# DCC and AC Transformers



## Tom Bray (Jan 20, 2009)

I am sure this has been asked before but I just want to make sure.

If I get something like the MRC Dual AC powerpack that puts out up to 21V AC and about 7A per side, can I plan on being able to plug the unit into a pair of DCC boosters and expect it to power them properly?

It appears that they will drive the MTH locomotives just fine, with or without the DCS connected. I am just worried about when the system gets "upgraded" to DCC.

Tom Bray


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## Greg Elmassian (Jan 3, 2008)

Sure, although you need to see how the output of the pack drops under load... and also what load you expect to need. 

Say you think you will have 5 amp max... try drawing a 5 amp load and see how much the output voltage sags... 

A sort of industry standard for an AC power supply is dropping output voltage 10% at full rated current. 

You might be surprised on how your power supply acts under load. 

I went to regulated DC power supplies because of the variation in voltage with load. 

Regards, Greg


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## Tom Bray (Jan 20, 2009)

The main loops are quite level so the load really won't be changing very much. The transformer I was looking at has the two sides rated at 7A each. They also have meters for both current and voltage. 

Currently the way I have the MTH engines set up, they have a max top end when run in conventional mode so that really don't slow down very much until the voltage drops too low to sustain the speed. The DC supply that I am running (also an MRC and isn't regulated) runs everything pretty well. Most of the time that the locomotives slowed down was due to the distance from the power pack and I have that pretty much under control now. 

I am not sure how much current I will be drawing. I was able to run my F7AA diesel with a 3A fuse, the same for the Hudson and 4 lighted passenger cars. That is, until I got both of them on the same track and the fuse lasted about 20 seconds. 

Tom Bray


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## Greg Elmassian (Jan 3, 2008)

Well, you need to really figure out the stuff I asked, how much load you really have and how much the transformer sags under load... 

"ratings" can be correct, misleading, or just plain wrong... you have to check them yourself. 

Also, you cannot tell by what amp fuse blows what the actual amperage is, you have to measure. MOST (but not all) fuses are designed to handle the rated load, and blow at 200 to 210% of the rating... but this also varies widely by fuse type. Also, you have no sense of the short term current draw... 

There's really no substitute for actually measuring stuff.... voltmeters with amp reading capability are cheap nowadays... 

Regards, Greg


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## Tom Bray (Jan 20, 2009)

As far as current draw goes, I don't have a good way to measure it, I will have to work on that. Plus that fact that currently the system is running on DC which has a capacitor to take care of the instantaneous load. Up until recently, the biggest source of voltage drop has been where on the track the train is, that is more under control now but not entirely. 

Also the MTH locomotives are pretty well behaved so they probably aren't a good representation of what I might need in the future. What I don't know is: if I use the direction controls to start up the MTH locomotives, will they slam into high speed or will they walk up the speed curve nicely.


Finally, since I don't have the transformer yet, it is a bit difficult to know how much the voltage will drop due the the winding resistance and other losses. I assume that the voltage control is a variable transformer (variac style). The manual for the transformer does indicate that the voltage will drop if either the whistle or bell buttons are pushed which puts a DC component on the AC voltage.

I do have a couple of Lionel transformers that I could test the whole concept out on and see if I like its behavior. I am not sure either transformer is big enough or goes to a high enough voltage for a valid test.


Right now the real question is: do I drop $250 or so on a new transformer setup or not. 

I haven't made up my mind and you comments are indicating that I should wait.


Tom


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## Greg Elmassian (Jan 3, 2008)

So this is a variable/adjustable output AC supply? 

Is this to try to solve your DCS problem? 

Regards, Greg


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## Tom Bray (Jan 20, 2009)

It is a hedge in case I decide that it is too much horsing around with the DCS issues to make it reliable enough for my tastes. 

I am not dedicated to DCS, its nice and when I first started playing with it, it was and is very impressive. But it is missing a key feature ... I can't hook my computer up to it and control the trains with software. 

My ultimate plan, if and when MTH releases PS3 for G Scale is to upgrade to that and run everything on DCC. If it looks like MTH isn't going to do that, the F7AA set will get upgraded to another DCC decoder, actually two decoders, so I can run the two engines back to back or both facing forward or powering separate trains. 

Tom


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