In-line fuses or Circuit beakers

[lescar]

I've been doing searches on this forums for posts containing information on this subject, but all my searches keep coming up empty or something that's not even close to what I'm looking for. 

What I'm trying to find out is the best way to connect to the booster, do I need a fuses holder/circuit breaker on both the A and B rails.  I'm using an 8 Amp. Booster so normally the fuse size should be 8 Amp.. I was thinking of cutting down the fuses size to about 5 Amps so it would blow at a lower current rating,  since I don't need the whole 8 Amps. At this time.

But on the other hand using a lower fuse rating would not allow the command station to do it's job in indicating a short, it would just blow the fuse. My main concern is welding something to the rails with the higher Amperage.

Thanks 
Les

[rich1998]

Use circuit breakers or 1156 auto lamps or 1157 auto lamps. The breaker or lamp is in seires with one booster lead.
DCC circuit breakers come with instructions. Try to follow the instructions first.

Below is a less inexpensive way the many use on layouts. A short in that booster section will light the bulb but not shut down the booster if you use say, three different bulbs to feed three different sections of the layout. We do that in our local club witha three amp NCE system. Works very well.
We put the three bulbs where we split the three feeds just after leaving the booster.

The same if you use three circuit breakers.

Fuses will put you at a disadvantage when you run out of fuses on a Sunday night.

Below are some links from a Google search.

http://members.optusnet.com.au/nswmn/1156.htm

http://model-trains-video.com/e107_plugins/forum/forum_viewtopic.php?25

http://www.greenspun.com/bboard/q-and-a-fetch-msg.tcl?msg_id=001jdi

Lex

[Nathan]

Look at circuit protectors made for DCC.
NCE, Digitrax, Lenz and DCC Specialties among others make such units.

Your Booster will react much faster then any Fuse or regular Circuit Breaker you can buy.

[rich1998]

NCE has a module with six lamps on it. The lamps will light up and limit the current. The booster will not shut down in most circumstances. This is from experience, not opnion.

NCE CP6 circuit protector. It can protect six circuits/sections of your layout. There is even a manual you can download.

http://www.ncedcc.com/index.php?page=shop.product_details&flypage=flypage.tpl&product_id=9&category_id=1&option=com_virtuemart&Itemid=1

Many, many users of the light bulb or circuit breakers will tell you that.

Lex

[Jim Banner]

Main advantage of lamps is that they are cheap.  Main disadvantage of lamps is that they limit the current, not shut it off.  Take for example an H0 layout with an 8 amp booster.  Conventional wisdom says that is too high.  So lets cut the layout up into say five sub-districts and limit the current in each district using lamps.  If it is a flat land layout running trains with single locomotives, we will probably get away with #1157 automotive lamps.  But make that a heavy hauler with steep grades, heavy trains and lots of them.  The time table might show only one or two trains in any sub-district at any one time, so even if they are both double headers, we can probably still use #1157 bulbs.  But Mr. Murphy is a member of the operating crew.  Which means from time to time a third train, running either early or late, will also be in the sub-district.  Let's see.  Three trains times 2 locomotives each times 1/2 amp per locomotive is 3 amps.  Those #1157 lamps will definitely be in limiting mode, dropping all the power and shutting down the sub-district.  So how about using two #1157 lamps in parallel.  We will limit the current to 4 amps or so, which is only half of our booster output.  And 4 amps is less than the five amps maximum that conventional wisdom says is the maximum safe current for H0. Now we will be okay with 3 trains in a sub-district as long as they are not all pulled by A-B-A consists.

At this point, we hold an operating session.  Everything runs fine until Mr. Murphy runs his train complete with three diesels at the point into a sub-district that already contains two A-B-A sets.  On come the twin 1157's, startling Mr. Murphy's brother-in-law who promptly runs his train wrong way through a switch, shorting out his sub-district.  At this point, the booster goes into overload mode, shutting down the remaining three sub-districts as well.  The whole railroad comes to a crashing halt.  Mr. Murphy quickly takes all three of his locomotives off the track, leaving only 6 locomotives in that sub-district.  And his brother-in-law moves his locomotive back away from the switch, unshorting that sub-district.  They and the rest of the operators wait expectantly for the power to come back on.  And wait.  And wait.  And wait.

In fact, the power never does come back on.  Why?  Because the booster is in overload mode.  Every second or so, it applies power to the tracks, all of them, detects that they are drawing more than 8 amps, and turns the power off again.  It keeps on cycling, hoping that sooner or later it will find that the load has dropped to less than 8 amps so that it can turn on again.  But the load never does drop.  Trying to start up all those sub-districts at once requires more current than in takes to keep them running, much more current.  And it is not just a matter of the operators all turning their throttles to zero so that their trains draw no current.  Without power on the rails, the necessary signals have no way of getting through.

What would a power management unit do in this case?  A power management  unit, also known as a DCC circuit breaker, contains circuits similar to the current monitoring circuits in the outputs of DCC command stations.  They are NOT normal circuit breakers and work in a completely different way.  They do not simply limit the currents in their sub-districts, they turn the power right off.  Suppose we used five of them in place of the lamps in the same layout just described.  We can quite happily set each breaker for 5 amps, knowing that it will apply that current for only a few milliseconds at a time, not long enough to build up enough heat to melt turnouts or weld wheels (ever wonder what damage 4 amps applied continuously can do?)  When Mr. Murphy overloads a sub-district, that sub-district's breaker shuts it down, leaving all 8 amps from the booster to run the remaining sub-districts.  If a second sub-district is shut down by the brother-in-law, all of the booster's 8 amps are still available.  In fact, you could shut down four out of the five sub-districts and the operators running the fifth sub-district would not even notice.

So how do power managers determine when to turn back on?  Each breaker in turn applies power to its sub-district to see if it is still shorted, just like a booster would do to the whole layout.  But it does its testing faster, so that the booster never has a chance to shut down.  And if a sub-district is no longer shorted, its breaker will turn on that sub-district only, avoiding shutting down the booster by the whole layout being turned back on all at once.

Bottom line, lamps cannot replace power managers with one exception - if the total limiting current of all the lamps is less than the booster output.  So with an 8 amp booster, you would only be able to run 3 sub-districts limited by lamps to 2 amps each.  In my opinion, that is not a very efficient use of booster power, although on a small layout with a large booster, it is still better than having to use multiple boosters.

That above example is based loosely on my own layout.  Biggest difference is that we don't have a Mr. Murphy on the team.  We do have a fellow who seems to have more trouble than most, and when anything goes wrong, the first person we look for is "The Usual Suspect."

Jim

[lescar]

lexon:  Nathan:

Thank you both for your inputs.

Jim: I was hoping you would chime in, I've downloaded the manual for the PM-42 and  after reading through it, it's going to do what I want, which is limit the current to the layout so the full 8 Amp's is not going to the rails all at once, and it's also going to be nice to be able to adjust the amount of current that dose, so as the layout grows it can be changed as needed.  So that will be my next purchase along with a few DS-64's for switch operations.

Thanks 
Les