This subject has been discussed at some length, but I am still lacking total understanding.The printed current rating on the relays is 10 amps;however,I seem to remember MTH and Formites quoting 4 amps as a suggested maximum. What am I missing? Barry? MTH tech support has recommended both 4 amps and 10 amps.

Thanks, Bob H.

Bob,

quote:

The printed current rating on the relays is 10 amps

Where did you see this?

My understanding is that the relays in the AIU are rated at 4 amps. However, TIU channels are rated at 10 amps. Perhaps that's where the confusion lies.

Barry,
Thanks for the reply.
I opened the AIU and observed the rating printed on the relay. Maybe the traces or another component are causing the derating.

Bob H.

quote:

Originally posted by nobsbob:
Barry,
Thanks for the reply.
I opened the AIU and observed the rating printed on the relay. Maybe the traces or another component are causing the derating.

Bob H.

There are two issues here.
First the rating of the relay coil or 'Pick' rating which I believe is correct at 10 amps. The fusing of the inputs to the TIU channels at 10 amp fast blow through the TIU - AIU cables protects this.

Second is the rating of the relay points or 'transfer' rating which I believe to be 4 amps. This is to prevent the relay points from fusing together should there be a prolonged high current (as from a short) passing through them.

Hugh,

quote:

The fusing of the inputs to the TIU channels at 10 amp fast blow through the TIU - AIU cables protects this.

That's incorrect.

Wile you are correct that the relay coil gets its power from the TIU, that power comes from the power that the TIU uses for itself, rather than track power. Even when the TIU is powered through Fixed #1 In, the fuse for Fixed #1 is protecting the TIU itself from an overdraw situation on the output side of Fixed #1 (the tracks). An overdraw on the output side of the TIU can not affect the AIU in any case since the draw doesn't pass through the AIU's relay coils.

Further, in the extremely unlikely event that there was an overdraw situation in the coil circuit of an AIU port (I can't see that happening, however, for the sake of argument let's say it can occur), the fuses would offer no protection since they would not be in the circuit with the relay coil.

In short (pun intended) any short circuit that would trigger circuit protection from the TIU's fuses would not have the AIU's coils as part of that circuit, and vice-versa.

quote:

Originally posted by Barry Broskowitz:
Further, in the extremely unlikely event that there was an overdraw situation in the coil circuit of an AIU port (I can't see that happening, however, for the sake of argument let's say it can occur), the fuses would offer no protection since they would not be in the circuit with the relay coil.

In short (pun intended) any short circuit that would trigger circuit protection from the TIU's fuses would not have the AIU's coils as part of that circuit, and vice-versa.

If the fuse is connected to Fxd 1 input terminal how could it not be in the circuit ?????

Gary,

quote:

If the fuse is connected to Fxd 1 input terminal how could it not be in the circuit ?????

The fuse is connected to Fixed 1 Output.

quote:

Originally posted by Barry Broskowitz:
Hugh,

quote:

The fusing of the inputs to the TIU channels at 10 amp fast blow through the TIU - AIU cables protects this.

That's incorrect.

Wile you are correct that the relay coil gets its power from the TIU, that power comes from the power that the TIU uses for itself, rather than track power. Even when the TIU is powered through Fixed #1 In, the fuse for Fixed #1 is protecting the TIU itself from an overdraw situation on the output side of Fixed #1 (the tracks). An overdraw on the output side of the TIU can not affect the AIU in any case since the draw doesn't pass through the AIU's relay coils.

Further, in the extremely unlikely event that there was an overdraw situation in the coil circuit of an AIU port (I can't see that happening, however, for the sake of argument let's say it can occur), the fuses would offer no protection since they would not be in the circuit with the relay coil.

In short (pun intended) any short circuit that would trigger circuit protection from the TIU's fuses would not have the AIU's coils as part of that circuit, and vice-versa.

Boy Barry can you come up with a bunch of gobbly-gook in an attempt to make your badge shine. My comments stand!

quote:

Originally posted by Barry Broskowitz:
Gary,

quote:

If the fuse is connected to Fxd 1 input terminal how could it not be in the circuit ?????

The fuse is connected to Fixed 1 Output.

Input, Output. The fuse is still in the circuit carrying the total current load.

quote:

Input, Output. The fuse is still in the circuit carrying the total current load.

The difference is where in the circuit is the fuse.

It's there to protect the TIU from a short circuit on the tracks and will sit as close as possible to the output of the channel, thereby placing the circuitry of the TIU on the "transformer" side of the fuse. The only power that passes through the fuse is track power.

quote:

Originally posted by Barry Broskowitz:

quote:

Input, Output. The fuse is still in the circuit carrying the total current load.

The difference is where in the circuit is the fuse.

It's there to protect the TIU from a short circuit on the tracks and will sit as close as possible to the output of the channel, thereby placing the circuitry of the TIU on the "transformer" side of the fuse. The only power that passes through the fuse is track power.

Sorry for my stupidity. Guess I'll have to see someone about getting my eye and my ohm meter recalibrated. They both think the fuses in my I3A are connected to the black input terminals. Stupid instruments.

Gary,

Of course the fuses are connected to the input port terminals. However, they do not protect the coils in the AIU. Rather than continue to attempt to explain this myself, particularly since my use of large words has caused one other (not you) to view my explanation as "gobbledegook", I'll simply let MTH Development have the last word:

...there is no protection from a shorted out AIU coil. There is a 12V regulator on the TIU that would thermal limit after a short duration.

Hopefully, the words are small enough that everyone can understand them.

quote:

Originally posted by Barry Broskowitz:
Gary,

Of course the fuses are connected to the input port terminals. However, they do not protect the coils in the AIU. Rather than continue to attempt to explain this myself, particularly since my use of large words has caused one other (not you) to view my explanation as "gobbledegook", I'll simply let MTH Development have the last word:

...there is no protection from a shorted out AIU coil. There is a 12V regulator on the TIU that would thermal limit after a short duration.

Hopefully, the words are small enough that everyone can understand them.

Of course there is no protection on the "pick" circuit across the coil. Never said there was. Picking the relay is internal to the TIU and code. What I was refering to was placing the 10 amp AGC fuses in the input circuit to protect the TCU (which by default protects the AIU).
The issue of AIU relay protection has always meant "transfer" protection or protecting the points from overload and a 5 amp AGC in the circuit of the power feed to sidings and power blocks switched on / off by the AIU are protected by such.
There is so much gobblygook been posted here that I am afraid that poor BOB H. will never figure out the answer to his question.

Bob, just put some 10 amp agc's between the transformer output and the TIU inputs to protect the TIU/AIU units and a (one) 5 amp agc in between the hot power source input to the AIU relay input points if you are feeding power block and sidings that run engines or lots of passenger car lights.

Forget the rest of this chest popping gobblygook!

Hugh,

Once again you're reversing your field and adding more misinformation.

You previously stated:

quote:

First the rating of the relay coil or 'Pick' rating which I believe is correct at 10 amps. The fusing of the inputs to the TIU channels at 10 amp fast blow through the TIU - AIU cables protects this.

Now you say:

quote:

Of course there is no protection on the "pick" circuit across the coil. Never said there was.

You can't have it both ways.

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Bob, just put some 10 amp agc's between the transformer output and the TIU inputs to protect the TIU/AIU units

Once again, you're mistaken. That will protect the TIU, of course, however, it won't do a thing for the AIU.

quote:

Forget the rest of this chest popping gobblygook!

Why not just admit that you were mistaken in your initial statement instead of compounding your error while taking cheap shots at me for daring to correct you?

Barry!
Get a life!

Hugh,

Thanks for the suggestion, however, why not just respond to my question regarding that you were mistaken in your statements instead of continuing to be insulting?

Interesting thread

quote:

Originally posted by Barry Broskowitz:

quote:

Further, in the extremely unlikely event that there was an overdraw situation in the coil circuit of an AIU port (I can't see that happening, however, for the sake of argument let's say it can occur), the fuses would offer no protection since they would not be in the circuit with the relay coil.

In short (pun intended) any short circuit that would trigger circuit protection from the TIU's fuses would not have the AIU's coils as part of that circuit, and vice-versa.

quote:

The fuse is connected to Fixed 1 Output.

quote:

The difference is where in the circuit is the fuse.

quote:

Of course the fuses are connected to the input port terminals.

quote:

...there is no protection from a shorted out AIU coil. There is a 12V regulator on the TIU that would thermal limit after a short duration.

Barry,

It's time to give it up on this topic. Fuses on the TIU Input will protect the AIU relay coils. And, yes, Hugh did contradict himself. Granted, there are circuit elements between the fuse and the coils (e.g. 12v regulator) that would probably fail open long before the fuse rating was exceeded. But, things don't always fail in the expected mode and there's always the possibility of a "sneak circuit" (look it up). Ultimately, the fuse does limit the current for any and all uses in the TIU and through the TIU/AIU connecting cable.

There's something else that this topic has made me think of that is possibly far more important than relay coil ratings. I had always assumed that the TIU fuses were connected in series with the Input red terminals. After your erroneous output statement last night I pulled the cover on a I3A to find the fuses were attached to the Input black terminals. That got me to thinking of something else.

It's not an uncommon practice to have "common grounds" for multiple power supplies, track power, TIU Outputs, etc. As a result, I now realize that there can be/is current flowing through a TIU even if the TIU is not powered and has no power fed to any of its red inputs. I'm not saying this is bad or wrong. I just find it a bit disconcerting. Gonna have to think about it.

A quick example. Layout with upper and lower divisions, two post-war ZWs w/ "U" terminals ited together, two TIUs with black outputs tied together. One ZW/TIU pair for the upper and lower. The lower division with its ZW/TIU not in use, turned off. The current for the upper division flowing out to the rails and returning through the black channels of both TIUs, i.e. all eight TIU black paths are effectively wired in parallel.

Maybe that's been evident to everyone else, but I just realized it. It almost fits the technical definition for a "sneak circuit"?? I guess it's just something to be aware of when things start acting squirelly.

Gary,

quote:

Fuses on the TIU Input will protect the AIU relay coils.

With all due respect, I'll stay with MTH Development's position, which is that they will not protect the AIU coils.Regardless, the possibility of an AIU coil shorting out is rather remote and testing what happens in this regard would present difficulties. You, and MTH and I, will just have to agree to disagree on this one.

quote:

After your erroneous output statement last night I pulled the cover on a I3A to find the fuses were attached to the Input black terminals.

Regarding my assertion that the fuses are connected to Fixed #1 Out, my intended point (which I obviously made poorly if at all) was that the fuses are connected to a circuit that includes both Fixed #1 IN and Fixed #1 OUT. As such, they are connected to both ports and sit electrically between them. Regardless, in terms of physical connection, my statement was mistaken and yours was correct.

quote:

And, yes, Hugh did contradict himself.

I find it somewhat ironic that Hugh took such great exception to my contradictory statement and then turned around and agreed with me.

Your discussion of a "sneak circuit" is right on the money. This "feature" allows a TIU to operate in passive mode without any power connected to the TIU at all. The TIU gets it's power "sneakily" from Fixed 1 Out.

quote:

Your discussion of a "sneak circuit" is right on the money. This "feature" allows a TIU to operate in passive mode without any power connected to the TIU at all. The TIU gets it's power "sneakily" from Fixed 1 Out.

I agree that passive mode is a "sneaky" way of powering a TIU, applied voltage across the red and black outputs, but I don't think it qualifies as a "sneak circuit" as illustrated by a situation where current flows through the ground path of an unpowered TIU. True sneak circuits can be a bear, especially when they do something like reversing an autopilot's pitch up and pitch down commands while in terrain following mode.

I'll stand by my position that the fuse does limit available current to an AIU's relay coil. And, Hugh's position. I think he inadvertently switched "pick" and "transfer" in his second post.

Gary,

quote:

And, Hugh's position. I think he inadvertently switched "pick" and "transfer" in his second post.

Good out for Hugh, however, if true why didn't he say that himself instead of insulting me?

Regardless, now he can sleep at night, knowing that he didn't agree with me.

quote:

Originally posted by nobsbob:
This subject has been discussed at some length, but I am still lacking total understanding.The printed current rating on the relays is 10 amps;however,I seem to remember MTH and Formites quoting 4 amps as a suggested maximum. What am I missing? Barry? MTH tech support has recommended both 4 amps and 10 amps.

Thanks, Bob H.

After all the fuse discussion, what is the answer to my question?
MTH tech says 5 amps. What say you?
Thanks, Bob H.

Bob,

4 amps.