# DCC Booster Newbie questions.....



## rreiffer (Jan 14, 2009)

Hello all,

Ok, so I will probably drive some of you nuts with my questions but....Here are some questions that I have about DCC Boosters:
[*]Is common ground a better way to go for boosters?[*]How many feet of track should you allocate to a given booster?[*]What is the maximum booster size you would recommend (or minimum)?[*]Has anyone built any of the MERG DCC boosters?[/list] 

Thanks all


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## George Schreyer (Jan 16, 2009)

Boosters are normally designed to NOT use a common rail. They should be hard grounded together because there are cases where a fault current wants to flow between booster chassis. If the only ground connecting them is the one is the signal that drives the boosters, there might be smoke in the wires. 

The length of a power district depends on lots of stuff like your rail size, material, joiners and wiring topology and wire feeder size. I run about 75 foot sections but I have only one booster. My rail is brass with soldered jumpers across the joiners. Most sections are fed at one end because that resulted in the fewest places that I needed to run wires. Note that code 332 brass rail is a very good bus bar in it's own right, no additional bus needed. I originally had a 300 foot loop connected in just one spot and that worked too. That resulted in the worst spot being fed by two 150 sections of rail. 

For large scale trains, 5 amps simply will not cut it, even if you have many power districts. One train can draw more than 5 amps. I use an 8 amp booster on my indoor layout (again, just one booster but many switched "districts" as a result of my older cab control system). That layout uses smaller locos and the booster hardly breaks a sweat. My outdoor booster is rated at 10 amps, but it actually sources 20 before it trips. This is too much. A fault that has resistance can easily prevent a trip with up to 20 amps flowing continuously. This is not good so I added a PSX electronic circuit breaker that was initially set at 9 amps. I eventually had to bump it to about 13 amps to prevent it from false tripping. 

I don't know what a MERG booster is.


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## rreiffer (Jan 14, 2009)

GWS, 

Take a look at this link for more info on MERG. 

http://www.merg.org.uk/resources/dcc.htm#NB1A


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## StanleyAmes (Jan 3, 2008)

Posted By rreiffer on 09 Feb 2011 02:35 PM 
Hello all,

Ok, so I will probably drive some of you nuts with my questions but....Here are some questions that I have about DCC Boosters:
[*]Is common ground a better way to go for boosters?[*]How many feet of track should you allocate to a given booster?[*]What is the maximum booster size you would recommend (or minimum)?[*]Has anyone built any of the MERG DCC boosters?[/list] 

Thanks all
1) This all depends on the design of the booster. Some manufacturers support common rail, some do not. In the smaller scales there are locomotives with pickips that are offset, one side on the locomotive and the other side on the locomotive. For these locomotives some form of common between boosters is required. In large scale we have pickups on both side so no common is necessary. The proper way of hooking up a common is something best checked with the manufacturer you are using.

2) Feet is not, power consumption is. It all depends on how many locomotives you desire in a particular area. For example in my locomotive storage area the size or the power district is small while on the mainline it goes 500 ft or more.

3) While I am aware of 20 amp boosters, I tend to only recommend 10 amp ones.

4) Not me

Stan


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## Greg Elmassian (Jan 3, 2008)

Ditto on all the above. 

I did read the MERG booster documentation, the circuit operational explanation. Looks ok. There's several points in the design, which he mentions, that could be issues with autoreversers and with high current. 

For as little as the boosters cost themselves, I would probably stick to my NCE than build one. I use the same technique as George, since I also have the 10 amp NCE booster that can source 20... 

Greg


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## MrDCC (Dec 27, 2007)

George and Greg - 

Per Jim at NCE, the PB110 (with an adequate power supply) will source 30 amps for 1/4 second and 60 amps during the time that any circuit breaker, including the PSx series, will take to trip. 

Perhaps the regulated supplies you are using, Greg, limit this in your case.


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## Greg Elmassian (Jan 3, 2008)

Yes, there is method in my madness! I use individual 11 amp supplies for each PB110 booster, due to what it can source. I'm outfitting PSR series breakers and PSR-AX breaker/autoreversers. 

So far the madness is working. 

Greg


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## krs (Feb 29, 2008)

Posted By MrDCC on 16 Feb 2011 06:37 AM 

Per Jim at NCE, the PB110 (with an adequate power supply) will source 30 amps for 1/4 second and 60 amps during the time that any circuit breaker, including the PSx series, will take to trip. 


Ouch........that doesn't sound very healthy!


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## Greg Elmassian (Jan 3, 2008)

how many amps will others source for 1/4 second? 

Actually, it sounds very healthy, since other boosters are often overrated, like the 8 amp Digitrax that is not. 

My breaker in the PB110 trips just fine when it's a nice short. And my PSX series trips even faster, at lower amps (about 9)... 

There's a point here, and maybe you aren't quite getting it... if you have a system that can put out 10 amps continuously, you need to be sure you protect your locos from a 9 amp short. You can't have a high amperage load, but expect the system to trip prematurely. 

Greg


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## krs (Feb 29, 2008)

Greg, 

You won't see the 60 amps or even 30 amps if you use a Meanwell supply to drive the booster. 
Those supplies deliver current to a little bit above their rating and that's it. 

In model railroading, under normal operation one can occasionally get momentary shorts as you yourself have pointed out in the past. 
I just don't want 60 or even 30 amps flowing through my train equipment - what would be the purpose. 

Bottom line seems to be that there is no current limiting in the PB110 booster, it just pumps out whatever it can until the breaker trips. 

Knut


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## Greg Elmassian (Jan 3, 2008)

Knut, do you have a PB110 booster or the circuit diagram? 

There is no circuit breaker, when it senses a short it cuts the power. What are you trying to say? You want current limiting AND a circuit breaker? 

Maybe you do not realize that most supplies (and batteries) can put out a lot of current for a short instant. 

Also, maybe you are unaware of power requirements from motors, and short duration power requirements? 

If you think this is an unusual situation in electronics, you need to learn some more, there are surges, inrush currents, spikes, etc. in most everything in the electronic world. 

You are implying that there's 60 amps flowing steady state in one sentence, and then indicate the power supply won't put it out. 

What is your underlying point? 

Greg


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## krs (Feb 29, 2008)

Posted By Greg Elmassian on 06 Mar 2011 10:37 AM 
Knut, do you have a PB110 booster or the circuit diagram? 

There is no circuit breaker, when it senses a short it cuts the power. What are you trying to say? You want current limiting AND a circuit breaker? 

Maybe you do not realize that most supplies (and batteries) can put out a lot of current for a short instant. 

Also, maybe you are unaware of power requirements from motors, and short duration power requirements? 

If you think this is an unusual situation in electronics, you need to learn some more, there are surges, inrush currents, spikes, etc. in most everything in the electronic world. 

You are implying that there's 60 amps flowing steady state in one sentence, and then indicate the power supply won't put it out. 

What is your underlying point? 

Greg 


No Greg, I don't have a PB110 booster.
Sounded as if it had a breaker based on your statement in your previous post:
"My breaker in the PB110 trips just fine when it's a nice short."

I'm not talking about batteries or most supplies, I'm talking specifically about a DCC booster that is supposed to shut down when a short occurs to protect the equipment it's connected to, not try to push 60 amps of current out.

Sure, motors have a start up current, but the ones we use in Large Scale don't require anything near 60 amps.

I'm not implying anywhere that there is 60 amps of steady state current flowing - it's a *10 amp* booster, why would anyone think it can deliver 60 amps steady state? Doesn't make sense.




This statement doesn't really deserve an answer:
"If you think this is an unusual situation in electronics, you need to learn some more, there are surges, inrush currents, spikes, etc. in most everything in the electronic world."

however.....in any commercial or industrial design activity I have ever been involved in, surges, in-rush currents, spikes etc are always controlled. 


Knut


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## rreiffer (Jan 14, 2009)

Greg, 
I don't know if this question is out of line here but what is the maximum (and then average) current you would like to see per segment?


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## Greg Elmassian (Jan 3, 2008)

Knut: the surges are absorbed in your experience and mine. That's why we don't have DCC meltdowns from 60 amps, because of the limitation of the power supply, parasitic resistance, how quickly the PB110 cuts out... you seem to have siezed on the 60 amp number like a bulldog. Just wondering if you think the short term surge current capability of the PB110 is any different than the common light bulb, or any ordinary AC motor? You are acting like this is different than the rest of the world. That's why my last statement. Well enough, your bulldog grip on the 60 amp capability for 1/4 second is fine. I'll speak no further on this. 

Rich: Average would be a weird term. If I could protect my "power districts" and my locos properly, I'd like to be able to run 20 amps. Why? Because some long trains with multiple units can take 5 amps or so, and a reasonable lighted passenger train can take close to 10 in my direct experience. 

So 20 amps per power district would allow 2 trains in the same district worst case. This way, for most people, you could power one main line with one booster and have 2 trains on it at once, which I often do. 

I have effectively 2 main lines, although one is a bit short, and a switchyard. Three 20 amp boosters would work very nicely, the switchyard might have a number of locos on all at once, maybe 10, even if they are not all moving at once. I have designed my switchyard to allow 2 operators, so having 3 trains moving would not be unusual (one entering or departing, 2 switchers making up trains). 

I would also fuse all my loco pickup wires, so the typical short from a derailment at a switch, where the short is between the front and rear truck on a diesel, would be detected. Aristo already does this pretty well in some cases, where you have polyfuses at the pickup wires on each truck. 

Greg


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## George Schreyer (Jan 16, 2009)

Even if a PB110 can source 60 amps at it's terminals, by the time that it gets wired to a layout, the parasitic series resistance of the wiring will provide a current limit much lower than that. Mine is just over 20 at the furthest point from the booster so that, before I put in a PSX to reduce the trip point, I could trip it with a hard short anywhere. 

The issue is when you have a "smart short." This is a term that is used in the spacecraft business to describe an overcurrent fault that draws JUST enough current to NOT trip any protection mechanism. They were called smart because of Mr. Murphy who will almost always arrange it so that this happens. 

When your loco derails, it probably doesn't short the rails like a screwdriver shaft would during a test. There will be parasitic resistance. This resistance can limit the fault current to something under the booster trip value. That means that the booster just sees a high load and keeps pumping current. The poor loco probably can't stand that and it will likely issue magic smoke. 

The higher the trip current in a power district, the more likely that you can have a smart short situation. Even if a smart short exists on a section with a lower trip current, the current is lower and the likelyhood of survival of the impacted equipment is higher. 

Digitrax boosters, recent ones anyway, are rated at 8 amps and that is exactly what they will do. They run fine at less than 8 and trip at just about 8. Older ones would sag badly at 5 and trip at 8. IMHO, 8 amps of running current isn't quite enough. The 5 amps that my "8 amp" DCS100 would do is clearly not enough. A PSX set to 8.9 amps does better, but it will still trip on peaks which is annoying. I fudged it to about 13 amps (with the recommended added heat sinks) and it seems to be fine. It trips reliably and I can run at least 3 trains at once without it tripping. I can't drive more than 2 at a time anyway.


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## Greg Elmassian (Jan 3, 2008)

Ha ha! Reminds me of when you were last over, I was running 3 but only driving 2 !!! Wasn't my E8 that tried to "eat" your Davenport? 

Greg


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## George Schreyer (Jan 16, 2009)

It was... and it almost did. Every time I've tried to run 3 at once, it's been a disaster. I don't do that anymore unless one of them is on a different loop.


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