300W Resistive load?
in [Design]
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From: Joerg on 18 Jul 2010 16:26 Vladimir Vassilevsky wrote: > > > Joerg wrote: >> Hammy wrote: >> >>> What is something cheap and simple that can be used to dissapate 300W >>> on a 200Vdc bus. I'm trying to think of something I could maybe pick >>> up at a local homedepot or similiar. >>> >>> I need a 300W load to test out my PFC. >> > > Take a 25W wirewound resistor and put it into a bucket of water. > I've done that in the past. Sometimes I used oil though because with water the whole thing often let off an evil hiss and that was a bit spooky. >> >> Light bulbs? Two in series and then as many of those in parallel as >> needed. > > IIRC John Fields posted some measurements on the transient behavior of > the incandescent lightbulbs. There is huge inrush current (~x10 of > nominal) for few dozens of milliseconds. > Yup. Got to connect them one by one, or pair by pair in this case, if the circuit can't handle a short (it should ..). -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Nico Coesel on 18 Jul 2010 16:27 "Tim Williams" <tmoranwms(a)charter.net> wrote: >"Nico Coesel" <nico(a)puntnl.niks> wrote in message = >news:4c431fff.249648812(a)news.planet.nl... >> If you use transistors that can handle 200V (or way more) like I did >> there is no problem. > >I'm just wondering if they were MOSFET or bipolar. TO-3 MOSFETs are = >somewhat old and rare. MJ15025 for instance won't handle more than = >0.17A at 200V, according to the SOA, which is only 34W, out of a rated = >250W. The ones I used are bipolar. I got them from a 150A or 300A 5V PSU. I don't know the part number but IIRC it is some sort of special type for switching purposes anyway. Each transistor is bolted to the heatsink directly for optimum heat transfer (the heatsink is live!). My dummy load actually is an adjustable current sink. A potmeter, a darlington emittor follower and series resistor make the drive for the 'end stage'. The maximum load I ever tested was 400W. -- Failure does not prove something is impossible, failure simply indicates you are not using the right tools... nico(a)nctdevpuntnl (punt=.) --------------------------------------------------------------
From: John Fields on 18 Jul 2010 18:04 On Sat, 17 Jul 2010 09:36:24 -0400, Hammy <spam(a)spam.com> wrote: >What is something cheap and simple that can be used to dissapate 300W >on a 200Vdc bus. I'm trying to think of something I could maybe pick >up at a local homedepot or similiar. > >I need a 300W load to test out my PFC. --- An electric iron?
From: ehsjr on 18 Jul 2010 18:07 Jim Thompson wrote: > On Sun, 18 Jul 2010 08:05:57 -0400, Hammy <spam(a)spam.com> wrote: > > >>On Sun, 18 Jul 2010 06:25:40 -0500, "Tim Williams" >><tmoranwms(a)charter.net> wrote: >> >> >>>"Nico Coesel" <nico(a)puntnl.niks> wrote in message news:4c42bd4b.224380781(a)news.planet.nl... >>> >>>>>What is something cheap and simple that can be used to dissapate 300W >>>>>on a 200Vdc bus. I'm trying to think of something I could maybe pick >>> >>> ^^^^^^ >>> >>>>>up at a local homedepot or similiar. >>>>> >>>>>I need a 300W load to test out my PFC. >>>> >>>>I've constructed an adjustable dummy load by using 4 TO3 transistors >>>>from an old switching power supply. A heatsink and a couple of fans >>>>take care of the heat. The whole thing isn't much larger than a shoe >>>>box. >>> >>>Doesn't work in this case though, you'll be in the second breakdown region. Unless it was slightly less old and used TO-3 MOSFETs, which Idunno, might be worth something on eBay. :^) >>> >>>Hammy might have a few FETs left over from the boost though, they would handle the voltage just fine, as long as there's enough for the power. >>> >>>Tim >> >>FETS I have a lot of. I also have some nice(2) brick heatsinks I >>scavenged from some old microwave oven and car stero ampslifier. >> >>Thta was my original thought but I was thinking it would take to many >>to dissapate the power 275W. >> >>The biggest I have in quantity is the FQA24N50 TO-3PN >> >>http://www.fairchildsemi.com/ds/FQ/FQA24N50.pdf >> >>I have about 30 of those. >> >>Actually those are in a pretty beefy package maybe 5 on a brick with >>a fan might work. >> >> >>I also have about 40 of these FQP27N25 TO-220 >> >>http://www.fairchildsemi.com/ds/FQ/FQP27N25.pdf >> >>Both of those Newark had on for dirt cheap and I was buying ten of >>each everytime I did an order. Figured they might come in handy at >>some time.;-) >> >>I have 1 or 2 IRF350 in to-3 no suitable heatsink for that power >>level. > > > Finned heat sinks, arranged as a square tunnel, fins inward, file, > mill, whatever so they fit together nicely, and the "square" is > muffin-fan size... which fits on one end. > > ...Jim Thompson Clever! Ed
From: John Fields on 18 Jul 2010 18:17
On Sat, 17 Jul 2010 17:06:10 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote: >On Sun, 18 Jul 2010 09:30:22 +1000, Grant <omg(a)grrr.id.au> wrote: > >>On Sat, 17 Jul 2010 09:25:42 -0700, Joerg <invalid(a)invalid.invalid> wrote: >> >>>Hammy wrote: >>>> On Sat, 17 Jul 2010 07:37:28 -0700, Joerg <invalid(a)invalid.invalid> >>>> wrote: >>>> >>>>> Hammy wrote: >>>>>> On Sat, 17 Jul 2010 07:00:35 -0700, Joerg <invalid(a)invalid.invalid> >>>>>> wrote: >>>>>> >>>>>>> Hammy wrote: >>>>>>>> What is something cheap and simple that can be used to dissapate 300W >>>>>>>> on a 200Vdc bus. I'm trying to think of something I could maybe pick >>>>>>>> up at a local homedepot or similiar. >>>>>>>> >>>>>>>> I need a 300W load to test out my PFC. >>>>>>> Light bulbs? Two in series and then as many of those in parallel as needed. >>>>>> Sounds good one 60W bulb is about 200 ohms. ... >>>>> >>>>> At 200V each bulb gets only 100V so the resistance will be a little >>>>> lower. You could measure that if it must be precise. >>>> >>>> I don't need high precision if I can test at even 80% rated load and >>>> maybe do some pulse test and off course use a CT to check the input >>>> current I'll be happy. >>> >>> >>>Well, just wanted to mention that because when at undervoltage the bulbs >>>will present a higher load. Also, when you start any kind of converter >>>from zero they will almost look like a short initially. Same if you >>>connect a cold bulb (cold filament) to a running converter. It's not >>>like a power resistor. >>> >>> >>>>>> ... I'll look around for some small cheap bulb mounts. >>>>> >>>>> You can also solder to them. If careful they can later still be used for >>>>> their intended purpose. But make sure you place them onto a heat >>>>> resistant surface during the test :-) >>>> >>>> Your taking all the fun out of this :-) >>>> >>> >>>The fun might come back when connecting the cold bulbs not two by two, >>>but all at once. Tchk ... *POOF*. >> >>Decent converter should handle that? Not like 8:1 lamp hot:cold is >>a short circuit, almost a short ;) >> >> >>I keep an old fuser element in the cupboard for hi voltage loads, and >>have light bulbs setup for 24V with 12V halogens in series, then proper >>high wattage resistors picked up over time. >> >>Lamps are easiest to hook up, perhaps three or more in series at first? >> >>Over here they've banned incandescent lamps already, only those new and >>expensive hi-voltage halogens available :( >> >>What about an electric heater on low? Got a couple or more to wire >>in series? Raid an electric stove, put elements in series? >>> >>> >>>>> Good news is you may not even have to drive all the way to Home Depot. >>>>> Supermarkets also have a variety of them. Of course, then your wife >>>>> might hand you a lengthy "while you are there anyhow" list and you don't >>>>> get to look at all the new power tools, barbecues and stuff. Man's toy >>>>> store ... >>>> We call that a honey do list here.;-) >>>> >>> >>>Nah, a honey-do list isn't grocery shooping, it's when the missus wants >>>you to get that tree stump out over yonder, and it's 105F :-) >> >>Grant. > >I've been known to take two sheets of copper clad, drill a grid of >holes and solder a hundred or so 2W resistors between the planes, put >a muffin fan on it and away you go... :-) Why copper clad (assuming you meant something like G-10 from back then (FR-4 today)) when copper sheet would have been so much cheaper and, for the same thickness, would have had _much_ better thermal conductivity? JF |