# Compatibility of MTH power brick and MTH TIU?



## Lynn D Bennett (Jul 27, 2013)

If you have followed any of my posts recently you know I am fighting a circuit breaker/fuse problem. But first heres the setup:

New MTH 100watt Power Brick 18VAC fixed output
New Version L TIU
Power Brick connected to input of fixed channel #! of the TIU and output, Fixed Output #1, connected to the track.

Dumb things like pushing an engine to assure all wheels are on the track shorts out the track. Now, one would think that the 6 amp circuit breaker in the MTH Power Brick would trip. But no, the 20 amp fuse inside the TIU pops. This has happened to me more than a half dozen times. Obviously a faster circuit breaker is necessary and one is on the way but I popped two fuses just yesterday while waiting for the fast circuit breaker to arrive.

You might think that MTH would have designed both of these items (Power Brick and TIU) to work together but that does not seem to be the case. How a 6 amp circuit breaker fails to pop in a shorted situation and a automotive 20 amp fuse blows instead from a source that is spec'ed at 5.5 amps at 18 VAC is perplexing to me. I have two of the bricks so I interchanged them thinking one might have a bad Circuit breaker in it and they both do the same thing (circuit breaker fails to protect the TIU). What was MTH thinking????

I realize the Lionel 180 watt Power Brick has the fast acting circuit breaker that really works but I could not find one new at the time so I bought the MTH 100 watt Poser Brick instead.

There is a way to wire the Power Brick so that its current doesn't go through the TIU and that would protect the TIU and its internal fuses. How many more excursion to over 20 amps can my TIU take? That wiring configuration is *"Passive Mode".* According to the DCS Companion book the only shortfall of this mode is the emergency stop button on the hand held remote will not work. Everything else supposedly will. I am really tired of having to break open the TIU to change the fuse every time there is a short problem on the layout and I now worry that my TIU will eventually be hurt by these very excessive over excursions in current.

Anyone got any insight on the *"Passive Mode"* operation of the TIU?

LDBennett


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## Big Mike (Dec 2, 2011)

Lynn D Bennett said:


> If you have followed any of my posts recently you know I am fighting a circuit breaker/fuse problem. But first heres the setup:
> 
> New MTH 100watt Power Brick 18VAC fixed output
> New Version L TIU
> ...


 

It sounds like every thing is wired ok, for a simple loop , I would disconnect the track from all power[not just turned off] with a DVOM set to continuity, between center rail and the outer rails, check if you have OL, open loop ,you should, if not, find the short.
I have had my TIU for two years now? and have not had to replace any fuses yet, I hope you figure it out...... some how I don't think this helped much, sorry Mike


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## gunrunnerjohn (Nov 10, 2010)

Like I said, the thermal breakers used in most transformers are pretty slow acting, however the fuses in the TIU are standard fast blowing fuses. The 100W transformer is capable of producing 20+ amps for a brief period of time into a direct short, all that's necessary for the TIU fuse to go.

FWIW, I've had many breaker trips on my TIU and never lost a fuse using the Lionel PH180 bricks. I'd really consider just going to eBay and bagging a couple of them.


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## Lynn D Bennett (Jul 27, 2013)

gunrunnerjohn:

I have a fast trip breaker coming but I wonder if getting the TIU out of the path of track current is a better solution. I could use the fast trip CB too.

I hear you on the Lionel 180 watt brick but I worry that the CB in it could also be bad or slow. It would be a used item as Lionel has NO schedule for delivery of new ones. 

The new fast circuit breaker that is coming may also be not be fast enough or the impedance of the trip coil of the CB may effect the quality of the control signals placed on it by the TIU. Why send heavy power through the TIU when that is not necessary (except for the emergency shutoff).

I don't have a schematic for the TIU so I don't know what the track current goes through in the fixed channel. Is it only a relay or is there semiconductors in the path or ????? If the TIU is designed for 12 amps (according to MTH) then these 20+ amp excursion can not be all that good for it. Why not completely eliminate the possibility with the Passive Mode wiring? Anyone got experience and any negatives?

It still bothers me MTH does not make the 100 watt brick compatible with the TIU. Do they expect that you will only use their expensive big 400 watt transformer/controller even in the
"fixed" mode?

I was just wondering if anyone else is using the Passive Mode wiring scheme and what their results were, good or bad.


Is Lionel any better in details like this?

LDBennett


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## gunrunnerjohn (Nov 10, 2010)

You can run the TIU in passive mode, we're doing that on our club layout as it was very inconvenient to wire it in any other way as we're setup right now. The one thing you lose that way is the emergency stop button no longer functions on the DCS remote since it's no longer controlling the power.

You also lose the ability to control conventional engines with the DCS remote if that's important to you.

Some say that passive mode may result in slightly less DCS signal, but so far that's not been a major issue.


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## Lynn D Bennett (Jul 27, 2013)

I wired up the system in the Passive Mode and did a track signal test around the layout. It actually passed with most of the track at 8 or above. I have a section where the trains go through two O-71 switches back to back and it drops drastically there but it is only a very short section.

When I get the circuit breaker Friday I'll run the track signal test again and see if the impedance of the coil effects the signal strength. With the Passive Mode there is no more concern about blowing the 20 amp fuses or hurting the TIU with excessive current. I may just leave it that way.

Someone on the Internet suggested one of those thumb remote controlled ac outlet adapters for $20 to act as an emergency power off which is the only function lost when going to the Passive Mode. I think I'll get one if I stay in the Passive Mode.

LDBennett


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## gunrunnerjohn (Nov 10, 2010)

Live dangerous and just dash for the transformer.


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