Path: ...!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail From: legg Newsgroups: sci.electronics.design Subject: Re: dumping a lot of heat Date: Sat, 07 Dec 2024 11:49:14 -0500 Organization: A noiseless patient Spider Lines: 60 Message-ID: References: <1r434eh.9mfcivcsdztaN%liz@poppyrecords.invalid.invalid> <1r43vdz.1x4sizvmjxptrN%liz@poppyrecords.invalid.invalid> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Injection-Date: Sat, 07 Dec 2024 17:46:46 +0100 (CET) Injection-Info: dont-email.me; posting-host="e48186248ce5f74a0ca780657656abea"; logging-data="3369205"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX1/7pGdS2f3fRtqKdHhke0po" Cancel-Lock: sha1:hYyWH1/oFwQtVsuSh4TYKVnRN64= X-Newsreader: Forte Agent 4.2/32.1118 Bytes: 3535 On Thu, 5 Dec 2024 22:03:41 +0000, liz@poppyrecords.invalid.invalid (Liz Tuddenham) wrote: >legg wrote: > >> On Thu, 5 Dec 2024 08:55:32 +0000, liz@poppyrecords.invalid.invalid >> (Liz Tuddenham) wrote: >> >> >john larkin wrote: >> > >> >> I'm thinking about building a biggish rackmount dummy load box. It >> >> would simulate series resistance and inductance. Part of the problem >> >> is that it will need to dump a lot of heat. >> >> >> >> We are using copper CPU coolers on PC boards, which are great up to a >> >> couple of hundred watts, but I'd like to do a kilowatt or two. >> >> >> >> https://highlandtechnology.com/Product/P945 >> >> >> >> It would take a heap of expensive extruded heat sinks and fans to get >> >> rid of a kilowatt. At 1 K/W, a pretty good heat sink, that's 1000 degC >> >> temp rise. >> >> >> >> A small hair dryer can dump a kilowatt. So some sort of red-hot >> >> nichrome coils and a vicious fan might work. >> >> >> >> I'd prefer to not use water. >> >> >> >> I wonder if there is some sort of runs-red-hot power resistor. >> > >> >If you are using elements at near red heat, remember you need to keep >> >the radiant heat away from the outer walls of the cabinet. Reflectors >> >just throw the problem elsewhere and eventually will tarnish, the best >> >system is several spaced blackened steel baffle plates with vertical air >> >passages between them (visual black is not always IR black). >> > >> >If you need a rapidly-controllable load, valves can dissipate energy at >> >a much higher temperature than transistors, so they might be worth >> >considering. >> >> https://ve3ute.ca/2000a.html > >Most of my valve designs err on the safe side. Putting electrolytic >capacitors where they can get hot is just plain stupid. I have seen >loads of shoddy radio/audio designs where the cathode resistor was >strapped along the side of the bypass capacitor or the main smoother was >stood up right next to the rectifier or the output valve. By standard 'safe' design, tubes have a pretty limited life. By 1956, the heater was no longer the weakest element in the life equation for these parts - glass electrolysis was. Electrolytic caps and their use has always been an issue. Cuffing the tubes not only enforces distance to other components, but reduces radiant effects in the viscinity. Win, win. RL