Blair & Rasa

Steve.ï¿½

Thanks for the quick reply.ï¿½ Halfway through writing that, I realized that a quick sketch of the layout and location selections was going to be needed to short-circuit a whole lot of back and forth.ï¿½ I should have not posted until that sketch was available.ï¿½ I'll post the sketch later today, but to give you a quick answer, 40' is half of the approximate distance between boosters.ï¿½ Due to the topology of the layout, it makes sense to reduce that in some instances, to make more sense of the bus runs, but in general that's what I worked with.ï¿½ The room is 28x52, and the layout is a 2 1/4 turn "nolix" running ccw up around the room, but also feeding three separate peninsulas running the length of the room.ï¿½ So there's a lot of bench run.ï¿½ All of this will become clear with a diagram.

Probably best if comments are held off until I give you all the diagram.

Blair

On 17/06/09 00:20, 'Steve Haas' Goatfisher2@... [WiringForDCC] wrote:

>>I'm starting to contemplate my layout power requirements, and I need a

sanity check (quiet out there).<<

>>I've laid out the booster positions so that no track

point is more than 40' from a booster/PM42 location.ï¿½ In a couple of

cases, one booster/PM42 feeds three levels of track, which encompass

four differ mainline sections;ï¿½ in other cases, a Yard on one level

takes two PM42 sections, while trackage above and below use the other

two.ï¿½ PM42s will not be used for reversing, just power management.<<

1) It sounds like you are determining booster positions and quantities based on a maximum bus length or 40'.ï¿½ The number of boosters, with boosters being expensive items, is usually determined by determining the total power load of the of the layout (how many engines running at the same time, plus passenger car and caboose lighting) and then dividing by the amperage capacity of the booster (usually 5 amps for a N or HO layout).ï¿½ Having done that, you can define your booster districts so no booster is expected to have more than a 4 amp load.

2) You want to maintain a max length of bus runs of 40' - that's a reasonable upper limit. But, don't forget, you can split the booster output at the booster and run 40' (your designated bus length) in _each_ direction for 40'.ï¿½ Beyond that, bus lengths can be extended further if the bus pairs are twisted (3-5 turns/foot), and R/C "filters" are used at the ends of the buses.

ï¿½>>All that being said, I find that I only have one location where I can

justify an 8A booster; the rest will happily be managed by 5A boosters.<<

Conventional wisdom suggests that you limit yourself to 5 Amp boosters.ï¿½ In a short situation the section of track served by that booster could potentially receive the entire 8 amps of current, and that's a hefty amount and could lead to damage to equipment.ï¿½ Far better to use two 5 amp boosters in lieu of the 8 amp.

>>So I guess I'm asking, have others encountered this?ï¿½ In my case, my

max-bus-length rules force me into far more booster/PM42 combos than I

As I mentioned above, consider splitting the bus at the booster and run 40' in each direction, and create booster areas where the _expected_ max current draw on each 5 amp booster is between 3 and 4 amps - that leaves you a bit of ceiling room for the occasional extra current draw.

I'm headed out on a long trip either Saturday or Sunday, and don't know yet what e-mail access I'll have on the way.ï¿½ If/when I do, I'll check in to see if you have any followup questions.

Others will also most likely step in to assist you, too.

Best regards,

Steve

Steve Haas

Snoqualmie, WA

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