RMweb Premium corneliuslundie Posted February 2, 2015 RMweb Premium Share Posted February 2, 2015 Some time ago I bought a couple of 240:16V transformers to build a power pack; also two bridge rectifiers to give me two nominally 12V dc supplies. I cannot now for the life of me find the rectifiers. Can anyone suggest a suitable source? I looked at the RS website but it completely confused me. Jonathan Link to post Share on other sites More sharing options...
Brian Posted February 2, 2015 Share Posted February 2, 2015 Hi Assuming your transformers are not able to provide more than a couple of Amps per winding then.. these?.... http://www.bitsbox.co.uk/index.php?main_page=product_info&cPath=140_141_146&products_id=946 Just £1.75 P & P charges too. These will suit any transformer up to around a 5Amp output.. From your local Maplin store (More expensive though) http://www.maplin.co.uk/p/kbpc601-6a-bridge-rectifier-ar80b Link to post Share on other sites More sharing options...
RMweb Premium corneliuslundie Posted February 2, 2015 Author RMweb Premium Share Posted February 2, 2015 Many thanks both of you. I'll, follow up your suggestions. Jonathan Link to post Share on other sites More sharing options...
CourthsVeil Posted February 2, 2015 Share Posted February 2, 2015 Jonathan, pls bear in mind that a rectifier will not simply reduce the output to 12V. In addition a transformer rated at 16V (this is the average) will deliver waves with max 1.4x16V = 22.5V. Much too much for analog technique (OO, N should even be less). Regards Armin +edit: you might get more info reading this page… Link to post Share on other sites More sharing options...
Simond Posted February 2, 2015 Share Posted February 2, 2015 Good link Armin Thx Simon Link to post Share on other sites More sharing options...
DCB Posted February 3, 2015 Share Posted February 3, 2015 Maplin have 10 amp and 25 amp bridge rectifiers fpr £2.50, 25 amp should last for ever, big chunky Lucar connectors etc, just bolt it to a metal case for a heatsink. Not sure what CorthsVeil is on about, passage through the four diodes will knock the nominal voltage back anything from 0.7 to over 1 volt per diode so the nominal 16 volts will drop to a nominal 12 volts ish, many controllers peak at 22 volts or more but actually measuring it is a challenge. Link to post Share on other sites More sharing options...
kit basher Posted February 3, 2015 Share Posted February 3, 2015 Alternatively, you could just use an old computer P.S.U. I swear by them, all my building and street lamps run off one and I use another one as a bench supply. Almost perfect rectification and you can have 3, 5 & 12 volt outputs. Link to post Share on other sites More sharing options...
Simond Posted February 3, 2015 Share Posted February 3, 2015 And they're cheap, and the pin-out data is available on Wikipedia and elsewhere on line. Best Simon Link to post Share on other sites More sharing options...
Crosland Posted February 3, 2015 Share Posted February 3, 2015 PSU's from PC's have indeed been (ab)used in the past, but if you need to ask, you don't have the knowledge to use it safely! Besides, Using a (fully enclosed) PC power supply is a lot safer than building something connected to the mains, which got the topic banned last time we tried to discuss it. You might burn yourself on the load resistor that is often needed to get them to turn on, but there is no shock hazard. Andrew Link to post Share on other sites More sharing options...
DCB Posted February 3, 2015 Share Posted February 3, 2015 Sorry David, but there's a flaw in your reasoning: the 16V is AC, so any rectified DC will have a peak of 16x1.4=22.6V, while the voltage drop due to the diodes is only 2x0.7=1.4V It is therefore entirely reasonable to expect at least 20V DC on the output of the rectifier. Yes. I forgot current only passes through 2 diodes at any one time, but the same peak voltage applies to mass produced controllers anyway so why is this a problem? Computer PSU's may be the answer, they are widely available for free in old computers so why not just stick an old computer under the baseboard and plug your 5 volt gizmos into the USB ports. The old CD drives have some great motors in as well...and gears. Link to post Share on other sites More sharing options...
Crosland Posted February 3, 2015 Share Posted February 3, 2015 Some time ago I bought a couple of 240:16V transformers to build a power pack; also two bridge rectifiers to give me two nominally 12V dc supplies. What is the application? I.E. is the 12V critical? If so then you will also need smoothing capacitors and voltage regulators, chosen appropriately for the current you need to supply. Even if it's not critical, the rectified supply will still only be full-wave and not smooth. The smoothing capacitors may still be needed, which will give you roughly 20V, with some ripple, on full load. Expect it to be higher with a light load due to poor regulation in the transformer. Andrew Link to post Share on other sites More sharing options...
kit basher Posted February 3, 2015 Share Posted February 3, 2015 Without a smoother circuit, the effect of poor rectification would really be noticed if LEDs are to be connected to it, they will flicker like a bonfire, Incandescent light bulbs (grain of wheat etc.) will still flicker but not as noticeable. Motors will work, but at low revs may sound like they are running on diesel Link to post Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.