Although I'm not familiar with MRR reed switches and magnets, I know them from the security systems. The other name for this is "magnetic contact".

You can easily test your switch and magnet size. Connect an ohmmeter to both terminals of the reed switch. Move the magnet you plan to use closer to the reed switch. When you read 0 ohms, bingo. Now you know which magnet operates the switch at what distance.

One more issue, although I do not know the prices for MRR reed switches, I am sure there are cheaper alternatives. If you go to a security shop and ask for a magnetic contact for your window or door, it will cost you like 5-6 euros. Dismantle the plastic covers and use the switch and magnet. Another cheaper alternative may be those Chinese manufacture battery powered door contacts you may find in 1 Euro shops. You usually mount the alarm sounder part to your door and magnet piece to the door frame. An alarm sounds when you open the door. You may buy from these and take of electronic and plastic parts and use the switch with magnet.

Although I know these may be possible, I did not try these before. If somebody tried, please write here.

Ozgur

Hi Ozgur - welcome to The Forum

Hi Hans,

I have just gone through this exercise of installing reed switches and magnets. I did not use marklin reed switches, too expensive. I bought some glass tube reed switches from a local electronics store, and used black shrinktube to insulate/protect/disguise them. They install easily on my M tracks, close to a rail on either side, by drilling 2 holes for each wire. A neat and far less intrusive install than a marklin one.

The magnets were a problem however. I could not find a place on any of my loco's for them, and the marklin ones I tried did not seem powerful enough to activate my reeds. I ended up buying stronger "rare earth" magnets locally and installing them under the first wagon or coach in the train, where there is more room. You then have to locate your reeds accordingly of course. I have glued or used double sided tape to hold the magnet in place to prevent it leaving the wagon and heading for the track! (sometimes).

The most my reed switches switch, is two turnout solenoids and a solid state relay combined. There is a noticable "blue arch" in a non disguised reed switch when these solenoids are activated, but so far, after several hours of operation, no problems. The only issue may be some turnouts may be becoming magnetised, although I'm not sure of this yet. I'm using a cassette head demagnetiser to combat this.

Hi Suart,

For locos and cars I prefer small rare earth magnets, too, but space is still a problem on some locos. Installing them on the first wagon instead of the lok is a possible way to go.

I also noticed the arcing of the reed contacts, and I wonder how long these tiny SMD devices can withstand that. For this reason my turnout and signal solenoids run with DC, not with AC, and have a free running diode in parallel.

Hans Martin

Hi,

Got some small Iron-Neodymium-Bor magnets this week, small cubes with 3 mm in size, and they are extremely strong. Quite easy to find space now on the lok, and after paintig them in the lok color they are almost invisible.

I fixed them on the side, not in the center. The steamers who always run in forward direction got only one magnet, 2-cab locos as the GG-1 which run in both directions get two magnets, one under each front bogie!):



Works perfect with SMD reed relays. Very accurate stop position at halts now.



It is most important to align der magnetization direction of the cube parallel, not perpendicular to the reed contact. This gives the best reliability of the reed relay.

Hans Martin

Hi Rowan,

No problem here so far with car magnets, allthough the rails, pukos, and turnout tongues might be magnetizes as they are made of magnetic material.

Only thing is with couplers. The magnet should not have the chance to "catch" them.

Hans Martin

Hans,

This might be too late, but please experiment and place the magnets as far as possible from the reed switch so that the magnetic field that is sensed by the reed switch is the least amount it needs. Having said that, it is not always possible.

I am trying to say something that is not the easiest thing to say, but after some time, some reed switches tend to lock up as their reeds get magnetized. This happens as the magnet is moving over the reed in the same direction every time. This may not happen if the magnets were placed across. In my case they are linear along the motion of the loco.

I am using at least 10 reed switches at different places but mainly to activate turnouts and not stop the loco at an exact point or with other sensors. Some are activating a relay. In my case, I am using them inside the track (all K track in my case) and the magnets are fixed in a linear direction. In some cases the reed switches on the opposite side are for another direction of travel. I had to cut the magnets in half to reduce their power very crudely, test the polarity and then fix. So under my loco, I have another magnet at the end of the loco (or the first car) that is fixed with the opposite polarity. Since the turnout would be already activated, a second magnet repeating the same thing does no harm. I also activate a couple of semaphores this way.

The matter may be compounded in your case by the fact that the loco may stop with the magnet being very close to the reed switch. Then the magnetic field would be affecting it for a longer period.

Just passing some notes from my experiences.....

The reed switches in my case are from Marklin and so are the magnets except in one case.

(If anyone has suggestions on cheaper reed switches that are reliable against such magnetization, my thanks in advance for that information. I have tried a few, but they did jam up too.)

While we are on this subject, I have also heard that some diodes or some other protective device should be connected across the reed switch to protect against the backfeed from a CDU (Capacitor Discharge Unit). I am using CDU's to provide power to the turnouts primarily because some of my reed switches had jammed up earlier and burnt my solenoids. So this is prevention. All solutions welcome.....

antrains48

Hi all,
The reeds I am using are for the security industry and have the following rating:

Rating: 200VDC 0.5A, Glass Size:12.7mm x 1.8mm, Switch: Normally Closed (with Magnet).

So by their application they are designed to be held closed by the magnet for most of the time. eg when a door is shut. The issue of the reed becoming magnetised and holding closed without a magnet should not occur with these particular reeds..?

Has anyone a circuit diagram available that uses either a Capacitive Discharge unit and/or DC with diodes to protect the reed. So far, as I have said, one of my reeds is switching two M track solenoids and a solid state bi-stable relay simultaneously without any problems, although I am unsure as to how long this will last.

Hi all,

I've posted a copy of the circuit diagram at:

http://bigdaddynz.f2g.ne...iac/triac_switch_new.jpg

You should be able to make this up on a small piece of veroboard. Im not sure whether this type of triac is still available (I couldn't find it here in NZ), hopefully substitutes are available.

Cheers

Cool link,Very good layout pictures

Wellcome to the forum, bigdaddynz! And thanks for the link to the New Zeeland Maerklin club, it is superb.[:p]

I suppose that the type of triac in your circuit is not very critical, almost any type with suitable current rating should do. Using triacs is a very good idea as one needs not rectify the AC voltage.

Hans Martin

Thankyou for the kind words.

The Elektor magazine I mention is the July/August 2006 Summer edition.

As for the NZ Marklin Club, there has been a link on the Marklin-Users Links & Downloads section for quite some time (under the Wellington Märklin club link). If you would like a treat, check out Earl Wyatt's old and new layouts under the 'Home Layouts' section of the club's website (www.mmrc.org.nz).