DaveDDS wrote on 2025-07-15, 12:22:I've never been a huge fan of using bulbs for dummy loads (but I do sometimes which it's the only choice)
The main problem with […]
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I've never been a huge fan of using bulbs for dummy loads (but I do sometimes which it's the only choice)
The main problem with them is that they are designed to "come on fast" which means the resistance is quite
a bit lower when they are cold, and increases as they get to temperature.. in other words the resistance (and
hence the current drawn) changes more than it normally would)
Correct.
Which is why I almost never use bulbs higher than 30-35 Watts - the "cold" resistance gets really low with the higher wattage bulbs, and that sometimes can trigger PSU short-circuit protection. On that note, halogen bulbs are even worse. But in any case, even with those, I can usually use up to 35W bulbs - at least on the 5V rail. The 12V rail being higher voltage, I stick to 20-25W or less.
DaveDDS wrote on 2025-07-15, 12:22:
This can have effects like: The PSU comes on, up to voltage and then goes into an oscillation as the load goes in/out
of it's required regulation range - fortunately this is usually visible as the bulb "flashing".
I don't think I've ever had that happen... or not quickly enough anyways.
PSUs are supposed to "crowbar" and not be able to restart after short-circuit protection kicks in until PSU is power-cycled.
Of course, a lot of the older TL494 / KA7500 -based (voltage-mode PWM controller half-bridge) PSUs don't always do that... so I guess you may indeed see the bulb flash in 1-2 second intervals as the PSU starts up, trips SCP, then restarts and repeats the whole cycle again.
DaveDDS wrote on 2025-07-15, 12:22:
Very good as "current limiters" however - I use bulbs when testing low- draw equipment which might have a
short - as the current draw goes up so does in inline resistance (and also gives you a nice visual indication the
current in excessive)... FWIW
Same here.
I use these on a lot of my low-power breadboard projects.
Really helpful if you mis-wire anything, so instead of magic smoke, you get a bulb lit.
Of course in the case of electrolytic caps connected backwards (Electroboom moments 🤣 ), the bulb still might not save you (0r rather, the cap that was connected backwards.)
DaveDDS wrote on 2025-07-15, 12:22:When I was designing the windmill controllers, there were times when you had to quickly "slow it down" when the
wind got too str […]
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When I was designing the windmill controllers, there were times when you had to quickly "slow it down" when the
wind got too strong .. as you turned it out of the wind - this was done with "heavy load". Which means I still have a few
HUGE wire-wound heavy load 150 Ohm resistors (think 12x4 inches) - these make really good dummy PSU
loads (but most people won't have them)
Well, if you want high-power "resistors" that everyone likely has in their home: toasters, sandwich makers, space heaters/radiators, stove/burner elements (if you're in the US/NA and have an older stove with user-replaceable "coiled" burners), hair dryers, heat guns, coffee makers, clothes irons ... well, I could probably go on and on here.
But basically, any of these can be used as a high-power resistor, usually - just have to make sure they don't have any "smart" electronics or MCU-based controls, as those will get in the way.