Hey gang,
I'm in Electric Confusion Land again. I bought two of these Miniatronics distribution boards so that I can wire my ten power blocks for use by two different DC throttles, and I'm worried about overloading them because of the warning (at yellow arrow):
I have an MRC throttle that declares its total output at 18VA and an old Troller at 22VA. I have 22 gauge feeder wiress down to 14 gauge bus wires from the rails in each block. I'm all set to wire the buses to these distro blocks (after putting in my DPDTs first, natch) and I see this warning that the distribution blocks can only "handle" 15 amps. I know you divide the VA by 12 volts to get amps, which means my packs are outputting 1.5 amps and 1.83 amps, but I don't know what that means about how many amps are going through my distribution blocks.
So first, I need help understanding specifically what "handle" means here. If there are more than 15 amps going through, does it refuse the excess electrons and send them back to the house current with their tails between their legs? Or does it explode? Or does the light bulb or locomotive explode? It's just a bunch of screws connected by a metal band, so what's not to handle?
And second, obviously the picture that has developed in my head about electrical current still has inaccuracies. I imagine amps rushing from the house into the power packs to be converted to volt-amperes, thence into these distro boards and out to the rails. But maybe no current is "drawn" until a light is switched on or a loco motor revs up. So then where does the threat of "more than 15 amps" come from?
The flip side of the blue sheet pictured above gives you a chart where you can list and total up the amps your accessories "draw", but I'm not powering lights or grade crossing gates, I'm just powering locos, probably never more than two at a time, three if I doublehead two F7s in a consist. How would I know if I'm overloading the boards? And the word "draw" confuses me. I think of current as being pushed, not pulled. Maybe that's incorrect?
I'm hoping that with the details provided, someone can tell me not to worry about maxing out the boards, or else tell me what I need to do if that's a potential issue.
Thanks,
-Matt
Returning to model railroading after 40 years and taking unconscionable liberties with the SP&S, Northern Pacific and Great Northern roads in the '40s and '50s.
Most power pack can usually go up to about 16 volts but simplicity sake lets stick with . 15 amp capacity is way more than the powerpack you described can output. to answer you question, if you were able to draw 15 amps of power (highly unlikely in this case) it would most like cause the circuit board traces (think little wires) to heat up and break like a wire in a fuse. Probably would smell bad and in worse case cause a fire. 15 amps at 12 volts would be 180VA.
The maximum current you can get through it would be a dead short. This would cause the greatest current draw and will cause the component with the largest resistance to heat up. Usually the maximum current draw on the system is how much current the motor of the locomotive pulls (modern locos are about 1/2 amp max). You are correct that current is not drawn from the powerpack unless there is something there to pull it like a motor or light bulb.
The 15 amp rating probably comes into play for larger DCC systems that power layouts and or other large power systems. For example I use a 30 amp 12 volt power supply to run my Layout lighting. The power supply in this case would be able to put out more current than the distro board could handle which mean i would need to make sure that all the devices I have attached to it draw less than 15 amps.
In your case your throttle will not output anywhere near the 15 amps rating of this component.
Here is the best visual method I have of descrbing the relationship of current voltage and resistance. Voltage is the driving force, Resistance restricts how many amps can move and amps is amount of electrons moving.
Colorado Front Range Railroad: http://www.coloradofrontrangerr.com/
It just occurred to me that I didn't answer your title question. To measure current load (draw) you need to put an DVM (Digital Volt Meter) in series with the distro block and the power supply. imagine connecting the negative lead of the ditro block to your controller. Attach the other lead of the controller to your DVM. attach the other lead of the DVM to the distro block. Set the DVM to measure amps and you should be able to read your current draw. Please note that there is a current limit on the DVM so check before hooking it or you will blow the internal fuse.
crossthedogI'm worried about overloading them because of the warning (at yellow arrow):
that's the max current thru the board.
if each of your locos draws 1 A (most draw much less), you shouldn't drive more than 15 locos at the same time thru that board.
do you think that's likely to happen?
greg - Philadelphia & Reading / Reading
For these sorts of application, think of voltage as how hard your power supply PUSHES electricity through the wire, and of current as how much electricity your load PULLS out of the wire. (Note that you don't have to define what the 'electricity' is at this point, which is a good thing if you're at all sleepy.)
If the pressure is too high, just as in plumbing when water pressure gets too high, there can be leaks, blown seals, etc. The issue with current is that the more of it that goes through the circuit, the more 'friction-like' heating of things there can be.
If your strips are rated a nominal 15 amps, that's the highest current that the manufacturer guarantees you can run continuously before something in the strip gets damaged. You did not officially hear this from me, but you can usually run more current for relatively short periods through them... but why would you need 15 amps at 12 to 14V to run even a model railroad completely scenicked with neighborhoods having a Christmas-lights war?
Oh, and a relatively easy thing to check amperage with is one of those clamp-on ammeters -- put it around each wire IN to the strip, read the result, and add them up to get supply amps, or read all the wires OUT of the strips to read the demand... they will be the same for any purposes that matter here.
You would need a custom built power supply to get more than 15 amps. It just is not going to happen.
I measure current with my Fluke digital meter in series with the power pack output. I have always installed banana jacks in the layout fascia to hook up the meter easily.
My "big" Troller packs can only put out 2.5 amps.
-Kevin
Living the dream.
Thanks guys. I'm relieved and somewhat enlightened. Renegade, thanks for the illustration, it was very helpful. It makes sense that Mr. Volt does all the pushing (I think of him as a functional manager) but Mr. Amp has to do all the actual production work. The Resistance guy Mr. Ohm seems like an accountant to me, but I guess you can only take these metaphors so far.
Thanks to your help here, I've already installed both boards behind where my control panel will be. Not wired yet because I have another question and since you guys are knocking them out of the park just as fast as I can serve 'em over the plate... here it is.
My feeders are 22 gauge AWG, my buses 14. That tells me that at least in one direction, you can mix wire sizes along a circuit, even though this seems weird to me. Like we're now going to tighten the pipe that Mr. Amp has to squeeze through even more for reasons obscure to me. Nevertheless, onward...
The distro boards suggest using 18-22 gauge for hooking up to them, but I've already strung the 14 guage from all the blocks around the layout, so at least down one side of the boards the connections will be 14. Is it okay if I use an 18 gauge down the other side, for the connections from the DPDTs and from the power packs?
Or, again... does it explode?
My assumption is I can use 18 or even 22, even though the buses are 14. It will be slightly easier to connect the smaller gauge wire to the board terminals than the larger wire.
Thanks again,
Remember you can use crimp or solder terminals with spade ends to attach 14ga to those screw terminals.
If you don't mind paying for the copper overkill, the only real issue with what you propose is how the larger-gauge wire attaches to the rails. It can be hard to file the wire for tight solder contact to the bottom of the rail; it can look unseemly if in the side (or require detailing as a fishplate/joint bar or something... )
I use several of these digital V-A meters:
IMG_6338 by Edmund, on Flickr
Accurate enough for our model RR needs. At a glance I can see what's going on with my accessory supplies. When I had DC control I also had several LCD digital displays at various locations around the layout.
There are dozens of styles available out there.
https://www.amazon.com/Eiechip0-28-Digital-display-Volt-Meter/dp/B079L33VG2/ref=sr_1_15?dchild=1&keywords=dc+voltmeter+amp&qid=1627620802&sr=8-15
https://www.amazon.com/diymore-Digital-Voltmeter-Ammeter-Red-Blue/dp/B08HQM1RMF/ref=sr_1_8?dchild=1&keywords=dc+voltmeter+amp&qid=1627620901&sr=8-8
Some of the higher amperage models use a shunt. You wouldn't need anything like that.
The meters I used for my DC track required a separate 5.5v. supply, otherwise the meter wouldn't read down to zero volts.
Good Luck, Ed
crossthedogI see this warning that the distribution blocks can only "handle" 15 amps. I know you divide the VA by 12 volts to get amps, which means my packs are outputting 1.5 amps and 1.83 amps, but I don't know what that means about how many amps are going through my distribution blocks.
IF your logic is correct that VA/V = A, then you answered your own question. Let me explain.
If your power packs can only supply a maximum of 1.83A (and even if the two were combined in parallel the maximum current they can supply is only 3.33A but that's besides the point). Basically, your power packs will never be able to deliver anything even close to 15A. AT MOST they will be able to deliver less than 2A. You said it yourself.
Current will never force itself out of a supply and into a load. The source has to be able to supply the required current by the load, but it will never push more than the load is requesting. So unless your HO trains are drawing 15A (crazy talk) you're fine.
Overmodthe only real issue with what you propose is how the larger-gauge wire attaches to the rails.
mthobbiesCurrent will never force itself out of a supply and into a load. The source has to be able to supply the required current by the load, but it will never push more than the load is requesting.
crossthedog4) coming back to the control panel (DPDTs, distro strips, and power packs). My question is whether I can then use smaller wires again (say 22) at the control panel.
it would be better if you used 18g wire.
bear in mind that there are many feeders supplying current to the track and current reaches the loco from both ends of each rail.
but there is only one wire to your control panel
.
The general rule with wiring is to have the thickest cross-sections closest to the power supply... just like with extension cords in 'multiple'. With DC wiring for railroads that's less about 'voltage drop' than potential overheating.
The feeder rails are heavy because they supply a great many drops of #22 or less in parallel. That helps equalize the voltage across sections. The distribution board supplies the different feeder sections, likewise tapping them off in parallel, so its 'bus' thickness should be greater than the aggregate cross-section of the feeders... again, to keep all the feeders near a common voltage.
All that would probably happen 'performance-wise' with thin connection to the power pack is that the voltage drop through the thin wire would affect what the terminal block 'sees', and of course what eventually gets to the track. That would require you to turn the pack up a bit to get the 'same' speed from the locomotives, but all the voltages at the track sections would remain comparable with each other (so I'd expect little of the speeding up and slowing down that comes when the feeders are inconsistent). Note that this would heat those little wires even a bit more... quite possibly, to where they become a hazard to the touch.
If you are spending the money on 14ga feeders, there is no reason not to go with at least "15 amp capacity" in the feeder wires to the 15amp terminal block -- that's 18 or even 16 gauge. And larger would be better.
As a note, there are distribution blocks with side-entrance terminals clamped by setscrews into which wires, bundles of wires, or tinned bundles of wires are easily inserted straight and clamped down. These have more metal in their terminal buses and are rated at higher current; without any trouble I found one with a comparable number of terminals rated 30A for $6.99. I think those might be better suited for wiring 14ga than those little screw clamps you have...
crossthedog I don't want to go with bigger wires at the rails. I have small feeders (22) at the rails, larger wires (14) coming back to the control panel (DPDTs, distro strips, and power packs). My question is whether I can then use smaller wires again (say 22) at the control panel.
I would not use lower capacity (anything smaller that 16ga) wires between the power pack and the toggle, including all connections to the distribution block.
At the lower voltages we use, internal resistance of smaller wires becomes more of a factor than a lamp cord at 120 volts.
I use small runs of 22 gauge for track feeders, and 24 or smaller inside of locomotives. However, to get the voltage/signal at a good even supply to where it needs to be, bigger is better.
OvermodAs a note, there are distribution blocks with side-entrance terminals clamped by setscrews into which wires, bundles of wires, or tinned bundles of wires are easily inserted straight and clamped down. These have more metal in their terminal buses and are rated at higher current; without any trouble I found one with a comparable number of terminals rated 30A for $6.99. I think those might be better suited for wiring 14ga than those little screw clamps you have.
Thanks guys.
crossthedogMy feeders are 22 gauge AWG, my buses 14. That tells me that at least in one direction, you can mix wire sizes along a circuit, even though this seems weird to me. Like we're now going to tighten the pipe that Mr. Amp has to squeeze through even more for reasons obscure to me. Nevertheless, onward... The distro boards suggest using 18-22 gauge for hooking up to them, but I've already strung the 14 guage from all the blocks around the layout, so at least down one side of the boards the connections will be 14. Is it okay if I use an 18 gauge down the other side, for the connections from the DPDTs and from the power packs?
Generally speaking larger wire is almost always better if you can use it, but there are times when it would be easier to mix in smaller gauge wires and you certainly can do this if desired as long as the smaler wire will handle the load. In your case, you're not going to be pulling more than two amps through any wires, and 22 gauge can handle that fine. One of the issues with smaller wire, however, is voltage drop. The smaller the wire the higher the resistance, and resistance is also directly proportional to the length of the wire. Voltage drop is directly proportional to the resistance and therefore the length, so you don't want to use too small of a gauge of wire even if it will handle the load if it causes too much voltage drop. Using a smaller wire at both ends of a run, and even at other places throughout, but a larger wire through most of it, will limit the length of the smaller wire and the additional voltage drop from it.