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Author Topic: 48vDC/300watt switching power supply and RFI noise?  (Read 4301 times)
WB2WIK
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Posts: 20611




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« Reply #15 on: August 23, 2012, 09:37:04 AM »

That's an expensive resistor.  However four 12V automotive headlamps wired in series could be a fairly cheap load that should draw about 200W.  Double that up with another string in parallel with the first and it should draw about 400W.  Headlamps are pretty inexpensive.

I can get two 24V/250watt overhead projector bulbs for $4 on amazon. If these specs expect an AC source, could I expect the DC resistance here to be too much different than the AC impedance at 60hz?

I doubt it.  I'd try them.  O/H projector bulbs get very, very, very hot and are almost always forced-air cooled by a fan to keep them from destroying themselves.  Watch out.
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AC5UP
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Posts: 3893




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« Reply #16 on: August 23, 2012, 10:08:23 AM »

...and many of those lamps are of the quartz halogen variety with an exposed quartz glass envelope.  Fingerprints on the glass can etch and weaken the structure when exposed to the heat of the lamp and in rare cases will implode.  They're high vacuum lamps and can spray extremely hot shards of glass if this happens.

Translation: Quartz halogen lamps are best used inside a proper enclosure and should be cleaned with isopropyl alcohol if there's a chance the glass has been exposed to grease or any other contaminant.

BTW: If you look closely at quartz lamps for common household lighting you'll notice there's a capsule inside the bulb. Lamp within a lamp, so to speak, and that's to prevent the capsule from going ballistic should it fail "ugly".
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N4CR
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Posts: 1672




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« Reply #17 on: August 23, 2012, 02:09:12 PM »

Any idea how I can go about getting some sort of 6.25ohm 400watt resistive load to test it?  I dont really want to "test" it on my expensive new amp.

4 12v headlights in series.
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73 de N4CR, Phil

We are Coulomb of Borg. Resistance is futile. Voltage, on the other hand, has potential.
KB1LKR
Member

Posts: 1898




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« Reply #18 on: August 23, 2012, 05:23:53 PM »

24V 250W projector lamps should be fine, AC or DC. Also 12V 100W (high wattage off road type) halogen headlight bulbs -- string 4 in series for 48V. The projector bulbs sound cheaper though.

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AK4YA
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Posts: 106




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« Reply #19 on: August 24, 2012, 11:25:12 AM »

wow this community is great.  thanks everyone for the suggestions.  and safety warnings
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