Re-magnetisation

[bertiedog]

I know this came up before, but I can't find the postings, but who does a re-magnetising service for older motors, I know X04 was mentioned but this is an older Zenith / Rowell, which would have fitted the old Meccano magnetiser unit fine, being just a fraction thicker than the Tri-ang motor.

The Zenith / Rowell is a solid block magnet, no steel sides so cannot be replaced by a neodymium magnet. The motor works but the field strength is now low, and needs a boost

 

Stephen

[stewartingram]

As someone who formally did repairs for a number of model shops, including Hornby agents, I later purchased the remag unit from one of them. For the cost of return postage, I do offer a free remag service to RMWebbers.

Only criteria is that you don't send magnets removed from motors. They must be left in situ, and the whole motor (or loco if you prefer) sent to me.

 

Stewart

[bertiedog]

I may take you up on the offer, but net research has revealed the circuit used by the re-magnetisers like the old Hornby along with suggested coil size etc. It is the near lethal, but exciting, capacitor type, a high voltage cap is charge on half wave rectified mains via a bulb, which goes out when charged, and then the pulse of about 50 amps at about 170 volts is discharged through the coil, with a bang! ( about 8.5 KW burst!).

 

I was a GPO electrical engineer, and such a device is easy to make, except the wire is a bit costly new! I will have a go and see what happens, as the method is better than DC from a battery, which can easily be applied for too long, the cap value limits it to a nice single pulse.

 

Stephen

[DCB]

I may take you up on the offer, but net research has revealed the circuit used by the re-magnetisers like the old Hornby along with suggested coil size etc. It is the near lethal, but exciting, capacitor type, a high voltage cap is charge on half wave rectified mains via a bulb, which goes out when charged, and then the pulse of about 50 amps at about 170 volts is discharged through the coil, with a bang! ( about 8.5 KW burst!).

 

I was a GPO electrical engineer, and such a device is easy to make, except the wire is a bit costly new! I will have a go and see what happens, as the method is better than DC from a battery, which can easily be applied for too long, the cap value limits it to a nice single pulse.

 

Stephen

Sounds like fun, even if it doesn't actually remagnetise  magnets..    Sounds ideal for scaring cats off the outside line.....

[bertiedog]

It certainly does re-do the magnets, it is the same circuit as Hornby Dublo used or very near. Although the power appears high it is applied by the capacitor for only a moment. The old units went off with a bit of a thump! This type only works with alnico magnets like Dublo used along with Tri-ang.

Stephen.

[bertiedog]

A quick build of the circuit with a coil re-wound from a TV coil, and a 250uF 500 volt cap, reveals the circuit works, but with a real thump! I have some other motors with the Alnico magnets so will try one of them first, after doing a steel slug to fit the coil.

I would not recommend trying the circuit, it stores a lot of power in the cap, enough to kill if touched even with the power off, so only qualified people to try this one! I would add a high value bleed resistor across the cap to discharge the cap after use. It was tested on an isolation variable transformer as well.

 

[Il Grifone]

I recall a circuit published once (a long time ago in the States - Model Railroader?) which involved the use of TV smoothing chokes. These components have not been used for decades so obtaining them today is not going to be easy.

 

Care should be exercised with the above circuit. The capacitors can give a nasty jolt!

 

It presumably needs some sort of horseshoe core to complete the magnetic circuit or two coils and two cores?

 

 waffle warning

 

I can remember an old (early seventies) Philips Chassis (G8) which was notable for its excellent picture and being one of the first all transistor colour sets, This used two of these things in a common can with a large dropper resistor connecting them. This latter would go open circuit at the drop of a hat, leaving something like 300 volts across the break ready to catch the unwary....  The quality of the components meant that the charge remained for a long time after the set's failure.

 

We used a similar circuit (less the capacitor) for regenerating TV cathode ray tubes. Philips tubes almost always came back to life. Other makes were less successful.

Edited December 22, 2016 by Il Grifone

[bertiedog]

Tried the full coil and it works without a return path, the single pole seems to magnetise the motor correctly, although it may be more efficient with a horseshoe return path, but it is substantial engineering to fit with 1x1 in bar to cut out. Also the Anvil has to be adjustable to get the best contact with the motor block. I had wondered about the power rating of the switch, but it seems the burst is so quick that there is no strain on a good quality mains switch.

[Il Grifone]

Tried the full coil and it works without a return path, the single pole seems to magnetise the motor correctly, although it may be more efficient with a horseshoe return path, but it is substantial engineering to fit with 1x1 in bar to cut out. Also the Anvil has to be adjustable to get the best contact with the motor block. I had wondered about the power rating of the switch, but it seems the burst is so quick that there is no strain on a good quality mains switch.

 

The switch does not have to break the circuit, so just needs to be fairly robust, as opposed to extremely robust.

 

I have thought about building a remagnetiser, but time is limited and a couple of 6mm cube neodymium magnets work just as well. (I almost need to order some more.) I have assisted some tired Tri-ang 4 wheel motor bogies with a couple just stuck on (polarity in phase of course - the way they just stick on rather than jumping across the room (exaggerating a little but...)). The results were encouraging; the tired unit then operated as well as a good one. The 6 wheel (4 wheel plus 2 fake really) don't have room but smaller magnets are available.

 

I was thinking of two coils with an adjustable iron core so that both sides of the motor can be  in contact with the remagnetiser. Maybe one day I'll try it.... Alternatively, I would have thought that a few straight lengths of iron bar or rod to make a yoke would have done, as it doesn't need to be super-efficient.

Edited December 26, 2016 by Il Grifone

[bertiedog]

The reason I cannot use the Neodymium magnets is that the motors are the cast single piece Alnico magnets favoured by Taycol, Romford, and Zenith for may years in the 1940's and 50's.

 

I am winding a heavier gauge coil in a few days, will extra turns, and will have access to a lab gauss meter to check the magnets before and after. The capacitor can be increased in value as well, but there is a limit, mainly to your health!

 

The same coil could be "Flashed " across a 12 volt car battery, this draws as much power as the wire can take. but risks a burn out if the wire fuses momentarily on the battery stud or contact.

 

The capacitor circuit works at half mains voltage and lower current, with the 12 volt one the current is massive, but the power is about the same.

 

The more I think about  a magnetic return path will be needed, unless the coil is split top and bottom around the gap. Even then a return path might improve the efficiency. Looks like a few more experiments will be needed. I will have to find some coil formulas to determine the field to be expected with different numbers of turns and gauge wire.

 

Stephen.

[Il Grifone]

From memory, the magnetic force is proportional to the number of turns, but the wire gauge has no effect and needs to be chosen for the current flow. The limit is set by saturation of the core. Air gaps weaken the effect of course.

 

I saw once a suggestion of 30 (IIRC) turns of thick wire around the motor and then 'flashed' on a car battery. I've never had the courage to try this....

 

I seem to recall the figure of 10,000 gauss for the Dublo magnetic strength but don't quote me!

Edited December 28, 2016 by Il Grifone

[bertiedog]

After checking several net sources (never a really good idea), the inch diameter 800 turn coil would generate a field of about 8000/10000 gauss on the half wave rectified mains voltage stored in the capacitor, This assumes a complete iron core, no air gap, so the presence of the motor reduces the figure, but is obviously enough to get re-magnetisation. Just how often the capacitor can stand the surge current is open to debate! I know the old Hornby unit had warnings to use and then switch off.

I will make the U frame over the next few days in mild steel, with one pole adjustable to clamp the motor.

[pacerfan]

The earlier thread regarding this topic is here:- http://www.rmweb.co.uk/community/index.php?/topic/29096-revitalizing-wrenn-locos/

 

I have got a copy of the schematic for the original Meccano Magnetiser dated 1.9.54. I downloaded it a good few years ago. I cannot give the link to it as it is now defunct. There are no capacitors shown in the circuit diagram. The magnetiser coil consists of 2840 turns of 19 SWG wire. There are two time lags shown, a bridge rectifier, a rotary mains switch and a GEC high voltage push switch.

Edited December 9, 2017 by pacerfan

[pacerfan]

I have attached the schematic.

[Il Grifone]

Thanks I might have a go at building one.  A few thoughts:-

 

Some (all?) of the parts are long since unobtainable, so it looks like the large capacitor, rather than the time-lag devices to power it.

 

The 30A input fuses look like being useless. They would need 60A to break the circuit.... Modern practice would only use one in the live feed in any case.

 

Interestingly the drawing predates today's mains voltage by some time.

 

19 S.W.G. has a current capacity of about 2A (presumably free air) so the coil would get hot very quickly.

[Golden Fleece 30]

Why not just buy the very safe one Ron Dodd advertises on Ebay. The coils work on 12 volts and you get a compass and meter included. I have used mine many times on Dublo, 00 and TT motors with great results.

 

I will not use Neo's anymore due to them splitting and chipping (personal issues) and then peeling and bearing wear (other peoples issues), then, the matter of attracting nearby metallic objects when a train passes.

 

Garry

[pacerfan]

I already have a Ronald Dodd remagnetiser. It is an excellent piece of kit. However, I have found that some of the Hornby Dublo/Wrenn 1/2 Inch motor magnets lose some of their strength a few days after being remagnetised. I am wondering if the magnets are defective and are not retaining their full magnetism. (A fully magnetised 1/2" motor can be picked up by a small screwdriver by touching the top or bottom pole piece above the magnet poles). The Tri-ang X04 magnets seem to retain their full magnetism after being remagnetised.

 

I was also wondering if these magnets coud be rejuvenated with a high voltage magnetiser using capacitors?

Edited December 11, 2017 by pacerfan

[Golden Fleece 30]

I already have a Ronald Dodd remagnetiser. It is an excellent piece of kit. However, I have found that some of the Hornby Dublo/Wrenn 1/2 Inch motor magnets lose some of their strength a few days after being remagnetised. I am wondering if the magnets are defective and are not retaining their full magnetism. (A fully magnetised 1/2" motor can be picked up by a small screwdriver by touching the top or bottom pole piece above the magnet poles). The Tri-ang X04 magnets seem to retain their full magnetism after being remagnetised.

That's correct, Hornby Dublo did have a few poor magnets that would not hold their magnetism, thankfully not on a big scale but it also affected some of their Ringfields so it is not the magnetisers fault but the magnet.  Dublo magnets can be bought quite cheap and usually then they are better than the defective ones (you would be most unlucky to get another dud).  As you say Tri-ang had very few issues with their magnets.

 

Garry

[pacerfan]

Another strange anomaly with the 1/2" motors is with the pole pieces. The Hornby Dublo ones were painted black, the later ones by Wrenn were unpainted. The magnets that seemed to start losing magnetism were in motors that had the later (unpainted) pole pieces. I tried swapping the magnets on two motors a Hornby Dublo and a Wrenn, then remagnetising them. The weakened magnet didn't lose it's strength in the motor with older pole pieces, but the other magnet after being swapped did. Could the pole pieces on later motors have been made from a different grade of metal and not retain their magnetism as well?

[Golden Fleece 30]

Another strange anomaly with the 1/2" motors is with the pole pieces. The Hornby Dublo ones were painted black, the later ones by Wrenn were unpainted. The magnets that seemed to start losing magnetism were in motors that had the later (unpainted) pole pieces. I tried swapping the magnets on two motors a Hornby Dublo and a Wrenn, then remagnetising them. The weakened magnet didn't lose it's strength in the motor with older pole pieces, but the other magnet after being swapped did. Could the pole pieces on later motors have been made from a different grade of metal and not retain their magnetism as well?

You have got me there, I have never heard of that before. Hopefully someone on here may know more about magnetism to inform us. In my experience any dud magnets were Dublo not Wrenn and if still no good after a remag than a new magnet was obtained which works fine in the same pole pieces.

 

Garry

[locomad]

Another strange anomaly with the 1/2" motors is with the pole pieces. The Hornby Dublo ones were painted black, the later ones by Wrenn were unpainted. The magnets that seemed to start losing magnetism were in motors that had the later (unpainted) pole pieces. I tried swapping the magnets on two motors a Hornby Dublo and a Wrenn, then remagnetising them. The weakened magnet didn't lose it's strength in the motor with older pole pieces, but the other magnet after being swapped did. Could the pole pieces on later motors have been made from a different grade of metal and not retain their magnetism as well?

 

This has puzzled us for years, same loco, same 1/2 motor, same setting worm etc, same oil, yet one loco performs well using say 0.3 amp on a test run the other not so well using up to 0.6 amp on a test run both at 12v exact.

 

I've a "guass" meter on my phone, placed in a jig near motor it does show that one magnet is weaker, I've tried remag both, but some motors still don't improve.

 

In general I've found those wrenn products made in the Triang Hornby 65-71 period to be the worse, but there were other quality issues as well.

 

I've an old remag machine simple thing made as a teenager uses a car battery 12v and some coils, nothing fancy, I've watched with great interest the Ron Dodd machine on the hrca website. However I'am not quite up to all this capacitor 240v stuff not even sure I can read/ understand these wiring diagram, however sure I've got all the bits to build one.

 

Wondering if large remag machines are needed here? are some magnets harder to remag than others.

 

It's not a new problem either, reading some early 1960 RM's modellers had the same problems then with some Dublo stuff, course I'am aware it's not just the magnet, even clearing the worm and using a different lubricant can cut the amp draw in half. Thinking after my 100 wagon experience of starting a thread improving performance of Hornby-dublo wrenn locos there is some vast differences

[Golden Fleece 30]

This has puzzled us for years, same loco, same 1/2 motor, same setting worm etc, same oil, yet one loco performs well using say 0.3 amp on a test run the other not so well using up to 0.6 amp on a test run both at 12v exact.

 

I've a "guass" meter on my phone, placed in a jig near motor it does show that one magnet is weaker, I've tried remag both, but some motors still don't improve.

 

In general I've found those wrenn products made in the Triang Hornby 65-71 period to be the worse, but there were other quality issues as well.

 

I've an old remag machine simple thing made as a teenager uses a car battery 12v and some coils, nothing fancy, I've watched with great interest the Ron Dodd machine on the hrca website. However I'am not quite up to all this capacitor 240v stuff not even sure I can read/ understand these wiring diagram, however sure I've got all the bits to build one.

 

Wondering if large remag machines are needed here? are some magnets harder to remag than others.

 

It's not a new problem either, reading some early 1960 RM's modellers had the same problems then with some Dublo stuff, course I'am aware it's not just the magnet, even clearing the worm and using a different lubricant can cut the amp draw in half. Thinking after my 100 wagon experience of starting a thread improving performance of Hornby-dublo wrenn locos there is some vast differences

If you are on the HRCA website there are plenty of people there who could help you.  Apart from using the magnetiser everything else is above me in relation to the issues.

 

Garry

[Il Grifone]

I've not had problems with neodymium magnets beyond them being too strong. I remember a Dublo magnet when new would attract small objects sufficiently to attach them to the diecast body, but a full size neo exaggerates. Two 6mm cubes padded with washers to minimise the airgap and hold everything together work well and give roughhly the correct field strength. I do have a couple of weak Tri-ang magnets in motor bogies but the X.04 type is very reliable. Dublo magnets on the other hand are very variable. I have two that are as good as new  (a Horseshoe Duchess and a Southern N2), but the others vary considerably from good to useless (the latter get replaced). It would appear that there were quality issues with the AlNiCo alloy.

 

I use the Dublo test of 5 laps of the standard oval in 25 seconds* with four SD6 coaches (usually I use four D3/12s). In deference to their age, I allow a bit of leeway (even Meccano Ltd. allowed an extra second for repaired locomotives).

 

* some models were allowed longer times

[Golden Fleece 30]

Here are my problem Neo's.  The flaking one is not my loco but from someone else showing their issue.

 

Garry

[Il Grifone]

Nasty! Especially the piece of plating sitting on top of the armature. I've not had that sort of trouble luckily.