Marty Fitzhenry method to augment AIU voltage by backfeeding AIU#5

This is done by putting 12 VDC into the AIU output of your last AIU in the run.   I will find my notes later and let you know what pins are used for the 12 VDC.  I have had luck with the AIUs working a good distance from the TIU without help.  On my layout I come off the TIU with the factory cable and with my own cable go 35 feet to the next bank and I have not had any issues.  My layout uses many switches going into the passenger yard and the route feature is very helpful to me.

Thanks Marty.

I would also need a recommended 12VDC transformer and amp rating. I have an old HO Triang transformer at 14VDC and 1 ampere, which I do not believe will be suitable. A fixed voltage transformer would be best.

Thanks: Joe K

I'd make sure you have a regulated 12VDC power source, many of the wall wart type units are not regulated.

What is meant by "AIU signal power?" 

My understanding is when you have too much cable length between the AIUs, the signal strength weakens, and some of the AIUs may not respond properly, or be found by the TIU. Adding power from a transformer (not sure of Volt & Amp rating yet) to the last used AIU in the chain can resolve this issue.

I am having trouble identifying the 12VDC, 1 Amp power supply that I need. Has anyone done this, and exactly what power supply did you use, and where did you get it?

Thanks: Joe K

I'd dig in my box of discarded wall warts and find a regulated 12V model. 

Are you referring to the type of wall transformer used by laptop computers?

Thanks Joe K

I'm guessing that it's not a signal issue, but rather a power supply issue.  All the power for the AIU goes down that telephone cable.  When you get three or four AIU boxes all strung in serial on that #24 telephone wire, the voltage drop starts to be significant, probably why it's an issue.

Joe, I am indeed referring to a wall transformer.  Many items like disk drives and routers have regulated supplies with sufficient power for the task, a typical 3.5" disk enclosure power supply has 2 amps at 12 volts and it's usually regulated.

I'm wondering what happens if you backfeed the AIU's with a voltage that is not exactly equal to the voltage furnished to the AIUs from the TIUs.

Given that you have significant voltage drop to even justify this measure, I'm sure that the slight difference in voltage will not be a factor, it's coming from the other end of what is presumably a long and fairly small gauge wire. 

Polarity observation is essential

I'd be a little nervous about trying this, Remember the posts of fried AIU  because of plugging the cable from tiu  into the wrong AIU port.

Polarity is key, that's for sure!  Gregg, I don't think this is the same kind of issue as plugging the cable into the wrong port, as that was putting voltage on parts that didn't handle it. 

Obviously, this "modification" is one that you'd want to be careful in making!

Where's Marty when you need him?

Found it, have company here for a few minutes.  Will get back shortly.

Looking down at the output plug from the top, pins are numbered 1-6 going r to l.  Put the 12V positive on pin 5 and the ground on pin 3.

333.3. 

Thanks Marty:

I will hook my AIU connector plug and short wire up to a terminal strip, to easily connect the 12VDC transformer to the correct AIU wires.

I will test the polarity of the transformer by using my multi meter, with black on ground, and red on 12VDC, to ensure the reading is +12VDC (-ve would mean I must reverse the transformer wires on the terminal strip connecting the transformer to the AIU wires 5 & 3 in your post.)

Thanks: Joe K

Joe, this will work for you.  How far away is your last AIU?

My TIU cable lengths are:

Tiu-AIU1 = 12ft

AIU2 = 12ft

AIU3=12ft

AIU4=20ft

AIU5=15ft

I have purchased a 12VDC regulated power supply at 2.5amp. I have an adapter that will convert the plug to screw on wires. I was going to run 18ga wire from my power bar (where I have a few transformers plugged in) to the location of AIU5, which is about 25ft. There I will have a terminal strip to take the 12VDC to the two AIU wires needed for the 6 wire cable connection.

I will check for polarity. Do you think the 2.5amp transformer is OK? I was going to also use the same transformer to boost the signal on my track detection boards for running the Hikel system.

Alternatively, I could use individual 1amp power supplies, but I thought combining them would be better, as both AIU5 and the signal boost I need for my NCE track detection AIUs are at the same location.

Please let me know if you think this transformer is OK at 2.5amp rating. My understanding is the MTH AIU will pull the load it needs, so as long as the transformer can supply the required amps, extra amps will go unused.

Thanks: JK

In the curious minds want to know category, did you happen to measure the voltage between pins 3 and 5 at your last AIU?  Of course it will depend on how many relays are "active" in any upstream AIU's but would be interesting to see how much it has dropped from +12V.  If nothing else it would confirm you have the right pins AND polarity...

I gave the pins and polarity.  Good way you stated if anyone does not have the information.  When first asked I did not remember the pins off the top of my brain.  I have used this a few times and it will help.