If you use transistors that can handle 200V (or way more) like I did there is no problem.
Take a 25W wirewound resistor and put it into a bucket of water.
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.
Vladimir Vassilevsky DSP and Mixed Signal Design Consultant
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 average HOT may do. Then again, maybe not; 2SC5404 shows only 0.11A = at 200V.
Tim
--=20 Deep Friar: a very philosophical monk. Website:
On a sunny day (Sun, 18 Jul 2010 13:31:49 -0500) it happened "Tim Williams" wrote in :
TO3 MOSFET BUZ44A 4.8A 600 V (siemens) Was quite common.
I used hundreds.
1: Several space heaters of like wattage, all in series (assuming that their power consumption is in the 1kW range). 2: Several incandescent light bulbs. If you live in a 120VAC country, make series pairs and connect pairs in parallel until you're drawing your desired current. If you live in a 240VAC country, just use single bulbs, adding them in parallel until you're happy.
They'll draw somewhat less current, because of the lower voltage, but it won't be a simple 200/240 relationship because they'll run cooler and therefore with lower resistance.
So, e.g., three sets of two parallel 50W, 120V light bulbs should burn off something around 280 or 290W. Ditto three 100W, 240V bulbs.
Fine tune with 7W night light bulbs, and maybe 25W refrigerator bulbs.
12V car bulbs would work, too, but you'd need a string of 16 in series to get up to 200V; figuring out which bulbs to get -- if there are any small enough to be suitable -- is left as an exercise to the reader.
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.
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 ..).
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.
Unless it was slightly less old and used TO-3 MOSFETs, which Idunno, might be worth something on eBay. :^)
handle the voltage just fine, as long as there's enough for the power.
Clever! Ed
needed.
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
But not up at 200V? Low voltage, high current is easy, transistor SOA at high voltage not so easy?
I made a controlled load, eight transistors on one side of a two piece box type heatsink, eight 0R33, 50W resistors series/parallel on other side, with a fan at one end, could do up to 600W (30V @ 20A) loads.
Live heatsink 'cos insulator cost too much in thermal resistance. Needed a heat spreader piece of 3mm thick aluminium between transistors to heatsink to help the heat transfer.
Grant.
needed.
Why copper sheet, when I had G-10 all over the place? ...Jim Thompson
Hammy schrieb:
Hello,
the resistance of the bulb depends heavily on the filament temperature, take a resistance meter and measure the cold 60 W bulb, you will be surprised.
Bye
Hi Uwe
I already knew that, and it was also brought up several times in the thread.
Their are a few reasons why I'm not concerned about it I'm useing a
500VA isolation transformer (winding resistance) and the measured resistance from the fuse to the bridge rectifier is in excess of 4 oHms this includes a 2.5 oHm NTC. So when you consider all the R the inrush current cannot be above 35 to 40A worst case.This is a boost topology so whats in the inrush path? the bridge and the PFC choke and the output rectifier. The rectifiers are rated for
100A or better surge current. The inductor saturates at start-up, so what it would anyway just from the inrush from the 390uF output cap. The controller wont start probably until after the surge anyways,if it were actually to start it should enter hiccup mode.
The nice thing about high voltage is, you can just cascode them. Stack = collector to emitter and bases to voltage dividers. Put a rheostat in = the bottom emitter to control current. Then you don't have to worry = about emitter resistors at all, and 2nd breakdown is now hundreds of = volts away.
You get s***ty hFE on most HV transistors, so the bottom transistors = carry more current, but the base voltage divider will sag under load, = approximating equal power dissipation for some loads. So it's not = terrible.
Tim
--=20 Deep Friar: a very philosophical monk. Website:
Oh yea. They forced a stop of manufacturing, but the existing inventory should last well past 2020, allowed to be sold while the supply lasts. Moreover, it does not much affect specialty lamp versions.
Marketing. Just $9.99. Thus under $10. Humans tend to brain slip on this, sometimes to the point of thinking $8.88 is more than $9.99. Marketing. &,(
A typical electric clothes iron (flatiron for those that remember) is about 450 W rated, with a bang-bang temperature controller.
I have actually seen those sold for room heaters (with dish reflector) at powers a high as 1000 W.
Unless it was slightly less old and used TO-3 MOSFETs, which Idunno, might be worth something on eBay. :^)
handle the voltage just fine, as long as there's enough for the power.
Yup. Also works fine with pairs and any air blocker to make a tunnel. There will be a thermal gradient along the tunnel, with FETs this works in your favor though.
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