# Conversion of MTH F7



## Tom Bray (Jan 20, 2009)

While to some this is probably going to sound like sacrilege, I have decided to take my slave MTH F7 and convert it to DCC. The main reason is that I like the features of DCC over the DCS in that I can sense occupancy, tie it to the computer, DCC seems to be much less finicky compared to DCS, and I have several automation devices that only work with DCC (plus I can control DCC engines from my IPod which caters to the geek in me). I also really like my MTH trains in the 1:32 scale and I haven't found anything else that I would prefer to replace them with, so the conversion makes sense, at least to me. * (MTH Please take note ... I want several of your engines but I am waiting for PS3 to make another purchase!)*


By converting the slave F7, that still gives me two locomotives that run under DCS, the other F7A and my Hudson. If this conversion goes well, the other F7A may also be converted, that will give me two engines with full controllers in them so I can consist them in any way I want to. The Hudson, assuming I don't have to wait to long, will hopefully get converted to PS3 when it becomes available since I think that will be a better controller for that engine.


I am looking at using a Train-Li supplied Zimo MX690V decoder with sound. It has 2 outputs that will supply up to 1.5A and I think it has enough other outputs to control all the lights on the locomotive. Axel recommended sounds that are actually for the F3 but, at least the demo set on the computer with big speakers, sounds pretty good. The other important item is that compared to the Massoth decoder I used on the trolley, the Zimo manual is more complete and detailed, although it could still use a few more example connection diagrams. The real question of course is whether or not it is accurate or not and how many quirks it has.


The main question I have is related to the MTH smoke unit. This is going to be the first conversion I have done with one of these things. Of course documentation on MTH locomotives is a bit sparse so that makes it a bit more difficult.


There are 2 pairs of wires that go to the smoke unit, I assume one pair runs the heater and the other a blower/fan. Does anyone have any idea how much current the smoke unit uses. The PS2 controller has a relay on it which I assume is also for the smoke unit so I am concerned that I may need to do the same thing. My plan in the next few days is to hook up the two locomotives (outside) sitting on a table and activate the smoke functions and see if I can determine the behavior but any insight into this would be helpful. How do these get controlled? Is on an on/off and another either a variable output or pulsed output? I know on MTH there is some control over smoke volume (although there never seems to be enough of it regardless of the setting).


The other issue I have is related to the speaker. Train-Li has these great speakers but they are too large for the normal space MTH allocated to put a speaker (they are too tall). I have a tad over 1" of height and an opening designed for a traditional 3" speaker if I put it where MTH designed it to go. I have a 3" speaker that fits perfectly but it is 45 ohms, not the traditional 8 ohms. Would it be better to use an 8 ohm speaker that was larger and baffle it somehow having it inside the shell of the engine instead of facing down under the trucks as it is implemented by MTH? 


Tom


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## blueregal (Jan 3, 2008)

Tom, on the speaker issue, look at 1-1scale sound in Oregon. He has a set of 4 speakers that fit nicely into the boiler of at least an Aristo Mallet, thereby the sound coming from the engine and not the tender!! I have used two sets of his speakers with no problems very economical, sound good, and are already wired all you do is connect two wires. Two speakers are by themselves, and the other two are facing away from each other in a small type drink can configuration the size of a red bull can!! Take a look! Regal 
1 to 1 Scale Sound


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## Greg Elmassian (Jan 3, 2008)

I think your idea to run the loco and measure the voltage and current is a wise one. 

You will want to do this for both the heater and the fan. You might find that this is really not worth the effort and sell your MTH smoke unit and put in a DCC one that will notch up and down and be able to be configured by DCC, like the Massoth unit. 

I don't know about the heating unit, i.e. is the smarts in the unit to not overheat. If so then maybe you can run the fan from a small DCC decoder and set a custom speed curve to get the effects you want. 

Regards, Greg


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## Tom Bray (Jan 20, 2009)

I am planning on using a scope in case the controller outputs any funny waveforms. I have a couple of low ohm resistors that I can use for current measurements. 

I have considered the Massoth smoke unit ... it looks pretty cool in their little video. I am not sure if having the F7s generate more smoke than the steam locomotive would be right ... that might not look quite appropriate either. 

The controls for the MTH smoke unit appear to be pretty basic. There are also lots of warnings about not running the smoke generator out of fluid as that will damage it. 

Once I get a handle on it I'll post my findings, unless someone comes along and just answers my questions about it. 

Tom


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## Greg Elmassian (Jan 3, 2008)

The MTH units have a reputation for prodigious smoke. I have not seen the F7's in operation but I've seen the steamers and they smoke a lot. 

I would think that the Massoth would be fine, not overdoing it. You could also pipe it to the 2 exhausts. 

Let us know what you find. 

Regards, Greg


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## Tom Bray (Jan 20, 2009)

The F7 has one smoke unit for the two exhaust vents. There is a manifold along the roof that directs the smoke to the vents and any water that gets into the fan vents around the critical components inside directly onto the track. It is a nice design and I don't want to have to mess with that portion of the engine if I don't have to. 

Tom


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## Tom Bray (Jan 20, 2009)

Here is the test setup:











The PS2 controller does some interesting things. It PWMs the track voltage to the smoke generator heater. At 22V of track voltage, the PWM is shown below. At around 12V input, the pulse approaches a 50% duty cycle and averages around 4V going to the heater. The heater measures 6 ohms (DC) so the current averages less than an amp.The fan drive is a fixed DC level of around 4.3V:






















I am noticing that the heater in the slave unit is putting out a lot less smoke than the master F7. I am not sure why but I think I have seen this behavior before. I am going to let it sit there and generate smoke and see how it does. One issue is that I rarely run the slave F7 because it ends up making the engine longer than the freight cars that it usually pulls and I don't have enough passenger cars to do it justice either.


If I want to measure current through the heater I need to bring home a special current probe and use the scope since the voltmeter isn't going to average this out reliably. 
So that is what I know so far. 



Tom


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## Greg Elmassian (Jan 3, 2008)

Tom, I'm surprised the fan speed does not vary... according to videos from Ray Manley it seems to speed up and slow down with the "notch". He had a video showing this recently if I was not mistaken. 

PWM is not surprising for the heater, it's a way to keep down heat on the output transistors, effectively they are either off (no heat) or full on (very little heat), linear output takes a lot of heatsink and most likely forced cooling. It's also somewhat easier to control from a microprocessor. 

Regards, Greg


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## Tom Bray (Jan 20, 2009)

I haven't figured out how to make the fan change speed, maybe something is set wrong. I tried having the engine standing still (that is state it was in when I took the pictures) and running 30 SMPH and didn't see any difference. Regardless, the Zimo decoder is going to be programmed to do something along those lines. 

I did figure out why there was only a little bit of smoke... the wick had apparently gotten dried out and cooked to death. I cut out the bad bad portion and re-installed the wick and it now generates smoke like is supposed to. The directions for smoke say you should use only a few drops - there is space for about 1/8 cup of smoke fluid in that thing. I'll have to see if I can get a replacement wick. It was pretty impressive when I put the cover on but it didn't mate completely with the smoke generator - there was smoke coming out of everything.

I just ordered the decode from Train-Li - Axel went through a bunch of stuff about the decoder which should make this installation go a lot smoother. I hope to have it by Friday so I can start installing it. 

I am going to have to go looking around my junque drawers, maybe I have a buck type 5V supply that would be perfect for this application (5V plus 2 diodes in series should do the trick). 

I have a week of forced low activity vacation which this sort of project is perfect for. It is too hot to be outside during the day and the activity level is higher than I am being allowed for working on the layout itself. 

Tom


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## Greg Elmassian (Jan 3, 2008)

I'm always surprised how the recommendations from the manufacturer seem to have no relation to the true capacity of the smoke unit. 

I'm guessing their idea is to not overfill, so put in a few drops and then add more when it quits. The reality is that when it quits that often, you are overheating it real often and you glaze the wick, or other stuff. 

The MTH have pretty big "tanks". I actually took my smoke units apart and measured the capacity of the reservoirs to know how much to fill from "dry"... it was an educational experience. 

I use a syringe to add fluid, then I know what volume I am using, because drops of fluid are NOT all the same for different smoke fluids. 

Regards, Greg


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## N1CW (Jan 3, 2008)

Tom[/b]

While you have the TDS Scope and B unit COOKING together,








how about some info on how the signals look[/b]
compared to the position of the SMOKE pot.[/b]

Just wondering about the differences between MAX and MIN rotation.

....cough..cough....Glad that is not some of that MAGIC SMOKE....







[/b]
I can not see between your smoke unit output and Greg's Ci-GAR...







[/b]


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## Tom Bray (Jan 20, 2009)

I thought about that ... The thing is that the smoke control pot is really only supposed to be functional when in analog mode. I was running the engines under DCS control. I probably should figure out how to get at the menu for that option. I'll add that to my list for this afternoon.


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## Tom Bray (Jan 20, 2009)

So this is what I discovered today playing with the locked down setup:

I measured the total current used by the system which includes the DCS controller. I was lazy and just used a Fluke meter on the 10A current setting. That seemed to work just fine.

Track voltage was around 18.5V for the first part of the tests. This is using a MRC Power G transformer feeding a filter circuit I built that has a high current 50V full wave bridge, 10,000 uF cap, and a direction switch. This makes the measurement much easier because it eliminates most of the 60Hz hum, the bridge also lowers the voltage a bit, at least under load. The latter is actually a good thing because I originally tried putting a cap across the rectifier inside the MRC transformer and while that worked OK, the top voltage ended up over 28V with the transformer set to 100% ... that's too high for safe operation.


Both engines shutdown but on the track: 100mA
Engines turned on idling: 240mA (I also got a measurement that showed 190mA but that was before I turned on the smoke and turned it back off) 

Engines turned on, idling with smoke turned on: 720mA - the pulse width was pretty much the same as I published before


Running at 10 SMPH, with smoke: 1088mA (PWM on heater is 3.5uS repeated every 45uS) 

10 SMPH no smoke: 438mA

20 SMPH with smoke: 1300mA (Pulse is 4.3uS, still repeated every 45uS - the 45uS seems pretty stable, it never seems to change)
No smoke: 550mA 


At 30 SMPH I started getting some random speed changes so I changed the power supply to a regulated 24VDC supply that would supply up to 4A. I monitored the track and it stayed a constant 24V for the remainder of the tests, even though the speed varied to a certain degree.

30 SMPH with smoke on: 1420mA (4.0uS pulse width at approximately 23V for the pulses - varied a few 1/10th but was pretty steady) 

With smoke off: 513mA

60 and 100 SMPH pretty much had the same current draw so I am not sure they were actually running any faster, although the sound system made it sound like it was. There was also a lot of smoke being generated between the two smoke generators ... it looked appropriate.

Smoke on: 2150mA (5uS pulse width)

Smoke off: 1200mA

So worst case, for one smoke unit, the current draw is:

At idle: (720 - 240)/ 2 = 240mA. Assuming the 6 ohms remains constant over heating that would mean: .240 * 6 = 1.44V (that is about what I was measuring using the scope)
At 10 SMPH: (1088 - 438) / 2 = 325mA or approximately 2V across the heater

At 20 SMPH: ( 1300 - 550) /2 = 375mA or 2.25V across the heater

At 30 SMPH: (1420 - 513) /2 = 454mA or 2.7V across the heater

At 60 SMPH: (2150 - 1200)/2 = 475ma or 2.9V across the heater


Assuming that the scope measurements are also valid, 5uS on time over 45uS => 0.111 if multiplied by 23V => 2.5V at full speed


I did notice that as the voltage made slight changes, the pulse width also changed so there is a fair amount of calculation going on inside the controller. 


I think I have beaten this to death so I am off to other activities. I am thrilled that the smoke unit can't be using more than 1/2A so I don't need a relay. I will need to have a supply set to approximately 4V to run the smoke unit and then PWM the heater. 


I will post the conversion progress as it happens ... this will probably take several iterations before I am happy with it.

Tom


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## Tom Bray (Jan 20, 2009)

I had an interesting revelation about what uses power in my system. With the one F7 running with the smoke turned off and 4 of the long passenger cars installed, the layout was peaking over 4A which is close to the limit of my small 24VDC supply. Turning on the smoke caused the supply to occasionally drop out which must crash the controller because everything stops and won't start again till I cycle power. 

Those lights use a lot of power ... need to think about LEDs for them. 

Tom


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## Tom Bray (Jan 20, 2009)

The engine has now gone around the track on under its own power so it is getting closer. There is still a lot of work to do.

An interesting observation is that it may be the case that the slave F7 runs better in reverse compared to going forward. I am not totally sure about this though. I have recently modified the track that was causing problems so that may be the ultimate culprit. I did check to see if there were any obvious differences between the master and slave locomotives ... nothing that jumps out.


Lights turned out to be pretty simple. Almost all the lights are incandescent, not LEDs. MTH PWMs these lights straight off of the track voltage, I decided not to do it that way.


The MX690V has a programmable low voltage output which is set for 6V, swapping the resistor gives 5V. The difficulty is that the resistors are the tiny 603 type resistors and are a royal pain to deal with.

Lights got connected to function outputs 0,3,4,5,and 6. The order isn't particularly important but you need to stay in that lower set of function outputs to be able to implement any special effects. Currently I have a 1K resistor in series with the pair of LEDs used for marker lights. One feature I am not real found of is that the cab lights and the headlight are on the same circuit. I will probably change that at some point. I also want to add a beacon on the top of the engine and I may end up adding the lower lights that many of the F7s seem to have (I don't know if they qualify as ditch lights or not but quite a few engines have them). Also I need something to be on when the engine is running in reverse - maybe several LEDs are in order..


The smoke generator is still on hold at the moment because I am still collecting parts. I am putting a switch into the smoke circuit so that it can't get turned on by accident. 

The documentation recommends installing capacitor hold up circuits for the sound and the decoder itself. I still have to implement those but it is obvious that they are a good idea. 


Sounds have been a minor issue. The horn and bell are not on the correct (standard) function keys and right now there isn't a fully user controlled horn. There are several examples of horns that are on different function keys but nothing basic. I have asked Axel what is the best way to proceed, I tried following the example in the manual but that isn't working the way it says it should for moving sound around. 


I did install a volume control. When I first powered the engine up I hadn't installed it and I started hitting buttons. The horn was the first thing I stumbled on and it almost blew me out of the room ... very impressive and capable of being very loud. The volume control is now installed. The start up and idling sequence is also very impressive. 


So that is where I am at at the moment. Pictures will be coming.


Tom


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## Tom Bray (Jan 20, 2009)

I talked to Axel at Train-LI and found out what the problem is with the sounds. First, the manual assumes that you have stock sounds in the decoder. Stock sounds are either European Steam or European Diesel sounds. American sounds are all custom projects. You can't adjust the sounds much on a custom project without having the special programmer. 

Axel apparently got hit with a pair of emails today with very similar issues about the sounds and the function key to sound mapping. He has decided that he needs to ask more questions before programing a custom sound set for someone. 

From my perspective, I'd rather just be able to play with the entire sound project so I ordered the programming interface and he will be sending me the sound files. I am pretty happy with this decoder and it will probably replace the PS2 modules in my other two locomotives ... that now has to wait for the funds to do it plus I will need at least one more booster to be able to run all the trains at once on DCC.


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## Greg Elmassian (Jan 3, 2008)

I have the interface, the software can be a little goofy, in the last rev I used, there were still some German words in some of the menus. Axel knows these and is a good resource. 

The software is not too back and I ordered a new decoder from him today, so I'll be updating to the latest rev of s/w, so if you have questions, we can work together... 

Regards, Greg


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## Tom Bray (Jan 20, 2009)

Well I got the Zimo Sound Loader to successfully load the locomotive. It would really be nice if Google could translate the German names better. 

I made some minor changes to the lighting probably with more to come. I separated the interior lights from the headlight and stuck the light on an output that I can dim. 

Decoder Pro needs a bit of work on the 690V, to really configure it requires editing the CV's. 

The engine is put back together and runs and sounds pretty good. I plan on running it and most of the rest of the trains tomorrow and possibly on Monday. 

My big problem right now is that my old faithful PC isn't any more. Have new computer (IMac with Win7 installed) but I need to back up the old one ... this isn't fun. So far nothing has been lost!


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