# Zimo MX695 and 2x USAT smoke units



## supagav (Feb 8, 2008)

Hi,

Just wondering if anyone can help me please?

I recently installed a Zimo MX695KN (no sound version) in a USA Trains F3A.

The problem I'm having is how to get both USAT fan smoke units to run together?

I have it hooked up on the bench running one of the two smke units and it woks very well, with a nice load dependant sync, but I'm wondering how to connect up a pair of fan driven smoke units? The Zimo has a dedicated fan output which I'm currently using but again I don't know how to best hook up the second smoke unit to this?

Do need any extra components here or another extra circuit?
Any ideas of suggestions would be gratefully received!

Thanks,
Gavin


----------



## Dan Pierce (Jan 2, 2008)

Fans in parallel and heaters in series.
Heaters draw a lot of current so series works best in order not to over load the function current limit of the decoder.
This works real well on DCC systems, but not well at slow speeds with analog running as the values entered in CV 137 to 139 are pulse power controls for the heater element.

I tune the heaters for 24 volts when installing the smoke units, but end users could have a 21 volt system and less power would be applied to the heaters if tied to V+.
For analog operation, one would need to have a regulator installed to keep the voltage constant for the elements and this would also work for differences in digital systems.


----------



## supagav (Feb 8, 2008)

Thanks Dan, that's great! I just tried that and it works nicely! Thank you 

What do you program in CV137, CV138 & CV139 please? I'm running around 23V through my Massoth system so it should be similar just get me started and for reference.

Also one unit seems to be putting out a stronger output than the other? I've switched the connections and changed the smoke units but it seems to have the same effect?

Thanks again,
Gavin


----------



## supagav (Feb 8, 2008)

I measured the two smoke unit heaters at cruising speed, and one measures 5.4V and the other measures 4.8V. Whilst they do work well, one unit has quite considerably less output when I wire he heaters in series. Is there anything I can do to even them out?

Thanks,
G


----------



## Dan Pierce (Jan 2, 2008)

Add a resistor across the 5.4 volt unit to even out the voltage.
Try 30 ohms to start and see what the difference is.
You could use a current meter to measure the amps and then try to figure out a resistor.

Where did you tie the power for the smoke units?
what is the function dimming value in cv 60 (all functions get lowered average voltage from this register).
Did you set the cv for smoke control (between 125 and 132) to 80?
SO, if I use F6 for smoke, I set CV 132 to 80.
THen I check cv 60 for a non zero value, and if it has a value I set cv 114 to ignore dimming of f6 (32).
Then I can use cv137 to 139 to control smoke dimming.
CV137 is idle. 138 is cruising and cv 139 is acceleration.

Send me a private message with your phone number and I can walk you through all this.

I set up the zimo decoders for Train-li customers almost weekly and have most of the info memorized.

[email protected]


----------



## supagav (Feb 8, 2008)

Dan,

Thanks again for your reply and your help, much appreciated! 

First the easy things...

-I have already set CV132 for F6 is set to 80 for load-dependant diesel smoke, and this is working well so far.

-I don't know about the dimming value of CV60, but I will check that out and set CV114 accordingly to avoid dimming on F6.

-I have already been experimenting with CVs 137, 138 & 139 and I can see how they work, so again that shouldn't be a problem either.

I will experiment with a resistor on the higher output heater and see how I get on as this sounds like it should sort it out. I have plenty lying around of various ratings so I will investigate further, plus we have a good multimeter that can measure current which should help too if I need it.

I apologise if this is a dumb question, but will the wattage of the resistor make a difference? What should I look for, 1/4 watt or 1/2 watt?

Thanks again for all your help!
Gavin

PS: PM sent...


----------



## Dan Pierce (Jan 2, 2008)

At least 1 watt, you can use 2 1/2 watt at double the value.
resistors come in 47, 51, 56, 62 and 68 ohms values and at these lower values one can find 30 ohms at 2 watts.
Results will be interesting on what happens when you 'tune' the unit with the higher voltage drop.


----------



## qora01m (Jun 12, 2013)

Hi Gavin,

the pictures below are from Oliver Zoffi's web site. Oliver Zoffi is an Austrian DCC guru related to Zimo. This is what he suggests how to wire the smoke generator. Advantage here is that the power for the resistor is taken from the track directly and so there's no limitation in Watts or uneven output with two smoke generators. Using a rectifyer and a 9V stabilizer this circiut needs to be made for each smoke unit. 
The picture refers to MX690 decoders thus the wiring of the fan is no longer as shown here but directly to the respective pins at the MX695 decoder as shown in the manual. The Voltage at the fan as well as the Amps at the resistor is still load dependent. If you don't mind soldering, you could use this. I converted all my locos using this approach and it works perfect. CV137 = 128, CV138 =180, CV139 =255. Don't forget CV353 for automatic power stop for the smoke unit after the programmed number of minutes.

Best regards
Frank










in the lowe part of this picture the wiring of the Smoke unit is shown.


----------



## Dan Pierce (Jan 2, 2008)

The only issue I would have with the circuit above is when using 2 USA heater elements in parallel, you could exceed the 1 amp rating of the voltage regulator and at 9 volts the heat on a 24 volt system running at 1 amp would be excessive in a plastic engine. A good metal heat sink is needed for the regulator!!
Of course full power is only needed while accelerating as this is when the heater elements are hottest (most current applied).

And watch the specs, I have seen cheap regulators rated at 1/2 amp instead of 1 amp.

So, wire the heater elements in series and use the 12 or 15 volt regulator.


----------



## qora01m (Jun 12, 2013)

The weights above the trucks are the heat sink you need. That's crucial. The circuit above is intended to be set up for each smoke generator. Otherwise Dan would be right and you would exceed the 1Amp. I never tried to wire in series but that should work, too.


----------



## Greg Elmassian (Jan 3, 2008)

The weights have no fins, and while the surface area is somewhat large, the lack of air blowing across it and the boundary effect of the flat surface makes it not work very well, if you ever run a USAT loco for a while, you will find that these weights get somewhat warm and they are NOT dissipating nearly what the circuit above needs.

Also, it's REALLY hard to get a 1 amp regulator to pass 1 amp without some significant heat sinking and airflow... if you look at the data sheet and see the temp data (and understood it, no offense) you would see that that thing needs to be pretty darn cool to get max current, and the heat dissipated also has to do with the amount of voltage you are dripping, and as Dan has stated the heat would be excessive... 24-9 = 15 volts, times one amp is 15 watts... that is a bit of heat.

Greg


----------



## supagav (Feb 8, 2008)

Thanks again for all the input on this guys, I really appreciate your thoughts!

Work and modern life haven't left me much modelling time lately so I haven't had a chance to do much more with this project, but I will let you know how I get on as soon as I have some time to sit down at the workbench.

Many thanks,
Gavin


----------



## ewarhol (Mar 3, 2014)

What about using a large resistor?

For example I have a Train Li Proline Pulsed smoke unit I'm putting into a USAT engine with a QSI decoder. 

Fan is hooked up through the 5v common. Heater will be hooked up through track power common which is 18.81v. Axel informed me the heater needs 5v and will draw 1.5 amps.

So if I did my math right 

R= (18.81-5)/1.5 
R= 13.81/1.5 
R = 9.20 ohms

Watts would be 13.81 x 1.5 = 20 watts

So would a 8 or 9 ohm 20 watt resistor work? Actually I'd probably say a 8 or 9 ohm 30 watt resistor so it doesn't get so hot.


----------



## Dan Pierce (Jan 2, 2008)

If you ever run this engine on a different layout (like Greg's or mine) than the track voltage will go to 24 volts so using a larger wattage resistor is good.
Usually wattage is doubled for resistors to be safe and where does all this heat go inside an engine?? 20 watts in a confined area is a lot of heat (read plastic can melt).

So, a DC to DC converter would be a better way to get power without a lot of heat.


----------



## Greg Elmassian (Jan 3, 2008)

What he said.

By the way, although the surface temperature of a larger wattage resistor (given the same current and voltage) than a smaller one, STILL, 20 watts of heat will be given off inside the loco, and the heat has to go somewhere.

I know a lot of people who have had excessive heat buildup inside an unvented loco using large resistors, who did not realize that no matter what size of resistor, the same volume of heat is generated.

Regards, Greg

Greg


----------



## ewarhol (Mar 3, 2014)

Thanks Dan and Greg. 

Was just curious. I'll go with a 5 volt 3 amp regulator. Mount it to a cooling block with fins.


----------



## Greg Elmassian (Jan 3, 2008)

that will work, and should be bulletproof, but also spend some time looking for DC to DC switching regulators, smaller, cheaper, less heat.

Greg


----------

