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bcer960

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Discussion starter · #1 ·
Hello,

I have been running a DB 150 and have just purchased a DB 200+. I am trying to figure out if the transformer I have is big enough. It is a 120v, 150 VA with a 12v output. I tried to look it up a formula on the internet, and it came back with this having only 1.25 A. That seems small. Could someone verify that for me... Thanks

Ray
 
#4 ·
Remember that VA is NOT always max amps at max volts. It only specifies that at SOME voltage, the product of that voltage and the current AT that voltage is the VA number.

Most products rated in VA will NOT put out VA/amps at max voltage... the voltage often sags greatly under load.

So the best thing is to measure the actual voltage and current.

If you cannot measure the amps and voltage under load, at least measure the voltage unloaded and under max load. If it drops more than 10%, then you have a poor quality transformer. Industry standard is for the output voltage only sags a max of 10% under rated max amps.

Regards, Greg
 
#5 ·
I would only accept 18 volts or more for large scale train running in analog/DC mode as the electronics in many engines need a higher voltage to run properly. I use 24 votls on my outdoor layout for running passenger trains, but I do keep moguls and other such engines running art lower speeds.

My outdoor layout has selectable power of the Train Engineer or DCC. Same for indoors.
 
#6 ·
Posted By Greg Elmassian on 03 Feb 2011 08:03 PM
Remember that VA is NOT always max amps at max volts. It only specifies that at SOME voltage, the product of that voltage and the current AT that voltage is the VA number.

Most products rated in VA will NOT put out VA/amps at max voltage... the voltage often sags greatly under load.

So the best thing is to measure the actual voltage and current.

If you cannot measure the amps and voltage under load, at least measure the voltage unloaded and under max load. If it drops more than 10%, then you have a poor quality transformer. Industry standard is for the output voltage only sags a max of 10% under rated max amps.

Regards, Greg I like to give more finite detail on Greg's explanation:

VA is a product also often defined Virtual Power which as a product of V (volt) * A (Ampere) = V * A and in standards values V*A= W (watts). Unfortunately VA=Watts is only true in analog (DC). In AC the VA rating is a nice distortion figure introduced to confuse (impress consumers) and consists of Vmas * Amax and as you might realize in AC you only get .707 medium value of Vmax. Hence the VA rating is at minimum overrated by 1.4. This number is increased by the "weakness" of the transformer which knows a "unloaded" voltage and a "loaded" voltage. The loaded voltage can be up to 40% or more below the unloaded voltage and depends on the core material of the transformer, the density of the core, the design of the core (e.g conventional or toroid), the winding thickness and so on. The weaker the design (typically be done to get a good nominal voltage) the more break in you will experience. In addition a conventional transformer is a very insufficient way because a lot of the electric energy is lost in heat. So to make matters worse if a company likes to cheat they can even up the anty and give you a primary side VA rating which is even higher then the secondary side VA rating.

Hence we can be glad about the arrival of new power supplies a side effect of the computer industry because our notebooks have been for a long time powered now by transformer less power supplies. If those babies give you a VA rating (although I checked a few they all rate in Watt you can rely on it. We carry one that is rate 240W at 10A (24V 10A).
 
Discussion starter · #7 ·
Thanks all for responding. These transformers are from a telecommunications company. I tried to look them up on line, but the company that made them was bought out in the 80's and there is no listing for the transformers. I originally hooked the first one up to "play" with the DCC. It was all new to me. I remember that the voltage was 14.? and that it dropped to 12.? when it had a load on it. I have been using this for about 5 years now, and have no problems running. This is on an indoor layout run by a pc with RR&Co and the DB150. I am expanding the layout to include a traction line in the near future (probably years at the rate I am going) anyway, and also have a full set of aristo streamline passenger coaches that my USA Trains F3 could not pull up my 3% grade. I have recently bought a USA Trains GP-7 for this train and am going to MU them to pull the train hopefully up the hill. This was prototypical up here in Canada in the 50's. And, although I run long trains,this is the only MU I have. I thought it may overload he DB150, so I bought the DB200+ for the mainline and am going to switch the DB150 to the traction which is relitively flat. I had always planned to use sepparate transformers for the two DB stations, I just wanted to know if it had the capacity to run the higher current.

Thanks

Ray
 
#8 ·
The short answer is that a 12 or 14 volt transformer is not sufficient for large scale usage unless you run a logging operation. You won't get enough track voltage. You should use 22 to 24 VAC into a Digitrax booster or command station for outdoor use.

That being said, neither of the previous descriptions of VA are completely correct. For DC, VA does equal watts. However, in the AC world there can be a phase shift between the voltage in a circuit and the current flowing through it. This phase shift is determined mostly by the load. If the load is resistive, then the voltage and current are in phase and VA still equals watts. However, if the load is reactive (either inductive or capacitive) the voltage and current are out of phase to some extent. Then VA is greater than watts. If the load is purely reactive, there is still a VA number (absolute RMS voltage x absolute RMS current) but the power delivered is zero. VA is good for determining the requirements for insulation resistance and conductor size, but it IS NOT power.

In your case, you can probably assume that the rating was for a resistive load so your 150 VA transformer can supply 12.5 amps, more than your booster can use. Your booster will also present a load that looks resistive. It's the 12 volt part that makes it ok for HO but not OK for large scale. HOWEVER, if you have two of them, you can wire the primaries in parallel and the secondaries in series and end up with a 24 VAC, 12.5 A transformer which will be just right. If you do that and find that the output voltage is zero, reverse the polarity of one of the secondaries and the voltage will be 24 volts RMS.
 
#10 ·
Increased track voltage will allow higher maximum speeds. You don't have to go as fast as the max though. Note that to actually achieve a high track voltage you will need to set the scale switch to the O/G setting AND use the voltage adjustment which is only accessible by removing the case. Refer to the Digitrax instructions for your DB200+.
 
Discussion starter · #11 ·
George,

The reason I ask is that all my trains run automatically with RR&Co, if the increased track voltage will increase the speed of the trains, not talking about the top speed as I do not go anywhere near that, then they will/may not stop where programmed. To re-program every schedule would be quite a task.
I do have the DB150 on the O/G setting.

Note that to actually achieve a high track voltage you will need to set the scale switch to the O/G setting AND use the voltage adjustment which is only accessible by removing the case. Refer to the Digitrax instructions for your DB200+.
If I am not having a problem running the trains on 12v, what is the benifit of increaseing to 24v if the track voltage is not increasing?
Sorry for asking what might seem like basic questions.

Ray
 
#12 ·
Are you using Large Scale trains or some smaller scale?

HO and smaller will do just fine with 12 VAC into a DB150. Many large scale trains need much higher input voltage to achieve the necessary track voltage to reach scale speeds.

The decoder knows nothing about it's input voltage. Vmax (CV5) just sets the maximum duty factor that the decoder will allow. If you increase the track voltage on a train, the max duty factor will be the same but the peak motor voltage will follow the track voltage causing a speed increase.

If you are just wanting to add a DB200+ to an existing DB150 system to set up a new power district, then just use the same transformer to power it. It will work the same as the DB150 and the transformer has plenty of capability to power the larger booster.
 
#14 ·
yeah, but an almost 20% drop in voltage under load is kind of crummy.

Most industry standards are rated at 10% drop from open circuit for a quality transformer.

In the case of DCC and model train motors, the speed of a motor is nonlinear, all the "top speed" is in the last few volts.

So, to make this clear, losing 3 volts out of 17 will make a significant difference "wide open throttle"...

Basically that transformer is way too low in voltage off the mark for DCC (you lose 3 volts in the booster), so you are at 14 volts, and under heavy load, you get to 11 volts.

Really a totally unacceptable transformer for LS DCC.

OK for HO.

Regards, Greg
 
#15 ·
Greg, that would be ok for large scale too if the operation is always slow, such as on a logging line. I run my test track from the booster that runs the HO layout. It is set to 14 volts, the same as the HO club that I joined. This works ok for testing and everything runs on it, just not very fast.
 
#16 ·
Ray:

The question that comes to my mind is, does the engine stop on the 3% grade with wheels spinning, or the motor stops turning? If the wheels are spinning, there is enough voltage, if motor stops there isn't. If it is the latter, you need a power supply that can put out 20+ volts. You probably won't need the full 20 volts for a USAT F3, but you will find that somewhere between 12 and 22 volts will be necessary.


Chuck
 
Discussion starter · #17 ·
Ok, you asked for it, here's the ful run down.

I have a "G" scale indoot layout (1:29). It consists of about 450' of track some 50 switches run by either tortois or LGB switch machines depending if you would see them. The premiss is a metropolitain city with a traction line and the CPR mainline yard, set in the 50's. The traction line which is about 50% complete is a curved dog bone and the mainline is over/under dog bone with about 75% of the track under the layout in a series of storage tracks. The grades to and from these storage tracks are 3.5% all on curves. All the track that is seen is Aluminium, all the track you can't see is LGB or Aritso. This includes switches. Minimum curves is 8' under and 10' on top. The mainline trains come and go in both directions seemingly without reason as a real railroad would do. The traction will have a series of stop and go's. All this is run by a PC with Railroad & Co. I have 4 USA Trains GP-7's, 1 USA Trains F3, 1 Aristo "B" unit, 2 Aristo RDC's, 1 Aristo RS-3, 1 Bachmann Shay and a Bachmann 10 wheeler converted to a 0-6-0, and a bunch of scratch built interurbans and electric loco's. Top speed is by the RS-3 , this is required to get it to run up the grade to bring it to the top of the layout and it is set at 50 mph for about 20 actual feet. All the other engines have a speed limit of 30 mph with a yard speed of only 20 mph for everything, so as you can see, none of these trains are running fast. All this is programmed through the PC so it doesn't vary. The whole program takes about 56 min. to repeat itself.
The reason I bought the DB200+ is that the F3 will not pull my aristo streamliners up the grade. I bought the Aristo "B" unit to help, but after many hours of trying to speed match, I gave up. (this is another problem for another day) I tried it anyway, and the 2 engines would not pull the train. So, I recently bought another GP-7 to put behind the F3. I am worried that the two engines would overload the DB150. I had always planned from the start to switch the DB150 over to the traction line and buy a DB 200. Now I am back to power requirements.......

Ray
 
Discussion starter · #18 ·
Chuck,

None of the engines stop on the grade. It is just a track to take the trains from the lower yard to the upper yard. The only one that I have had problems with is the RS-3. It didn't want to make it to the top and would spin on the "S' portion of the grade. (ya I know it gets better and better). Anyway, I increased it speed for the RS-3 at the bottom before the grade and it now makes it up everytime.

Ray
 
#19 ·
"and also have a full set of aristo streamline passenger coaches that my USA Trains F3 could not pull up my 3% grade." You made this comment, my question was about what happened when the F3, with a full set of streamliners, stopped. So we know what you are talking about, what is a full set of Aristo streamline passenger coaches ( how many cars)?

Chuck
 
Discussion starter · #20 ·
Chuck

I have 6 cars. I would like to add a heavy weight baggage car and a box car to this train. The engine striped the plastic between the gear and the wheel on the traction tire when it stalled. I have since fixed this, and started with one car and added until it would only crawl at the top of the grade. This was with 3 cars. I did not add a forth, as I do not want to do perminant damage.

Ray
 
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Bob in Kalamazoo
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