AC and DC
- Thread starter dumpy
- Start date
dumpy said:
As has been said before, the only stupid question is the one you don't ask!
The simple answer is that DCC systems usually have an ac track supply. Its actually a bit more complicated, but if you have dc relays that you cannot energize even with a diode in series you are going to need a separate supply. MTS originally required a nominal 24V ac supply but that's been reduced to 18V ac now.
But I would not use the track supply which also has the DCC control signals, effectively a high frequency ac signal on top of the 'power' 50 / 60 Hz. Use the transformer output, not the central station output.
If that's still not clear just ask.
regards,
Don
Thanks. That's really helpful in clarifying my ideas. I thought about diodes just after I'd posted. So all I need is to take the AC output from the transformer with a diode to the relay. There's more to it I know with activating switches etc but now I see where my supply is coming from.
Steve
I didn’t say it was your fault, I said I was b
What are you powering the MTS 11 with , if its the 50110 it also has lighting ect power .
http://lgb.vanelten.nl/Database/bedieningshandleidingen/5011x.pdf
http://lgb.vanelten.nl/Database/bedieningshandleidingen/5011x.pdf
whatlep
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Have you tried using a simple bridge rectifier to get a DC source from your track power? I use them very happily to get points to change automatically with reed switches. A W04 design rated for 1.5 amps/ 400 volts works well for me. Available for pence quite widely, or go to EBay. This is just one example: http://cgi.ebay.co.uk/W04-FULL-BRID...omputing_PowerSupplies_EH?hash=item20aecdf09bdumpy said:
Obviously whatever power you take from the track reduces that available for locos, but if the items you want to power are remote from the DCC central station it may be an easy solution.
ntpntpntp
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don9GLC said:
Well, not quite ... there is no 50/60 Hz AC component, just the DCC waveform (at around 10 KHz I think). You'll sometimes hear or read the expression "the DCC signal IS the power" .
http://www.dccwiki.com/DCC_Tutorial_(Power) < Link To dcc Wiki (power page)
You should be able to derive a usable DC supply from the track via a bridge rectifier and a smoothing capacitor, as has been said in other posts. Be mindful of what you power with it though: - for example if you drive point motors from the track supply and there's a short that trips out the command station then you loose point power too. Some DCC experts advocate a separate DCC bus for point control etc. I've gone down this route, but more for the reason that I want to keep the pointwork operational while feeding analogue DC to track when I wish to run unchipped locos or use alternative controllers (eg. if a mate brings a Train Engineer round to play!)
Thanks for all your input. This is a fun project for me to while away the time until my track resurfaces from under the snow. The project is to have a passing loop so can run in one train and start off another complete with appropriate colours on signal lights, Am sure you experts have all done it, no problem, but its a learning curve for me. So far have got track contact switches to operate points as train comes in to loop. Then supplementary switches on points to switch current between dead sections in loops. Was using a relay coupled to live and dead sections with a diode to switch lights between red and green. Lights powered from transformer. Does all that make sense? I have drawn it out but its so rough I'd hesitate to show it here.
ntpntpntp
Registered
Doug said:
I understand where you're coming from, but no it shouldn't have that effect. The capacitor is on the DC side of the rectifier and simply acts as a reservoir, supplying energy into the DC side of the circuit when the input voltage from the ripppling rectified DC drops.
ntpntpntp said:
Well technically, you are quite correct, but it does not in my opinion help understanding. Much as I love Fourier Analysis and all the other mathematical techniques required to understand what is going on with a DCC signal, I suspect they will be lost on most members of this forum.
Without getting technical, a DCC waveform is nominally a square wave and it can be thought of as a power signal (actually 8.62Hz) and a control signal which has a range of higher frequencies. (and yes, its actually much more complex with 'long' zero bits). The NMRA standard specifies a minimum rise time which corresponds to 156.25Hz but in practice there will be (much) higher frequencies. These are electrically 'fragile' and can be affected by other devices connected to the track.
The risk in connecting 'homemade' circuits to a DCC track supply is that the effect on these higher control frequencies has not been tested and unexpected things can happen. Without doubt, the power from a DCC track supply can be used to supply auxiliary components, but there could be unexpected (sometimes random) effects, not limited to loss of control of locos, damage to the command station and radio / TV interference.
Its simple and easy to avoid this risk.
On the subject of a separate DCC bus to power auxiliaries, as far as I am aware, normally every auxiliary component is connected to the bus through an interface unit, designed for connection to the DCC system. So even in this case measures are taken to avoid interference.
Its also extremely wasteful to load up a DCC command station with non DCC devices which could instead be connected to a simple power supply. Basically more load, equals more heat, equals shorter lifetime.
The simple rule should be use DCC power for DCC, and nothing else.
I'm sorry if this seems to be laboring the point, but I originally tried to respond to a 'simple' technical question with a simple 'non-technical' answer. I apologize for being 'economical with the truth' but its not Ohm's Law or anything like as simple
whatlep
Registered
Well chaps, I've been fascinated by the technical stuff here. Very interesting indeed.
However, in my simple universe, an ounce of practice is worth a ton of theory. I've been using the bridge rectifier arrangement quoted in my earlier post for a couple of years so far. It works. No ill effects to MTS Type 1, and Type 3 central stations, locos or associated LGB & Massoth chips, reversing loop modules and point modules, plus Bachmann, Piko and LGB motive power. Fair enough?
However, in my simple universe, an ounce of practice is worth a ton of theory. I've been using the bridge rectifier arrangement quoted in my earlier post for a couple of years so far. It works. No ill effects to MTS Type 1, and Type 3 central stations, locos or associated LGB & Massoth chips, reversing loop modules and point modules, plus Bachmann, Piko and LGB motive power. Fair enough?
whatlep said:
Yes of course.
When I retired I ended my membership of the (then) Institution of Electrical Engineers. Under their code of ethics, any advice I gave was required to consider the risks. Habits of a lifetime are hard to change.
Rectified DCC may work, but then again it may cause problems. Using simple ac avoids the risk and has other advantages.
I'll just enjoy my retirement, and go play with trains
GrahamMills
Many & various. In G scale it is American Diesel.
whatlep said:
I am sorry to piggy back on this topic but I found it very interesting because I had not previously considered the issue that a DCC track supply is not DC. I knew of course but had not thought of the ramifications.
I have the problem that my knowledge of electronics is small and I would not know a Full Bridge Rectifier if I saw one and certainly not how to use it.
I run DCC through the track and I have a couple of points/switches on a remote part of the layout that I want to put under DCC control. I was intending using the LGB 12010 Switch Drive and the 55024 Switch Decoder to drive it. I assumed that all I needed to do in terms of power was to connect the 55024 to the tracks. Have I got that wrong and actually I need to get rectified?
whatlep
Registered
GrahamMills said:
Hi Graham. You can run a 55024 or 55025 straight off the tracks no problem at all. I do so with my 55025 and its Massoth equivalent.
The reason I use a bridge rectifier for one point is simple. I've run out of spare ports on my 55025s and the point is only required to operate one way to ensure trains always enter a return loop in the same direction. Choice is therefore either buy a 55024 at £42 or the rectifier and some bell wire for under £5. The wiring could scarcely be easier. Two wires from the track to the AC side of the rectifier (marked with an AC symbol!). Two wires from the other two terminals on the rectifier to the point motor (one via a reed switch). Simples!
The attached photos show said rectifier as positioned in an ordinary 5 amp domestic junction box (which has survived happily outdoors). Blue/brown wires are the DCC feed and a link to another device. White wires are bog-standard bell wires to two points via two reed switches (i.e. multiple circuits powered off one rectifier). Logic probably clearer with the second picture.
GrahamMills
Many & various. In G scale it is American Diesel.
Thanks Whatlep & Nico.
Nico - why did you go with USATrains #6 switches rather than Aristo-Craft?
Whatlep - I can understand the wiring. No idea why it works
Nico - why did you go with USATrains #6 switches rather than Aristo-Craft?
Whatlep - I can understand the wiring. No idea why it works
When I started this thread with a simple but probably an ignoramus question I didn't expect it to take on a life of its own. Have been fascinated by all the erudite comments about wave form, fourier analysis etc.
So am daring to ask another probably ignorant question.
Upto going DCC everything was DC and I never thought about it. Now with a new season and my track emerging from the snow am rewiring using DCC. Do LGB switches operate OK with an AC supply (not from the track I hasten to add) using a passing contact switch or do I need to use a diode in series OR do I need to go down the route of full wave rectification?
So am daring to ask another probably ignorant question.
Upto going DCC everything was DC and I never thought about it. Now with a new season and my track emerging from the snow am rewiring using DCC. Do LGB switches operate OK with an AC supply (not from the track I hasten to add) using a passing contact switch or do I need to use a diode in series OR do I need to go down the route of full wave rectification?
ntpntpntp
Registered
The LGB point motor is driven by a DC motor and expects a DC supply that is reversable to control which way the point throws. Typically this is achieved using an AC supply and a diode for each switch contact or button, thus driving the motor with half-wave rectified DC.
This diagram might help:
http://www.altek.nl/graphtips/EPLsturing.gif < Link To EPL point motor wiring diagram
This diagram might help:
http://www.altek.nl/graphtips/EPLsturing.gif < Link To EPL point motor wiring diagram
nico
Registered
GrahamMills said:Thanks Whatlep & Nico.
Nico - why did you go with USATrains #6 switches rather than Aristo-Craft?
Whatlep - I can understand the wiring. No idea why it works
at the time there was a shortage of aristo switches,and i liked the signal lights on them, if i were to buy again i would'nt them,wiring them was a pain for DCC
whatlep
Registered
NO! LGB point motors are true motors (like Tortoise in HO/OO), not solenoids, so they need a DC supply. They don't seem to much care about the flavour, based on 10 years of use/ abuse. A simple, yet rugged solution if you are not yet into 55025s or similar would be to use a starter set controller and a pair of wires to each point via a "push to make" switch. Turn the controller in one direction or the other, press the relevant button and the point(s) will change. Changing the controller direction reverses your DC polarity for you, thus changing the direction the point motor moves. On my former layout, this arrangement happily shifted up to 5 points simultaneously for 6 years. No ill effects.dumpy said: