RMweb Premium figworthy Posted May 2, 2015 RMweb Premium Share Posted May 2, 2015 I'm building an enclosure for a Gaugemaster T1 transformer. The input is 230V, and the transformer has 2 x 16V 1amp outputs, how much ventilation should I allow in the enclosure ? The case is ~8 inches square and about 5 inches deep. and is likely to be sitting on the floor (it can be raised to allow air to pass underneath the case). I see that there has been a recent thread on a similar subject raising concerns on the safety side of things. So before anyone gets excited, the input will have a 3 amp fuse, and the output terminals will be fed via 1 amp fuses, and I have a colleague who does electrical safety testing, and he'll be giving it a good going over before it gets anywhere near a mains supply. It won't be used on a exhibition layout, and (unless the roof leaks - in which case I've got plenty of other problems), it will be in a dry location. Adrian Link to post Share on other sites More sharing options...
Brian Posted May 2, 2015 Share Posted May 2, 2015 None. The amount of heat generated by a transformer is minimal at these sort of currents. Look for example at the Gaugemaster M1 cased mains power supply which has no ventilation. Of course any ventilation will never hurt, so long as nothing can be poked in the ventilation apature to contract a live part. Hope the case is not wooden? It should idealy be Plastic - ABS etc or metal and then correctly earthed. Consider using self resetting thermal circuit breakers on the outputs instead of fuses! Example... http://www.maplin.co.uk/search?text=1.0A+Auto+Reset+Circuit+Breaker These will protect the transformers secondary. 1.0Amp Fuses on the outputs will probably need replacing frequently if there is a short on the controller etc! Edit to add M1 reference Link to post Share on other sites More sharing options...
RMweb Premium ColinK Posted May 2, 2015 RMweb Premium Share Posted May 2, 2015 Just curious, why shouldn't the case be wooden? Link to post Share on other sites More sharing options...
RMweb Premium figworthy Posted May 2, 2015 Author RMweb Premium Share Posted May 2, 2015 None. The amount of heat generated by a transformer is minimal at these sort of currents. Look for example at the Gaugemaster M1 cased mains power supply which has no ventilation. Of course any ventilation will never hurt, so long as nothing can be poked in the ventilation apature to contract a live part. Hope the case is not wooden? It should idealy be Plastic - ABS etc or metal and then correctly earthed. Consider using self resetting thermal circuit breakers on the outputs instead of fuses! Example... http://www.maplin.co.uk/search?text=1.0A+Auto+Reset+Circuit+Breaker These will protect the transformers secondary. 1.0Amp Fuses on the outputs will probably need replacing frequently if there is a short on the controller etc! Edit to add M1 reference Thanks for the quick reply. Sounds as though two or three 2mm deep slits down each side will do. I can't foresee the circumstances under which anything would be poked inside, but at that depth, it will limit the options. Adrian Link to post Share on other sites More sharing options...
Poor Old Bruce Posted May 3, 2015 Share Posted May 3, 2015 Just curious, why shouldn't the case be wooden? Wood isn't fireproof. Link to post Share on other sites More sharing options...
Grovenor Posted May 3, 2015 Share Posted May 3, 2015 Wood isn't fireproof. Neither is plastic. Keith Link to post Share on other sites More sharing options...
Poor Old Bruce Posted May 4, 2015 Share Posted May 4, 2015 Neither is plastic. Keith But some plastics are apparently acceptable. Link to post Share on other sites More sharing options...
RMweb Premium kevinlms Posted May 4, 2015 RMweb Premium Share Posted May 4, 2015 I'm building an enclosure for a Gaugemaster T1 transformer. The input is 230V, and the transformer has 2 x 16V 1amp outputs, how much ventilation should I allow in the enclosure ? The case is ~8 inches square and about 5 inches deep. and is likely to be sitting on the floor (it can be raised to allow air to pass underneath the case). I see that there has been a recent thread on a similar subject raising concerns on the safety side of things. So before anyone gets excited, the input will have a 3 amp fuse, and the output terminals will be fed via 1 amp fuses, and I have a colleague who does electrical safety testing, and he'll be giving it a good going over before it gets anywhere near a mains supply. It won't be used on a exhibition layout, and (unless the roof leaks - in which case I've got plenty of other problems), it will be in a dry location. Adrian There is already a pinned thread at the top of the page, which details most of your questions. http://www.rmweb.co.uk/community/index.php?/topic/96233-mains-power-supplies-for-analogue-model-railways/ It ought not matter whether its used for exhibitions or just at home. It needs to be constructed safely. Pointing out that 'it will be in a dry location' doesn't diminish any requirements. If you have a colleague who will be inspecting it, before its plugged in, why not get his input, before you start? Then build it once, correctly. Link to post Share on other sites More sharing options...
14Steve14 Posted May 14, 2015 Share Posted May 14, 2015 I sell open cased transformers and sometimes wonder what happens to them after they have been bought. At least the OP says he will get them tested professionally . Well done. I have for a very long time thought about having made a metal box that could hold up to six little and four large transformers for model railways. They would include all the strain relief bushes, inlet and outlet wiring, fuses, circuit breakers and a cooling fan run from its own small transformer, but as with most things price is always the factor. I have a rough built example somewhere, but but cannot get one made so that it could be sold and not be too expensive. Reading posts like this always makes me want to give it another try. Link to post Share on other sites More sharing options...
Crosland Posted May 14, 2015 Share Posted May 14, 2015 The only real reason to use a transformer is if you require an AC supply. That requirement i sgetting less and less common these days and a switch mode DC power supply will be cheaper, lighter, more efficient and well regulated. Andrew Link to post Share on other sites More sharing options...
RMweb Gold sjrixon Posted May 14, 2015 RMweb Gold Share Posted May 14, 2015 What controllers are on the open market that work with a DC supply then? Link to post Share on other sites More sharing options...
Crosland Posted May 14, 2015 Share Posted May 14, 2015 The OP doesn't tell us it's for a controller I use DCC, I only know one DCC system that requires AC. Link to post Share on other sites More sharing options...
CourthsVeil Posted May 14, 2015 Share Posted May 14, 2015 What controllers are on the open market that work with a DC supply then? For example, the Gaugemaster HH you named in the other thread. Armin Link to post Share on other sites More sharing options...
Crosland Posted May 14, 2015 Share Posted May 14, 2015 For example, the Gaugemaster HH you named in the other thread. Armin Yes, but that's not the sort of DC I was thinking of. It has a rather significant AC component Andrew Link to post Share on other sites More sharing options...
RMweb Premium figworthy Posted May 14, 2015 Author RMweb Premium Share Posted May 14, 2015 The OP doesn't tell us it's for a controller I use DCC, I only know one DCC system that requires AC. It isn't for a controller. There are a still a few accessories out that want a 15V AC supply. Adrian Link to post Share on other sites More sharing options...
CourthsVeil Posted May 15, 2015 Share Posted May 15, 2015 Yes, but that's not the sort of DC I was thinking of. It has a rather significant AC component Andrew A "sort of DC" with a "significant AC component" - an interesting concept, isn't it? Link to post Share on other sites More sharing options...
meil Posted May 15, 2015 Share Posted May 15, 2015 If you put ventilation holes in then you have to ensure that you can't poke a screwdriver (or anything else) in and touch the live mains. Link to post Share on other sites More sharing options...
Junctionmad Posted May 15, 2015 Share Posted May 15, 2015 A "sort of DC" with a "significant AC component" - an interesting concept, isn't it? The term AC is of course often used incorrectly , strictly speaking AC means that there is a reversing current flow, Dc means unidirectional. Hence for example a half or full wave sine wave is technically DC Link to post Share on other sites More sharing options...
Junctionmad Posted May 15, 2015 Share Posted May 15, 2015 If you put ventilation holes in then you have to ensure that you can't poke a screwdriver (or anything else) in and touch the live mains. Sometimes I think we take safety way over the top. why would anyone go to the bother of finding a screwdriver and then stick into into a hole of a box with mains inside. Link to post Share on other sites More sharing options...
Crosland Posted May 15, 2015 Share Posted May 15, 2015 The term AC is of course often used incorrectly , strictly speaking AC means that there is a reversing current flow, Dc means unidirectional. Hence for example a half or full wave sine wave is technically DC I hope you meant to write half wave rectified, or full wave rectified sine waves Andrew Link to post Share on other sites More sharing options...
RMweb Gold SHMD Posted May 15, 2015 RMweb Gold Share Posted May 15, 2015 Sometimes I think we take safety way over the top. why would anyone go to the bother of finding a screwdriver and then stick into into a hole of a box with mains inside. Ask a class full of four year olds this question! Think about their answers, and then ensure that the box is secure from 'foreign object penetration' for now and in the future AND even for when you are not there anymore. Look up IP ratings for electrical enclosures. Kev. Link to post Share on other sites More sharing options...
RMweb Premium kevinlms Posted May 15, 2015 RMweb Premium Share Posted May 15, 2015 Sometimes I think we take safety way over the top. why would anyone go to the bother of finding a screwdriver and then stick into into a hole of a box with mains inside. The OP made a statement on the lines (sorry!), 'that his layout will be kept/operated in a dry location'. Well a model railway usually is, with the way scenery etc is normally constructed. However the power supply ought to be constructed, in a manner where its safe to use. This could include the possibility where the power supply got damp, WITHOUT the owner realising - perhaps away for a period of time. That is why recommend practice is an ABS plastic box. That way its still safe, even if you pass away tomorrow (of course you're aware of the shortcuts of your own work, if any), but the new owner has no way of knowing. Link to post Share on other sites More sharing options...
Junctionmad Posted May 16, 2015 Share Posted May 16, 2015 I hope you meant to write half wave rectified, or full wave rectified sine waves Andrew Doh -yes Link to post Share on other sites More sharing options...
Junctionmad Posted May 16, 2015 Share Posted May 16, 2015 The OP made a statement on the lines (sorry!), 'that his layout will be kept/operated in a dry location'. Well a model railway usually is, with the way scenery etc is normally constructed. However the power supply ought to be constructed, in a manner where its safe to use. This could include the possibility where the power supply got damp, WITHOUT the owner realising - perhaps away for a period of time. That is why recommend practice is an ABS plastic box. That way its still safe, even if you pass away tomorrow (of course you're aware of the shortcuts of your own work, if any), but the new owner has no way of knowing. I would suggest ( and I'm a practicing EE ) that " regulations " allow all sorts of casings , not to mention that most of these apply to commercial offerings. If the OP wants to protect against damp, which is a rather strange specification, then an earthed metal box , that includes the transformer frame and optional electrostatic shield , be used along with a whole house , or local plug based RCD safety device. The metal box will provide a thermal heatsink , as well removing the need to provide ventilation, even then I would suggest a few louvres , these types of boxes are readily available and cheap. In the future standalone commercial linear supplies like this will be hard to get commercially , so we all be building our own. Link to post Share on other sites More sharing options...
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