Quote from: Curmudgeon on February 28, 2007, 06:17:51 PM
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To have a power supply drop 25% to 35% under load is not good, normal, to be expected, or "standard".
10%, which is 16.8V on an 18V supply.
You can factor in internal control station drops (readable as soon as the loco moves).

I am really quite happy to know that the dcc community accepts this kind of voltage drop as "acceptable".
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Once again, I just got to come down on TOC's side.

As for me, NO NO NO. I would absolutely NOT accept anywhere near that sort of voltage drop on a DCC system.

Not 35%
Not 25%
Not 10%

NOT EVEN 5%

That may be fine for battery or DC but not DCC.

Here is why.

On DC you run one train, maybe several locos, but one train.
Increase the throttle the train will speed up because you are increasing the POWER.

Lets say you increase the throttle one NOTCH or TICMARK on the control panel. You happen to know that unloaded each one equals a volt.
Under a load the voltage did not go up one volt because the power pack sages under load.

Does that really hurt anything on a DC layout? No, because the train goes a little faster. Unless you have a meter you would not even notice.


BUT FOR DCC YOU WILL NOTICE.

You are running more than one train. All the trains are running on 18 volts (on an 18 volt DCC system)

Lets say you have a light  passenger train, not drawing a lot, one loco, just a couple cars, but it is going FAST. Full speed, 72.6 scale miles per hour. Still, it's only drawing 1 amp or less. (the LGB LCE III Munich Train Set will do that)

Now you just crack the throttle on some shays and try to start a long string of logging cars. Lets say it draws 4 amps.

If the booster drop the output 35% that's 6.3 volts.
Does the fast passenger train slow down 35%

No, Actually it would slow to a crawl. The speed is not liner compared to voltage. There is a lot of difference in top speed between a 17 and 18 volts. For the LCE set it is about 30 scale MPH. a change of 1 volt in the 17 to 18 volt range would be very noticeable. A change of one volt in the 2 to 3 volt range would be hard to see.

Aside from the speed problems, one would really notice even a 5% sag on a DCC system. Sound cards would suddenly change volume, Most lighted cars would dim, fans on the tops of diesels will change the pitch of the sound they make.
At 10%, running trains suddenly slow and the cars slack up, you can get false uncoupling if using Kadees and if they happen to be over a magnet. You could even experience derailments if backing light logging disconnects through turnouts or sharp curves.

In my opinion, a 5 amp system should put out it's rated voltage with no more than a 2% drop from unloaded to it's full 5 amp capacity.

But that is just my preference.

Still, I think anyone using a DCC system that sags 10% to run more than one train at a time would soon become disappointed with the performance of their trains. They may not recognize the source of the problem or be able to explain exactly why they are unhappy, but when they visit a layout with a proper DCC system, they will surely notice how much better everything runs.

ASIDE:
I'm just a little surprised that the EZ DCC booster Stan tested did not automatically shut down at 5 amps. I would not want any system that puts out more than the rated capacity without some sort of shutdown provision. Some LS manufacturer's will not honor the warranty if the loco or car has been subjected to more than 5 amps. The resulting damage is fairly easy to see and the current that caused the damage can usually be calculated.

B0B

I have to agree with TOC on this one.

The "NEW" decoder accomplishes little that could not be done with any decoder where you can access the + and - outputs of the bridge. Added battery backup years ago with LGB and Digitrax decoders, ran the tape on track test and impressed visitors.
But what happens after a year of use? What will it take to manage battery levels and charging rates? Will it play nice with other non battery trains. What happens to the other trains when the battery backup returns to contact with the rails after a relative long period on the tape and needs to provide a heavy charge to the battery? How much surge current does it draw? What are the effects on programming the CV's? How does it effect Transponding or NMRA feedback from other locos on the same track. How does it effect block detection?

QuoteThe advantage of this would be that locomotives could be fitted with sophisticated DCC decoders at a fraction of the cost of radio receivers plus auxiliary function control modules.

Not really. You can only fit them with the gold decoders. the name alone should tell you the cost. Try adding a function decoder and see what happens when the loco runs on tape. Try adding a Sound decoder, know of one that will still blow a whistle on command while NOT getting the DCC signal? What about the battery backup for the sound? Can it share the one used by the Gold decoder?
How is this cheaper? You have the cost of DCC AND the cost of battery.
Try fitting the decoder, speaker, sound card, batteries for the sound card, AND BATTERIES AND CHARGING CIRCUITS for the Gold decoder in a Bachmann open trolley or a LGB Forney. For that matter, try putting just the stuff for the Gold decoder in any small 0-4-0 without a tender. Yea you can remove weights and get it in some of them. If you run big locos that weigh 50 pounds and have dozens of electrical pickups then why bother?

Try running six locos with battery backup on the decoders for ONE YEAR, then you will know the answers to these questions, or call me and I'll 'splain it t'ya.

Listen to TOC, he may be a curmudgeon, not go into detail, be a little   gruff at  times, but he is right.
BOB