High resistance leakage on hand laid turnouts

[bdennis]

Guys,
Thanks for the tip on the flux.. I will look into it.. And will bin the flux I have!...

I have now cleaned 3 turnouts and hair dryered one of them to test.... = SUCESS!......

A quick scrub with Alcahol and a dry and the problem is now fixed...

Now to clean the rest!

Thanks guys for your help!...

[Chris333]

This is me scrubbing a small layout at the sink:


With just turnouts I scrub them right after I'm done soldering, before the wood ties. I make sure to get up into the rail web.

[bdennis]

Chris,
Thanks for that..
I have just finished scrubing all the other not installed turnouts and will let them dry over night.

From now on I will not use that flux AND will scrub before installing the wood ties just to be sure.

As for the installed turnouts, I will have to do them in situ and then hair dryer them..

Thanks for the update.

[garethashenden]

I don't think you need to bin that flux, just don't use it on turnouts. Use it for non-electrical soldering.

[ednadolski]

I cut new gaps in some spare ties and found them to be full open circuit with NO resistance at all.

Sorry to nitpick again on the terminology:  a full open circuit is (theoretically) infinite resistance and no (zero) conductance.  "No resistance" means zero ohms, i.e., a short circuit.

Glad to see that the cleaning worked.  I'm not familiar with that flux, but it does not look like it is necessarily made for use in electronics circuits (which is what your trackwork basically is, esp. with DCC).   At minimum it should be scrupulously cleaned, better still to switch to a flux specifically designed for electronic circuit use.

Well, I still don't understand how 2.3 M-ohms is triggering a BDL

The DMM is only going to read the DC component of the impedance.

Here's a photo of some of my turnout work...

Nice Robert but it looks like your loco is about to run the wrong way thru some closed points.   Hope he is just waiting in the hole... 


Ed

[DKS]

I am not kidding.  Get it...

...or else!

[GaryHinshaw]

The DMM is only going to read the DC component of the impedance.

That's true, but I think the capacitance/reactance is a red herring.  The flux has no capacitance and the PC ties can't have much, otherwise lots of hand-laid track would be triggering BDLs all the time, and cleaning the flux would be irrelevant.  The only reason I'm harping on this is that I have hand-laid turnouts and I'm considering using BDLs, but before I make that investment, I'd like to understand the situation.  I think there are 3 explanations, in order of likelihood as I see it:

1. The DMM readings are uncertain because it is measuring a fluid circuit element, and the resistance of a complete turnout with flux residue is really in the K-ohm range.

2. The BDL is out of spec and is triggering on 2+ M-ohms.

3. There is some unaccounted for capacitance, like PC ties, that is lowering the impedance (complex resistance).  In that case, cleaning the flux won't help, and most people's hand-laid turnout will have the same problem.

I'll be quiet now.

[robert3985]

Sorry to nitpick again on the terminology:

Ed

What Ed?  You...nitpicking???   

Nice Robert but it looks like your loco is about to run the wrong way thru some closed points.   Hope he is just waiting in the hole... 

Ed

Haha!..Actually, in this photo, my Kato F3 is completely stalled on ME code 40 flextrack.  I had to sand the inside spikeheads to get anything to run on it!

...or else!

Yup.  Damnstraight! 

[ednadolski]

The flux has no capacitance and the PC ties can't have much, otherwise lots of hand-laid track would be triggering BDLs all the time, and cleaning the flux would be irrelevant.  The only reason I'm harping on this is that I have hand-laid turnouts and I'm considering using BDLs, but before I make that investment, I'd like to understand the situation.

The BDL is basically a current detection circuit, is that correct?   Consider each flux-contaminated PCB tie as creating a path for a small leakage current.  When you have a bunch of them in parallel, the total current is the sum of all the leakage current paths in the block, and if that gets large enough then perhaps that could trip a BDL.

As long as your gaps are clean I wouldn't think there's much to worry about.

Ed

[DKS]

The flux has no capacitance...

But the flux capacitor has been entirely overlooked in this case and would likely fix the problem in a jiffy.

Oh, wait...

[John]

While it is probable that if I change the sensitivity of the BDL will fix the issue, my concern is that ALL these turnouts should not have any resistance on them with tested in isolation (not installed on the layout). I would prefer to get to the bottom of the issue I am seeing with the multi meter before I install them and potentially create problems for my self over time.

check for crap thats fallen into the gaps around the frogs .. thats where it most often happens ..

[bdennis]

Just a quick update.
All the turnouts that I had built and not yet installed were cleaned last night and this morning they are all perfect.. No resistance readings on any part of the turnout at all.. So all is well.

I have also been out to the railroad room and cleaned all the installed turnouts and have left them to dry..
As only 3 of them were in a detected block im not expecting any issues..

Thanks again for all the input.

In terms of the BDL's and sensitivity. All there well there also.. I ahve never had a problem with them in the past and are my block detector of choice.

[sp org div]

Glad you didn't have to rip up all the turnouts.
Another happy BDL user here.
Saw it on your blog.
Highball!

Jeff

[victor miranda]

my guess didn't hold up?
oh the horror!

I have to add that I made the assumption that you were using
a soldering flux for electronics.
never crossed my mind ... yow.

zinc-cloride... ooof. lets save that for the pluming. 

victor

[peteski]

As someone who is familiar with electronic theory (and lots of practice), I rolled my eyes several times reading this thread. 

Most of the educational posts have already been presented in several posts, so no need to rehash them.

This thread might have been easier to troubleshoot if the proper terminology was used (I also understand that not every model railroader is an electrical wiz).  For example "M" and "m" were used interchangeably when describing resistance.  But they have very different meaning.  "M" means "mega" or million. "m" means "milli" or one one-thousand (0.001). And not in just resistance readings.

For our applications (running 12 Volt electric models) milli-ohm resistances would be in a range of a "dead short" and mega-ohm resistances would be considered on open circuit.

Also worth mentioning is that multimeters (at least all of the ones I have ever worked with) use DC voltage for measuring resistance, so the capacitive affect would not have played a role in the resistance readings.

While the dire warnings about not using acidic fluxes for soldering electrical circuitry is often mentioned (online and in magazine articles), asking about the type of flux being used (instead of assuming) would have also speeded up the solutions.

I know: hindsight is always 20-20.