AIU To TIU Modular Cable Question

eBay: 252337225831

25' Black 6 Conductor 26 Gauge Flat Modular Telephone Cable

Perhaps obvious by inspection of existing cable but note if crimping your own, make it the so-called reverse or crossover style.  So with retention clip facing up the wire colors are reversed as shown in below photo of supplied AIU-TIU cable:

eBay 360954480806 is a pre-crimped 14 ft. reverse cable for $3.99 shipped from Brooklyn.  Same seller has a 25 ft. for $4.89 shipped (361082215770).  Unfortunately doesn't specify AWG other than to say "heavy duty" wiring whatever that means!

Since I recall you saying you don't use the ACC ports (mostly if not exclusively SW ports), voltage drop may not be an issue.  The discussion about this gets a bit boring.  In any event, based on previous threads, I don't think you'll have a problem with 2 AIUs and distances you mention.  Just my 2 cents.

These cables are very inexpensive on Amazon.

Grj, Stan, Barry; thanks for all the ideas and info. I am going to ask the sellers what wire AWG they use before making any decisions. I may order a couple of lengths so as to have some options.  If no joy I will order the bulk cable grj mentioned and make my own up. I have a 6 pin/8 pin crimper and the RJ12 connectors are locally available.

Cheers,

Rod

Rod,

I am going to ask the sellers what wire AWG they use

If buying made-up cable, there's no need to query the sellers regarding wire gauge. There's an industry standard in effect. They all use the same wire.

Barry Broskowitz posted:

If buying made-up cable, there's no need to query the sellers regarding wire gauge. There's an industry standard in effect. They all use the same wire.

Are you a comedian?  I seriously doubt you can count on the Chinese to stick to industry standards, they sure don't in countless products!   I'd ask, it can't hurt...

I like rolling my own.  To me, that's part of the fun.      That way I can get the exact length I want and everything is nice and tidy.   I buy my phone, Cat 5 and Cat 6 bulk cable at a local electronics supply house.

I've been making my own cables (music instrument) for over 20 years, so cobbling these together for train stuff is easy, and again, fun.  To me 

John,

Are you a comedian?

Not by profession or training, however, I can tell a good joke or an amusing story!  

I've bought lots of cables from Amazon over the years, including those for use with the AIU, and I've never had a bad one. I buy only certified cables and only from US distributors. Further, if I ever got a bad cable from Amazon, it would be replaced or my purchase refunded in short order. Amazon has one of the best return/replacemnt policies in the industry.

I've also, rarely, had occasion to return other Amazon-purchased products that were outside of Amazon's return period. Any time that I've done so, I've had excellent results dealing directly with the Amazon sellers.

Regardless, if one was to contact a seller, do you actually believe that they'd state that their product was anything other than "perfect"?  

Well, I can't argue the point that the vendor could certainly lie.

So the response to the wire gauge question was that they cannot tell me the wire gauge. Since the standard for flat 6 conductor seems to be 28 gauge, I decided to order 2 x 25 ft of the 26 AWG black as suggested by grj. Just got notice that it is shipped already! Then I will pick up the RJ12 connectors and "roll my own". That way hopefully they have the best shot at working properly, and I'll know what I have. Just need to make sure I get the connectors installed so that the cable is "reversed".

Thanks, Rod

For future reference to those who may stumble onto this topic later...

Cat5 cable that you can buy at your local home store is 24AWG. This does come as 8 conductor, by default, however if you are making your own, you can leave one of the pairs unused. 

enginEErjon posted:

For future reference to those who may stumble onto this topic later...

Cat5 cable that you can buy at your local home store is 24AWG. This does come as 8 conductor, by default, however if you are making your own, you can leave one of the pairs unused. 

 

Not sure if this is relevant but cat 5 cable comes as 4 sets of twisted pairs. I am not sure if this architecture would be detrimental to the signal compared to flat cable, but I would not personally want to chance it. Anyone used cat 5 cable?

Rod

The flat vs twisted pair is a valid observation. Generally speaking, twisted pair has much better performance for signals that are AC signals (i.e. Communication between two devices) so with Cat 5, as long you make sure that you use the same 6 conductors at both ends, the Cat5 will behave better than the flat cable. 

The CAT5 "might" be better, but depending on the exact layout of the signals in the flat cable, the twisted pairs in the CAT5 could cause a problem.  The four twisted pairs are used with differential drivers to minimize crosstalk in the CAT5 cable.  I don't believe the 6-pin cable with the serial data has communications lines that match up with the twisted pairs, I suspect there's only one ground.

Interesting comments. So if cat 5 is better for communication, I wonder why MTH didn't use standard cat 5 cabling, with 2 unused wires? Cat 5 network cables are dirt cheap, and come in all kinds of standard lengths. Plus being 24 AWG they would handle the AIU power requirements without issue. Might it be because the AIU cabling needs to be "reversed" as opposed to "straight"?

Rod

Rod,

Great question. Pure speculation but I guess that is has to do with the fact that the AIU and TIU were designed back in the early years after the turn of the century. Back in 2001 I remember trying to buy a 10ft Cat5 cable and they were between $2.00 -$5.00 per foot.  So at that time, Cat5 was nowhere near the prices that it is today.

 Today Cat5 cables are dirt cheap. A 10' cable can be found for $1.25 and a 50' cable for $3.45. 

on the flip side, I think the 6pin flat cables have remained pretty stable in price since 2001 due to the lack of any huge volume volumes changes.  

So while cat 5 is cheaper now, we all would have been throwing a huge fit if we had to buy Cat5 cables back then for our AIU/TIU communications. 

John-

yes, I have not looked at the AIU to determine if it used Single Ended or Differential signaling but at the frequencies that we are talking about, the twisted pairs inside the Cat5 should not create any issues.

Now my curiosity is peaked...I just might have to pull the covers off and figure out what type of communication protocol this is using  

If the issue is choice of AWG (26 vs. 28) for long TIU-AIU cable runs wrt the 12V power supply out of the TIU, the discussion is not complete without mentioning a concept described by Marty here:

https://ogrforum.com/t...by-backfeeding-aiu-5

The voltage drop problem has been described in various threads but it's simple Ohm's law or Voltage = Current x Resistance.  So increase current or resistance and the voltage drop increases going down the cable.  Current increases as you increase the number of ACC relays "on" at a given time in the AIUs.  Resistance increases with longer cables runs or if you use 28 AWG instead of 26 wire. 

The Omron G5LA14 12V relay shown in various internal photos of the AIU draws 30mA when active.  So with up to 10 of these "on" at a time per AIU, the current can add up.  The resistance/foot can be readily calculated for your wire size and cable length...noting that this resistance is in both the +12V wire and the return wire so it's effectively doubled if estimating the voltage available at a downstream AIU.  Probably a conservative spec, but the Omron relay requires 9V DC to operate.

An observation with respect to discussion of the communications signals is the problem (intermittent AIU operation) of long TIU-AIU cable runs has always been with respect to the 12V DC voltage drop....as opposed to communication signal integrity (solved by twisted-pair cables or whatever).  That is, add the 12V DC adapter at the end of the line and the problem goes away.

An overlooked benefit of a $2 downstream 12V supply is this lessens the load on the TIU.  There is a power supply inside the TIU that converts Fixed 1 (or AUX PWR IN) to 12V DC to power the AIU(s).  I'd be curious if anyone knows how much power the TIU can supply to the AIU(s).  Whatever the spec, power supplies run hotter as you increase load.  To the extent this decreases reliability and ends up with a trip to the TIU repair shop, this could be another factor to consider if planning a layout with multiple AIUs.