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Author Topic: Arc flash generator  (Read 370 times)

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Offline GrahamB

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Arc flash generator
« on: January 31, 2019, 08:08:54 AM »
I'm toying with the idea of a 3rd rail arc flash.

Currently the system is worked by a reed relay feeding a superbright LED. The reed being activated by a magnet in the roof of a carriage. The idea being the reed will be mounted under an overbridge. I'm avoiding mounting the magnet under the carriage as it will cause problems with my easishunt magnets.

While it works, the lamp simply comes on and off with no flicker. Having hunted around I see that MERG produce a kit for just £1.70. That's excellent value, the problem is that it would cost £21 to join!

Has anyone come up with a circuit? Google has nothing to offer.

Offline Bealman

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Re: Arc flash generator
« Reply #1 on: January 31, 2019, 08:46:06 AM »
Late member TrainsDownunder produced a design using a PIC which is very effective. Unfortunately he was intending to market it as a kit. However the circuit is otherwise simple, and I'm sure there are many designs out there.

Basically you require a flashing effect when triggered?
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Offline ntpntpntp

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Re: Arc flash generator
« Reply #2 on: January 31, 2019, 08:53:01 AM »
There are several arc welder/flasher kits out there, and a few circuits can be found via google.  Some are better than others in terms of the effect they produce (pre-weld tacking etc.).
 
Here's one of the arc weld circuits (don't know if this one's actually any good):
http://www.talkingelectronics.com/projects/ArcWelder/ArcWelder.html

However for a 3rd-rail flash You'd want a shorter/different flash effect so the circuit would need modification.


I've had a simple little kit sitting in my "todo" box for years which I intended to use for an overhead panto flash, but  haven't got round to it yet (isn't that always the way?) It came from one of the lighting effect traders at an exhibition years ago, I think it was the Express Models kit
https://www.expressmodels.co.uk/catalogue/scenic-effects/overhead-3rd-rail-blue-flash-detail

It would be triggered by the panto bridging from the running wire to a second short parallel length and I was going to position it  at the exit to a tunnel.  Really must get on with installing it!


Alternatively you could create your own little module with a PIC microprocessor if you're into that sort of thing?  I created a photographer flash that way with various random single and multiple flashes, the programming could no doubt be altered to simulate the arcing/flickering flashes you'd want.
Nick.   2016 celebrating the 20th anniversary of "Königshafen" exhibition layout!

Offline Bealman

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Re: Arc flash generator
« Reply #3 on: January 31, 2019, 09:03:11 AM »
Yes, the PIC approach was used by TrainsDownunder. He sent his kit to myself and some other members to build and test.

I have not inspected the code and I'm not sure where I stand there. Mainly as a mark of respect,  I guess.

However, all the suggestions in the above post seem good.  :thumbsup:
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Offline GrahamB

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Re: Arc flash generator
« Reply #4 on: January 31, 2019, 09:30:08 AM »
Thanks for the suggestions. The kit looks quite complicated. I'll think on.

Online Dorsetmike

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Re: Arc flash generator
« Reply #5 on: January 31, 2019, 11:11:05 AM »
Graham Hedges had quite an effective one on Hedges Hill cutting, now owned IIRC by the Bentley group in Wiltshire, some of the members are on this forum, possibly they can comment further.
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Offline Fardap

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Re: Arc flash generator
« Reply #6 on: January 31, 2019, 11:25:15 AM »
Currently the system is worked by a reed relay feeding a superbright LED. The reed being activated by a magnet in the roof of a carriage. The idea being the reed will be mounted under an overbridge. I'm avoiding mounting the magnet under the carriage as it will cause problems with my easishunt magnets.

If you used an optical detection between the sleepers or alongside the track, like some signalling kits do then you would not have the issue with the magnets, it might need a circuit that is timed and flashes so that the arcing is only near the pickup and not near the non pickup stock though.


Offline GrahamB

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Re: Arc flash generator
« Reply #7 on: January 31, 2019, 04:02:45 PM »
The problem with optical detection is that it can't tell the difference between diesel and electric stock. This way I just fir magnets to the 3rd rail stock. The ED's present a different challenge. For now I'm just going to say they're working on diesel and rule one applies  :D

Offline GrahamB

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Re: Arc flash generator
« Reply #8 on: February 04, 2019, 11:02:28 AM »
So here's my first attempt at a 3rd rail flash https://youtu.be/59IMZTBLxXI

It's simply a reed switch activated by magnets in the roof and a superbright white LED. The different length of flash is due to different length magnets.

Some people have used a blue LED. Not sure.

Comments good and bad welcome.Either way the arc flash will be on Southwark Bridge at the Tonbridge show.

Online dannyboy

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Re: Arc flash generator
« Reply #9 on: February 04, 2019, 11:13:59 AM »
Certainly looks effective.
David.
I used to be indecisive - now I'm not - I don't think.
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Offline Bealman

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Re: Arc flash generator
« Reply #10 on: February 04, 2019, 11:42:04 AM »
Yes, that is a simple solution which has achieved an acceptable result.

I feel that the flash may be a bit long, though. Perhaps simply shortening the magnets?

Regarding the led colour, the TrainsDownunder design I referred to earlier uses a blue and white led together very effectively.  :thumbsup:
Vision over visibility. Bono, U2.

Offline ntpntpntp

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Re: Arc flash generator
« Reply #11 on: February 04, 2019, 12:10:14 PM »
I like that, it's quite effective!

You do see some quite long flashes from 3rd rail arcing - more so than panto flashes I think.  The only thought that crossed my mind was I was expecting the flashes to be at the outer ends of the unit passed over, ie. where the pickup shoes are located?  Difficult to place magnets under power bogies so would depend on the offset of the reed switch location as the unit passes over. 

Phase two maybe look for a simple circuit to add a little random flickering to the flash?
Nick.   2016 celebrating the 20th anniversary of "Königshafen" exhibition layout!

Offline GrahamB

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Re: Arc flash generator
« Reply #12 on: February 04, 2019, 04:55:10 PM »
I think I might order a blue LED just to see what difference it makes either using it with or instead of the white LED.

Re positioning, there are limitations. To be honest I think the fact the arc isn't exactly where it should be is only noticeable on the video.

There's no room in my ED's for a magnet unless I mill out a space which seems a bit drastic.


Online Farmer chap

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Re: Arc flash generator
« Reply #13 on: February 04, 2019, 06:17:14 PM »
Heathcote electronics make an effective arcing board with 3 blue led's using reed switch @ £16.00

Offline GrahamB

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Re: Arc flash generator
« Reply #14 on: February 08, 2019, 08:52:03 AM »
Well I ordered a "superbright" blue LED and it was rather disappointing. So much so I didn't even bother mounting it. For now I'll stick for the simple system.

 

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