Posted 27 July 2010 - 09:38
Posted 27 July 2010 - 16:57
If the Hornby Dublo ones dont fit, I think that there is probably a market for a Hornby ringfield Neo magnet. There seem to be many old HSTs etc that are for sale advertised as running slowly - this is most likely due to the original magnets losing their strength over the years. I would certainly have a few if I could lay my hands on them. If there are currently no manufacturers at all for these, you might buy the whole production run and try to sell the excess on ebay etc. You might cover the costs doing it that way.
Posted 27 July 2010 - 21:19
Posted 27 July 2010 - 22:04
The modern type magnet in neodymium would have to be specials, made to order. Hornby should have supplies of the Ringfield Magnets spares in the alnico type for replacement, or they can be re- magnetised, although few service shops have the equipment.
Posted 28 July 2010 - 08:52
Posted 28 July 2010 - 10:52
Both types have the same magnetic path, and the original Ringfield followed Lindsay patent, which with his skew slots gave a smooth transition between poles, as the poles are less distinct than say a horseshoe or twin magnet type. Hornby originals just copies the magnet, dropping the skew slot.
Posted 28 July 2010 - 11:17
The downside of neodymium magnets is that they have a remarkably low "Curie"point, the temperature at which the magnets fail.....and with some designs the wattage can warm the motor enough for the magnet to fail. In theory the temp is 320deg C, very hot!!, but in practice failure can occur at 170/200. I have seen one fail at about 110, just a bit above boiling water temperature.
The modern Hornby motor should not draw enough current to do this, but older original types might, and need re-winding with a smaller gauge wire to reduce the current. The thicker wire was to draw more current to work with the less efficient magnets, upping the power of the magnets still leaves the thicker wire, and with a high load lots of current and heat.
With the usual loads the motor draws less current for the power output, so it is only an overload that might cause concern.
If the magnets are specially commissioned make sure as high as possible Curie point is specified. I am told the problem ones are from some Chinese makers, who make the full specification magnets as well but also the production produces low curie versions which are sold in effect as second grade, perfectly all right as long as they are cold.
Posted 28 July 2010 - 16:18
Hi Simon further to your suggestion, I emailed the site you mentioned and respectfully asked about the dimensions of the ringfield magnets they supply for Dublo locos in an attempt to see if I could make them fit.. I got a RUDE reply telling me that they do not give out details on sizes and have supplied many replacements to date, which should suffice. My feelings toward this ignoramus is F*** U. I some times wonder why these PEOPLE are in business, c'est la vie.Further to your suggestion I have never used ebay,I would have thought that there were sufficient members in a similar position to myself to be be interested, perhaps early days for the post yet cheers. Beeman
I can only apologise for their lack of courtesy - I wish that I had tried to contact them myself, so I wouldnt have then put the link on this site. I entirely agree with you about suppliers being rude - there is nothing to put you off them faster than that.
I have bought Neo magnets for older Triang X04 and powered bogie motors from elsewhere, so I will see if that supplier can help (before I put their details on here!)
Posted 28 July 2010 - 21:38
Posted 28 July 2010 - 22:52
Posted 29 July 2010 - 11:05
Most suppliers are the Chinese and Japanese, and the quality varies a lot, maybe the compression moulding of the materials before firing varies, but I know as with LED lamps, the makers have few "failures", they just grade the output according to specification, the poorest going to "toy" magnet uses.
The magnets also suffer in the post production nickel or chrome plating, and this treatment also lowers the Curie point, where magnetism is lost. It is also not a sudden change, the increasing heat reduces the field, and in a motor would cause the current and the heat to rise as it fails.
It seems the main troubles come with the very thin rare earth magnets in enclosed can motors, they seem to fail at as low as 120c, so a run away failure must be occurring, with the current constant, and the heat increasing due to the failing magnetic field.
Trying to describe what happens to current/voltage/field inside what is a dynamic situation inside a motor is a bit beyond these postings.
Normally it is assumed for clarity that DC voltage and current works with DC motors, but I am sure you realise this is not what is going on, with alternating AC current, back emf, etc, driven by the coils.
There is a hidden effect adding to localise heating in the magnets and that is eddy currents within them, and in neodymium this is far higher than other magnets, and seems to quicken heating effects.
In the end I think it quite unlikely a big ring magnet would de-magnetise, it would be melting the plastic for a start, but it is possible, as Hollywood foundry experienced, to get the smaller motor types to loose the field.
Posted 23 August 2010 - 10:39
Posted 16 September 2010 - 14:54
Here is the update for fitting a Neo magnet to the older Ringfields. Loco chosen was an older Hornby A4 Seagull, having a 'rubber' magnet fitted of nominally 28x22x8mm, the 'replacement I obtained in N42 was 27x23x6. .....
Any chance of seeing the new magnet in-situ?
Posted 14 October 2010 - 10:25
"Sorry, we do not do motor magnets for Hornby Tender Drive Loco's. Development tests have proved that the magnets are just too strong to allow motor rotation due to lack of turns on armature and lack of armature mass."
Posted 24 October 2010 - 12:12
It was a bad move. Nothing happened, the armature refused to turn, a lot of buzzing from the motor and then smoke appeared from the armature. The loco was removed from the track and the original weakish magnet was replaced and tested again.
Luckily the loco still worked after refitting the original magnet.
In my opinion, these magnets are just too strong for the older motors to work properly.
Posted 17 August 2011 - 16:57
From what I saw in his ebay shop he does different magents for all different models.
Posted 29 August 2011 - 09:03
Posted 02 December 2012 - 11:53
Here is the update for fitting a Neo magnet to the older Ringfields. Loco chosen was an older Hornby A4 Seagull, having a 'rubber' magnet fitted of nominally 28x22x8mm, the 'replacement I obtained in N42 was 27x23x6. In my previous post I suggested that while this was u/s to the original the power of the magnet would compensate. This proved correct. I fitted an outer liner of mild steel strip to centralise it within the diecast frame which also acts as an external keeper. This was also quite sufficient to locate it. On the bench the drive would rotate at 50mA when supplied from an old transistor controller, ammeter connected in motor armature lead.This loco was prior converted to DCC and at best I could only get 1 rev.in 1 sec of the driving wheels. I then fitted a 5 pole armature which gave an improvement to 4-5 secs for 1 rev., on fitting the new magnet this halved to 1 rev taking 9-10 secs. I have attempted to measure the current taken after fitting the Neo magnet. I do not have a 'rolling road so the following had to suffice. The ammeter connected in one motor lead, the loco was 'held' on the track physically, and the power applied, [ Dynamis/Bachman chip ], with the loco held so that the wheels were skidding on the track it was only when the traction tyres were skidding that the current went up to 300mA , obviously it would have increasedthe load to stall, but it was certainly under excess load, and certainly wont produce overheating,!!!!.Must admit I adjust cv5 to give maximum speed to approx scale 70mph. This project has contradicted the 'doubters' who commented on my proposals previously. The economic downside is it cost approaching 10 pounds, and on visiting a Toy & Train sale a week ago find drive units for sale at 10 pounds, these are advertised elsewhere around 20+, having brushes.springs.traction tyres.wheels,and should have a good magnet as they were fitted with a 5 pole armature. so perhaps next time I shall indulge if still available..Beeman.
Hi Beeman, Restoring 8F 2-8-0 tender drive and City of Nottingham tender drive type 6 ringfields. Really interesting. I contacted power magnet store and, although they have Neo ring magnets easily physically adapted, the guy states they were all axially (face) polarized and not diametrically polarized. So, do you know summat I don't cos I'm hornswoggled? I believe one needs diamtetrically polarized magnets (as per originals) in order to be successful? I have found segmented magnets for sale as "sets" with diametrically polarized (North O/D ; South I/D & vice versa), bur, harder to adapt + I'm not sure what angle to cover for optimum performance (one can make them up to a full circle, each segment is approx 45 degs). MTrains (firstname.lastname@example.org) has diametrically polarized magnets for the old Dublo. Big one is very near! BUT I/D is 20 m.m., so, such a shame as Neo is almost impossible to machine I think. I got the superb beautifully constructed 5 pole armatures from Earlesmeade/Ebay. Shafts are sleeved with excellent brass bearings to create correct diameter. If you have time I would greatly appreciate your input /support. Regards Borsini.
Posted 02 December 2012 - 16:57
Good luck to those that have introduced new types of 'super-magnets', I'm sure there are some that will find use for them, I'm not decrying that. But certainly with the Triang/Hornby range, I don't believe there is a need to replace magnets. If anyone does need a remag done, please contact me. (Note - not a sneaky advert for services, I still have the re-magnetiser, and will gladly re-mag for you at minimal cost, ie postage)
Posted 03 December 2012 - 10:57
Posted 03 December 2012 - 14:47
I might add that 1) I use a homebuilt PWM dc controller, which uses current itself; 2) supply voltage to the controller is around 18-20v dc ( a tad higher than normal 12v); 3) the ammeter is not accurately calibrated, other than to show roughly 1A on fsd. All these factors mean that my meter indication is just that, an indication, which I aim for, any variation is therefore not normal.But the general idea of around 200-250mA on dc is about right. Any cheap multimeter is probably capable of reading that I suspect. If you have a known good motor, use that for a comparison.
If you need any assistance, please get back to me.
Edited by stewartingram, 03 December 2012 - 14:47 .