Dave B

I have to correct something I posted a while ago. I said that the Powermaster and the Safety Minor don't have any evidence of asbestos because they use a variable transformer. My Powermaster has the slider control variable resistor for full-wave to half-wave which is wound on what is most likely asbestos. My Safetyminor does not have any asbestos at all though. I would assume that the Powermaster versions with a switch, rather than the slider resistance, would not have this asbestos. I have removed the slider control, shorted out the wires to it and blanked off the slot. Also to say, that when I replaced the selenium rectifiers with a semiconductor bridge, I found that on no load the o/p rose to 80V or so when measured by my high impedance DVM. Not dangerous because this would be due to a small charge build up which is easily discharged with a load of any sort. I assume this build up of charge was kept low by the leaky selenium rectifiers. Modern semiconductors don't have such a high reverse leakage current, and thus allow the build up of charge. The solution was simply to put a 10K or thereabouts resistor across the + and - pins of the bridge rectifier.

This H&M rheostat control unit is presently on e-bay, so there can be no argument that it is sealed away or anything. E-bay should ascertain if it is asbestos or not. I strongly suspect it is.

H&M controllers are becoming more frequently available on e-bay and such in recent years, no doubt because of nostalgia. That is the attraction for me. I bought a number of them about 20 years ago for little more than the postage, but prices nowadays have risen to over £50 for some items. From what I know now, I would not be happy to buy any H&M items apart from the Power Master and the Safety Minor which don't use rheostat controls. We now find that even the transistorised version contains what looks very much like one of H&M's standard rheostats as the control element.

I would certainly think that the whiteish material under the nichrome resistance windings could be asbestos. When you magnify the pictures you can see what look like fibrous material with the "hairy" bits capable of flaking off. I am disappointed in e-bay and the web in general in selling exposed bits of H&M controllers that show evidence of asbestos. In the UK our Health and Safety Executive and our local Environmental Health departments no longer consider they should be testing for asbestos, so I wonder if e-bay could be held responsible for any health effects caused by asbestos. Of course difficult to prove, but at the very least is there no way of stopping e-bay selling these items. Do they take their responsibilities in this area seriously? With reference to asbestos testing 10 years ago we wanted to test some artex in a flat that our daughter was moving into. To my surprise I found that our local government H&S did not offer facilities to test for asbestos. We found a lab that did it for us for about £25 and thankfully it didn't contain asbestos. Going to be more expensive nowadays of course. https://www.haspod.com/blog/asbestos/asbestos-artex-ceiling-risk

My H&M Duette showing rather flaky looking material which may be asbestos. Also note the use of 1N4002 diodes to replace the selenium rectifier. I think these are under rated at 1 Amp, 200 volts. 200 volts probably ok, but 400V versions 1N4004 at virtually no extra cost would be better. However, 1 amp is definitely under rated considering that the short circuit current could easily exceed several amps whilst the thermal cut-outs could take an excessive time to operate. I would be happier with 1N504 diodes rated at 3 Amps.

The inside of my H&M Safety Minor showing no signs of anything asbestos so I will be happy to use it with my grandchildren. I have replaced the selenium rectifier with a semiconductor bridge rectifier on the rear panel. This is the rectifier on the controlled output. The remaining selenium rectifier that supplies the 16V DC can be seen on the right side of the case. I have no use for this supply so I may just remove the selenium rectifier rather than replace it with a semiconductor device. The variable transformer mechanism can be seen bearing on the transformer secondary windings but the picture does not show the clever mechanism for moving the transformer wiper in the same direction whilst reversing the electrical output when moving the control through the centre off position. I didn't want to dismantle this mechanism, but simply changing the rectifiers presented no problem. The semiconductor bridge rectifier is a KBPC2504 rated at 400V, 25 Amp that was on offer when I bought them. I would think there are others at a better price now. 25 Amp rating gives a sizable working margin which may not be necessary but for the money it made little difference. However, I would suggest rating any bridge at 400V to be able to cope with inductive spikes which it will be subjected to in use. I have observed spikes of this magnitude in transformers. It was also the same physical size and had a centre hole to be able to bolt it into place. In comparison, my Duette most certainly has what looks pretty much like asbestos. I can not find my pics of the Duette to show here though. After dismantling to have a look, it is presently in a sealed plastic bag in the back of my garage whilst I decide what to do with it.

A quick google confirms this is the case in Australia (very sensible!), but a longer google for the UK seems to show that our Health and Safety Executive only give advisory guidance concerning the sale of asbestos containing equipment. There do not seem to be any laws or sanctions actually stopping selling it in the UK. Just to remind people, over 5000 people die of asbestos related diseases every year in the UK alone. file:///C:/Users/Whato/Downloads/Asbestos-related_disease_statistics_Great_Britain_2022.pdf

I can't argue with this.

I was going to say this, too. Like this one. https://uk.banggood.com/Topshak-NPS605W-110V-or-220V-0-60V-0-5A-Adjustable-Digital-DC-Power-Supply-300W-Regulated-Laboratory-Switching-Power-Supply-p-1587471.html?rmmds=detail-topright-recommendation&cur_warehouse=HK&ID=47757&trace_id=a6f11689854732771 On offer presently at £67 which fits in well with what we normally spend on our hobby. Besides complete voltage control, there is one major advantage to using something like this for testing. It has a readout of the current your locomotive may be taking. A very important and useful bit of info telling you about the health of your electric motor and wheel bearings etc. You could use your multimeter, but it is so much easier and convenient to have the facility built into your power supply. And once you have such a power supply you will find it useful for many other things. The one I have referenced here would work well as a automobile battery or other types of battery charger (But you would have to know what you were doing). I was able to experiment with my veteran Hornbydublo and see the effect of using modern magnets etc. by monitoring the current. As to your desire to use an old laptop power supply, I think that is a useful question here. There must be many of these supplies lying around in junk boxes. I think though that the problem will be in the cutout sensing abilities of these supplies. See: https://electronics.stackexchange.com/questions/264862/how-can-i-use-this-hp-power-supply-as-hobby-power-supplly And then you have the problem of controlling the output which has already been discussed here. Edit addition Just found this very cheap PSU. On offer for £7 approx. Made in China so who knows what the quality may be? Worth a punt? Doesn't go below 4V which may be a problem. Also only voltage reading, no ammeter. https://uk.banggood.com/AC-or-DC-Adjustable-Power-Adapter-Supply-4-24V-2_5A-60W-Speed-Control-Volt-Display-EU-or-US-or-AU-or-UK-Plug-p-1988898.html?cur_warehouse=CN&ID=47184&rmmds=search

I grew up in Montreal, Canada in the 1950's and had the now very rare 3 rail Hornbydublo CPR freight set complete with the rare CPR caboose. When we returned to the UK I decided to return the engine and the caboose back to their British bases. So I pulled the top cabin off of the caboose and sawed off the cow catcher off of the engine! I never finished the re-conversion and most of my Hornbydublo disappeared when I left home. However, I did find some of my track and rolling stock. Best of all, my F8 2-4-0 which I had bought at our local five and dime shop with my hard earned paper round money, had survived. Many years later I was at a local model train exhibition and I heard this wonderful sound from across the room. It was the sound of Hornbydublo metal wheels running on the tin plate 3 rail track. It brought back such terrific boyhood memories of my train set so I dug out my F8 engine and my remaining rolling stock and started building up a collection of Hornbydublo 3 rail. E-bay was new and provided a very easy way to source bits and pieces and I also found that model shops usually had a few. I have a couple of foldable tables and I occasionally get out my Hornbydublo but we don't have the space to set it up permanently. My collection has got a bit out of hand I'm afraid but I haven't replaced my CPR originals. I am just not prepared to spend the silly money required!

So you are an expert on asbestos and the harm it causes? And there are other causes of harm in our environment so that excuses us in ignoring it when we come across asbestos ? You just can not make statements like this.

If you are going to mess about with the insides of a H&M Duettee, be aware that the rheostat is wound on something that looks awfully like flaky asbestos. It is actually described as asbestos in a user manual, but in those days, "asbestos" was sometimes used generically for any heat resistance mat material.

2500 deaths in 2017 from mesothelioma which is almost exclusively caused by asbestos. https://www.theguardian.com/society/2019/jul/07/britains-death-toll-from-asbestos-at-crisis-level-figures-reveal

Basically I don't think I could recommend these old H&M controllers.

I was given a Duette that was making a buzzing noise. The first thing that I saw was that the case had been riveted in place, instead of the self tapping screws I have noted in all my other H&M controllers. In view of the possibility of there being asbestos inside, I did wonder if this was H&M's response to the presence of the asbestos. They could have deemed it safe if it can not be disturbed. In the pic you can clearly see the material holding the nichrome wire of the rheostat / potentiometer to be a white flaky material which could well be asbestos. It is apparently the flaky nature that indicates the hazard. The asbestos dust of around 5 microns in size can be breathed in but can not be removed by the body and remains in the lungs doing mechanical damage to the vulnerable parts of the lungs which can result in cancers 20 years later. This Duette does not have selenium rectifiers but has two bridge circuits using 1N4002 silicon diodes which are 1 Amp, 100V rating. This worries me because the output of each half of the Duette is rated at 1 Amp, so presumably the thermal cutouts shown beside the diodes are set to trip at slightly more than an amp, and considering the comparative slow cut out time of the thermal device, I would think that the diodes could be subject to quite a bit of stress in normal operation. Coupled to that, I would also have to wonder if the inductive spikes that can be caused by making and breaking the current through the inductance of the transformer (L dI/dt ) exceed 100V. You can see that the transformer itself has two separate windings, one for mains and one for the 16V secondary windings and thus complying with double insulation requirements, not needing or having an earth. I think this dates this particular Duette to later than the mid 70's. Mind you, I am not impressed with the cardboard type material that is separating the mains connections to the transformer windings from the case metal work. You can see this in the picture as the blue sheet just behind the nut and bolt holding the cable clamp. The fault with this particular Duette would appear to be something causing one of the thermal cut outs to oscillate on and off with a period of about a second. Either a faulty cut out or a short circuit somewhere in the circuit such as a faulty diode. In any case, looking at the state of the asbestos looking material I am loathe to investigate any further.