# How do you connect both smoke units in a USA GP38-2 when installing AirWire?



## Fred L. (Dec 11, 2020)

I'm putting in the AirWire900 decoder (and Phoenix P8) in a USA GP38-2. How do you hook up both smoke units to work? Or is it possible? The instructions mention moving the second smoke unit board to the roof of the shell but then apparently assume you're not actually going to use it as later in the instructions it only mentions plugging into one. I called them and they seemed irritated saying everything was in the instructions. Well, it's not in the book I have. And not on the online one either. There is a jumper wire that connects both smoke unit boards that's disconnected so you can plug in the wires from the decoder. Obviously when it's disconnected the other smoke unit won't work. The jumper wire has a black female connector midway that is different from the white one coming from the decoder. Is it ok to splice the wires from the decoder to the jumper wire so both smoke units work? (I'd probably wire in a matching set of plugs so I could unplug it if needed). The guy I'm doing it for would like both to work. But I don't want to fry the decoder if it's not built to run both smoke units. He has 3 more GP38's he wants done so I'd like to get it figured out. Thanks for the help.


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## Paul Burch (Jan 2, 2008)

The smoke generator output on the Airwire drop-in is rated at 3 amps. I would think that should be enough to run both units if you want to splice in the second smoke unit control board.


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## Michael Glavin (Jan 2, 2009)

Paul, 

I haven't looked at specifications of late for Airwire's decoders, isn't/wasn't the MAX current draw 120W for their decoders? 120 Watts was divided between motor driver, smoke and lights and such? Another consideration is what model decoder is in play, are the newest units rated different than say an earlier model? Greg E might have recorded USAT smoker current draw. As I recall Greg made a video showing the USA smoker driven with QSI decoder.

Fred,

What size and voltage battery do you intend to use for the GP38's? If the USAT smokers like 5V and your using the stock regulators to get there, your wasting/shedding power to get to 5V. 


Michael


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## Paul Burch (Jan 2, 2008)

Michael,
Haven't seen you post in awhile. Here is where I got the 3 amps for the smoke output function. Page seven in user guide. Also, I think the newer decoders have a higher power rating then the older versions. I don't run smoke units in any of my diesels due to the current draw. I will take longer run time, but you can always assign it to a function key for on/off and also take advantage of the timer options to shut the smoke off after a set period to conserve battery.


 http://www.cvpusa.com/doc_center/r4_May2020_DropIn_UsrGid_WEB.pdf


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## Michael Glavin (Jan 2, 2009)

Paul,

I read the 2017 or later Drop-in decoder spec sheet of your link; motor driver is rated at 8 Amps @ 15V, 8Ax15V = 120 Watts, 3.0 Amps for smoke and 1.0 Amps for lighting. I want to clarify that decoder can handle the combined loads with 120W motor load and or will the decoder carry the 12 Amps? I have several iterations of the AirWire large scale decoders in play, as noted above I recall 120 Watts was the MAX load the decoder could carry. That said I emailed CVP inquiring about NEW and OLD specifications for said decoders. Makes sense that the newer generation stuff is more efficient and able to carry increased loads.

Michael


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## Greg Elmassian (Jan 3, 2008)

First of all, the AirWire instructions are flawed (heavens!)

The instructions indicate the heater is a resistive element. Well, that used to be true, so you need to first determine if you have the little white pancakes (2 wires) or the larger unit with the fan. (4 wires)

His instructions are for the pancakes, which are a little wire coil in a bath of fluid. They normally run from about 5 volts.

Looking at the instructions, I don't see any reference as to the voltage, in fact the link Paul gave does not even have a connection diagram.

Yes, 120 watts is the max load... so many people read that as 10 amps (I think it was advertised that way too), but who runs 12 volts in large scale?

14.7 makes more sense...

You need to calculate watts, not amps... I don't think his output stages are any more robust or handle increased loads, but let's see what you get back.

Anyway back to the smoke units, which ones are in this loco? Let's start there, since power and voltage requirements are different.

Greg


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## Michael Glavin (Jan 2, 2009)

AirWire responded to me email right away and answered all my question(s) below with regard to how much power AirWire decoders can handle.

1_20W is the absolute maximum and assumes the driver transistor temperatures are kept below 175F. This is the rating on all of the AirWire decoders. 

As for protection, the first decoder, AW10DSS, had no protection for the driver transistors. Starting with the G2, there was thermal protection on half of the driver transistors. The latest G4X has protection on all the driver transistors.

Maximum output current derates based on transistor temperature and input voltage. Remember Power = Volts x Current. The power value is fixed at 120W. SO as the volts go up, the current goes down. Also as the transistor temperature goes up, the maximum current goes down. See the manuals for suggestions on cooling the driver transistors._

My thoughts:
Looks like any AirWire decoder will handle the GP38 with smoke. GP38 @18V will consume about 2.5A under a 16 car load, lighting maybe .5A and two smokers about 1.0A. 4.0Ax18V=72 Watts

Michael


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## Greg Elmassian (Jan 3, 2008)

Seems Airwire only responded on the motor drivers, not the ancillary outputs. 

Greg


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