How Much Power is Enough/ Too Much? Volts vs. AMPS

There is no difference between 15V from two bricks vs. 15V from one brick.

I'm guessing the difference in operation is due to some power drop somewhere in the system, perhaps if you're close to the limit of one of the PH supplies, it's voltage sags.

I just did an experiment.  I connected a PH180 open circuit (no load) and the voltage measured 18.94VAC.  I put an 8 amp load (measured) on it and the voltage falls to 16.80 under load.  I then reduced the load to 4.3 amps (measured) and the voltage measured 17.86 VAC.  Obviously with two in parallel sharing the load, that voltage will fall less.  Since the TPC is just controlling the "voltage" based on a percentage of the input, having two bricks powering it with a 4A load will result in slightly more voltage coming from the TPC.

Bottom line is you are not actually working with exactly the same voltage where the rubber meets the road.

Consider cranking up the TPC to read the same voltage with one and two bricks with a full load, I think you'll find that the trains run the same.

Thanks John, so what would be "safer" for my equipment, one brick at 18v or two at 15v? What indicates not enough power, popping the breaker on the brick?

Two...at 18.

Much ado about nothing.

I appreciate you chiming in Rich, aren't you a bit busy these days? Anyhow, funny you should say that, I ran two bricks at 18v for some time, had a few derailments now and then with no consequences. Ultimatley I got spooked here on the forum(go figure) with mentions of electronics damaging amps. I lowered my operating voltage and added TVS's to my tpc as folks recommended. I figured better be safe than sorry. 

Most of this is amusing.  When you "reduce" the voltage from 18 to 15 volts with a TPC or any of the other phase-angle controllers (new ZW and Powermaster) you DO NOT change the peak voltage to the track one bit!  You are simply slicing off some of the early rise of the AC sinewave, but not changing the peak part of the waveform.

Bottom trace- input voltage  Top trace- output voltage  The small "points" just after zero crossing are the waveform segments reserved for horn/whistle and bell control.

Reducing the voltage may slightly reduce the "arc welding" heating phenomenon, but the instantaneous peak current for a derailment probably doesn't change.

Likewise, you do not change the performance for the locomotive at low and mid speeds because the locomotive's controller is also slicing off the leading edge of the waveform.  It is only when the locomotive's desired "slice" is wider than the power controller's available slice that you will see any effect from the reduced voltage.

All true Dale, but if the input voltage to the TPC is less, the output voltage at the same setting will also be less.  The TPC is not measuring the input voltage and correcting for a true output, it's just operating like it has a fixed input voltage.

My points about the input voltage changing under load are still valid.

 So if the TPC doesn't "really" reduce the voltage, why does my voltmeter say so? What is happening when the TPC is in conventional mode and locos start off at lower voltages?  FWIW reducing the voltage on the two parallel bricks via the tpc eliminated the arcing altogether, no one believes me on  this. This is a rather popular way to power o-guage trains but it seems there are alot of "unknowns", I would have thought it would be more "cut and dry".

I lowered the voltage on my TPC to 16 volts on the track and it has been a great idea.  I don't fry the DZ-1008 relay when I accidentally run over the back end of the double xover turned the wrong way.  The shorts are not as dramatic and potentially harmful.  There is a definite difference and an advantage, in my opinion, to doing this.

One problem I have with reduced voltage on the track is some electrocouplers don't fire properly on the lower voltages.

Rick, your voltmeter probably reads the average voltage, not the peak of the voltage waveform.  (If your meter is expensive, it might read the RMS voltage, but most meter just read the rectified average value.)  Very few meters read the peak value.  The oscilloscope trace shows how the peak of the sinewave is unaffected once you reach half power.

John, your measurement of the internal loss in the brick is useful.  Thanks for taking the time to "do the science".  Two bricks in parallel are certainly "stiffer" than a single unit.  From your measurements, it looks like the difference is more than half a volt at high currents.

From 4A to 8A I got a volt of drop, I'm guessing if you don't have cruise control that much will be significant in the operation of the train.  I put a TMCC locomotive on the rails and powered it with the KW, changing the track voltage by a volt did have a noticeable effect on the speed, especially at low speed.  I figured that would be about the same effect as paralleling two bricks, which I didn't try.

You really shouldn't separate voltage and current in some of these discussions.  Power matters and a single PM can provide significant power even at 15V. 10 amps of current or more.  All power sources have a voltage drop under load (unless compensated) due to the resistance value changes of wire when heated.

Reducing voltage of the power sources lowers the potential arcing because of the smaller voltage difference, but the high current available can still be a problem.  The concern with 2 PM in parallel is the 20 amps of current available, that can cause some serious heat damage in a much shorter time.

In theory, regardless how big your layout is as long as the PM provides 18 volts around the layout and the load you apply (engine, lights, smoke) doesn't exceed 180 watts (VA) then only one is needed.

The reason folks use larger power sources is that they run  ABBA all powered, plus have more than one train on a block.  This usually exceeds the 180 watt power source.  The risk is heavily damaged trains when there is a derailement, or a train gets caught across a block and it's internal wiring becomes a conduit feed for the other block.   G

Don't see where I was separating voltage and current.  I was talking about the voltage drop under different loads.  If you're running a conventional mode or even TMCC without cruise control, the change in voltage will affect the operation.  Sure it provides significant power, but we were talking about voltage drops and their effects.

Why do you assume I was talking about you? :-)  I was just commenting about the overall discussion of lowering voltage a few volts preventing equipment damage.

As you know, put a thin wire across a fully charged 9V battery and watch what happens.  My only comment was current with voltage matters in support of the original question posed.  G

Well, I can't argue with that, current does the work.

Something mentioned once but not picked up.

ADD a TVS across the power lines at each track connection. (Middle to outer rail)

Spikes come from many sources and those are what will kill your electronics.

A TVS at each track connection will eat the spikes and save your engine with very near zero power consumption.

I will also note, MTH Z series bricks seem to be a lot "Stiffer" under load than some other brands. I use a Z-1000 brick and have no trouble with voltage sags since I added another power drop at the far end of the layout.

That's why I recommend a TVS right on the pickups of any electronic engine or tender.

In truth, the major damage that transients do is to semiconductors, but other than that the reasoning is correct. A TVS anywhere in the circuit is good protection, but the closer it is to the item being protected, the better and more complete the protection is.  Since I'm protecting the locomotive electronics, I like to get them right at the target location if possible.

Specifically where do you put them when attaching them to the pickups & 1 or 2 pickups?

Thank You

Ken

You only need them on one pickup, normally the pickups are in parallel.  For  steamers with pickups on the tender, I put them in there as well to protect the sound boards.