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300W Resistive load?

G

Grant

Jan 1, 1970
0
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.



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?
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.
 
G

Grant

Jan 1, 1970
0
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... :)

Yup, fairly easy to make and use.

I'm doing something like that with 17W resistors for a hybrid power
DAC I'm building. Except I'm using a strip of copper clad each end
of 8 x 17W resistors, and they'll be bolted to a framework made with
M5 allthread and spacers with a 120mm fan at one end for cooling.

Also done low value 0.1% resistors: 121 x 12R1, 0.1% for 100 mOhm
and 120 x 120R 0.1% for 1 Ohm calibration resistors at reasonable
currents.

Grant.
 
H

Hammy

Jan 1, 1970
0
[snip]
Decent converter should handle that? Not like 8:1 lamp hot:cold is
a short circuit, almost a short ;)

It should be able to handle starting into a short. The inductor would
saturate but the controller wont come on until on the caps charge up
and it passes its UVLO anyway's.

I measured the resistance from the fuse to the bridge rectifier its 4
ohms that includes a 5A, 2.5oHm NTC. So at the max current at worst
case line peak would only be about 40A. That's well within the ratings
of anything in the inrush currents path.

You should test a supply into a short anyway's, this just saves me
some time two birds with one stone.;-)

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?

Yep that's what I'm going to do. Its the easiest and takes up the
least room. I can just put the lamps down on the floor out of the way.

Over here they've banned incandescent lamps already, only those new and
expensive hi-voltage halogens available :(

I suspect that will eventually start happening here as well.
 
H

Hammy

Jan 1, 1970
0
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... :)

...Jim Thompson
I'm starting to get a collection of 5 to 10W resistors but I dont have
quite that many yet.;-)
 
N

Nico Coesel

Jan 1, 1970
0
Hammy said:
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.
 
T

Tim Williams

Jan 1, 1970
0
Nico Coesel said:
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
 
H

Hammy

Jan 1, 1970
0
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.
 
J

Joerg

Jan 1, 1970
0
Paul said:
Ceramic lamp sockets are cheap and available at any hardware store. And
they are UL listed and approved for the purpose. No need to hack
soething for which an easy solution exists.

Ceramic sockets usually cost several times the price of a bulb:

http://www.acehardwareoutlet.com/productdetails.aspx?sku=32508&source=GoogleBase

Just take every other bulb out of the bathroom fixture. And if the wifes
makeup looks a bit funny afterwards, just keep your mouth shut.

Oh, that'll get you several slaps with the handbag next time she looks
into a mirror :)
 
N

Nico Coesel

Jan 1, 1970
0
Tim Williams said:
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. :^)

If you use transistors that can handle 200V (or way more) like I did
there is no problem.
 
T

Tim Williams

Jan 1, 1970
0
Nico Coesel said:
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 average HOT may do. Then again, maybe not; 2SC5404 shows only 0.11A at 200V.

Tim
 
J

Joerg

Jan 1, 1970
0
Vladimir said:
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.
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 ..).
 
N

Nico Coesel

Jan 1, 1970
0
Tim Williams said:
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.
 
E

ehsjr

Jan 1, 1970
0
Jim said:
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
 
G

Grant

Jan 1, 1970
0
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.

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.
 
U

Uwe Hercksen

Jan 1, 1970
0
Hammy said:
Sounds good one 60W bulb is about 200 ohms.I'll look around for some
small cheap bulb mounts.

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
 
H

Hammy

Jan 1, 1970
0
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.
 
T

Tim Williams

Jan 1, 1970
0
Grant said:
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.

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 shitty 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
 
J

JosephKK

Jan 1, 1970
0
Probably not quite. First, there'll be another election before then and
... well, we'll see.

Then the ban extends down to 40W AFAIK. I am sure some clever business
will start selling 39W light bulbs. The basic idea seems to come from
Poland:

http://mojapolskadomowa.blox.pl/resource/zarwka99w.jpg

A gray market might also develop. In Germany where 100W bulbs have been
banned long since they are still happily selling them:

http://www.lampenwelt.de/Leuchtmittel/Gluehlampen/E27-Gluehlampen/E27-15W-100W-Gluehlampe-matt.html

As for frosted ones which were particularly frowned upon by regulators
the page states "Bei Lampenwelt.de erhalten Sie matte Glühlampen noch
aus größeren Restbeständen. Lieferung sofort ab Lager solange der Vorrat
reicht!" which means " ... frosted light bulbs from large overstock.
Prompt delivery as long as stock lasts!". For some reason it must have
lasted more than a year by now :)

Ban, compliance, two different things it seems.

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.
 
J

JosephKK

Jan 1, 1970
0
Yeah.... and then we'll have to deal with all the advertising hype for
those "innovative" companies that come up with a 39.9 W bulb and claim
some benefit derived therefrom.

I wonder if this is how that extra 9/10th of a cent per gallon we pay
at the gas pump came into being..??? :)

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. &,(
 
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