Electro magnets for AJs

[steve howe]

Having found I probably can use AJs on Horsley Bank, can anyone suggest a source of electromagnets? I know the purists will be shouting "make your own!" but for the few I need, there just aren't enough hours in the day...

Steve

[Tim V]

Seep!

[Rod Cameron]

What Tim said

http://www.gaugemaster.com/item_details ... de=EM1&r=1

(and other retail outlets, e.g. Kernow)

[Jol Wilkinson]

Also available from Andrew at MSE.

I've been testing one for the extension to London Road and found it draws 1.75A, so will need suitably rated switches and ideally a protection diode across the feed.

Jol

[steve howe]

Thanks chaps, I'll get one and experiment accordingly. Didn't the MMRS also produce one at sometime?

[Andy G]

Didn't the MMRS also produce one at sometime?

Not that I'm aware of and I've been a member of MMRS for 27 years (yikes!). I think what you may be thinking of are the instructions on how to wind your own, though I can find no reference to them in the current information.

Regards
Andy

[steve howe]

Persevering doggedly with the AJ, I have succeeded in makiing and fitting a batch of about a dozen pairs using the admirable jigs now available and all seem to do exactly what it says on the tin. I should say I have gone mainly down the hinged/counterbalanced route as the whole unit is much easier to fit and adjust. Having achieved reliable coupling, now the hard part - getting the blighters to separate droppers from sawn off panel pins with the rest of the pin minus point, soldered on as the weight. Now, here's the snag I'm finding: there does not seem to be enough pull on the magnets to get the tails of the couplings to pass each other, despite using 12v on the magnet. The couplings dip beautifully individually, and some even perform as intended, but the general trend is for the tails to stick and fail to release. I'm tempted to try a more powerful magnet to kick-start them, but everyone else seems to manage on 12v magnets? Currently I have been experimenting with the Dingham magnet, and the MSE version both on 12v, should I try upping the voltage?

Steve

[grovenor-2685]

Look carefully at the uncoupling action, you may find both couplings are being pulled down.
This can happen if:
the droppers are both in the influence zone of the magnets,
or the counterbalance weight is insufficient and the coupling pulled down by the dropper has enough magnetic attraction to the other coupler to pull that down as well.
It can be qyuite tricky getting these factors right.

Alternatively you might see that the coupler just does not pull down far enough, in which case you can try increasing the voltage.
Regards

[garethashenden]

We had this problem with Empire Mills. The small 12V power supplies provide 12V, but not very many amps. We substituted a bigger (laptop style) power supply and it's been quite reliable ever since.

[steve howe]

We had this problem with Empire Mills. The small 12V power supplies provide 12V, but not very many amps. We substituted a bigger (laptop style) power supply and it's been quite reliable ever since.

I have been using a plug-in transformer I got from Maplins which has 7 settings from 3v up to 12v to power the magnets on my bit of test track, I checked the rating tonight and it says "100 - 240v 60/50Hz 0.16A" being electrically illiterate, that does not sound like much amp to me...?

I see from MRJ 223 that Chris Pendlenton uses 24v for his magnets.

Steve

[nigelcliffe]

We had this problem with Empire Mills. The small 12V power supplies provide 12V, but not very many amps. We substituted a bigger (laptop style) power supply and it's been quite reliable ever since.

I have been using a plug-in transformer I got from Maplins which has 7 settings from 3v up to 12v to power the magnets on my bit of test track, I checked the rating tonight and it says "100 - 240v 60/50Hz 0.16A" being electrically illiterate, that does not sound like much amp to me...?

1/6th of an amp, or 0.16A according to what you wrote. Or, in electromagnet terms, won't cause a ripple on the surface of a rice pudding....

Get a decent 12v power supply. Around 2.5A should be cheap in a small "brick". That will be more than adequate.

I see from MRJ 223 that Chris Pendlenton uses 24v for his magnets.

24v and a decent number of amps is fine. 24v and not many amps won't work. Coldfair Green also has 24v (and measures at a bit more than that). But, I tested the layout last winter with 12v (and supply with potential to deliver 2.5A) and its completely fine at 12v. So, when we re-fit the power systems, chances are we'll go to 12v.


- Nigel

[shipbadger]

I must admit that when I wound my own electtromagnets I forgot that the late 40's early 50's leading lights of the MMRS (Sid Stubbs, AJ etc.) were using 24V for their systems. I copied the MMRS design and was disappointed to find they hardly worked on the 12V to which I had connected them. I then changed to a 24V system and they've worked fine ever since. And now a cautionary tale, I tried winding some magnets to work with Microtrains uncouplers (N scale Kadees) and they didn't work very well. So I increased the voltage until they worked, the only snag was they now heated up to the point where the plastic sleepers above melted!

Tony Comber

[nigelcliffe]

I must admit that when I wound my own electtromagnets ....

I too have wound my own. http://nigelcliffe.blogspot.co.uk/2008/ ... plers.html

But, if its available off the shelf at a reasonable price, I'll buy it.


- Nigel

[steve howe]

Looking at adding electro magnetic uncouplers to my current Roseladden project which will probably need about 8, plus some permanent magnets.

As only one train is likely to be moving at any time, I am wondering, in the interests of simplicity of wiring, if it is possible or feasible to operate the magnets with one push button switch, rather than locating individual switches on the panel diagram. It would mean of course all the magnets energise simultaneously, but with only one train in motion I don't see this as being a difficulty. I'm just not sure if the current draw would be too great?

Steve

[nigelcliffe]

Looking at adding electro magnetic uncouplers to my current Roseladden project which will probably need about 8, plus some permanent magnets.

As only one train is likely to be moving at any time, I am wondering, in the interests of simplicity of wiring, if it is possible or feasible to operate the magnets with one push button switch, rather than locating individual switches on the panel diagram. It would mean of course all the magnets energise simultaneously, but with only one train in motion I don't see this as being a difficulty. I'm just not sure if the current draw would be too great?

You'll have to measure the current draw to work it out, but it would be possible without a stupidly expensive power supply, and provided the switch was up to the job.
The SEEP units draw well under 0.2A each (I can't remember the number, though have measured them). On that basis, eight together would be 1.6A. So, a 2A 12v power supply is just about enough, 3A 12v would be sensible. That makes the power supply side simple, a suitable power brick is well under £20 (and probably under £10).

That leaves the switching side. Typical cheap push buttons are NOT suitable for those switching currents. So, either need to seek out a switch with adequate contact rating, or (preferably in my view) use devices to allow a small switching current. Such a device might be a transistor circuit, or a relay, to energise the coils. The uncoupler coils would ideally need a reverse diode across the coils to stop the back-emf pulse when turning off, but this is good practise for a single coil when fed with a DC supply.


Think through carefully whether the layout can really be worked with all magnets "on", and that there are no circumstances where it would create difficulties.

- Nigel

[martin goodall]

As a result of experience, I have now installed a separate power supply for the electro-magnets, due to the current that my magnets draw when fired up (only one at a time, of course, but the type I have - designed and formerly supplied by Ray Hodson - do draw a significant current).

I have purchased diodes to put across the coils, but still haven't got round to fitting them. I haven't encountered a problem yet in operating the electro-magnets without the diodes.

[garethashenden]

I would wire them separately. Getting enough amps to actuate the couplings thoroughly is a concern, you don't really want unnecessary current draw. Another potential issue is you could accidentally uncouple wagons if they happened to be over one of the other uncouplers.

You don't have to run two wires to each uncoupler however, I've had success with a common wire going to all of them. Wire one side of all the push buttons together, then run that wire to one side of all the uncouplers. Then run individual wires from each push button to the corresponding uncoupler.

[grovenor-2685]

You don't have to run two wires to each uncoupler however, I've had success with a common wire going to all of them. Wire one side of all the push buttons together, then run that wire to one side of all the uncouplers. Then run individual wires from each push button to the corresponding uncoupler.

That won't work, you have no connection to the power supply!
Connect one side of all the buttons together and connect that to one side of the power supply. Connect one side of all the uncouplers together then connect that to the other side of the power supply. Then run individual wires from each push button to the corresponding uncoupler. Add diodes across the coils as above.
Regards

[junctionmad]

sorry to hijack this

but I'm looking for electromagnets that would activate dinghams, has anyone any experience of the chineese 20mm 3W 12V units, would they work ?

[stevecarr]

You could always 'roll your own'

Look for Chris Pendleton writings in MRJ. I use home made to operate Dinham and they work fine. I also took his advice and run on 20 volts.

Steve

[steve howe]

Thanks for the clarification Keith, I will try that approach,

Dingham does his own magnets, I have found them very good and robust.

[junctionmad]

Thanks for the clarification Keith, I will try that approach,

Dingham does his own magnets, I have found them very good and robust.

I know that, thanks , but I was wondering if anyone has experience of the 12v 3W 20mm magnets from China , about 3 dollars a pop

[steve howe]

The uncoupler coils would ideally need a reverse diode across the coils to stop the back-emf pulse when turning off, but this is good practise for a single coil when fed with a DC supply.

Experimenting with my newly installed electromagnets (Dingham) I have noticed residual magnetism in the pole after the current is switched off. Can anyone with more knowledge in these things than I please give me a steer as to the appropriate diode, rating etc. as referred to above, and can they be had from Maplins? Also which direction should the diode be installed?

Thanks

Steve

[nigelcliffe]

Diode - 1N5401 would be slightly overkill, but should be readily available. Maplins tend to be expensive (six times the price of an electronics specialist such as Rapid or Farnell/CPC !), so unless you only need a few, I'd suggest looking elsewhere.

With DC power supply (don't use the diode on AC!), the power arrives at either side of the electromagnet coil, one side being (+) and the other (-). Arrange the diode so it doesn't conduct with normal power connected, so the stripe on the diode goes to the (+), the other end to the (-) of the electromagnet.

The diode won't stop the residual magnetism you are finding, that's down to the metal in the core retaining some magnetic field. The diode is only stopping the back EMF "spark" which will lead to premature failure of a switch which operates the coil.



- Nigel

[steve howe]

Thanks for that Nigel, I only need 6 so it shouldn't break the bank.

I wonder if the residual magnetism is a problem experienced by others or if it has no effect under normal operating conditions?

Steve