Thank you for the technical info
I am convinced
I will be using 3 dc cab power supplies
Tony
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On Aug 23, 2019, at 2:04 AM, Dave Heap <dgheap@...> wrote:
Tony,
On 23 Aug 2019, at 1:52 PM, AD <bklyns_baseball_club@...> wrote:
I am Trying to understand what you said:
So 2 diagonal parts of the h were damaged but the other 2 were not so the motor runs at full speed in one direction and the damage to the first 2 clauses the inability to control the engines speed.
Correct. For some illustrations, see:
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You said failing like this is a common occurrence. But decoders are normally connected to motors inside the engine and both decoder and motor are isolated from the frame so how does the short occur?
It's extremely unlikely to occur if the decoder is normally connected to motors inside the engine and both decoder and motor are isolated from the frame.
It is highly likely to occur if the motor connections touch each other, the frame, another decoder wire, the track...
It is also highly likely to occur if the motor connections are connected to a length of isolated track with a DC loco on the track. At some stage during operation/rerailing of the DC loco, a momentary short is likely to occur.
But when i address the decoder and command station shuts down that means a short is occurring on the input side of the decoder. I assume the decoder has some circuitry on the input side that interprets the command and then creates a dc voltage to be placed on the output side.
What happens is that the speed commands (in one direction or other) will turn on the 2 undamaged diagonal parts to drive the loco in the opposite direction. But it can't turn off the 2 damaged diagonal parts, so you have a double short circuit inside the decoder.
Why wouldn¡¯t the problems of a short risk go away if a quick reacting circuit breaker
Electronic components fail in microseconds if the peak current is well above the rated capacity.
The DCC booster will have a short-term current capability well above its continuous rating. In these circumstances, circuit breakers are unlikely to be able to operate fast enough, but even if they did, your layout would be frequently experiencing nuisance shut downs as momentary shorts are not uncommon on a layout (wheels, frames, frogs). So they deliberately have a delay, often between 25 and 250 milliseconds. Plenty of time to fry your decoder.
rated to trigger below the peak value of current the decoder can handle but above its max operating current was placed in series with an output lead. In the case of the decoder i am using its max operating current is .7 amps, n scale motors run at .25 amps
And its peak is 1 amp doable for about 1 second. Thus a 1 amp breaker which requires manual reset should protect the decoder.
You underestimate the peak current capability of the DCC booster. Using a low current (say 1 amp) electronic peak current limiting circuit on the entire layout will lead to poor layout operation.
Your configuration (decoder motor outputs connected to a length of track with a loco on the track) is high risk and certainly not recommended by the manufacturer. You have paid the price for the high-risk setup you have devised.
Dave in Australia
