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I've seen replies here and in DIYAudio where people suggested the use of light bulb when testing new DIY project. Is the light bulb used because it limits current? if not, what's the principle behind it?Also, do I need to use the light bulb all the time when testing?
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I have been using this setup for more than 30 years in the repair shop, it saves me alot of fuses, output transistors, HOT in the TV.
Hi.A lightbulb will act as a series current limiter to the load (the amp) downstream of it. But once the amp warms up, the lightbulb got
to be bypassed ASAP to provide the full voltage supply needed for the load.Why? A lightbulb tends to consume a MAJOR part of the supply voltage (being in series of the load downstream) when it is lit up due to its pretty high operation resitance.
I am still working on a better solution to half down the 220V AC mains voltage to an 110V rated audio equipment, without using a step-down transformer (a good one without impairing the sound will be hard to find let alone the cost), or a huge piece of series wire-wound resistor which runs hot hot.
I tried serieing lightbulbs of different wattage (hence dfferent operation resistances) but so far I've found the serie lightbulb
eats up to 70% of the mains voltage. No good for testing or running any audio components. Only for limiting starting currents, yes.For my purpose pf halving down the AC mains voltage, a last resort may be a serie AC capactor upstream of the load. Again, where to get the cap of the right capacitive reactance is another hugh issue.
Let's see.
John Curl's suggestion has saved my tweaking butt more than once. I use this approach whenever I apply power to a new project or following a significant tweak. If the bulb comes on and stays on, my project is drawing a lot of power and I shut it down immediately.Peter
The 'light bulb' you refer to is popularly known as "The Fuse Saver", but it saves a lot more than just fuses. The Fuse saver is easily constructed using a common outlet box for wall plugs. You will also need a duplex outlet cover plate and a duplex outlet and a single pole double throw toggle switch, a romex clamp and about a 2-3 ft. line cord with a plug on one end. First, break the strap on the duplex outlet that ties both plugs together. Drill a hole thru the 'knock-out' at one end of the box to accomodate the spdt toggle switch and mount it in that hole. Run the line cord thru the romex clamp at one end of the box and connect it to one pole of the switch and the top outlet and then to the second outlet. Then connect the other pole of the switch to the the bottom outlet.if you have wired it correctly one throw of the switch will connect the top outlet to the bottom outlet, and the other pole will bypass the top outlet and go directly to the bottom outlet. Mark the position of the switch that connects the top outlet to the bottom outlet "Test" and the position that bypasses the top outlet "Run". Finally, get a plug-in adapter to use a lightbulb in a duplex plug available at any hardware store. The wiring has now placed the top outlet in series with the bottom outlet with the switch at the "test" position, and bypasses the top outlet at the "Run" position. To use the "Fuse Saver" install a lightbulb that draws approximately as much curent as the 'device under test', which is plugged into the the bottom outlet. With the switch set to "Test" plug the linecord in. If the lightbulb, which is in series with the 'device under test' and "pads" the circuit glows brightly The DUT is drawing too much current and their is a fault in the DUT that needs to be found and fixed but has prevewnted letting the smoke out of any number of parts. If the bulb glows dimly or not at all everything is O.K. Happy Testing !
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