Improving BLI F unit pickups/Wire gauge?

[Cajonpassfan]

I'd like to modify a dummy BLI B unit to pick up power to supplement its powered A's electrical pickup.
Fortunately, the dummy trucks do include the metal sideframe insets; they do not include the copper? contact strips found inside the A's. Unless I can get the contact strips from BLI, I'll need to solder a short thin stranded wire onto the insert nubs and run them to a distribution point, from where a second set of thin wires will connect with the powered unit.

Two questions: what size wire should I use between the units, and what minimum size on the pickups? The pickup wires especially need to be very flexible, yet durable and able to withstand the current should the powered unit stall.
Photo attached. Thoughts and suggestions appreciated.
Thanks,
Otto K.

[jdcolombo]

Get some of the ESU 36-gauge decoder wire.

None of your hookups is going to be carrying more than 1/2 amp at most, and none will be longer than 6".  ESU's 36-gauge wire is perfect for this application, and it is stranded, flexible, easy-to-strip and easy to solder.  It's what I use between engines and tenders, and to hard-wire tender trucks when needed.  Works.

https://store.sbs4dcc.com/search.aspx?find=ESU+wire

John C.

[peteski]

That is a loaded question. 

While it is difficult to try to measure gauge of a very thin stranded wire, it seems that what manufacturers most commonly use is around 30 AWG for all the internal wiring in N scale models.  Same wire as used on wired DCC decoders.

But of course that wire can't carry much current withotu overheating.  It is plenty capable of carrying enough current for what N scale loco needs, but will get damaged (as seen few times on this forum) if subjected to a higher current of a short (where the wire conducts current between front and rear trucks).

So , when interconnecting 2 locos, for safety you could use thicker (More robust) wire. But the trade-off then is less flexibility and it is more visible.

[C855B]

For truck pickups I recommend Ngineering's "Super Flexible Wire", also known in the trade as "litz wire". The #29 should be about right.

Pete's concern about shorts is valid, and this problem multiplies when you have lashups connected together with lots of track pickups. The likelihood of a damaging short increases with the total length of the connected units, where one end derails and lands on the opposite rail. I've been mulling over this issue at length in designing a track-cleaning train and have concluded it might be a good idea to have some manner of short protection in the line.

[Steveruger45]

Peteski et al raise good points. I was just wondering if a small fuse could be placed one on each leg of the power pickup installed in the dummy loco would be beneficial/ doable or even possible to protect the decodered loco and the flexible small gauge wire in the dummy?

[peteski]

Peteski et al raise good points. I was just wondering if a small fuse could be placed one on each leg of the power pickup installed in the dummy loco would be beneficial/ doable or even possible to protect the decodered loco and the flexible small gauge wire in the dummy?

You could probably fit some small fuses - it all depends on how far you want to take this.  But we are discussing both, wires from the trucks to the chassis, and between interconnected models.  If you do install fuses, you will still have to replace them when they blow. So it is either replacing the wire or the fuse.  And the smallest fuses available are usually soldered into the circuit (they look like resistors).  So, replacement will be just as complicated as replacing a melted wire. Maybe a self-resetting solid-state fuse would work, if they act fast enough.  Also, fuses add some resistance to the circuit.

[Steveruger45]

Thanks Pete.  You have articulated what started forming in my own head plus some I hadn’t considered, yet.   Yeah, any type of protection is going to need access, but so is fixing melted wires like you say.  I was thinking something like plug-in glass tube fuses in a holder. Something like what you sometimes find in incandescent Christmas lights or in UK receptacle plugs or even automotive fuses.   Not sure if any of these or similar on the market that would be suitable for this application or if they would even be fast enough.  It looks like cajonpassfan dummy loco is sans metal frame so lots of space inside.

[jdcolombo]

Hi guys.

Maybe it's just me, but perhaps there's a bit of over-thinking going on here?

1.  In a properly-wired DCC system, a short (from the truck to the frame; across wheels on a truck, between trucks, or whatever), will immediately cause a booster shut down.  In milliseconds.  At least, it always has on my Digitrax system.  I've used the ESU decoder wire to do runs between a steam engine and the tender, which should be similar to a run between two diesels (or a diesel and a dummy unit), and to hard-wire tender trucks to a common soldering point for a decoder installations.  I've had those engines short the layout dozens of times (I wish one could eliminate operator error, like going across a switch thrown the wrong way, but alas it seems humans will be humans and even the guy who built the darn layout can't seem to remember how to run it) and never, ever had a wire melt.  The booster simply shuts stuff off.  Instantly.  Of course, if you are running DC, then that's different and I did assume Otto is using DCC (from his other DCC-oriented posts). 

2.  As Peteski has noted, even if you DO run a dead short long enough to create a melted wire, you simply replace the wire.  In fact, I've always thought this was a plus of using ESU's 36-gauge wire - it will essentially act like a fuse in serious dead short situations by melting before the wheel axle insulators do!  But I've never had that happen.

3.  We're not doing wiring inside house walls, where an error in current-capacity handling can cause a deadly fire.  We're talking about a melted wire here.  Take the shell off, fix the wire, and move on.  10 minutes.  Maybe there are circumstances where that melted wire could melt or deform a plastic shell, which WOULD be a problem given our limited-run locos and lack of spare parts, but I doubt that's much of risk given how such wiring will be routed inside and between locomotives.  Or at least, how I imagine it SHOULD be routed.

So . . . I just don't see the risks of using something like ESU's decoder wire offset the goal of having something acceptably thin (for looks) and flexible (for operational reasons).  We're not building the next Mars lander here . . .

John C.

[peteski]

Thanks Pete.  You have articulated what started forming in my own head plus some I hadn’t considered, yet.   Yeah, any type of protection is going to need access, but so is fixing melted wires like you say.  I was thinking something like plug-in glass tube fuses in a holder. Something like what you sometimes find in incandescent Christmas lights or in UK receptacle plugs or even automotive fuses.   Not sure if any of these or similar on the market that would be suitable for this application or if they would even be fast enough.

In N scale locos, every cubic millimeter of space matters.  A fuse will utilize space which could be otherwise used for weight, decoder, capacitors, or even speaker/enclosure.  Sure, those can be installed in a dummy loco, but that leaves the powered unit itself unprotected.  Is that worth the trouble?

[peteski]

Hi guys.

Maybe it's just me, but perhaps there's a bit of over-thinking going on here?

 Maybe there are circumstances where that melted wire could melt or deform a plastic shell, which WOULD be a problem given our limited-run locos and lack of spare parts, but I doubt that's much of risk given how such wiring will be routed inside and between locomotives.  Or at least, how I imagine it SHOULD be routed.

It can be worse too.  I have seen couple of instances where multiple wires melted in a DCC-sound-equipped models where the melted insulation caused the wires to short together. In another instance, a melted insulation caused the wire to contact and short to a metal part of a component on the decoder. In both examples, the decoder was damaged.  But yes, those are rare (and melted wires in models are also fairly infrequent occurrence).

[Steveruger45]

Yes, maybe a bit of overthinking is going on here but I think the discussion has helped establish  that the effort vs benefit equation of fuses in the dummy loco is probably not worth it overall.  Sorry I spoke.

[jdcolombo]

Yes, maybe a bit of overthinking is going on here but I think the discussion has helped establish  that the effort vs benefit equation of fuses in the dummy loco is probably not worth it overall.  Sorry I spoke.

Well, I'm NOT sorry you spoke.  Always worth thinking stuff through!  I didn't mean the "overthinking" comment as a criticism - just as a "wait a minute - let's take a breath."

John C.

[Cajonpassfan]

Lol guys, love it, leave it to TRW to get a bunch of helpful responses, in no time! Thank you all, you too Steve, all useful thoughts, even if I do end up underthinking it ala Colombo
Turns out I had some stranded Miniatronics #30 so I used it for the truck wire tails; they go straight up into the body through the openings where the wiper contacts would be if it had any. Using the little rechargeable battery ISO-TIP made it easy, didn't even have to disassemble the trucks.

The bigger challenge will be where to attach the wires to the decoder or powered loco (not a split frame) and routing it to a plug in the B unit (I do want to be able to separate these for maintenance and troubleshooting). The board has this tiny connector and I'm frankly a bit intimidated. Only place I can think of soldering to is the wiper contact, and even that is a bit iffy...it's a rats nest of tiny wires in there 😬 See pics...
Otto

[jdcolombo]

Hi Otto.

If all you're after is redundant electrical pickup, don't try to solder the wires from the non-decoder unit to the decoder in the powered unit.  I see a screw on the frame so that must be one power lead for the powered unit.  Where is the other?  Run two wires from the FRAME of the powered unit back to the B unit, and attach those wires to whatever point you wired the trucks to.

Wouldn't that provide the electrical contact redundancy you're looking for?

John

[peteski]

Since this loco has an electrically-neutral frame, I would trace the wires from the trucks (which lead to that connector), then using the soldering iron, melt a short section of the insulation on each of those wires, then wrap and solder the wires coming from the other loco. Basically, you are splicing the wires.  Then insulate the exposed wire using some liquid electrical tape, or some other insulating material.