Separate Track and Accessory Buses

[Benefield]

My layout consists of Digikeijs DR5000, points controlled by DR4018s but using a separate non DCC power feed to power the MTB MP1 point motors all fed from a single DCC bus. I am not short of overall power from the DCC circuit so have no need for a booster from that perspective. However, I would like to have separate buses for the track power and DR4018s so that in the event of a short, I only lose either track power or accessory power, not both. Can this be achieved by simply splitting the DCC feed from the DR500 into two separate supplies going to the separate buses and running each through a circuit breaker such as the NCE EB1? If not other suggestions are welcome.

[RedgateModels]

Yes, personally I don't bother protecting the accessory bus with a breaker, just the track bus. Chances of an accessory decoder causing a short are remote. Save yourself 30 quid 😉

 

I use MERG DC01's on my layouts - 1 per board so that each board has it's own track power district. 

[RobinofLoxley]

Having a breaker on the track power only means that you can still operate turnouts or anything else on the accessory bus if the main power is out due to a short; this may help if the short was caused by a wrongly set turnout.

[Nigelcliffe]

I would point out that the trip-sensitivity on the DR5000 is amongst the fastest of any command station. 

So, very few commercial district cut outs will trip fast enough to be reliable - the command station will trip first.   

 

The MERG DCO does trip fast enough, but that's a DIY kit, and was designed to trip extremely fast so it worked with an ECoS (another device which has an extremely fast trip).

Edited September 23, 2022 by Nigelcliffe

[RobinofLoxley]

16 hours ago, Nigelcliffe said:

I would point out that the trip-sensitivity on the DR5000 is amongst the fastest of any command station. 

So, very few commercial district cut outs will trip fast enough to be reliable - the command station will trip first.   

 

The MERG DCO does trip fast enough, but that's a DIY kit, and was designed to trip extremely fast so it worked with an ECoS (another device which has an extremely fast trip).

Just a question as a complete non-expert for clarification, I thought that trip outs were a feature to do with overload situations, generally caused by shorts. So if you had a commercial overload cut-out it could be set to a current value lower than that of the command station itself so that control over accessories wouldnt be lost even if the main power was shorted out. You seem to be suggesting that the command station may trip anyway?

[Dungrange]

I'm equally a non-expert, but I understand that what @Nigelcliffe has said is correct.  Setting a circuit breaker to a lower current level should cause it to trip first if both the circuit breaker and the command station have similar response times to a short circuit, but ultimately it is the time that each unit takes to trip that is the most important.

 

When you get a short, the current being drawn may rise from 1 Amp to 10 Amps, but it won't rise instantaneously.  It will increase over several milliseconds and therefore will reach the 3 Amps that the circuit breaker is set to trip at before the 5 Amps that the command station will trip at.  However, if the command station has a very fast trip rate, then it may be that it detects and responds to the 5 Amp overload before the circuit breaker has had sufficient time to respond to 3 Amps.

[Hamburger]

1 hour ago, Dungrange said:

When you get a short, the current being drawn may rise from 1 Amp to 10 Amps, but it won't rise instantaneously.  It will increase over several milliseconds and therefore will reach the 3 Amps that the circuit breaker is set to trip at before the 5 Amps that the command station will trip at.  However, if the command station has a very fast trip rate, then it may be that it detects and responds to the 5 Amp overload before the circuit breaker has had sufficient time to respond to 3 Amps.

That is correct. This is even different with some controllers: they have a dI/dt cut-off, which means that if the current rises by more than a certain value within a very short time, this is defined as a short circuit. A controller with 5A can even switch off when the current increases extremely quickly from 0.5 amps to 2.9 amps. In this case, an additional circuit breaker with 3.0 amp will not respond.

[Nigelcliffe]

3 hours ago, RobinofLoxley said:

Just a question as a complete non-expert for clarification, I thought that trip outs were a feature to do with overload situations, generally caused by shorts. So if you had a commercial overload cut-out it could be set to a current value lower than that of the command station itself so that control over accessories wouldnt be lost even if the main power was shorted out. You seem to be suggesting that the command station may trip anyway?

 

Yes, if the command station has a fast trip speed, it will trip first, even with a lower current overload device fitted.        

 

Current only matters if the trip speeds are about the same, or if the command station trip is slower than the cutout trip.  

 

 

If you ask Digikeijs about it, they will tell the customer to buy their boosters, as there aren't any cutouts which Digikeijs know to be fast enough for the DR5000.  And thus isolate the problem at booster level.    I know the MERG cut out works, because that is fitted to some layouts with DR5000's and it works. 

 

 

- Nigel

[Crosland]

It's also worth looking at Tam Valley cutouts. They also operate very fast.

[Uksid]

I use 1 of these with my DR5000 and it works perfectly https://tonystrains.com/product/dcc-specialties-psxx2-circuit-breakers

 

Not sure how easy they are to source in the UK.

 

One runs the track bus and the other runs my DCC Concepts accessory decoders.  The great thing about these is that when there is a short it keeps retrying to power back up until the problem is fixed.

 

I had a power up issue with the DCC Concepts decoders and frog power, for a split second on power up it all shorts out, this device worked like a charm and now I don’t need to keep switching things manually.

[DCB]

Duplicate

Edited September 30, 2022 by DCB

[WIMorrison]

On 24/09/2022 at 16:52, Crosland said:

It's also worth looking at Tam Valley cutouts. They also operate very fast.

As does NCE EB1