Am i doing this LED work correct?

Basic electrical and electronics, such as DC/Analog control.
collectors
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Am i doing this LED work correct?

Postby collectors » Sat Oct 20, 2018 4:42 pm

Hi, i am just starting to fit some LED lighting to my carriages. When i started i used 2 short lengths of LED tape "Like photo" with 3 LED's on each piece, 6 led's per carriage. I popped the carriage on the DCC track & it worked. So far so good. But if i push it along it flickers & when i turn it around, it stops working. So a quick read up on this, it seems i need a bridge rectifier & a capacitor, but am i getting the right values?? Each carriage i will do as an individual item with its own tiny on/off switch.

1. Bridge rectifier SIP4 3amp 50volt
2. Capacitor 330uF 25 volt
Or are other values better?

The other thing i wasn't sure on was the DCC track is around 19 volt & the led's are 12 volt? IE: Will i cook the led's.
Should i add somthing??

Thankss.

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End2end
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Re: Am i doing this LED work correct?

Postby End2end » Sat Oct 20, 2018 5:32 pm

This might help you.
viewtopic.php?f=1&t=50754&hilit=competition&start=30#p623330
Basically the light bar I built for the LED's and thier resistors is the same as your LED strip. It's more to show the other components needed.
Hope it helps.
Thanks
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Ironduke
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Re: Am i doing this LED work correct?

Postby Ironduke » Sat Oct 20, 2018 10:10 pm

The rectifier is huge. You don't need anything like 3A just for LEDs. Nothing wrong with that if you have room in your carriage but, if you need something smaller, a small DIP package with a forward current of maybe 1A would be ample.
Say a DF04M or similar
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I like these DIP package rectifiers because they have AC in one side and DC out the other, so they are easy to use on a small piece of Vero board. (Always check the datasheet for pin-out details before you order.)
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Rob

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Re: Am i doing this LED work correct?

Postby TimberSurf » Sat Oct 20, 2018 10:35 pm

This is a pet subject of mine. One that I have not cracked the ultimate circuit for! (as yet)
What DCC are you using? (determines the voltage it puts out). The LED strips have current limiting resistors (or current limiters), if the voltage is excessive you could use an LM7812 (100mA) or a voltage PCB see here
As said by Ironduke, a bridge rectifier greater than 40mA is needed so anything above that will do. (i.e. 100mA or 0.5mA) [Technically it should be a Schmitt type]
The greater the size of capacitor the longer they will stay alive, 1000uF would be better, but they must be 16V or greater, smaller ones can be connected in parallel.
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Ironduke
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Re: Am i doing this LED work correct?

Postby Ironduke » Sat Oct 20, 2018 11:59 pm

TimberSurf wrote:As said by Ironduke, a bridge rectifier greater than 40mA is needed so anything above that will do. (i.e. 100mA or 0.5mA) [Technically it should be a Schmitt type]


If a big electrolytic cap is included then you need to account for a short burst of higher current when it first charges up but most rectifiers should handle that easily. Look for something like "peak forward current" in datasheet.
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Rob

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Re: Am i doing this LED work correct?

Postby TimberSurf » Sun Oct 21, 2018 12:35 am

Good point Rob, a 50 to 200 ohm resister can be fitted in the supply to limit capacitor charge inrush.
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Re: Am i doing this LED work correct?

Postby Bramshot » Sun Oct 21, 2018 9:50 am

I don’t understand why it goes out when you turn the carriage around? On dcc track it should stay on. On dc track it would go out one way and you need a rectifier.

With mine, I reverse connect the two pieces of flexi , each with 3 leds. Not all flexis are the same though. Mine have 3 leds in series in each section, with a single resistor for all three, sized for 12 V. Yours seem to have a resistor for each led, so presumably they ( each resistor and led) are connected in parallel. I snip the tape where the scissors are shown and reconnect with one set reversed so that one set comes on in each half of the ac dcc cycle. This spreads the load accross the power devices in your dcc supply. 17 V is on the high side, though the leds only illuminate every half cycle of the dcc and the resulting illumination is dimmer than it would be on dc, (as the leds are off half the time). You can add another resistor in the supply to the light strip, probably you would need to to get the brightness to look right.

If you want a capacitor, then for sure you need a rectifier, dcc or dc. However, I find mine do not flicker much, if at all, provided the wheels are clean. Are you fitting your own wheel contacts, if so to how many wheels? On my self fitted coaches I use two ar each end, and have settled on the two contacting the same rail, as this reduces the complexity and gives the same performance in terms of bridging dead track as having one on each rail at each end.

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Re: Am i doing this LED work correct?

Postby collectors » Sun Oct 21, 2018 11:35 am

Ah! Many Thanks for all the reply's, i am surprised i only got 1 email saying there was posts.. Slight hiccup, my short piece of test track was plugged into the reserve aux power connections on the back of my Hornby elite. :oops: 16v dc
But your all helping me. A friend has some DB107 DIP4 Single Phase 1A Glass Passivized Bridge Rectifiers, will these be OK,?
I am also a bit tight for space on the 3300 capacitor, would a couple of 100's in parallel be OK. Not quite the same, but 200 should be enough for 6 led's.
Hi Bramshot, the carriages a Bachmann on30's & come with one led in each carriage that's not very good, hence the upgrade. So the wheel connections are in place.

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Re: Am i doing this LED work correct?

Postby Bramshot » Sun Oct 21, 2018 9:36 pm

collectors wrote:Hi Bramshot, the carriages a Bachmann on30's & come with one led in each carriage that's not very good, hence the upgrade. So the wheel connections are in place.


I’m not familiar with those carriages or pickups. How many wheels, what sort of contacts?
Whatever, make sure the wheel and contact surfaces are clean and the contacts are in proper mechanical contact.

If you are using a capacitor, make sure you get the polarity right!

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Ironduke
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Re: Am i doing this LED work correct?

Postby Ironduke » Sun Oct 21, 2018 9:59 pm

collectors wrote:DB107 DIP4 Single Phase 1A Glass Passivized Bridge Rectifiers, will these be OK,?


They look great.
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Rob

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Ironduke
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Re: Am i doing this LED work correct?

Postby Ironduke » Sun Oct 21, 2018 10:12 pm

Ironduke wrote:
collectors wrote:DB107 DIP4 Single Phase 1A Glass Passivized Bridge Rectifiers, will these be OK,?


They look great.


Here is the datasheet

http://www.farnell.com/datasheets/1684825.pdf
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Rob

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Re: Am i doing this LED work correct?

Postby TimberSurf » Sun Oct 21, 2018 10:44 pm

I may be scaremongering here, as you may NOT have a problem, but technically, you should use a fast recovery diode network (bridge rectifier) or commonly known as Schottky1 diode.
Normal diodes are only designed for (50Hz) 'mains' frequency, but DCC is in the region of 20,000hz (20KHZ) and normal diodes cannot react fast enough, causing an unwanted spike that distorts the waveform, most notably on Hornby systems (non NMRA compliant)!

I would recommend something like a MB6 (example) / pdf

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Last edited by TimberSurf on Sun Oct 21, 2018 11:17 pm, edited 1 time in total.
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Ironduke
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Re: Am i doing this LED work correct?

Postby Ironduke » Sun Oct 21, 2018 11:01 pm

I couldn't find any Schmitt trigger diodes or rectifiers when i was searching. Do you mean Schottky?
I believe Dcc is 10KHz.
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Rob

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TimberSurf
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Re: Am i doing this LED work correct?

Postby TimberSurf » Sun Oct 21, 2018 11:12 pm

Sorry, yes, I meant Schottky
DCC is not a fixed frequency, it varies dependant on the signals being sent! Technically it could be from 10kHz to 17Khz or anywhere in between, at any given segment in time, I was rounding up to simplify.
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Re: Am i doing this LED work correct?

Postby Ironduke » Mon Oct 22, 2018 12:38 am

Oh OK. Good point.
Regards
Rob


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