How long can 20 AWG feeders be without significant loss?
You’ll need to determine what you consider ‘significant loss’ to be electrically. I presume you have DCC, say about 14.5 nominal, and would use something like 5A as a reference load.
The resources I’m familiar with ‘advise’ that 20ga feeders (I presume in solid wire) be ‘as short as possible’ and not longer than ~12" from bus to soldered attachment point on the track, with the connections at both ends being considerably larger in area than the gauge of the wire. That would be the “answer” I’d give, but it isn’t the answer I think you’re asking for.
In practice the run can be much longer than a foot or two. Use this calculator to see where the voltage drop becomes too great for your purpose… and design your feeders to be shorter than that Change the variables in the URL to what you want if the ones you want to use are different.
The size of your bus should remain heavy; I wouldn’t use smaller than 14ga just on general principles.
Understood on the main bus. That isn’t the droid i was looking for.
For reference purposes, what is the distance a 20 AWG feeder can go with a 3A reference load and not experience a drop of more than 1/2 volt?
https://tonystrains.com/news/wire-sizes-to-use-in-dcc/
I did see this from Tony’s Trains but it isn’t clear what the yellow blocked area in the chart stands for.
ASSuming 14 to 14.5V, 8’2".
Note that the calculator assumes a pair, not just a single wire. If you are going to ground through something like a common rail, the resistance may be effectively higher. In that case you’d likely have to measure the actual drop with a meter, then add this to the feeder resistance and do the calculation.
For reference, one inch = 0.08333… foot, with the terminal 3 repeating. (If anyone knows how to put a bar over a number on the forums, let him speak…)
I’m presuming the yellow means ‘marginal’. It would presumably be red if ‘not recommended at all’. If you compare the number from the (presumably more precise) calculator, you can compare the yellow values with the indicated length to produce an 0.5V nominal drop.
Thanks. The application here is staging where staging tracks will only have one train on each one so I am providing sub-busses (so to speak), and each will be electrically isolated and can be disconnected from the main bus by way of a switch. The staging tracks range from about 17 - 24 feet in length so it appears I can gang drops together to a larger bus as long as they are 8 feet or less to the buss.
Rio:
I use 22 AWG feeder wires soldered to the bottoms of my rails. I allow these to be 24 inches long to reach distribution blocks. I have noticed no difference in locomotive operation from one block into another with different length feeders.
I hope this helps.
-Kevin
The yellow area is “not recommended”
I would use something a little heavier to run from a toggle on a control panel out to the tracks, like #18. I think #18 is a bit large to solder to HO rail, so I would use #20 or #22 feeders - depending on how long each staging track is, you can run multiple feeders from the #18 coming from the control panel.
–Randy
The drops themselves are about 11 inches long of 20 AWG wire. I wanted to use the thickest which was still workable.
Since this is staging, I’m making no effort to hide the drops near the track.
If what Overmod says is true, I can tie the drops together no more than 8’ length using the 20 AWG and connect them to the sub-bus of larger wire which will go to a switch, which will tie-in to a 14 AWG main bus.
The actual lengths of the isolated staging tracks range from about 18 to 25 feet long approximately.
I have used longish feeders of 22 gauge wire to feed an off-layout five track staging yard. I had a bridge about six feet long to a shelf on a bookcase, on which was the five-track ladder, the longest about 6 feet. That’s a total of 12 feet of track on the one ladder, the others diminishing, all fed with one pair of 3’ feeders at the proximal end to the layout. A test confirmed that all ladders provided enough signal/voltage to trip the shorts circuitry.
I’m building my layout now. All feeders are 22 AWG soldered to rail joiners prior to installing the joiners.
When in the test faze, I simply placed one feeder pair on one end of my 18 linear feet of track where the interchange/yard is. That part of the layout has 72 inch passing siding and several long spur tracks, all connected only with rail joiners…no solder.
That one feeder pair was probably 24 inches long, which is what it took to run from the temporary locaton of the command station to the end of the track.
I was able to run two DCC Sound locomotives with no problems anywhere on that 18 foot section. I didn’t try more because of amperage limitations of my NCE Power cab. (It could probably run 3, but I have no need for it to do that so I did not try)
I have since installed feeders on all three legs of each turnout. The longest stretch of track without feeders is planned at 10 feet. Feeders themselves are no longer than 12 inches. Every joint will be soldered, including turnouts.
I expect no problems.
nvm
Some years ago our club used six to seven inches of #24 solid. We changed from DC to DCC. I was under the layout doing the switching with a #14 buss. We had the NCE Five amp system. No issues.
The DCC amp meter never showed more than four amps. Maybe ten HO sound locos.
Edit. We measure about 13.6 vac at different points. Verified by a Scope. Handlaid track.
Rich
Put another way, how much voltage drop would make an operational difference?
It seems to me that gearing may be more limiting than voltage, practically speaking.
We have a MRC 780 and a 760. Locomotives are more sprightly when powered by the “24v” maximum voltage 760 but I do not see them running any faster. Pulling power might be the difference? But just how often does anyone run a train at full speed or needing maximum power?
At what point does voltage drop with distance actually make a practical difference?
From a practicality standpoint, you can go with much longer feeders than the table on Tony’s Train Exchange website shows. The voltage drops he’s showing is if you’re pulling the full amperage through that one set of feeders. You’ll probably be doing that only if you have a dead short in that section, and even then the current load will be shared by however many sets of feeders are in the shorted section.
Allowing for an average loco pulling 1/2 amp (for simplicity), you’ll get a 1/2 voltage drop at 14.5 volts by running the current through 49 feet of 20 ga wire. At 5A the voltage drop is about 5 volts.
Not that I recommend such long feeders. I use 12 ga stranded buss wire that feeds 22 ga feeders that typically aren’t longer than about a foot.
Here’s a page I consider a useful resource on practical wire sizing:
http://www.wiringfordcc.com/trakwire.htm
I invite others with experience to comment in detail on any part of what he says.
Note that DCC being actively used for control has a slight inherent voltage drop from ‘nominal’ due to the data modulation. This was as I recall a reason for the ~2V nominal increase over legacy “12-volt DC”. I would tend to agree with the effect being relatively slight at low peak current (amp) draw, as I think recovery of the data signal from DCC is robust even down to large amounts of voltage sag. The issue I’d see cropping up first with respect to small feeders is that transient voltage might drop below that at which some function on the decoder, perhaps sound, would drop out and reboot itself … say at even a short sag below 7.2V. Cure for this, as noted in other threads, is a suitable keepalive … which when present in equipment ought to be recognized as potentially allowing longer 20ga feeders.
i believe the 2V increase for DCC track voltage is to make up for the 2 diode drops in the decoder
presumably the reason for having a feeder on at least every other rail joiner and that rail joiner soldered to the rail is to guard against a faulty non-soldered rail joiner. this implies that the all the current to a loco may have to flow thru a single feeder and rail instead of flowing from both ends of the rail
measurements don’t differ much from standard measurements
while rail is much thicker compared to wire, code 100, 83 an d70 nickle-silver rails has an ~equivalent resistance of 24, 26 and 28g wire. with a faulty rail joiner, code 70 rail looks like 3’ of 28g wire. there’s a ~0.15V drop/ft across a pair of 28g conductors, ~0.45 across 3’.
while bus wire that carries current to more than one loco should be thicker, feeders need not be when compared to the rail itself.
i’ve used 4" pieces of bare copper 14g wire which are easier to hold in place against the rail while holding it from under the benchwork
A lot of you are not looking at real world numbers, sure if you have one set of feeders you can have voltage drops but we typicaly use many and the places with less are ussually smaller lengths of track so you don’t have multiple engines drawing power. I mean you can look at a lot of tecnical losses in voltage etc, but for our uses they are ussually moot.
But that’s why DCC track voltage starts a bit higher - 14-15V is typical for HO. Not 12V. So after the diode drop, you have 12V or better available to the motor drive. With adequate wiring, I don’t see such a sag as even happening - I’ve seen some big layouts, few home layouts are bigger then Ken McCorry’s, and his trains run around the entire layout just fine. Or club layout is fairly large, with #12 bus lines there are no problems with control or trains slowing anywhere other than those oft-mentioned fitter sections between some older modules, which have only rail joiners for power - a prime exampel of relying on unsoldered rail joiners to power a section of track is a bad idea.
–Randy
I noticed the very small gauge wires inside the locomotives and concluded that voltage drop from feeder wires likely isn’t much of an issue practically.
We used 16 gauge for the main return wires (white or red) and 18 gauge for the main power wires (black) because with common rail or bus wiring through block switches only the return wire is drawing full amperage. The block feed wires are all operating in parallel (and yes, we used 16 gauge black wire to feed the block switches from the power pack). Feeders become extensions of locomotive internal pick up and motor connection wires.
Those decoder wires are very high gauge.
Highest resistance may turn out to be at the pickup points of the wheels on the rails.
I could not agree more. Over time unsoldered rail joints have become a source of problems for me on my previous layouts.
-Kevin