DIY Power buffer

ge_rik

ge_rik

British narrow gauge (esp. Southwold and W&LLR)
24 Oct 2009
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285
Cheshire
www.riksrailway.blogspot.com
Just been browsing through the latest edition of Voie Libre (#73) http://www.gscalecentral.net/tm?m=277016&high= < Link To http://www.forum.gscalece...spx?m=277016&high=
and it looks to me as if there is an article on making your own power buffers. My French is not sufficiently adept to be able to translate the article and as yet they've not yet posted an English translation on their website.

From my shaky translation and looking at the photos it looks as if it's little more than a large (or several smaller) electrolytic capacitor, a diode and a resistor wired somewhere into the circuitry (between pick-ups and decoder? "Le décodeur est juste intercalé entre le moteur et le bloc condensatuers").

Clearly, I don't want to risk making my own based on my rather dubious translation. I just wondered if anyone else has made their own power buffer and if so how. I seem to remember an article on electronic flywheels in a Railway Modeller several decades ago and presumably the principles are the same.

Rik
 
Gizzy

Gizzy

A gentleman, a scholar, and a railway modeller....
26 Oct 2009
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Neil Robinson is your man here....
 
ge_rik

ge_rik

British narrow gauge (esp. Southwold and W&LLR)
24 Oct 2009
9,703
285
Cheshire
www.riksrailway.blogspot.com
Doing a bit more browsing I came across this
http://www.rmweb.co.uk/forum/viewtopic.php?f=10&p=604189 < Link To http://www.rmweb.co.uk/fo....php?f=10&p=604189

It looks as if you can fit a DIY buffer to the decoder via any + and negative connections - which of course is relatively easy on Massoth/LGB decoders.

I'm just a bit wary of blowing a perfectly good decoder by getting it wrong. I'm not sure what values the resistor and diode need to be.

Rik
 
ge_rik

ge_rik

British narrow gauge (esp. Southwold and W&LLR)
24 Oct 2009
9,703
285
Cheshire
www.riksrailway.blogspot.com
Furthermore, found this on the Massoth forum
http://forum.massoth.org/viewtopic.php?t=216

On this authority I'm willing to give it a go. Will keep you posted as to how I get on.
Mind you this warning looks comforting (not!)

Important:
The buffer should be connected on the decoder only on internal decoder voltage behind the commutator.
If you connect them directly on track, he can on extreme case explode and also it would make track signal unreadable.

If you see a small mushroom cloud rising over Cheshire you can assume that my experiments have been less than successful.

Rik
 
ge_rik

ge_rik

British narrow gauge (esp. Southwold and W&LLR)
24 Oct 2009
9,703
285
Cheshire
www.riksrailway.blogspot.com
PS - Did you see the contributor's joke at the end of the posting?

What have Windows and a Submarine together? [presumably 'in common'?]
If you open a window, trouble starts.

Who says Germans don't have a sense of humour?

Rik
 
bobg

bobg

Registered
3 May 2010
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Middle Earth
Have you tied Google for translation (or one of the many others on-line), it is reasonable, though of course not at all technical, but it does usually get the words that I cant, and I can then usually pick the bones and a bit more out.
 
ge_rik

ge_rik

British narrow gauge (esp. Southwold and W&LLR)
24 Oct 2009
9,703
285
Cheshire
www.riksrailway.blogspot.com
Have you tied Google for translation (or one of the many others on-line), it is reasonable, though of course not at all technical, but it does usually get the words that I cant, and I can then usually pick the bones and a bit more out.
Thanks Bob
I've given that a go on some of the more impenetrable phrases and got the gist of the original article but either the article is a bit vague on detail or I'm missing something. I think the Massoth forum posting is the most helpful and as it seems to have come from one of their technical guys (with a sense of humour) I'm feeling sufficiently confident to give it a go when I get back home.

Rik
 
Neil Robinson

Neil Robinson

Registered
24 Oct 2009
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N W Leicestershire
Important:
The buffer should be connected on the decoder only on internal decoder voltage behind the commutator.
If you connect them directly on track, he can on extreme case explode and also it would make track signal unreadable.
If you see a small mushroom cloud rising over Cheshire you can assume that my experiments have been less than successful.
Rik
I suspect "commutator" means rectifier as electrolytic capacitors are polarity sensitive and really don't like reverse polarity. If connected to reversed polarity or AC they may indeed explode. Exactly the same could happen if an"official" buffer were to be incorrectly connected. No problem with either if connected to the correct decoder terminals.
 
muns

muns

Moderator
Staff member
GSC Moderator
Peter (the Massoth guy) does indeed mean rectifier in this case.
 
ge_rik

ge_rik

British narrow gauge (esp. Southwold and W&LLR)
24 Oct 2009
9,703
285
Cheshire
www.riksrailway.blogspot.com
From section 3.4.5 of the manual for Massoth decoders

Additional capacitors acting as power
buffers may be used to bridge contami
-nated track sections. The buffers must
be connected to dec+ and GND.

Rik
 
Rhinochugger

Rhinochugger

Retired Oik (IBT)
27 Oct 2009
26,363
942
North West Norfolk
So can you only use a power buffer on DCC?
 
whatlep

whatlep

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So can you only use a power buffer on DCC?
You can use a power buffer with a Massoth DCC chip on analogue if you wire it correctly. See my review here:
http://www.gscalecentral.net/tm?m=236918&mpage=1#277339 < Link To http://www.forum.gscalece...918&mpage=1#277339

Presumably it's electrically possible to create a charging circuit for a buffer on DC, but I can see issues with the amount of time needed to charge the capacitors. DCC buffers charge quickly because the input voltage and available amperage is always relatively high (nominally 18 volts for DCC).
 
ntpntpntp

ntpntpntp

Registered
24 Oct 2009
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So can you only use a power buffer on DCC?
The problem with such a power buffer on DC is how does the loco "know" whether it's meant to keep going because the loss of power is due to a dead spot, or is it meant to stop because you turned the controller off?

The purpose of the power buffer is to keep the eletronics of the decoder alive and provide power to the motor for a short time. With a decoder fitted loco which has a power buffer, the normal action of the decoder is to keep the loco moving at the last known speed and direction until the DCC signal is regained. If the decoder encounters DC instead, it may interpret this as running in analogue mode, or it may be programmed with "brake on DC" which is a way of getting a loco to come to a gentle stop until DCC is restored.

Some decoders with power buffers can tend to "run away" if they encounter (or think they encounter) DC, hence often the ability to run on analogue DC is turned off in the decoder to prevent this.
 
ge_rik

ge_rik

British narrow gauge (esp. Southwold and W&LLR)
24 Oct 2009
9,703
285
Cheshire
www.riksrailway.blogspot.com
It seems to be possible. I remember seeing an article in a model railway mag many many years ago about 'electronic flywheels' and I've just come across a reference to these in a 1999 edition of MRJ. There's also a fair degree of discussion on other railway forums with some who pronounce it's not possible in small scales because of the physical size of the capacitor needed, and yet there seem to be a couple of videos on YouTube which suggest it is possible.

http://youtu.be/GWAWz8Grc8M [url]http://youtu.be/GBBcFTKVaaE But so far I've not found any details about how it's done Rik
 
Rhinochugger

Rhinochugger

Retired Oik (IBT)
27 Oct 2009
26,363
942
North West Norfolk
So can you only use a power buffer on DCC?
The problem with such a power buffer on DC is how does the loco "know" whether it's meant to keep going because the loss of power is due to a dead spot, or is it meant to stop because you turned the controller off?
Yes, good question well presented.

So, would it be possible to produce the electronic flywheel effect for G Scale engines?

Mr Robinson?

:eek:nphone::eek:nphone:
 
Neil Robinson

Neil Robinson

Registered
24 Oct 2009
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86
N W Leicestershire
So can you only use a power buffer on DCC?
The problem with such a power buffer on DC is how does the loco "know" whether it's meant to keep going because the loss of power is due to a dead spot, or is it meant to stop because you turned the controller off?
Yes, good question well presented.

So, would it be possible to produce the electronic flywheel effect for G Scale engines?

Mr Robinson?

:eek:nphone::eek:nphone:
I recommend reading this http://www.trainelectronics.com/artcles/capacitor/index.htm < Link To http://www.trainelectroni...es/capacitor/index.htm in particular from halfway down starting with the heading IGNORING DIRTY TRACK.
It won't know the difference between a dead spot or an emergency stop but for most of the time bringing a train to a steady rather than a sudden stop is an advantage. The main problem in all applications is the physical size of the capacitors.
 
Rhinochugger

Rhinochugger

Retired Oik (IBT)
27 Oct 2009
26,363
942
North West Norfolk
Nice one sir :clap::clap::clap:
 
gregh

gregh

electronics, computers and scratchbuilding
I was working on this reply before Neil Robinson directed us in post #16 to Dave Bodnar's great work. But I'll post this anyhow. (It?s nice to know I was on the right track.)
Theoretically a big electrolytic capacitor will provide a buffer against loss of supply due to dirty track, or allow a soft stop feature when power is suddenly removed. But electrolytics are polarity sensitive so our usual arrangement where the track power changes polarity to change direction makes their use more difficult. (You can buy non-polarised electros but only up to around 1000uF ? they are used in loudspeaker crossover networks.)
This is my simplified circuit:


C1 & C2 are electrolytics, both the same capacity and a voltage rating greater than max track volts.
NOTE the connections of negative to negative ! (You can connect positive to positive if you like as long as the diode 'bar' is connected to the capacitor positive.)
But the capacitors have to be very large to provide the sort of 'buffering' we need ? in the range 100,000 to 500,000 uF
To theoretically determine the value of C1, C2

C (Farad) = 2 x motor current (A) x time to maintain supply (sec)
acceptable voltage drop in this time

This is a very approximate equation, as the interaction of the inductive motor as it slows, and capacitor is hard to predict. Also, electrolytics usually have more capacitance than their rated value to allow for manufacturing tolerances. I?m sure it will always result in a calculated bigger capacitor than is really needed, by a factor between 2 and 4 ! I?d suggest you could leave out the factor of ?2? in the eqn above.

Example1: to allow a ?soft stop? from 12V in 2 seconds, motor taking 1 amp,
C =2 x 1 x 2s / 12V = 330,000 uF approximately!!!! (by test I needed only 100,000uF)

Example2: to allow loco to cross an insulated frog, taking 0.1 sec and only allow a 1V drop, at 1 amp
C = 2 x 1 x 0.1s/1V = 200,000 uF

I did some tests with two, 4700uF caps (the biggest I had) running a motor block with its wheels in the air taking only 140mA. When I removed power it took 0.9 sec for the voltage to reach zero, and the voltage fall was very linear (theoretically it should be more exponential) ? see pic here (which I have fudged to make it legible. The blueish line is the motor voltage). The motor would have stopped in less time probably when the volts got down to around 2 or 3V.


It is possible to buy reasonable size capacitors of this rating these days, ? see here.
http://www.hobbyking.com/hobbyking/store/__17098__Turnigy_Voltage_Protector_550000uf_1_4sec_.html
It?s 550,000 uF, size26x26x45mm and costs around $6 - you need two for the above cct.
But it's only good for a max 15V. It seems to be made up from six, 3.3Farad, 2.5V capacitors in series (C=3.3/6=0.55F)

How's the circuit work?
Say the top wire from the wheels is positive. C1 will charge via D2 to track voltage. C2 will have only minus 0.6V so it is not damaged by reverse voltage. If incoming supply from the rails is lost, C1 will start to discharge through the motor (keeping it powering) and will start to charge C2. The current will slowly decay as the C1 capacitor charge is reduced. After a time set by the amount of motor current and the size of the capacitors, both C1 and C2 will have half the original volts across them, but with the polarity shown by the + signs. This means there is no volts across the motor.
If track voltage is now restored, the motor will instantly have full track volts. C1 & C2 will have a large current through them until C1 is fully charged to track voltage and C2 is fully discharged.

The time taken to charge/discharge when supply is applied/restored is determined by the capacitance and the supply resistance which is quite low (maybe one to a couple of ohms) so the capacitors could carry maybe 10-20 amps for a tenth of a second.

Dave Bodnar recommends a resistor and led across each capacitor to discharge it when supply is removed. I wouldn't bother with the led, but maybe a couple of 1k resistors are worthwhile if you have the room.

Actually the energy stored in the capacitors is not all that large comparatively. In a 100,000uF charged to 15V it is just ½ x 0.1 x 15^2 = 11 joules whereas the energy in a single 2Ah, NiMH cell is 2Ah x 1.3V = 2.6 Watthours = 9360 joules.

(Although high voltage capacitors are dangerous ? I have personal experience of getting across a cap charged to 300V at work. I remember watching others initially laughing as I danced around, not being able to let go, and then rushing to my aid.) :mad:










 
T

Tim Brien

Registered
29 May 2011
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3
Having an interest in 'OO' scale locomotives, some time I came across the following info to help a 'stuttering' Lima 12 volt motor. Take two 4700uF capacitors and solder the two negative leads together. Then solder the positive leads, one to each motor terminal. The info suggested electrolytic caps across the motor terminals to 'smooth' out motor pulses. I will need to source some suitable caps.

The end result is that two 'polarised' 4700uF capacitors become a 2350uF rating NON-polarised capacitor. This info was intended for DC power only, so using in a DCC circuit would be as per Greg's instructions.
 
ge_rik

ge_rik

British narrow gauge (esp. Southwold and W&LLR)
24 Oct 2009
9,703
285
Cheshire
www.riksrailway.blogspot.com
Thanks Greg
I felt sure there was an answer - just didn't have enough (well any) technical knowledge to know what it was. Given the large physical size of these capacitors, I was trying to figure out if there was a way of using just one - I suppose the difficulty would not be with charging it up, it would be trying to find a way of discharging it in the right direction (if you get my drift).
Rik