# Input Power to a Booster AC or DC?



## rreiffer (Jan 14, 2009)

I have seen several booster schematics and have looked at some of the commercial boosters? The question is: is the input to a booster AC or DC, if it can be either is there a preference? I happen to own a 24V center tapped transformer capable of 200A (I could weld with it) and wanted to know if that would be good source (provided you protect each booster).


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## George Schreyer (Jan 16, 2009)

It depends on the booster design. Digitrax and NCE boosters rectify anything coming in and filter internally so it doesn't matter if it is AC or DC. The voltage matters however, 24 VAC is probably too much for most boosters. With an AC input, the internal bus charges to approximately the peak value of the AC input or 35 volts minus the rectifier drop. This is probably too much. 

A DC input suffers only the rectifier drop, about 1.5 volts. 

- gws


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## Greg Elmassian (Jan 3, 2008)

I have noticed much better and consistent operation using a regulated supply. Regulated DC supplies are easy to find. Regulated AC supplies much harder and more expensive. 

But some boosters will take AC only. 

In my case, where I am pushing the limit, I have to use a regulated supply, otherwise the variation in voltage from an ordinary transformer would either damage my booster or provide a voltage lower than I want. 

Regards, Greg


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## George Schreyer (Jan 16, 2009)

Greg, our milage differs. 

I have run resistive load tests for extended periods at several current levels up to 15 amps (so that the internal 15 amp fuse on the PB110 doesn't blow) and at lower currents. I use an unregulated AC source at 22 VAC (transformer purchased from NCE). The voltage does sag, but I've never lost anything more than a fuse.


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## Greg Elmassian (Jan 3, 2008)

I knew I needed to explain it in more detail! 

I will assume that your comment is based on my 3rd sentence: (and I apologize in advance if this is wrong) 

"In my case, where I am pushing the limit, I have to use a regulated supply, otherwise the variation in voltage from an ordinary transformer would either damage my booster or provide a voltage lower than I want. " 

So, I want to get 24 volts on the track. To get this, I need to use the max input voltage of the NCE booster. To keep it simple, let's talk DC. So 27 volts is the max according to NCE. I have measured approximately a 3 volt drop from input to track on my system. 

So I get 24 volts out. 

If I raised the input level, then I have exceeded the max rating. 

If I was using a basic unregulated DC supply, then the NO LOAD voltage has to be 27 volts. 

Most transformers are rated between 10% and 20% voltage sag under max current. Let's assume a very high quality transformer, 10% max. 

So now under load, my 27 volt DC becomes 24.3 volts input to the booster, and 21.3 volts to the track. 

Now, by actual measurement, my top speed on my E8s with QSI decoders goes from 92 smph (acceptable) to 65 smph (unacceptable). 

So, using an unregulated supply AND as stated, wanting to get max DCC voltage on the rails, REQUIRES me to use a regulated supply IN MY CASE. 

It's not for everyone, but 65 smph absolute top speed (and losing a little from speed matching) was not acceptable to me. If you never need the "top speed" from your locos, then you may never run into this, but I could not run reasonable (70-75) passenger train speeds until I "pushed the limit". 

Is this a better explanation of my statement? The damage I spoke of was if someone wanted a transformer set up to supply 24 volts to the rails under full current, then I would need 27 volts (under full load input), and 10% higher unloaded, or 29.7 volts into the NCE unloaded, which, I am told, will damage the NCE booster. 

It gets MUCH worse if your transformer sags 20% at full load as I have found with MOST "recommended" transformers. (Anyone want to buy a nice transformer in a box? This is the NCE 10 amp one) 


Regards, Greg


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## George Schreyer (Jan 16, 2009)

If you are in the "no margin" case, then you have to use a regulated supply. I suspect that few others have your requirements. I am perfectly happy with the top speeds I get at 22 VRMS on the track. It does sags at high current, but that hasn't been an issue for me because I rarely run at more than 40 smph anyway. My layout is too small, the straights are too short and the curves are too tight to make faster running practical.


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