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Hi All,
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I'm considering putting a fuse box on the hot (red) side of my 12V bus. It's an automotive-type fusebox and I'm wondering if I should put 2Amp or 3Amp fuses in it.
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Thoughts?
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Dan
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I left out of my original message that my power supply is a 12V 30Amp supply. My logic for adding a fuse block is to ensure that low (controlled) amperage goes to each section of the layout and to the expensive LCC devices I'm deploying. Make sense?
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anyone?
dan
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Dan, what is providing the 12V power? What size wire are you trying to protect?
DonV
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In addition to the wire size and the ampacity of the wire, what is the expected maximum current drawn by the individual loads?? In practice, the wire size and the fuse should not be smaller than the load current, and the fuse should not be larger than what the wire can safely carry.
Voltage drop considerations may suggest a larger wire, but there is no reason to make the fuse correspondingly larger.
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Dan, Wouldn't you use fuses that equal or are a bit lower than the maximum amps your system could draw? Jerry
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Jerry,
Protecting the wiring is a crucial element in choosing a fuse. You want the fuse to blow rather than have some wiring out under the layout melt or burn up. A thin drop wire might not be able to survive if there is a short circuit on the track, particularly if you have a beefy 10A booster which you chose to protect with a 10 Amp fuse. The fuse will indeed help protect the power supply, but the thin drop wire might instead start to burn up with only 5 A flowing through it. Whoops!
David
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On Sep 4, 2024, at 6:53?AM, Jerry Michels <gjmichels53@...> wrote:
Dan, Wouldn't you use fuses that equal or are a bit lower than the maximum amps your system could draw? Jerry
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Yes. Suggest ¡°quick blow¡± fuses or breakers. Charles
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On Sep 4, 2024, at 8:40?AM, Duff & Polly M via groups.io <dpmeans@...> wrote:
? In addition to the wire size and the ampacity of the wire, what is the expected maximum current drawn by the individual loads?? In practice, the wire size and the fuse should not be smaller than the load current, and the fuse should not be larger than what the wire can safely carry.
Voltage drop considerations may suggest a larger wire, but there is no reason to make the fuse correspondingly larger.
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Maybe it¡¯s me but the 12v 30 amp power supply gives me major cause for pause consistent with the comments about the wiring and ¡°ampacity¡± of said wiring. ??I have a layout with multiple power districts with multiple DCC between the boosters (power supplies) and track segments. That follows best practices and has been adequately short circuited intentionally for testing purposes. ??That much amperage needs a larger wire? (larger wires have less resistance than smaller ones) to carry the current without heating up.? ? Don¡¯t mean to be Debbie downer, and wasn¡¯t going to say anything, but somewhat concerned here.? No need to burn down the house for something that is supposed to be relaxing and fun! ?
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From: [email protected] <[email protected]> On Behalf Of Charles Brumbelow via groups.io
Sent: Wednesday, September 4, 2024 12:37 PM
To: [email protected]
Subject: Re: [w4dccqa] 12V Fuse Box? Yes. Suggest ¡°quick blow¡± fuses or breakers. Charles
On Sep 4, 2024, at 8:40?AM, Duff & Polly M via groups.io <dpmeans@...> wrote:
? In addition to the wire size and the ampacity of the wire, what is the expected maximum current drawn by the individual loads?? In practice, the wire size and the fuse should not be smaller than the load current, and the fuse should not be larger than what the wire can safely carry. Voltage drop considerations may suggest a larger wire, but there is no reason to make the fuse correspondingly larger.
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Thanks for the responses.
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The wire connected to the fuse box is 12AWG and then goes to terminal blocks in each of 12 power districts on 2 decks. Each district will power as little as 2 switch machines and building lighting and a crossing, to as many as 25 switch machines in a large yard along with buildings, etc.
The district bus in each area may have distributed terminals blocks in heavier use situations.
I chose the 30A power supply thinking 2-3 Amps per district with a little leeway for staging and the large yard.
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I appreciate the comments of concern and that¡¯s why I started this thread.
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dan
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Dan and others¡ EVERY DCC BOOSTER NEEDS IT¡¯S OWN ISOLATED POWER SUPPLY !!
The electrical design of practically every commercial DCC booster starts with a full wave rectifier, which means that you do not have direct access to the internal DC supply that feeds the DCC power switching bridge for the track. So Dan¡¯s idea of using a single power supply to feed and operate multiple boosters simply doesn¡¯t work. (Yes, one COULD somehow break into the boosters to gain access to the necessary connection. But doing so would certainly violate any warranty of the manufacturer.)
DonV
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AND¡ the boosters need more than 12 volts DC input to produce the 12-16 V DCC output to the track
DonV
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Hi Don,
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I wasn't very clear in my post; sorry.
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My question has nothing to do with DCC. It's about sending 12V power to the various industrial districts on my railroad.
It's about the 12V power bus used to power switches, lighting, and LCC components. I posted here as I wasn't sure where else to post a 12V question about wiring and protecting circuits.
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My NCE DCC components are all powered through an APC Surge Protector on an isolated outlet.
Dan
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Seems the more I read in this thread, the more confused I get.
We are using 8-amp MeanWell power supplies. Each power supply is connected to two DB220s, so four boosters per power supply. Our turnouts are all Tortoise and have their own power supply. We've operated this way for years. We used to use PM42s, now BXP88s, to provide short circuit protection. We had a breaker for each power supply, but when we made the changeover from PM42s to BXP88s, we took them out since we never tripped one of these breakers. The layout is routinely "abused" by operators derailing trains, running through turnouts, crap being left on the rail, etc. Even fools who use a piece of metal to intentionally short out a block for "fun." You name a way to short a block, and I have probably seen it.
Each booster runs through a separate, panel-mounted Ramp Meter (i.e. two meters for a DB220).
We can run up to six sound-equipped locomotives per block, perhaps more, but if we exceed six per block, if a locomotive derails, the in-rush of power is usually too much to start up all six locomotives at once.
Since the BXP88s instantly cut to power to a block with a short circuit, why is another breaker needed? Never melted a feeder, nor have I ever found a wire running hot.
FYI, wire from the command station/boosters to the BXP88s and from the BXP88s to a terminal block that connects the busses is 18ga., bus wire is 12ga., track feeders are 22ga. All wire is stranded. We have a DSC240, three DB220, and three DB200+. Cooling fans are mounted to direct air flow to the heat sink fins on the rear of the command station/boosters
Jerry Michels, Amarillo Railroad Museum
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Since a full wave rectifier passes input power of both polarities, including AC, but rectified to be one polarity, you could connect multiple boosters to a single large DC supply. But, most boosters with AC inputs probably include voltage regulators, you would need to supply a higher voltage to leave some "headroom" for the regulator to reduce the input voltage to the track voltage, plus the 1.4V or more lost across the bridge rectifier.
My EasyDCC boosters use external regulated switching DC supplies for power, so definitely could be connected to a shared supply. But, there is danger here that one rail might not have short circuit protection in the booster circuit.?
Effectively, it would be the same as powering them from different supplies, but then connecting their commons together, which is recommended. So, if your boosters work the same as my EasyDCC boosters, they could share one supply. But, any one booster with its output shorted might pull down the supply voltage to all the boosters sharing the single power supply. Suitable switching power supplies?are pretty inexpensive. I would stick with a separate supply for each booster.
Don W
-- Don Weigt Connecticut
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Don,
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Ummmm, I'm confused. Where did boosters come into the discussion? The discussion that I have been following has been on a 12VDC buss for powering accessories (not boosters) and using a fuse box to protect the branches.
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? If you need separate power supplies for DCC boosters, why does Digitrax sell a big power supply to power more than one booster?
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Richard W
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On Thu, Sep 5, 2024 at 01:41 AM, Don Vollrath wrote:
Dan and others¡ EVERY DCC BOOSTER NEEDS IT¡¯S OWN ISOLATED POWER SUPPLY !!
The electrical design of practically every commercial DCC booster starts with a full wave rectifier, which means that you do not have direct access to the internal DC supply that feeds the DCC power switching bridge for the track. So Dan¡¯s idea of using a single power supply to feed and operate multiple boosters simply doesn¡¯t work. (Yes, one COULD somehow break into the boosters to gain access to the necessary connection. But doing so would certainly violate any warranty of the manufacturer.)
DonV
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Dan,
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I think it makes sense to fuse the various buses or branches powered by your 30 Amp supply, to protect devices that might accidentally short the 12V, and not have as much as 30 Amps heating up the circuit wiring and possibly welding the short circuit path. That's the same reason automobile fuse blocks exist.
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Normally, you should fuse for about 1.5 times the load current. Wiring that carries the normal load current without much voltage drop should be adequate for that much current without overheating or other harm. So, the ideal fuse sizes to use depends on each circuit's load. But, you could just standardize on one adequate value, perhaps 5 Amps, as long as the wiring is at about 18 gauge or heavier and the largest normal load is about 4 Amps or less.
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I don't think you normally would want to divide your 30 Amps available power into 10 to 15 separate fused circuits with 2 or 3 Amp fuses, and that many power buses. Four or five buses with 8 Amp or 10 Amp fuses should be adequate for most power distribution needs. Ten or more fused circuits probably aren't needed. If there is some unusual issue to justify it, please share what it is.
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Don Weigt
Connecticut
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Makes sense, thanks Don!
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dan
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Sorry, I went off on the wrong tangent. Since this is a wiring for DCC site, I assumed too much. Jerry Michels
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I¡¯m with Jerry M. On this one too. I assumed that the only accessories that would need that much power (12V x 30A) would be multiple boosters.
And if a manufacturer puts multiple boosters in the same package with a single power input connection¡ they can do that because they have all the internal DC connections available to them. (The ¡°booster common¡± connection spoken of elsewhere is the internal negative wire to the DCC output switching section)
DonV
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DanBrewer
David Gibbons
fire5506