voltage drop in function outputs

[Howard Smith]

Hello everybody,

I'm a bit stuck here as I'm trying to find a solution to the following problem.

 

I have a Loksound 3.5 XL decoder in a 31 (O gauge). It is wired to a peter clark smoke unit.

The output to the motor in this smoke unit is set to "flickering", so that on-time = off-time = 0.262s Doing this makes the speed of the motor vary enough to create "puffs of smoke" rather than the typical "fag smoke". This works fine and has done for some time, however, it creates a small voltage drop on the "lit" function outputs ie: cab lights, and both directional lights. (In other words on 3 of my function outputs) This is annoying as it creates a visible flicker. I am looking for a way of suppressing or filtering this flicker, but my knowledge in electronics isn't that good.

I had thought of a solution which consists of individual relays triggered by each of the outputs of the decoder which act as switches between the lights and current directly from the track thus theoretically eliminating the problem. However you would get the "clack" of the relay every time you switch something on or off and it remains a mechanical solution (something might stick). Relays also take up a lot of space (which I haven't got) and are very dated.

Does anyone know if I can use capacitors or an integrated circuit???

Thanks,

Howard Smith

[Marty Mc]

Hi

 

I assume you have all the resistance on the blue wire. I had something like this so the easiest way to solve the problem was to put the resistors on the negative legs for your functions.

 

Try that first.

 

Now if you plan to put the smoke on a relay you will lose what control you have, as the relay needs to be on or off. I use relays with dcc all the time in my steam locos.

 

Next the cap solution have a look here.

 

http://www.dccconcepts.com/index_files/DCCflickerfree.htm

 

DCC Concepts make a flicker free 2 unit that can be directly wired into your loksound but you retain control, the only problem is when you turn the mains power off the LEDs may stay on for a while. Available from Broomsgrove models DCC Supplies Trains and railways etc in the UK.

 

Cheapest is the resistors.

 

Best of luck.

 

m

[CB47]

It sounds like your problem is you are momentarily drawing more power than the decoder can output from its functions. This would cause a voltage drop such as you described. The fact that you are only switching it for a brief period is possibly why the decoder has tolerated it so far. the simplest solution would probably be to replace the decoder with one that has a higher capacity output for the functions, but if this is not possible:

 

Have you considered using the smoke motor output from the decoder to switch a solid state relay (SSR) to switch the smoke motor on and off and then supply the smoke motor direct from the track power via a bridge rectifier (Assuming the smoke motor needs a DC supply). An SSR does not make any noise at all when it operates as there are no moving parts.

 

Most Solid state relays will work on voltages from 3 to 32 volts DC for the switching supply, they take very little current as they are an encapsulated semi conductor circuit rather than an electro mechanical device. They are available in sizes down to DIL chip size so you should be able to find one to fit in the space available.

 

Be warned though some will only switch an AC load on and off, so you need to make sure the SSR you buy can switch a DC load on and off unless you put it in circuit before you rectify the supply from the track. A good website to look at is RSonline (rswww.co.uk) they supply lots of electronics bits and pieces and have technical spec sheets available as well to work out exactly which device you need. Hope this is helpful.

[Howard Smith]

Many thanks to both of you for your quick and detailed replies,

 

I think the best solution would be SSR's then.

 

1- Because I can't get to the led's anymore, as they are sealed in the cab now behind filler, so I wouldn't be able to change the resistors (the directional lights are 12v leds so no resistors).

 

and 2 - SSR's look to be a much cheaper solution.

 

Funnily enough the smoke unit heater actually takes juice through an SSR from the track as per the instructions, although I'd forgotten about this. So theoretically, I just need to wire 3 more SSR's to get the desired effect. Fingers crossed folks!

 

Once again, many thanks to both of you,

 

 

Howard

[CB47]

If the unit already uses an SSR to switch the smoke motor it may be that the SSR could be changed for one which uses less current to trigger it. It would be worth checking how much current the SSR draws for switching. If you can read the type number on the SSR you will be able to find a datasheet on the web, which will tell you how much it draws. I work on older machinery in my job and some of the earlier SSRs were quite thirsty on their control current, whereas the modern day replacements seem to operate on a lot less. Good luck anyway.

[Howard Smith]

If the unit already uses an SSR to switch the smoke motor it may be that the SSR could be changed for one which uses less current to trigger it. It would be worth checking how much current the SSR draws for switching. If you can read the type number on the SSR you will be able to find a datasheet on the web, which will tell you how much it draws. I work on older machinery in my job and some of the earlier SSRs were quite thirsty on their control current, whereas the modern day replacements seem to operate on a lot less. Good luck anyway.

 

CB47- no don't worry about that, the ssr that controls the smoke unit is not for the fan, but the heater. It's set to a non varying voltage output and works fine (the ssr is brand new: rs components 244-9019).

However, interestingly things have complicated since this morning. I happened to have two spare ssr's floating around and upon installing them realised that it would be impossible, as the common from each led and other function is soldered to the loco (the common from the decoder being attached to the chassis) under all that filler.

If I install an ssr, the led's must take their juice from the track and not the decoder.

Now with all that work done (the cab interiors are painted, nearly finished being glazed and ready for sealing) I don't want to start grinding away to find my led's.

So is there really a solution, as the only thing I can now modify would be the return wires back from the functions?