KingBollock Posted February 24, 2015 Share Posted February 24, 2015 (edited) I didn't really know where to put this... I was mucking about with a PSU I am making and managed to make a stupid, rookie mistake and shorted the live across and earthed chassis of a transformer, tripping the electricity in the house. This causes alsort of problems, but the main thing is that it has destroyed something that is going to cost to repair. My next project is to finish making my own bench power supply. It will have 240v, 12v, 9v and a variable 1.2v to 30v output. I am not thinking that I would like to build a trip switch into it, something more sensitive than the houses trip. I am using fuses, but they're not ideal. If they blow, which didn't happen tonight, they need replacing. Other than wiring a couple of household consumer units, I have never tried working with trip stuff, and I was wondering if anyone might be able to give me a clue where to start, what to be looking at? When I have worked in repair places in the past we always used [url=http://www.amazon.co.uk/dp/B000KFTHUY/ref=wl_it_dp_o_pd_nS_ttl?_encoding=UTF8&colid=17XQW8G0NYZJK&coliid=IQX31EE3IT3PL#productDetails]rat traps[/url], I have been thinking of getting one, but I wonder if there's a version with a built in trip circuit? Edited February 24, 2015 by KingBollock Quote Link to comment Share on other sites More sharing options...
dincz Posted February 25, 2015 Share Posted February 25, 2015 How about including current limiting? This could work: http://www.zen22142.zen.co.uk/Circuits/Power/add-on.html Quote Link to comment Share on other sites More sharing options...
KingBollock Posted February 25, 2015 Author Share Posted February 25, 2015 Thanks. There are quite a few other interesting things on that site, too. At the moment I am considering taking apart an RCD thingumy and installing that. I could just use it as is and have it inline with the mains input, but the layout of my workbench would make this awkward. Quote Link to comment Share on other sites More sharing options...
Woodinblack Posted February 25, 2015 Share Posted February 25, 2015 Most bench power supplies (I have a couple here) have current limiting, which is not only useful for protection, but also a very useful thing for a bench power supply anyway (in fact I am not sure what good one would be without it). On my main one I have a voltage knob and a current limit knob. Doesn't matter if your bench power supply trips at 3 amps if the board you are testing blows up at 50ma! Quote Link to comment Share on other sites More sharing options...
KingBollock Posted February 25, 2015 Author Share Posted February 25, 2015 [quote name='Woodinblack' timestamp='1424890596' post='2701651'] Most bench power supplies (I have a couple here) have current limiting, which is not only useful for protection, but also a very useful thing for a bench power supply anyway (in fact I am not sure what good one would be without it). On my main one I have a voltage knob and a current limit knob. Doesn't matter if your bench power supply trips at 3 amps if the board you are testing blows up at 50ma! [/quote] I will more than likely include current limiting. I haven't come anywhere near to a final design yet. I mostly just wanted a 9v supply in a convenient place on my bench for testing home made pedals but, as the mains goes into the box as is, I decided to include a 240v output, too, mostly for the earth connection for the anti-static mat and wristband. While experimenting recently, I knocked up nicely filtered 9v and 12v outputs, so I will include those, too. And I bought a couple of variable voltage regulators, with the vague idea that I might use them for something. The main reason for including a trip wasn't really for protecting my projects, but to stop anything I did wrong from tripping the house electric. But the ideas are still growing and once I have finished my current projects I will make a proper start on the bench PSU. Quote Link to comment Share on other sites More sharing options...
6v6 Posted February 26, 2015 Share Posted February 26, 2015 tbh a 240v *output* from a bench power supply sounds terrifying As does the fact that a temporary short on your house electrics "destroyed something" - if it's wired properly (you do have a decent/recent consumer unit with RCD trips and MCB's right?) all it should do is trip a breaker. Back on topic, you might consider an auto-resetting fuse of some sort: http://www.maplin.co.uk/p/16a-auto-reset-circuit-breaker-ak08j Not as good as a proper current limiting circuit, but it could be a decent saftey net on the outputs to protect the regulators and transformer. IMHO a normal (low rating) fuse and RCD plug on the 240v side should suffice - if you're regularly shorting mains wiring something is really wrong (sorry, that sounds harsh, but don't hurt yourself! ) Quote Link to comment Share on other sites More sharing options...
KingBollock Posted February 26, 2015 Author Share Posted February 26, 2015 [quote name='6v6' timestamp='1424973022' post='2702527'] tbh a 240v *output* from a bench power supply sounds terrifying As does the fact that a temporary short on your house electrics "destroyed something" - if it's wired properly (you do have a decent/recent consumer unit with RCD trips and MCB's right?) all it should do is trip a breaker. Back on topic, you might consider an auto-resetting fuse of some sort: http://www.maplin.co.uk/p/16a-auto-reset-circuit-breaker-ak08j Not as good as a proper current limiting circuit, but it could be a decent saftey net on the outputs to protect the regulators and transformer. IMHO a normal (low rating) fuse and RCD plug on the 240v side should suffice - if you're regularly shorting mains wiring something is really wrong (sorry, that sounds harsh, but don't hurt yourself! ) [/quote] Our consumer unit was fiddled with last year when we had solar panels installed and has been more sensitive since then, we can't run the washing machine and the dishwasher at the same time, for instance. I didn't fiddle with it. The thing that got destroyed was a UV lamp in a wall mounted fly zapper that I use as a night light (long story). The damned thing is quite temperamental anyway, I just need to have a proper look at it. Last year we had a power cut (caused by a tree branch against the overhead power line, so not my fault) and it also killed one of the lamps in the same unit, along with a UV lamp in a terrarium and a PC monitor. The 240v output on the PSU I am currently using, which is just a plastic box with a fuse, switch and three banana plug sockets, isn't ideal. Which is why I'd like to switch to one of those rat traps when I start putting a proper PSU together. The last time I shorted mains wiring was in 1991. I don't really make a habit of it... That circuit breaker you linked to is just the sort of thing I was hoping for. Quote Link to comment Share on other sites More sharing options...
Dad3353 Posted February 26, 2015 Share Posted February 26, 2015 [quote name='KingBollock' timestamp='1424976519' post='2702550']... The 240v output on the PSU I am currently using, which is just a plastic box with a fuse, switch and three banana plug sockets, isn't ideal. ... [/quote] It's doubtless a dumb question, but could you explain what advantage this has over a normal mains socket..? I'm a bit confused as to its utility. Why use banana plugs with mains..? Quote Link to comment Share on other sites More sharing options...
KingBollock Posted February 26, 2015 Author Share Posted February 26, 2015 (edited) [quote name='Dad3353' timestamp='1424978359' post='2702577'] It's doubtless a dumb question, but could you explain what advantage this has over a normal mains socket..? I'm a bit confused as to its utility. Why use banana plugs with mains..? [/quote] The banana plug sockets are the type that unscrew so you can attach a bare wire to it and fasten it down. It's just handy for when you want to test something quickly without having to install a plug, just like the rat traps. I only really did it because I was going to run mains into a transformer in the box anyway, for a variable supply that I was going to make using a pre made circuit that I thought had just blown a fuse, but it turned out that there was more wrong with it than I thought, so I didn't use it. I also wanted a banana plug for a connection to the earth for my anti-static mat and wristband. Plug sockets are a precious commodity in my hobby room, and most of them are in very awkward places. Which is why I want to bring as much as I can onto the top of my workbench. Edited February 26, 2015 by KingBollock Quote Link to comment Share on other sites More sharing options...
Dad3353 Posted February 26, 2015 Share Posted February 26, 2015 [quote name='KingBollock' timestamp='1424979028' post='2702597'] The banana plug sockets are the type that unscrew... [/quote] OK, I see; be careful with all that, though. I'd be circumspect with the notion of 'test something quickly' in this context. I've had enough warning jolts in my time to no longer (if ever I was...) in [i]that [/i]much of a hurry. Nice to see that you've such a passion for it all, though; you must be doing [i]something [/i]right..! Quote Link to comment Share on other sites More sharing options...
KingBollock Posted February 26, 2015 Author Share Posted February 26, 2015 [quote name='Dad3353' timestamp='1424981452' post='2702647'] OK, I see; be careful with all that, though. I'd be circumspect with the notion of 'test something quickly' in this context. I've had enough warning jolts in my time to no longer (if ever I was...) in [i]that [/i]much of a hurry. Nice to see that you've such a passion for it all, though; you must be doing [i]something [/i]right..! [/quote] I did electronics in college. Even though I have no GCSEs I do have qualifications in electronics (I can't remember what they are, though, either City & Guilds or BTEC. I did get credits in them, though, which is nice). I remember being on one work placement and being annoyed by people bragging about who had had the biggest electric shock. They didn't like it when I suggested that if they were any good they would have got any... I got my first shock when I was about 10. I was messing about with a broken camera and I came across the capacitor... Which I promptly put in a matchbox with a finger sized hole cut out of the side, and took to school... The second was when I was 14 and working in a guitar shop. The owner asked me to fix the phoneline outside the shop, which someone had cut. I got distracted by a police car stopping and arresting a couple of lads that had stolen a bike. The third was when I was 18 and I had forgotten that I had left the other end of the lead I was working on, plugged into the mains. That was the biggest and stupidest one. I haven't had another since. I think the way I usually work with electricity can be summed up by a remark made by a bloke interviewing me for a work placement. He said he had never known anyone go so slow, or be so neat and precise. I got the placement. Quote Link to comment Share on other sites More sharing options...
KingBollock Posted February 26, 2015 Author Share Posted February 26, 2015 I should add, that I have never actually used the mains output of that box, only the earth. In fact, just after fitting a plug to the thing I am currently mucking about with, I looked at it and thought "Huh, I could have just stuck it in there... Oh well.". Quote Link to comment Share on other sites More sharing options...
6v6 Posted February 27, 2015 Share Posted February 27, 2015 Good to hear you're taking care with all this Those rat traps have fuses on the live anyway don't they? Upgrading from the banana connectors (you could always leave just the earth there for the anti-static stuff?) to one of those sounds like an excellent plan, so fitting one with a small value fuse and and RCD plug sounds like cheap insurance to me - good luck! Quote Link to comment Share on other sites More sharing options...
BILL POSTERS Posted February 27, 2015 Share Posted February 27, 2015 I was in the TV trade in the late 60s and 70s. TVs back then had the chassis connected to one side of the mains supply, and there were still a lot of houses with 2 pin 5A sockets, so you couldnt count on it being the neutral side. Also you had to work live to fault find, so 'Pissers' were an everyday thing, both from raw mains and DC, anything up to 25kV. I stlll have the scars on my hands from high frequency EHT, which would jump out an inch and get you. ( There are two little round ones on the heel of my hand which I have been known to claim were where an Adder bit me ) I was always taught to keep one hand in my pocket, that way you wont grab anything earthed and have mains pass through your body. An isolating transformer is a good idea, and if your working on low current things like variable PSUs, wire a 100W bulb in series with the live lead. It wont make any real difference to the supply, but if you short it out, the only thing that will happen is the lamp will light up. Thats good for working on amps or anything else thats blowing fuses as well. Quote Link to comment Share on other sites More sharing options...
Dad3353 Posted February 27, 2015 Share Posted February 27, 2015 [quote name='BILL POSTERS' timestamp='1425039220' post='2703243']... wire a 100W bulb in series with the live lead. It wont make any real difference to the supply, but if you short it out, the only thing that will happen is the lamp will light up. Thats good for working on amps or anything else thats blowing fuses as well. [/quote] Sounds good, but surely one can't use this if that which you're working on draws nearer 100w, or more..? It'll be sharing 220v, and will only receive 110 (if 100w...), or am I missing something..? OK for low wattages, maybe, but not all..? Quote Link to comment Share on other sites More sharing options...
BILL POSTERS Posted February 27, 2015 Share Posted February 27, 2015 A 2A 24V bench power supply, or an amp thats idling wont draw much current through the bulb. No reason not to use a bigger bulb though, 150W say. But an amp when its idling wont light a 100W very brightly, and the point is it will restrict the current under fault conditions. I did say "Low current things" Car bulbs make great dummy loads for PSUs as well by the way. A 21W Stop lamp bulb draws just under 2A for example. Quote Link to comment Share on other sites More sharing options...
Dad3353 Posted February 27, 2015 Share Posted February 27, 2015 [sharedmedia=core:attachments:167485] Quote Link to comment Share on other sites More sharing options...
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