Electro magnets for AJs

Terry Bendall
Posts: 1639
Joined: Sun Jul 27, 2008 7:46 am

Re: Electro magnets for AJs

Postby Terry Bendall » Mon Aug 22, 2016 7:06 am

All Components, who attend a lot of exhibitions and also do mail order sell 1N5401 diodes at 20 pence each.

Terry Bendall

dal-t
Posts: 623
Joined: Mon Jan 11, 2010 8:06 pm

Re: Electro magnets for AJs

Postby dal-t » Mon Aug 22, 2016 7:49 am

You might be able to remove the residual magnetism with a degaussing plate salvaged from an old CRT - bet it runs on mains voltage, though, so might (literally!) be a bit of overkill. More seriously, I have in the past experienced soft-iron coupling links on S&W couplings becoming 'permanently' magnetised and behaving somewhat oddly if they got too close to other magnetic material - but it was relatively simple to change those (or just live with the occasional uncommanded 'tweek').
David L-T

User avatar
steve howe
Posts: 526
Joined: Sun Feb 01, 2009 10:16 pm

Re: Electro magnets for AJs

Postby steve howe » Tue Aug 30, 2016 9:42 pm

Am I missing something?
Having grappled with the making and fitting of Mr Jackson's bit of bent wire and mastered the pivot and counterweight system as proving most reliable, I set up my yard of test track with an electro magnet and experimented with a variety of different droppers ranging from the traditional bent paperclip to Mr Pendlenton's elegant 'clipped hanging loop'.

Pretty much all worked fine on the test track, so I went ahead and installed six magnets (Dingham) on the layout wiring them as Keith describes above; one tag on each magnet linked to its neighbour and then to the common (negative) supply, on the panel, one tag of each switch linked together to the positive supply, a separate wire then run from each switch to the appropriate tag on each magnet. In practice, despite using the same power supply - 12v @ 2.5A - the performance of the magnets on the layout is markedly less than on the test track, barely registering a twitch on the couplings, whereas the same coupling when checked on the TT functions perfectly. I'm guessing some kind of voltage loss - but on a small layout with the magnets individually switched, could it be so much as to radically affect the performance? I have tried swapping the push-to-make switches with centre-bias ones of higher rating, wondering if arcing contacts were to blame, but the performance seems much about the same. :?

Steve

User avatar
grovenor-2685
Posts: 3169
Joined: Sun Jun 29, 2008 8:02 pm

Re: Electro magnets for AJs

Postby grovenor-2685 » Tue Aug 30, 2016 11:41 pm

What size of wire have you used? And how does the wire length differ between test track and layout?

If you have a meter measure the voltage actually across the coil when you press the button, and also at the power suppply output when you press the button.
That will tell you if you are losing voltage due to a high resistance in the wiring.
Regards

nigelcliffe
Posts: 502
Joined: Mon Jul 21, 2008 8:31 am

Re: Electro magnets for AJs

Postby nigelcliffe » Wed Aug 31, 2016 7:49 am

As well as the electrical wiring which Keith mentions, the other factor is the height of the solid core of the electromagnet in relation to the rail-top in the two setups.

Magnetic fields decay on a square law of distance, the net result is a very small change in the distance from magnet to object results in a dramatic change in the magnetic field strength. So, are the magnets at a lower height on the layout compared to the test track ?


- Nigel

martin goodall
Posts: 994
Joined: Fri Oct 02, 2009 6:20 pm

Re: Electro magnets for AJs

Postby martin goodall » Wed Aug 31, 2016 4:30 pm

I don't use AJs, but when installing electro-magnets on my layout to work with other magnetically operated couplings, I have always tried to get the pole piece as near the level of the tops of the sleepers as is practically possible without it actually showing through the top-most layer of ballast.

As Nigel has pointed out, setting them lower can have a quite dramatic impact on their effectiveness.

User avatar
steve howe
Posts: 526
Joined: Sun Feb 01, 2009 10:16 pm

Re: Electro magnets for AJs

Postby steve howe » Wed Aug 31, 2016 6:31 pm

Thanks for the pointers guys, in terms of voltage, I need to get myself a meter before I can verify this further. Wiring is the usual multicore stuff 7/0.2. I agree with Nigel's comment on the height of the pole, mine are all flush with the sleeper tops but the pole in the Dingham is only 5mm which is a pretty small area.

Further struggles today have shown that the length/height of the dropper is pretty crucial. Close examination of some of my earlier efforts showed a larger than 1.5mm gap from railhead. Subsequent replacements have been more successful. Currently I'm making hanging loop droppers from 1mm soft iron wire using the milled steel jig which came my way a while back:
jig3.jpg

I don't know who the maker was, or if they are still available, but a useful addition to the increasing armoury of jigs and gadgets!
DSC_0222.JPG

The dropper is not as elegant as other versions, but no soldering in-situ and simple to make, initial results seem to be the most encouraging so far....

Steve
Last edited by steve howe on Fri Sep 02, 2016 4:37 pm, edited 1 time in total.

nigelcliffe
Posts: 502
Joined: Mon Jul 21, 2008 8:31 am

Re: Electro magnets for AJs

Postby nigelcliffe » Wed Aug 31, 2016 7:38 pm

For maximum magnetic field effect:
  • The dropper needs to be the thickest material possible, consistent with getting it under the wagon in an acceptable manner.
  • The dropper must hang as low as possible, without fouling the track at crossings.
  • The top of the rod through the coil needs to be as high as possible - just below sleeper top if it can be done.

Unfortunately (and just about every magnetic coupling system has this problem), the resting place for the coupling places the dropper at its furthest from the magnet. So, the magnetic field needs to be stronger to pull the dropper down. Once the dropper starts to move, it comes into more of the field, so experiences a stronger pull downwards.

Your wire thickness (7/0.2) is a bit on the stingy side (thicker, or more strands, would be better), though will probably work if the lengths are not excessive - lengths of a few feet probably OK, but many yards and I'd start to get a bit concerned.

A cheap multi-meter is all that's needed. Though I'd say buy two. One analogue and one digital. Neither should cost significantly over £10. Make sure at least one has a "continuity buzzer" because that's the most heavily used feature I have on any meter - check any wiring is actually connected without needing power applied. A digital is better for actual readings, but analogue is often quicker to just say "some current flowing" or "some volts here" with the flick of a needle visible without having to actually read a value. (I assemble electronics circuits, get into wiring components onto DCC decoders and all sorts, and I only have cheap multi-meters costing a few pounds. I don't need the calibrated accuracy of "professional" equipment. )

njggb
Posts: 20
Joined: Wed Oct 14, 2009 5:02 pm

Re: Electro magnets for AJs

Postby njggb » Wed Aug 31, 2016 7:52 pm

Hi, my tuppence worth.

Keith, above, is right about wire size. I have used 16/0.2 wire for this task, it's resistivity is a lot less than 7/0.2.

Avoid parallel feed, go for single magnet operation. I preference the SEEP magnet to others.

Wire obtained from City Electrical Factors, CEF, is generally cheaper than that from, even, Squires. They are always, the two branches I have had dealings with, very helpful. Get the chunkyest (is there such a word?) that you can accommodate. It might mean stripping cores from a multicore. Four core fan control cable is sold by the metre.

Ideally you should use a "switching circuit", a relay or better still a MOSFET, with an overswing diode, to reduce the current handled by the switch.

James

Phil O
Posts: 235
Joined: Sun May 05, 2013 5:23 pm

Re: Electro magnets for AJs

Postby Phil O » Thu Sep 01, 2016 7:05 am

In my local club we use Sprat and Winkle couplings and to get a bit more of a magnetic field we use a bit of steel plate about 25mm x 15mm under the sleepers and the magnet pole pushed up tight on to it, sometimes it helps to put a slight indentation in the plate to help with the contact between the two. you actual see the dropper chains move towards the magnet as a vehicle approaches it. We use electro magnets from Wizard Models.

Phil

User avatar
steve howe
Posts: 526
Joined: Sun Feb 01, 2009 10:16 pm

Re: Electro magnets for AJs

Postby steve howe » Fri Sep 02, 2016 4:48 pm

Having borrowed a meter from a clubmate, it seems an average of 11.9 - 12.5v is reaching the magnets so no significant drop, but I'm not convinced they pack enough punch so I have today wired in a laptop adapter which delivers around 19v and this seems to have made a considerable difference to the grab, I think I may also replace my push-to-make switches with something of a known higher rating, my present ones don't seem very substantial and there is no rating marked on them. Further experiments with the hanging U dropper are confirming my thoughts that this appears to be (for me anyway) the most effective so far. Curious that this version which I believe has been around a long while, and its jig get no mention in the Society AJ book.

nigelcliffe
Posts: 502
Joined: Mon Jul 21, 2008 8:31 am

Re: Electro magnets for AJs

Postby nigelcliffe » Fri Sep 02, 2016 5:51 pm

Increasing the volts will increase the magnetic field, though eventually things level out.

To protect your switches, with a DC power source, you need BEMF spike suppressor diodes fitted across each coil. Without the diodes, eventually the spark when the switch goes to "off" will erode the switch contacts. One diode per coil, fitted so it doesn't conduct with the normally connected DC power, and your DC power is then important to know which wires is + and -.

User avatar
steve howe
Posts: 526
Joined: Sun Feb 01, 2009 10:16 pm

Re: Electro magnets for AJs

Postby steve howe » Fri Sep 02, 2016 10:14 pm

Thanks Nigel, I shall acquire some with the switches!

Thanks for your advice
Steve

User avatar
David Thorpe
Posts: 819
Joined: Tue Oct 21, 2008 11:13 pm

Re: Electro magnets for AJs

Postby David Thorpe » Mon Sep 05, 2016 7:58 am

I use Dingham couplings and have some of their electro magnets, wired up as Steve has done his. They work and clearly get adequate current, but I do find them very fiddly - the coupling has to be positioned in exactly the right spot above the magnet, and should neither be pulled too tight or pushed too close. All too often by the time I've managed to get the train into exactly the right position and the couplings in just the right tension any extra realism that automatic coupling/uncoupling might have provided has been lost. The situation may of course be different with AJs.

DT

nigelcliffe
Posts: 502
Joined: Mon Jul 21, 2008 8:31 am

Re: Electro magnets for AJs

Postby nigelcliffe » Mon Sep 05, 2016 8:41 am

David Thorpe wrote:I use Dingham couplings and have some of their electro magnets, wired up as Steve has done his. They work and clearly get adequate current, but I do find them very fiddly - the coupling has to be positioned in exactly the right spot above the magnet, and should neither be pulled too tight or pushed too close. All too often by the time I've managed to get the train into exactly the right position and the couplings in just the right tension any extra realism that automatic coupling/uncoupling might have provided has been lost. The situation may of course be different with AJs.


AJ's work nicely if the train is being propelled. For example, dropping wagons in a siding. With this, the train can be moving, and the electromagnet fired as relevant wagon moves across the electromagnet. The train does not stop, the uncoupling is done without most observers noticing. When the correct place to spot the wagon(s) is reached, the train can stop, pause for the model train crew to lift the coupling links, and then pull away. Looks great. Other uncoupling systems will do this (eg. DG and BB, which I use in 2mm scale). I would hope that Dingham's can do it, but your comment above suggests they cannot ("neither... pushed too close"), or some other tweak in their assembly/dimensions is needed to allow them to work when propelling.

I find AJ's (and other uncouplers I've used) unsatisfactory if the train is being pulled. For example, bringing a train to a stop in a loop prior to running round.
Prototypically, the train would stop. The loco might need to backup a fraction to relieve coupling tension (though the weight of the train may have been used to make this unnecessary when stopping). Pause to uncouple, then pull away.
The problem I find in a model is hitting the exact place to stop the train and relieve coupling tension to allow uncoupling. Practise and markers placed on the track or platform help, but there is still a problem in that every train stops in exactly the same position regardless of its formation.
These two problems - hunting to find the electromagnet and having the same stop position when pulling trains - can be solved by putting the uncoupling control into the loco. But the downside is that its very fiddly to do.


- Nigel

User avatar
RobM
Posts: 943
Joined: Sun Feb 15, 2009 4:39 pm

Re: Electro magnets for AJs

Postby RobM » Mon Sep 05, 2016 5:05 pm

nigelcliffe wrote:
AJ's work nicely if the train is being propelled. For example, dropping wagons in a siding. With this, the train can be moving, and the electromagnet fired as relevant wagon moves across the electromagnet. The train does not stop, the uncoupling is done without most observers noticing. When the correct place to spot the wagon(s) is reached, the train can stop, pause for the model train crew to lift the coupling links, and then pull away. Looks great. Other uncoupling systems will do this (eg. DG and BB, which I use in 2mm scale). I would hope that Dingham's can do it, but your comment above suggests they cannot ("neither... pushed too close"), or some other tweak in their assembly/dimensions is needed to allow them to work when propelling.
- Nigel


As I understand Dinghams only work with wagons being propelled. I use Dinghams on Manston Brewery and they work well. The only trouble I had was when I bought a 12v - 1amp power source from Maplins which was insufficient but since replaced with 12v - 2 amp and no probs. As yet, no residual magnetism encountered.
Rob
http://www.robmilliken.co.uk
Updated December 2016

User avatar
David Thorpe
Posts: 819
Joined: Tue Oct 21, 2008 11:13 pm

Re: Electro magnets for AJs

Postby David Thorpe » Mon Sep 05, 2016 7:52 pm

No, electro magnets also work with Dinghams when the train is stationary provided the couplings are at the correct tension (or lack of it). Power is applied to the magnet, the loop on one vehicle lifts and the latch on the other falls, meaning that the vehicles remain uncoupled. They don't work when a train is in motion being pulled.

DT

User avatar
steve howe
Posts: 526
Joined: Sun Feb 01, 2009 10:16 pm

Re: Electro magnets for AJs

Postby steve howe » Mon Sep 05, 2016 9:12 pm

David Thorpe wrote:I use Dingham couplings and have some of their electro magnets, wired up as Steve has done his. They work and clearly get adequate current, but I do find them very fiddly - the coupling has to be positioned in exactly the right spot above the magnet, and should neither be pulled too tight or pushed too close. All too often by the time I've managed to get the train into exactly the right position and the couplings in just the right tension any extra realism that automatic coupling/uncoupling might have provided has been lost. The situation may of course be different with AJs.DT


Dingham supplies a M5 bolt as the core, the bolt is screwed up through a 4.5mm hole and shortened accordingly. It occurs to me that the bolt head could be narrowed to fit between the sleepers, inserted other way up and secured with a nut on the underside of the coil, this would increase the area of attraction. Alternatively a cut down 6" nail with the head filed to a lozenge shape might achieve the same effect?

User avatar
steve howe
Posts: 526
Joined: Sun Feb 01, 2009 10:16 pm

Re: Electro magnets for AJs

Postby steve howe » Tue Jan 23, 2018 12:13 pm

I'm looking for a more robust transformer for operating electromagnets (I use the MSN ones) All the ones on RSS website for 12v 3A to 20v 3A are AC, would that work for electromagnets? could anyone recommend a suitable 'power brick' please?

Steve

User avatar
steamraiser
Posts: 407
Joined: Thu Dec 31, 2009 4:49 pm

Re: Electro magnets for AJs

Postby steamraiser » Tue Jan 23, 2018 1:23 pm

I use a mains to 16 volt transformer with a 2 amp out put for my AJ electro magnets.
If it is just a basic transformer I then add a 5 amp rectifier from Maplins.
This may be of interest:
https://www.alibaba.com/product-detail/ ... 47230.html

My prefered electro magnets are those produced by Gaugemaster which pull 1 amp.
The button switches they come with I find too small so replace with something a bit bigger.
Kinder on the fingers.

Electro magnets set too top of sleeper level. This is fine ptoviding you do not have infilled track.
Coupling droppers to just above rail level - again fine if you don't have infilled track.

The big advantages with AJs are you only need to operate one out of the pair of couplings and delayed action uncoupling when propelling.
When uncoupling while propelling meens you do not have to be accurate when pushing the button.
If you push the button from the middle of the first wagon to the middle of the second wagon this will give you two goes at uncoupling. One for each coupling.

Gordon A

User avatar
steve howe
Posts: 526
Joined: Sun Feb 01, 2009 10:16 pm

Re: Electro magnets for AJs

Postby steve howe » Tue Jan 23, 2018 1:46 pm

Thanks Gordo,

I have been using a laptop charger which, according to the spec. gives 19.5v at 3.3A, seems to fire the magnets ok but my concern is if these things have some sort of built-in overload that can cause them to cut out? a bog standard chassis transformer might be more rugged. Just learning how to shunt with AJs.. your last comments strike a chord!

Steve :thumb

nigelcliffe
Posts: 502
Joined: Mon Jul 21, 2008 8:31 am

Re: Electro magnets for AJs

Postby nigelcliffe » Tue Jan 23, 2018 2:52 pm

steve howe wrote:Thanks Gordo,

I have been using a laptop charger which, according to the spec. gives 19.5v at 3.3A, seems to fire the magnets ok but my concern is if these things have some sort of built-in overload that can cause them to cut out? a bog standard chassis transformer might be more rugged. Just learning how to shunt with AJs.. your last comments strike a chord!

Steve :thumb


If the electromagnets need 3A, then they are really crap electromagnets and should be replaced.
The SEEP badged ones from Gaugemaster need about 0.25A to operate, and deliver a completely workable magnetic field for AJ's from a 12v DC supply.

I know there are some other designs kicking around the model railway world which need silly currents, but shouldn't require 3A.


As to buying DC power packs, I'd be cautious about Chinese ones. They won't have CE testing/approvals, so they might be fine, or they might be dangerous rubbish, impossible to tell from the outside of the package. Power supplies from more reputable sources are not expensive, for example the maker PowerPax available from several UK sources, including Rapid Electronics, cost between £20 and £30 for the voltages and currents discussed in this thread.

User avatar
steve howe
Posts: 526
Joined: Sun Feb 01, 2009 10:16 pm

Re: Electro magnets for AJs

Postby steve howe » Wed Jan 24, 2018 4:44 pm

If the electromagnets need 3A, then they are really crap electromagnets and should be replaced.
The SEEP badged ones from Gaugemaster need about 0.25A to operate, and deliver a completely workable magnetic field for AJ's from a 12v DC supply.

I know there are some other designs kicking around the model railway world which need silly currents, but shouldn't require 3A.


As to buying DC power packs, I'd be cautious about Chinese ones. They won't have CE testing/approvals, so they might be fine, or they might be dangerous rubbish, impossible to tell from the outside of the package. Power supplies from more reputable sources are not expensive, for example the maker PowerPax available from several UK sources, including Rapid Electronics, cost between £20 and £30 for the voltages and currents discussed in this thread.



Point well taken, thanks Nigel, I have today replaced the power pack with one of 12v 2A which seems fine and the comment about cheap push-button switches so often sold at shows, is totally correct, I have replaced mine with centre bias on-off-on toggle switches rated at 5A and performance is greatly improved. My magnets are labelled DG, sold (and I think made) at Andrew Hartshorne at MSN, they seem pretty neat units, but I don't know how they compare with SEEP or any others for current draw.

nigelcliffe
Posts: 502
Joined: Mon Jul 21, 2008 8:31 am

Re: Electro magnets for AJs

Postby nigelcliffe » Thu Jan 25, 2018 10:35 am

steve howe wrote:
Point well taken, thanks Nigel, I have today replaced the power pack with one of 12v 2A which seems fine and the comment about cheap push-button switches so often sold at shows, is totally correct, I have replaced mine with centre bias on-off-on toggle switches rated at 5A and performance is greatly improved. My magnets are labelled DG, sold (and I think made) at Andrew Hartshorne at MSN, they seem pretty neat units, but I don't know how they compare with SEEP or any others for current draw.


I think the "DG" labelled magnets are derived from the old "PK" design ( Phil Kerr was a major product developer in the 2mm Scale Association, many decades ago). The "PK" is a high current inefficient device. I'd use the SEEP in preference, lower current and more effective magnetic field.


With either, if using a DC supply, then recommend a diode over each coil to shunt the spark pulse which occurs as the magnet is turned off. The pulse is what causes the cheap switches to fail, and it will also cause damage to your more expensive switches (but takes a little longer to damage them). The diode provides a path for the pulse to follow which it takes in preference to causing a spark at the switch (and thus no longer eroding the switch contacts). The only issue with the diode is that you must not reverse the DC polarity into the coils (or all the diodes provide a short-circuit path and nothing works!). Diode 1N5401 will do the job (as will dozens of other numbers), they are 9p each at Maplin, and possibly 1/10th that price from other suppliers.



- Nigel

User avatar
martinm
Posts: 93
Joined: Sun Jul 20, 2008 5:49 pm

Re: Electro magnets for AJs

Postby martinm » Fri Jan 26, 2018 12:06 am

Electro magnets set to top of sleeper level. This is fine providing you do not have infilled track.
Coupling droppers to just above rail level - again fine if you don't have infilled track.

So what do people do with unfilled track?
Surely it should not be above rail level?
The droplets certainly must always be above rail level!
martin


Return to “Couplings”

Who is online

Users browsing this forum: No registered users and 2 guests