Electronics > Beginners
Thing I got on eBay...
ArthurDent:
"There are already millions of circuits like that in daily use. I hardly consider them dangerous."
All the examples that follow this statement on uses of dimmers/motor speed controllers are ones where the device and the load are completely enclosed and there isn’t any chance of a user touching any part of the circuit. Lamp with built-in dimmers, variable speed power tools, etc., do not allow you to touch any electrical connections. The uses that are listed are also examples where you don’t care about the waveform distortion. If you’ve ever tried to pull the trigger on a variable speed drill to just start it turning you can feel how jerky it reacts with the low duty cycle pulses fed to the motor.
What you show you want to use this dimmer for is powering a bench type power supply module where you will continually be touching connections to connect and test circuits you’ve thrown together and as some posters have pointed out, without isolation this will be very unsafe. You could easily destroy equipment or seriously shock yourself. Basically all commercially built bench supplies intended for general use have isolated outputs. This means either a line transformer in linear supplies or a high frequency transformer in SMPS units. I agree that a properly connected and grounded Meanwell or other quality SMPS would work well with the module you show and be safe, although I’d still prefer a dedicated bench supply where everything is in one case and I don’t have wires running between all manner of bits and pieces. Cost wise a commercially built bench supply from China is probably going to be about the same price as this thrown together mess and probably perform better.
6PTsocket:
Any line (mains) powered board style device use assumes the user has enough knowledge and common sense to provide proper insulation from exposure to high voltage. Are there better speed controls? Sure. But in many cases a triac is good enough and perfect smooth performance to the lowest speed is not an issue On routers the speed is preset before use. I have many variable speed trigger tools and I never even thought about the problem you mentioned and they always did the job.
--- Quote from: ArthurDent on September 06, 2018, 12:26:23 pm ---"There are already millions of circuits like that in daily use. I hardly consider them dangerous."
All the examples that follow this statement on uses of dimmers/motor speed controllers are ones where the device and the load are completely enclosed and there isn’t any chance of a user touching any part of the circuit. Lamp with built-in dimmers, variable speed power tools, etc., do not allow you to touch any electrical connections. The uses that are listed are also examples where you don’t care about the waveform distortion. If you’ve ever tried to pull the trigger on a variable speed drill to just start it turning you can feel how jerky it reacts with the low duty cycle pulses fed to the motor.
What you show you want to use this dimmer for is powering a bench type power supply module where you will continually be touching connections to connect and test circuits you’ve thrown together and as some posters have pointed out, without isolation this will be very unsafe. You could easily destroy equipment or seriously shock yourself. Basically all commercially built bench supplies intended for general use have isolated outputs. This means either a line transformer in linear supplies or a high frequency transformer in SMPS units. I agree that a properly connected and grounded Meanwell or other quality SMPS would work well with the module you show and be safe, although I’d still prefer a dedicated bench supply where everything is in one case and I don’t have wires running between all manner of bits and pieces. Cost wise a commercially built bench supply from China is probably going to be about the same price as this thrown together mess and probably perform better.
--- End quote ---
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ArthurDent:
6PTsocket - "I have many variable speed trigger tools and I never even thought about the problem you mentioned and they always did the job."
I'm not saying they are a problem in their intended use on power tools, just that you can see (or feel) from the pulsations when you just start to pull the trigger how a PWM speed control can produce narrow high voltage pulses. Some electronics are sensitive to input waveform and might not work or be damaged by things like D.C. to A.C. inverters that put out a square wave. That is why you see how inverters over the years have gone from square wave, to stepped square wave, to true sine wave outputs.
These lamp dimmer controls are more power controls than voltage controls and using one as a voltage control could easily destroy whatever low voltage device you connect it to. From a math standpoint the output is integrating the area under the curve but the pieces that make up the area can be narrow high voltage spikes of varying widths. See graph I grabbed off the internet.
drussell:
--- Quote from: oPossum on September 06, 2018, 08:43:24 am ---For example, some Sun midsized systems use 48V power supplies. Searching for 'Sun power supply' found this...
https://www.ebay.com/itm/312215564219
That is ~1 kW for under $20. Using a power supply like that will require figuring out the pinout, and dealing with the hot swap connectors. Usually not too difficult.
--- End quote ---
Wow, that is actually quite the deal. It even does 41A at 48V if you power it from 200-240V. It also has a 12V 20A output. That is a pretty good bargain for $20....
GadgetBoy:
--- Quote from: oPossum on September 06, 2018, 08:43:24 am ---48 VDC power supplies are used in telco, networking, and some computers. They can be found for cheap with the right search terms. The trick is to find some common product that used one and search for the part number of the product or the power supply used in it. Most sellers don't list the specs of the power supply so searching for '48V DC power supply' will not find the bargains.
For example, some Sun midsized systems use 48V power supplies. Searching for 'Sun power supply' found this...
https://www.ebay.com/itm/312215564219
That is ~1 kW for under $20. Using a power supply like that will require figuring out the pinout, and dealing with the hot swap connectors. Usually not too difficult.
--- End quote ---
Sadly, they won't ship it to Canada...
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