Reasons to NOT use Grain of Wheat bulbs.?

[250BOB]

Hi Guys,

Before I embark on my control panel......can you tell me why I shouldnt use grain of wheat bulbs to illuminate the point positions.

 

I would want to ideally use the frog polarity changing to do this. I know how it will work, and that it will work, but I want you to tell me the pros and cons on grain of wheat bulbs.

 

My layout is DCC......so I would be using track and power bus electrics.

 

Thanks..............Bob.

[cromptonnut]

Grain of wheat bulbs will get hot, and if you're using a plastic faced control panel (like one of the boxes Maplin sell) they'll melt the plastic.

 

Most grain of wheat bulbs work best on about 8-9 volts, although designed for 12v it will shorten their lives. DCC buses run on 16-18 volt so will burn out and require replacing fairly quickly - plus of course the heat issue mentioned above.

 

LEDs are without a doubt a much easier, safer and reliable option.

[250BOB]

Grain of wheat bulbs will get hot, and if you're using a plastic faced control panel (like one of the boxes Maplin sell) they'll melt the plastic.

 

Most grain of wheat bulbs work best on about 8-9 volts, although designed for 12v it will shorten their lives. DCC buses run on 16-18 volt so will burn out and require replacing fairly quickly - plus of course the heat issue mentioned above.

 

LEDs are without a doubt a much easier, safer and reliable option.

 

Yes....thought as much.....you are confirming all my suspicions.

 

So..........is there such a thing as a nice simple LED.......did I hear that some LED's have in built resistors.??

 

Bob

[SHMD]

Seconded.

 

Heat and reliability against bulbs.

LEDs, however, require a limiting resister, (easy to calculate and very cheap), that must be in series with the LED.

The big drawback with LEDs (not so big really) is that they are polarity sensitive. For DCC i would be tempted to have a small diode (in reverse) protecting the LED.

(Although you could use one diode to half rectify the DCC to the whole panel!)

 

So that's three components to the one bulb!

But, as previously stated, the bulb will require its own limiting resister for use with DCC.

 

 

Kev.

[cromptonnut]

You can get 12v LED's that have built in resistance - but seriously, for the sake of a few more wires, you're much better off running a separate power supply for the LED's.

 

Alternatively, and this is just a theory, as LED's are fairly low current you could possibly power those off of a basic decoder's accessory output. It all depends how many you're looking at running? How complex is your layout?

[250BOB]

You can get 12v LED's that have built in resistance - but seriously, for the sake of a few more wires, you're much better off running a separate power supply for the LED's.

 

Alternatively, and this is just a theory, as LED's are fairly low current you could possibly power those off of a basic decoder's accessory output. It all depends how many you're looking at running? How complex is your layout?

 

Over 60 points on the layout, code 75 electrofrogs........but I essentially will only be dealing with about 25 points on the control panel, and thats at least 2 bulbs per point.

 

The control panel will be a piece of 3mm white perspex, 500mm x 300mm.

 

If I use a separate power unit for the LED's.....I cant use the live frog polarity to change the bulbs.......perhaps I should mention, they are all surface mounted point motors, with no accessory switching.

 

Just a point.......two grain of wheat bulbs in series, cooler, half as bright but still bright enough...18v divided by 2.........is it wishful thinking on my part ???????

 

Bob.

 

.

[Sunnysa]

Seconded.

 

Heat and reliability against bulbs.

LEDs, however, require a limiting resister, (easy to calculate and very cheap), that must be in series with the LED.

The big drawback with LEDs (not so big really) is that they are polarity sensitive. For DCC i would be tempted to have a small diode (in reverse) protecting the LED.

(Although you could use one diode to half rectify the DCC to the whole panel!)

 

So that's three components to the one bulb!

But, as previously stated, the bulb will require its own limiting resister for use with DCC.

 

 

Kev.

 

You are right, LEDS are polarity sesitive but only on DC voltage.

 

Believe it or not LEDS will work on DCC/AC voltage, with the apropriate resister. I usually use 1/4 watt 1k ohm.

 

My DCC systems, ECoS/Lenz are set to 14.5 V at track

 

My aux voltage is 15Vac for building, panel lights etc.

 

Before the nay sayers start jumping up & down, get a LED with resister attached and put it accross DCC tracks, any way round. Then connect LED to nomal AC voltage any way round.

 

I have Leds that have been op on DCC/AC for many yrs and none have failed yet.

 

Cheers

 

Ian

[cromptonnut]

Did a quick look on Ebay (other suppliers of same items are available but these were the first I found) to compare prices.

 

 

Cost of 100 x 3mm grain of wheat bulbs - £7.48 plus £1.86 p&p http://www.ebay.co.uk/itm/Grain-Wheat-100-pcs-3mm-Clear-3V-Miniature-Bulbs-/390180059917?pt=Model_RR_Trains&hash=item5ad88b3b0d

 

 

Cost of 100 x 3mm yellow LED's - £3.00 free P&P http://www.ebay.co.uk/itm/100-YELLOW-3MM-LEDS-/180989424105?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item2a23cf71e9

 

Cost of 100 x 1k resistor - 99p free P&P http://www.ebay.co.uk/itm/100-1K-Resistors-Carbon-Film-1-4W-0-25W-CR25-/110966080315?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item19d618033b

 

Reel of solder £3.10 http://www.ebay.co.uk/itm/Reel-of-0-3MM-Diam-Soldering-Tin-Lead-63-37-1-2-Wire-/300806368221?pt=UK_Home_Garden_PowerTools_SM&hash=item460974ebdd

 

 

Pricewise, LED's are marginally cheaper, considerably so if you happen to have the roll of solder already at home

[SHMD]

LEDs are polarity sensitive full stop. Whether AC or DC.

 

On DC, (with a suitable limiting resister), the LED will either light up or not, depending on polarity.

On AC, (with a suitable limiting resister), the LED will light up, regardless of polarity, but the reverse voltage may cause damage to the LED which will reduce its life. How much damage will depend on the LED, the reverse voltage, the manufacturer, the Batch, and contaminants, etcetera.

 

I just knew, when I was typing my post above, that experience, (very valid experience), found within RMweb would contradict electronics conventions. Commercially, I could never risk a recall of a product because of allowing a LED to be reversed biased in a circuit!

 

But Ian (Sunnysa) is also right. It works for him and it will work in nearly all cases for quite a long time – probably longer than the life of a bulb!

 

Best thing to do is try it with a few LEDs first.

At the same time, try your own suggestion of using two bulbs in series.

I still recommend LEDs, over bulbs, in nearly all cases.

If you do decide on bulbs then give a thought on how you will be replacing popped bulbs in your panel before you build it

 

There are no right or wrong answers in electronics. Just lots of answers!

 

Regards,

Kev.

[Suzie]

I concur that grain of wheat bulbs are a bad idea, as well as the above they are not easy to mount. I use Kingbright 5mm bipolar LEDs from rapid, these will work on DCC OK with a 680R limiting resistor in series. Just connect a green bipolar LED with series resistor between the frog and the straight stock rail to indicate 'Normal', and a red bipolar LED with series limiting resistor between the frog and the curved stock rail to indicate 'reversed'.

 

Both LEDs on indicates that the point is in the middle or the frog switching has failed, both LEDs off indicates the power to the track section has failed. Couldn't be simpler and less than 50p per point.

 

It can also be done with red/green 'tri-colour' three legged LEDs as well but you will need 1N4148 reverse protection diodes (anode or non stripe ends connected to the middle common leg of the tri-colour LED) and the resistors need to go between the LED anodes and the stock rails.

 

Indications will then be Green for 'normal', Red for 'reversed', Yellow for 'in between' and Dark for track power failed. Probably a neater solution and cheaper too!

 

To recap on the parts:-

 

Part Rapid p/n Maplin p/n

Resistor 680R 62-0812 M680R

 

Bipolar Red LED 56-1250 -

Bipolar Green LED 56-1260 -

 

Tricolour LED 56-0350 YH75S

1N4148 diode 47-5608 QL80B

 

Here is the back of my control panel showing the simple wiring of the bipolar LEDs:-

 

 

The red and black wires are the track supply, and the green wire goes to the frog.

 

Here are some diagrams of how to use bi-colour and tri-colour LEDs:-

 

(Edited to remove incorrect diagram, here is the replacement)

 

[cromptonnut]

Neat solution Suzie, one I might just pinch myself... although for an 8ft long scenic section with just two points I do wonder if point position indication is a bit of an overkill when the good old mk 1 eyeball should be more than adequate:)

[Nigelcliffe]

A few things on Suzie's information above.

 

It took me a few reads of Suzie's post to catch that she has describe three arrangements;

 

BiPolar LED. These, with a single resistor, behave like a light bulb, except that its far more reliable. The issue of "reverse polarity" damaging the LED is removed by the way the bipolar component is packaged at the maker. There is no diagram showing this application.

 

BiColour LED. These also have two pins, but change colour depending on how current is applied to them. Lower of the two diagrams.

 

TriColour LED. These have three pins, also offer colours depending on how current is applied. Upper of the two diagrams.

 

 

 

WIth any of these solutions there is a trade-off in the number of wires back from turnouts to control panel.

The lowest number of wires (* below) is to use one wire from the crossing (frog) for each turnout back to the panel, plus two wires for the DCC feed. This reduces the wire count. It shows the crossing polarity. BUT it does not indicate power to the rails at the turnout, only that DCC power is turned off before the panel.

For substantially more wires, three per turnout back to the panel, a LED not illuminated will indicate that power has failed at the rails.

 

 

( * one could reduce the wires to as few as two for status indication for the entire layout using a multiplexing scheme, but that's a pile of additional electronics, and other schemes could produce a wire count in between 3 per turnout and 2 per layout ).

 

 

- Nigel

[Suzie]

Although most of my points are underground which is why I put in the indication, the real boon is in proving that the frog switching is working. I have used PL13s in a lot of places where microswitches could not be hidden (they were going spare and the underground trains have good pickups) but they do fail on a regular basis and knowing straight away with the green + red indication is nice to have.

[250BOB]

Flippin eck...........You know, for a complete non electronics person like myself.....I think your explanations are beginning to help me make sense of all this.

 

The Grain of Wheat is simple....thats why it was appealing to a non electrics person like myself......but I secretly knew that was not the direction to proceed in....I just needed you to emphasise the point to me, which you kindly have.

 

It is really good of you all to explain it in simple terms like you have.....its clear that you are all very knowledgeable in this area.

 

Excuse my basic questions as the nearest thing to an LED I have had to deal with in the past could have been a Chistmas Tree bulb...???.

 

Is a bi polar LED just a normal LED........I have heard both phrases used "LED" and "Bi Polar LED"....? If they are different please explain.

 

I now see I can run just one wire back to the control panel, that being from the frog, then the track feed/power can just be at the panel. All the resistors etc can all be in the panel area........my understanding grows by the minute.

 

Thankyou all so much....please keep posting me any ideas and thoughts you have .

 

Cheers....................Bob.

[cromptonnut]

For convenience/neatness, you may prefer to use multicore cable from the layout to the control panel, found some on Ebay at less than 50p a metre.

 

http://www.ebay.co.uk/itm/4-Core-Multicore-Cable-7-0-2mm-by-the-5-Metres-CB598-/150822849932?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item231dbe0d8c

[Nigelcliffe]

 

Is a bi polar LED just a normal LED........I have heard both phrases used "LED" and "Bi Polar LED"....? If they are different please explain.

 

 

A BiPolar LED is a special type of LED.

 

 

A "normal" LED is a directional device. It only conducts (and lights) if power flows in one direction (with a DC battery, connect the LED and its resistor one way and it lights, connect it the other and it does not light). If connected the "wrong way round" it won't light. It is also suffering damage if connected the "wrong way round", though whether this damage is actually significant has some discussion above (even though there is a current resistor in series with the LED, because the LED hasn't lit, the reverse voltage over the LED is the full track voltage). This directional form is the most common form of LED.

 

A Bipolar LED is not directional. Like a normal LED it has two connectors. But, inside the package are actually two LEDs. One conducts in one direction, and the other in the opposite direction. Because there are two LEDs together, they protect each other against reverse connection. A BiPolar will be available in fewer options of size, power, etc. and will cost a lot more than a normal LED (though both are pennies at electronics retailers).

 

 

A normal LED or a BiPolar LED must have a current limiting resistor in series with the LED.

 

 

Other types of LED are available, BiColour and TriColour are mentioned above.

 

 

 

 

I now see I can run just one wire back to the control panel, that being from the frog, then the track feed/power can just be at the panel. All the resistors etc can all be in the panel area........my understanding grows by the minute.

 

Yes, this is fine, subject to realising my comment about the LED only showing the turnout setting, not the status of the track power at the turnout. For most people this is sufficinient information.

 

 

 

- Nigel

[cromptonnut]

Yes, this is fine, subject to realising my comment about the LED only showing the turnout setting, not the status of the track power at the turnout. For most people this is sufficinient information.

 

Usually indicated by the train stopping and occasionally the 'short' indicator on your controller as well...

[Oldddudders]

Before I turned to DCC in 1997, I constructed a switch panel for my layout which had bi-colour LEDs, thus enabling me to see at a glance which controller was connected to which section. I am not a techie type in any way, shape or form - but it worked. This thread is full of first-rate advice - as well as refreshing acknowledgements that theory and practice don't always exactly align.

 

I suggest that Bob buys a few el-cheapo LEDs, resistors of the suggested values etc and has a good play with them to see what happens when. A set of simple leads with croc-clips etc can be a real asset here. Then you can be confident that the slightly more expensive components which will make your panel look the biz are going to work first time, because you've been there and done it already.

[250BOB]

Before I turned to DCC in 1997, I constructed a switch panel for my layout which had bi-colour LEDs, thus enabling me to see at a glance which controller was connected to which section. I am not a techie type in any way, shape or form - but it worked. This thread is full of first-rate advice - as well as refreshing acknowledgements that theory and practice don't always exactly align.

 

I suggest that Bob buys a few el-cheapo LEDs, resistors of the suggested values etc and has a good play with them to see what happens when. A set of simple leads with croc-clips etc can be a real asset here. Then you can be confident that the slightly more expensive components which will make your panel look the biz are going to work first time, because you've been there and done it already.

 

Ian,

You read my mind...............I am going to get a selection of these things and have a damn good play. I think that will be the best way to fully understand and appreciate this technology.

Thankyou all.

Bob

[Brian]

Hmm... I see you're making good use of my Panel Indications on DCC wiring drawings Suzie!

[250BOB]

Hmm... I see you're making good use of my Panel Indications on DCC wiring drawings Suzie!

 

Hello Brian,

I'm the OP on this thread.....and I had seen these diagrams before on your website, but further explanation here on RMweb has been invaluable to me.

I am a regular user of your website, daily at the moment I might say, and it has been invaluable to me and many others on numerous occasions.

Great website you have there Brian,

Many thanks,

Bob.

[SHMD]

Apologies but am I reading the diagram right in suzie's post #10.

Won't there be a short with the components connected as shown or have I missed something?

 

Kev.

[Suzie]

The diagrams are from another thread, and yes the bi-colour one is wrong. There should be two resistors, one in each of the connections to the DCC supply rather than one in the frog connection. Here is the correct one.

 

[silverlink]

Hi Bob,

Best by far is to use LED's, my layout has loads on it! they're all Bi-directional green/red two wire type. I am using Peco electrofrog points with live frog which is all worked via a Tortoise switch machine (Point motor). Now this is the bonus with a Tortoise motor, you do not need resistors, just a DPDT switch. The motor is live all the time so all I have done is wire two LED's into one of the feed wires to the motor at the switch end (minimal wire required) & then when you throw the switch the point changes & the two LED's change colour. Just need to get them the right way round colour wise so you have green on the route you have set. This really is very simple to do. Are you at Warley by any chance because if you are I will gladly show on my layout how it all works, Stand F44 Haymarket Cross. If you go on the layouts thread my layout is there somewhere with a picture of the panal.

Cheers

Ian H

[250BOB]

Hi Bob,

Best by far is to use LED's, my layout has loads on it! they're all Bi-directional green/red two wire type. I am using Peco electrofrog points with live frog which is all worked via a Tortoise switch machine (Point motor). Now this is the bonus with a Tortoise motor, you do not need resistors, just a DPDT switch. The motor is live all the time so all I have done is wire two LED's into one of the feed wires to the motor at the switch end (minimal wire required) & then when you throw the switch the point changes & the two LED's change colour. Just need to get them the right way round colour wise so you have green on the route you have set. This really is very simple to do. Are you at Warley by any chance because if you are I will gladly show on my layout how it all works, Stand F44 Haymarket Cross. If you go on the layouts thread my layout is there somewhere with a picture of the panal.

Cheers

Ian H

 

Hi Ian,

I am indeed at Warley....thankyou for the invitation....I shall make myself known to you.

I seem to remember you did once before invite me to see your layout in Scarboro.....at the same time that I was maybe up there at the Gold Cup. Didnt get there this year I'm afriad.

Regards.......Bob