# Maximum Decoder voltage/amperage



## Engineercub (Oct 18, 2008)

I was kind of curious about something. Considering that G-scale is such a large scale and has much higher voltage/amperage requirements, why is it that there are so few sound and control decoders that are built to handle high voltage? I am not an electrician by any means and new to Digital Control so I have no clue to the reasoning behind this, but it seems that with several high voltage controllers out there, manufacturers would make decoders able to handle lots of power and huge power spikes. Why can they not achieve this or why don't they? My BigBoy's Phoenix sound system can withstand 30 volts and DCS is able to withstand 24+ volts so why aren't all manufacturers doing this? Does anyone know? Is it cost related? Thanks

-Will


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## Greg Elmassian (Jan 3, 2008)

Virtually all large scale decoders will handle 22 or 24 volts. The NMRA standard was not made by large scale people, it's obvious. Many LS locos need close to 20 volts to the decoder to get top speed, and that usually means 24v on the rails in DCC, which is the NMRA max. All the decoders I use are fine with this... the Quasinami is not... but it is a mess anyway, and no longer available. 

The QSI can actually handle something like 37 volts... read the specs... 

Regards, Greg


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## krs (Feb 29, 2008)

The NMRA DCC standard is actually not too bad when it comes to Large Scale. 
"Large Scale" is one of the scales reference in the spec - separate from the o/S/H0 group and the group Nscale and smaller. 

Many DCC decoders don't specify the maximum voltage they are designed to handle; initially I found that surprising, but when I read the spec the first time and read this: 

Digital Decoders intended for "N" and smaller scales shall be designed to withstand a DC voltage of at least 24 volts as measured at the track. 
Digital Decoders intended for scales larger than "N" shall be designed to withstand a DC voltage of at least 27 volts as measured at the track. 

I said to myself - ah, that explains that! Any NMRA compliant DCC decoder for Large Scale can handle at least 27 Volt DCC track voltage - says so right in the NMRA spec clear as day. 

Well, BIG mistake! I know of DCC decoders specifically sold for Large Scale that barely handle 18 volts! How manufacturers get away with that is beyond me - they certainly shouldn't be allowed to claim compliance to NMRA standards. 

The maximum DCC track voltage specified by NMRA is 22 volts which is really a bit shy of what it should be. In my opinion, the moter of an engine should see the same maximum voltage with DCC as with DC, and that is 24 volts. So the maximum Large Scale DCC track voltage should be around 26 volts to allow for a 2 volt drop through the decoder itself. 
That issue has been discussed at NMRA on and off for many years, but the powers to be can not come to a consensus to change that. 
The main issue of course is cost which affects price which in turn affects competitiveness and profitability. 

There are actually more Large Scale decoders available than what one typically sees in the US. Last time I checked there were about two dozen, but the ones from the small European suppliers never make it to the North American shore. The beefiest one I know of is the Heller decoder which is a Zimo decoder with the output boosted to 10 amps. 

Regards, Knut


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## Greg Elmassian (Jan 3, 2008)

I run 27 volts DC (regulated) into a modified (by NCE) NCE booster that puts out very close to 24v RMS to the rails, measured with an RMS voltmeter. 

Doing this, still some locomotives cannot achieve prototype speeds. When I only had 20 volts on the rails, my Aristo E8's were topped out at about 65 smph... moving it to 24 volts gave me 92. 

Motors are typically non-linear in their response to voltage, i.e. a lot of rpm is gained in the last few volts at the top end. 

The decoders I use: Zimo, NCE, QSI work fine at this voltage and do not have problems. 

Knut, which ones are limited to 18v? 

Thanks, 

Greg


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## krs (Feb 29, 2008)

Posted By Greg Elmassian on 14 Jul 2009 08:28 PM 

Knut, which ones are limited to 18v?


These are not decoders one can buy in the US. 

Greg, I sent you an email,

Regards, Knut


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## Dan Pierce (Jan 2, 2008)

MRC rates theirs at 21 volts max!!


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## Greg Elmassian (Jan 3, 2008)

I don't consider MRC decoders in the same league as the major brands for G scale, so I forgot them... also the Quasinami in the 3 truck shay spazzes out over 21 volts. 

The major companies, Zimo, NCE, Digitrax, QSI, etc, all handle the max NMRA voltage. 

Regards, Greg


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