “U” post (common) goes to the outside rail of both loops.
I have two KWs powering my conventional layout and, like Chief suggested, I also have the outside rails of my two loops both connected to the same common “U” binding post.
Rather than having two wires from the outside rails going to the “U” binding post, you can have the outside rail of one loop connected to the outside rail of the second loop, and then have one wire from the outside rail of the second loop go to the “U” post on the KW. This keeps connections at the binding post down to a minimum but still gives you a common for each loop.
If you moves trains between loops there is the potential for a train and cars to be straddling two different voltages. On the KW this means you will essentially be causing a bridge/short (for lack of a better term) on the transformer winding since both throttles have rollers on the same winding.
The safest way to do this is to use single pole double throw switches (SPDT) to be able to select which throttle a loop is being powered by. Then when you move between loops you can set the loops to the same throttle and you will not be causing a bridge/short on the winding of the transformer.
If you work with blocks you would have an SPDT switch for each block.
I have my layout configured with SPDT toggles controlling 11 blocks on two loops. I can:
set the whole layout to run from either throttle “A”, or throttle “B”
run two independent loops, one loop on “A” and one loop on “B”
move trains between loops using block control, switching blocks to the appropriate throttle at the transition points as trains cross from one loop to the other, and then move that block back to the throttle the rest of the loop is using
Im not 100% positive but Im pretty sure the TW and KW need to be phased (share a common) if you have the 022s powered by the TW and trains powered by the KW.
From what others have said, Id say as long as the voltages are the same there shouldnt be an issue. I do remember a thread on this issue where a device was brought up that would be able to not let more than 20 volts (or whatever voltages you want) be returned into the transformer. Im sure bob nelson and the other electrically inclined members would be a lot more help than myself in this area.
Also, If you will be switching loops you will need equal voltage. So if you are planning on having fast switching operations in an operating session there will be no need for having different speeds on each loop. If you arent planning on switching then have a switch to allow for separate control as well.
No, the SPDT switch solution is the BEST solution, and it wont cause any power interuption or reversing problems. You will need to have each loop seperated into multiple blocks (at least 2-3). You preselect the route by switching the SPDTs to which ever transformer that train is being controlled by, not allowing more than one train in each block, then turning off each block as you leave it, if operating more than one train, so the other “Engineer” has access to the unoccupied blocks. If only operating one train, all the SPDTs can be thrown the same way to allow the train to operate anywhere on the layout without worring about turning SPDTs on/off. Make sure that you try to find SPDTs that are “Center Off” this will allow you to park Locomotives on spurs/sidings and still be able to operate both throttles without running the parked equipment. An A/B no center off SPDT would not allow you to do this. One thing to remember when wiring Toggle switches, if the toggle is thrown “right” the contacts that are being used electrically will be the LEFT contacts on the output side of the SPDT, and vice-versa when thrown LEFT, the right contacts are powered.
I know that Bob Nelson (Lionelsoni) has many times in the past cautioned AGAINST crossing from one transformer’s control to another’s “On the Fly”, while many have had no problems doing so.
Bob Nelson has talked about Transient Voltage Suppressors (TVS) on here many times, those will prevent a voltage spike, but I don’t know if they would protect against mis-matched transformer voltages, which can also create a short circuit. Hopefully Bob will chime in soon, as I know that he has likely forgotten more than I will ever know concerning electrical theory, but I sure have learned A LOT from him, He is a real ASSET to this forum.
Is it necessary for all of a train to transition to the next throttle or transformer section before throwing the SPDT, or only the powered unit? What if there are illuminated pass. cars, or an illuminated cabose? And can different transformers be commoned?
My Dad never seems to have gotten this right, as he mentioned always shorting out his home built transformers.
I don’t think that you and stu understand block wiring correctly. The SPDTs should already be preselected for the transformer and route that you intend to use, the switch(SPDT) should already be set correctly for the blocks that you are entering, not after, that would cause a power interuption, resulting in cycling the reverse unit in the locomotives.
I trust some of the more electrical savvy folks will correct me if I share something that is incorrect… but here’s how this layman understands it.
Runtime,
The SPDT toggles are used to set an empty block to the proper throttle before the train arrives in the block. It also allows you to park a train on a block (such as a siding) and power it down so you can bring other engines into play. So it does require you to do a little route planning, but you can also do this planning as trains are running.
The concern with crossing loops is burning or scorching the transformer winding coil by creating a short between the two or more throttle positions (taps) on a single transformer coil winding.
Not everyone agrees that using two throttles to run trains across isolated blocks is harmful. You can find several respected books on wiring Lionel layouts that talk about using throttle settings at different voltages to control the speed of trains as the cross blocks (such as one side climbing a hill and the other side descending a hill) - and they don’t mention using SPDT switches.
It’s not just the engine that conducts current. Lit cars with rollers on the bottom conduct current. When they straddle two isolated loops they basically act as a jumper cable between the two loops. If the cars have die-cast couplers (and each car is lit with rollers underneath) then it’s one long jumper cable. If the cars have plastic couplers then each car is a separate jumper cable as the rollers on each car straddle the loops. These loops become tied together because the current flows through the cars.
As stated early, the concern with crossing loops is burning or scorching the transformer winding coil by creating a short between the two or more throttle positions (taps) on a single transformer coil winding.
The KW only uses one coil winding to vary the voltage for both
It’s not just the engine that conducts current. Lit cars with rollers on the bottom conduct current. When they straddle two isolated loops they basically act as a jumper cable between the two loops. If the cars have die-cast couplers (and each car is lit with rollers underneath) then it’s one long jumper cable. If the cars have plastic couplers then each car is a separate jumper cable as the rollers on each car straddle the loops. These loops become tied together because the current flows through the cars.
Birds,
Hopefully someone will correct Me, if I am wrong, but if there is any electrical continuity to the track through car frames and couplers, it should be through the trucks and bolsters, which would be common ground not HOT (center rail continuity). The only “Jumper Cable” connection(through the couplers), if any, should be of a grounding nature, which would not harm the transformer(s). As I understand Lionelsoni’s past explanations, the short circuiting would also be an issue between seperate transformers as well as with a single two throttle transformer. Others do seem to do this without any problems, but as I said earlier, I Trust Bob’s knowledge on electrical theory much more than my own, and I will defer to his advice in this matter.
As long as your transformers are in phase, I don’t see any thing wrong with your method of grounding your layout.
So if all passenger cars and engines had 1 roller rather than two this would not be an issue?
I also remember bob talking about a situation where crossing two circuits powered at 20 volts results in 40 volts going back to the transformer. Is this only when they are not phased?
With two rollers, they will bridge while one roller is in each section, but there should not be any HOT continuity from car to car, even with metal couplers, the trucks and couplers should only have grounding continuity if any, the HOT side of the circuit SHOULD be insulated from the car’s frames, trucks and couplers. A single roller would still briefly bridge both power sources, but not likely to do any harm, I wouldn’t think.
To get 40 volts in the scenario that you mention, I would suspect that it would be if the transformers are out of phase, but this is another that I will let Bob, or someone else more knowlegdable, give a definitive answer on.
Thank you for catching and correcting my statement about the hot connection on lit cars passing through the couplers. Yes, the wheels are on the outside rails that are grounded commons, which means that any couplers connected to die-cast trucks are also part of that same common connection.
This has been great. So my conclusions to this point are:
The length of the short generated equals the time it takes the two rollers on one engine, or one rolloer on any single roller engine or electrified car to cross from one block to another which is on a seperate controller on either the same or a seperate transformer.
Some folks say this causes damage to the transformer(s), some say not.
The shorts can be avoided by using SPDT switches. My understanding of this technique is still a little hazy (and I read what lionelsoni wrote on this a few months ago). I understand it to work like this - given block sections A and B, and train moving from A to B, the SPDT(s) should be initially set to power both blocks from Trans #1; after the powered parts of the train are all on section B, it is ok to switch B to power from Trans #2. If the train has an illuminated caboose, this would require the entire train to be on block B before switching power to Trans #2.
Have I got this right??
Finally, I’m still a bit hazy on phasing seperate transformers for use as above. Does is simply mean they need to have a common ground?
Looking froward to receiving further enlightenment from the community, thanks.
Connecting the transformer outputs together can indeed damage the transformers and wiring. As was pointed out, it amounts to a short circuit on the transformer secondary. As we all have experienced, a brief short circuit usually does no harm, since it takes a little while for the wiring to heat up. However, there are other dangers:
When you create a short circuit on a transformer and then remove it, you will probably generate a high-voltage spike as the magnetic field created in the stray inductance collapses. You may not want to do this very often if you have a lot of semiconductor electronics in your locomotives and accessories.
If the locomotive or lighted car bridging the gap between blocks has multiple pickups, the fault current will flow through the wire inside the vehicle that connects the pickups. That is usually a small wire and probably will be the first to go, if anything does.
The greatest danger to my mind is that, if both blocks are supplied from separate outputs from one transformer like a KW, as proposed, the transformer’s circuit breaker is not in the circuit and will never trip, no matter how long the fault lasts. Park a locomotive with the typical two-arm pickup across the gap with the outputs set to different voltages and wait for the smoke. Interestingly, the KW is the only transformer for which Lionel specifically warned against connecting outputs together: “Note that the circuit breaker does not protect binding post combinations A-B, B-D and C-U.”
When this topic comes up, there are always those who respond that they have always done it this way and nothing bad ever happened. They are either fortunate or they didn’t realize what it was that damaged whatever train or transformer that mysteriously stopped working.
If you are able to set your transformer outputs to almost exactly the same voltage, y
Bob, many thanks as always. Your patience in repeatedly explaining these electrical issues to the community is very appreciated. This thread seemed to indicate that I am not alone in being fuzzy on the finer points.
In reference to the quote above, can I assume it’s ok for seperate transformers used to run trains to share a common (outer rail) ground?
Also, any thoughts on this: if I want to be able to shut off a block (as I now do with an on/off in line switch) would I be better off choosing to add a SPDT, or (ie- in a new installation) use a SPDT with a center off position??
===================================
I’m trying hard to adjust my thinking, but this is such a change from how I ran trains with my Dad. We had seperate (seasonal) layouts in two rooms at opposite ends of the house, connected by a long meandering single track line. Each room had seperate multi-throttle transformers and the connecting straight ran off one of them. The throttles each controlled a dedicated loop or segment. In one room there were four throttles controlling segments of three loops. We could run three to four trains concurrently.
With the scheme you advocated, a train moving across three loops with three throttles would eventually have to change throttle control even using SPDT throttle control switching. I don’t have that kind of a layout yet, but I’m just trying to adjust my thinking on how to wire and power simultaneous multi train (conventional) operation.