Thing I got on eBay... - Page 1
Forum section: electronics / beginners

author: GadgetBoy
author_rank: Regular Contributor
timestamp: September 06, 2018, 12:00:52 am
content: So, I picked up a thing on eBay, claims it's a "4000W 220V SCR Motor Speed Controller Module Voltage Regulator Dimmer". I was hoping I could use it to reduce mains voltage to something I could rectify and feed to a power supply. Not trusting some random piece of Chinese electronics, I started doing some research, and it seems it doesn't actually regulate the voltage, it just nips parts of the waveform off - basically changing the duty cycle.Is there a way I could still use this to get 50v out, or should I look for a transformer? Is there a non transformer way I can turn mains (120V) into 50V without a transformer/switching power supply?Sent from my ONEPLUS A3000 using Tapatalk

author: ogden
author_rank: Super Contributor
timestamp: September 06, 2018, 12:21:07 am
content: Quote from: GadgetBoy on September 06, 2018, 12:00:52 amMotor coupled to generator

author: JS
author_rank: Frequent Contributor
timestamp: September 06, 2018, 12:37:30 am
content: capacitive divider?Resistive divider! Nah, not efficent, just a drop out resistor!Ha... 4kW @220V, so you need 18A, 3.9Ω resistor of barely 1260W, then you just connect your load (a bridge rectifier in between). Put a zener, so if the load is unconnected you still get 50V, that's a 900W zener, buy one in the drugstore!Now, seriously, what kind of what are you trying to power up... SCRs are like triacs for DC, or more precisely, to convert from DC to AC but with the kind of waveform triacs do. Power supplies are either linear (with transformer) or switching.You could use something like what you described to make what I think you want, in any case you could need some kind of storage (cap) if you actually need DC with any reasonable ripple. Now you can trigger the SCR at the point, about 3/8 wave after the zero crossing so the output has ~50V peak and you charge that cap for your load to use. Is that what you expect?JSEdit: one thing you might not notice, a half wave rectifier DC is 0.45 times the input voltage, so with a 36A diode you can have your 50V DC you want, it will be a half wave rectified signal, then if you want to get a steady DC and not just some average of a crappy thing, just a cap will make the voltage way too high, so you will need some inductance as well.

author: GadgetBoy
author_rank: Regular Contributor
timestamp: September 06, 2018, 01:05:26 am
content: Quote from: JS on September 06, 2018, 12:37:30 amI'm trying to get 50v DC for this thing -https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%2Fulk%2Fitm%2F401368742041just with materials I have on handSent from my ONEPLUS A3000 using Tapatalk

author: GadgetBoy
author_rank: Regular Contributor
timestamp: September 06, 2018, 01:36:08 am
content: Quote from: blueskull on September 06, 2018, 01:10:52 amSo basically, I should stay far, far away from it. It didn't look safe to useSent from my ONEPLUS A3000 using Tapatalk

author: JS
author_rank: Frequent Contributor
timestamp: September 06, 2018, 01:53:53 am
content: Wait, for that you must use an isolated supply, or it will be dangerous.You must use a transformer or a SMPS which has isolation between input and output. That thing is a SMPS so you won't have any lpwer noise avoiding another SMPS feeding it.JS

author: GadgetBoy
author_rank: Regular Contributor
timestamp: September 06, 2018, 02:57:02 am
content: Quote from: JS on September 06, 2018, 01:53:53 amSo, bite the bullet and get a 350w meanwell?Sent from my ONEPLUS A3000 using Tapatalk

author: Stray Electron
author_rank: Super Contributor
timestamp: September 06, 2018, 03:02:35 am
content: FWIW, I have a good number of Meanwell supplies that I've taken out of surplus equipment and they work very well.

author: Circlotron
author_rank: Super Contributor
timestamp: September 06, 2018, 03:21:03 am
content: If you are going to rectify and filter AC that has been chopped by a triac or scr you *must* use a choke input filter. If you don’t you will have very high peak currents flowing, high ripple and very low power factor. Also in this application there is no isolation so you can’t ground one side of the dc outlet. Touch actual ground and one of the dc wires and even if the dc is set to zero you WILL get a shock. Way better to use a transformer or SMPS.

author: GigaJoe
author_rank: Frequent Contributor
timestamp: September 06, 2018, 03:30:12 am
content: same thing ? :https://www.aliexpress.com/store/product/-/824214_32884751027.html

author: GadgetBoy
author_rank: Regular Contributor
timestamp: September 06, 2018, 03:31:13 am
content: Quote from: Stray Electron on September 06, 2018, 03:02:35 amWanna sell me one? Sent from my ONEPLUS A3000 using Tapatalk

author: GadgetBoy
author_rank: Regular Contributor
timestamp: September 06, 2018, 03:31:58 am
content: Quote from: GigaJoe on September 06, 2018, 03:30:12 amYah, something like that.Sent from my ONEPLUS A3000 using Tapatalk

author: 6PTsocket
author_rank: Regular Contributor
timestamp: September 06, 2018, 06:05:09 am
content: Quote from: GadgetBoy on September 06, 2018, 01:36:08 amThere are already millions of circuits like that in daily use. I hardly consider them dangerous. They control incandescent lamps and universal motors found in corded drills routers and other power tools. They even work well with some LED bulbs. I have a table lamp that dims to almost nothing with an LED and old style dimmer. They are wall mounted in many homes. I have heard nothing about outlawing them in the US. They are not the answer to your project but they have their uses. They are especially good for resistive loads thst don't care about wave shape. They are cheap and simple.Most dimmers of this type have a little noise suppression built in.Sent from my SM-G900V using Tapatalk

author: GadgetBoy
author_rank: Regular Contributor
timestamp: September 06, 2018, 06:34:04 am
content: Quote from: 6PTsocket on September 06, 2018, 06:05:09 am*blink* This is excellent information. You just helped me realize that I can use it for my carbon fibre heating cable. I attached a picture of the thing. I was working on tracing the schematic, if you're interested.Sent from my ONEPLUS A3000 using Tapatalk

author: oPossum
author_rank: Super Contributor
timestamp: September 06, 2018, 08:43:24 am
content: 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/312215564219That 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.

author: ArthurDent
author_rank: Super Contributor
timestamp: September 06, 2018, 12:26:23 pm
content: "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.

author: 6PTsocket
author_rank: Regular Contributor
timestamp: September 07, 2018, 05:21:24 am
content: 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 pmSent from my SM-G900V using Tapatalk

author: ArthurDent
author_rank: Super Contributor
timestamp: September 07, 2018, 01:12:46 pm
content: 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.

author: drussell
author_rank: Super Contributor
timestamp: September 07, 2018, 01:21:45 pm
content: Quote from: oPossum on September 06, 2018, 08:43:24 amWow, 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....

author: GadgetBoy
author_rank: Regular Contributor
timestamp: September 07, 2018, 07:40:07 pm
content: Quote from: oPossum on September 06, 2018, 08:43:24 amSadly, they won't ship it to Canada...Sent from my ONEPLUS A3000 using Tapatalk

author: drussell
author_rank: Super Contributor
timestamp: September 08, 2018, 02:45:51 am
content: Quote from: GadgetBoy on September 07, 2018, 07:40:07 pmAt that kind of price for the actual item, a person could probably use a re-shipping service and still come out ahead, even after paying for two rounds of shipping, if you don't happen to know anyone in the U.S. that could forward it on to you after shipping to their U.S. address.