Variable Voltage AC supply- Not a Variac - Page 1
Forum section: electronics / general

author: Purduephotog
author_rank: Regular Contributor
timestamp: February 29, 2024, 08:34:05 pm
content: I looked for this solution once before but came up blank. I currently have a large fan (pulls ~300W@120V), and I use a variac to regulate the speed. It does have multiple windings for low, medium and high, but even the 'low' is too high at times.What I'd love to find is some electronically controllable variable AC voltage supply. I know UPS units do this, as I've rebuilt some of the 'stepped' ones although I haven't tested one of those.I suppose I could also gear the knob in such a way that a standard IOT type device could control it- but with all the projects I still haven't completed...Anything out there you are aware of ?Thanks much-

author: Faringdon
author_rank: Super Contributor
timestamp: March 01, 2024, 08:20:43 pm
content: Hi,I will soon have the attached fully ready for you. (LTspice sim)It is 4 flybacks...acting together....a pair acts on the positive half sine, and another pair on theneg half sine. And you end up with a controlled sine voltage on the cap.You may have to swap the diodes for ones in your version of LTspice.As you can tell, it is superb, it allows you to have an variable output voltage sinusoidal mains inverter with very simple circuitry...and no software needed.Just enjoy the variable sine...and enjoy your slower fan!

author: David Hess
author_rank: Super Contributor
timestamp: March 01, 2024, 10:13:48 pm
content: The all electronic alternative is a sine source driving a class-d amplifier driving a step-up transformer. If only a limited output range is required, then the output of the transformer may be placed in series with the power line to produce an output, so only a fraction of the power has to be supplied from the class-d amplifier.Today lower voltage class-d amplifiers of suitable power are trivially available in the form of class-d audio amplifiers.A linear class-b or class-ab amplifier could so be used, but efficiency will be lower.

author: NiHaoMike
author_rank: Super Contributor
timestamp: March 02, 2024, 12:30:27 pm
content: Replace the motor with a variable speed BLDC one? (They're known as "ECM" in the HVAC industry.)

author: Purduephotog
author_rank: Regular Contributor
timestamp: March 03, 2024, 04:55:28 am
content: That would take all the fun out of rebuilding the fan .. but I'll take a look at the HVAC surplus place near meI'm going to have to read up on the class d amps. Apparently hardware at work uses them but I don't know nearly enough to be contact and certainly hasn't considered using them to drive this fan.And I'll be reloading spice on this machine or sending it into work to try out.Than you all.

author: David Hess
author_rank: Super Contributor
timestamp: March 03, 2024, 09:21:04 pm
content: Texas Instruments also has evaluation boards:https://www.ti.com/audio-ic/amplifiers/speaker-amplifiers/products.html#89=Class-D&2982=Analog%20Input&1055max=Stereo&sort=2622max;desc&The datasheets and application notes give a good idea about what is required. You could just buy an inexpensive audio amplifier.I do not know if anybody makes integrated class-d amplifiers for external discrete power transistors. Some switching regulator controllers can be configured to do it.

author: BrokenYugo
author_rank: Super Contributor
timestamp: March 03, 2024, 09:23:43 pm
content: Maybe hack an inverter for variable voltage?

author: Jeroen3
author_rank: Super Contributor
timestamp: March 04, 2024, 07:18:33 am
content: Quote from: Purduephotog on February 29, 2024, 08:34:05 pmBut you probably don't want to pay for them. They're expensive. Eg: GW-Instek ASR-2050R.

author: Faringdon
author_rank: Super Contributor
timestamp: March 04, 2024, 10:30:41 am
content: QuoteToo rightThis is why the post #2 above is the way forward...nice and simple.

author: Jeroen3
author_rank: Super Contributor
timestamp: March 04, 2024, 01:08:50 pm
content: Did you build one yet Faringdon?@Purduephotog, do you know single phase motors are very poor with speed control?

author: mag_therm
author_rank: Frequent Contributor
timestamp: March 04, 2024, 01:50:24 pm
content: Class D amp Transplant ( Like Post#2):In Dec 2023 I repaired a vintage 30W Electar Guitar amp that had a big pcb containing front panel tone controls etc, and a Class B amplifier at rear.Amplifier was blown up. It was a DC coupled amp something like an op amp with discrete trasistors.With no circuit and tracks melting off, (Hold my beer, ) I put theboard in the scroll saw and cut off the amp section !!Purchased Newark part 53Y1822 ~$17, a 2 by 15Watt single board amplifier by SURE Electronics. Instruction sheet showed how to connect as single 30W.DC Limit for the Class D is a strict +26V, so beefed up the amp's + supply and made a +24V regulator from the one of the original ouput transistors.The amp now gives 14Vrms into the original 4 speakers with equivalent 8 Ohm.One item to be careful of, the output is offset at half of the +DC supply. So I removed the external speaker socket.For present case, search on Newark "SURE Electronics" show a range of these Class D boards rated up to 400 Watt.

author: Stray Electron
author_rank: Super Contributor
timestamp: March 04, 2024, 02:07:12 pm
content: Quote from: Purduephotog on February 29, 2024, 08:34:05 pmHave you considered an AC Power Source made by Elgar or someone like them? They're big and heavy and are expensive to buy new or used but I bought two from an E-scrap yard for a very reasonable price because NO ONE wants to ship them. Look at E-Greed and see if you can find one in your area that you can pickup in person and you should be able buy it for literally scrap price. You can look up the Elgar manuals online and they have everything that you need to know and IIRC many of their models can be externally controlled via GP-IB and also by an external voltage or external resistance. The control panel is a separate unit that plugs in and you can change the frequency range, resolution and a host of other parameters by using different control panels. Elgar makes them in one and three phase output models and a wide range of power output.They're probably OVER-KILL for driving a fan but they'll certainly do the job.I have two of their 251 models and another even bigger three phase one that I bought for abut $75 each and I rarely use them but I keep them around for the odd job where I need a variable frequency, variable voltage AC power with a clean pure sine wave output.

author: f4eru
author_rank: Super Contributor
timestamp: March 04, 2024, 07:39:38 pm
content: A simple VFD with 1-pase input, 3ph output can do the job, even if the motor is single phase:https://www.ebay.com/itm/404171644362?itmmeta=01HR5FJ00N16PXKVPCME096VAH&hash=item5e1a81ddca:g:VRwAAOSwpRZj8xbW&itmprp=enc%3AAQAIAAAAwEQylzpLO4%2Bs7HdD0au1Jy7VshL5jT8ZFab8jJjMYaHQscecGu4HrAvdKC8msz6NUfjDDPlNdiN3ztnE8SNJmYDuXDDi4ERetJdugq0DZ%2BVtyygsAY4LRIvXOFpnrYBDEAZZJIPGunYcsv4w1ofmODWmTJJuI2lKQmc%2BYFHAG8mw6k7ln%2BZz8dRUczJ5n5QKKtwoswD4Xl6%2BAwmIzVppwQwpz3Yl6XDwA5PEi9O7zds2ov2U2RqVRSVdwIeRvVrLnw%3D%3D%7Ctkp%3ABk9SR_yAyK_BYw

author: boB
author_rank: Frequent Contributor
timestamp: March 04, 2024, 07:52:21 pm
content: How about trying the EG8010 sinewave inverter IC ?The module for it is almost complete. Alliexpress also has these for dirt cheap.https://www.amazon.com/EGS002-Inverter-EG8010-IR2110-Module/dp/B09N9RRMXM?th=1I don't know what they mean by LCD module though cuz that isn't part of this PCB AFAIK.boB

author: jonpaul
author_rank: Super Contributor
timestamp: March 08, 2024, 11:33:02 am
content: you describe an autotrsf if have hi/med/low .A Variac variable trsf is NOT what you have.A true Variac will do it and there exit motor controlled variacs.Finally depends on the fan motors type (usually induction motor) there are commercial controlsJon

author: Edison
author_rank: Frequent Contributor
timestamp: March 08, 2024, 12:30:53 pm
content: Single-phase motors can be regulated completely reliably and, above all, without loss of power, by changing the alternating frequency - in this way I have been regulating the motor of a stand-up drill for approx. 20 years - 1kWI made it myself, but a lot of commercial speed regulators are sold - especially for fans that require a running capacitor to run.

author: Purduephotog
author_rank: Regular Contributor
timestamp: March 08, 2024, 01:37:48 pm
content: *blech*https://www.newark.com/gw-instek/asr-2050r/power-supply-prog-500va-5a-350vrms/dp/64AH1904...only 2400$. For a 120$ fan (at the time of purchase).Actually, that sounds about like most of my projects.

author: langwadt
author_rank: Super Contributor
timestamp: March 08, 2024, 01:43:23 pm
content: https://www.aliexpress.com/item/1005003503525539.html

author: Edison
author_rank: Frequent Contributor
timestamp: March 08, 2024, 02:10:43 pm
content: This one is for 230V 300W (here in the CZ it is 230), but you can certainly find it for 120V. It costs 943.20 CZK = 40.86 USD - at our exchange rate. There is a huge variety of types - according to fan control and their power consumption.

author: themadhippy
author_rank: Super Contributor
timestamp: March 08, 2024, 02:14:24 pm
content: QuoteThat looks more like a dimmer switch and not a variable frequency drive

author: David Hess
author_rank: Super Contributor
timestamp: March 08, 2024, 02:31:12 pm
content: Quote from: themadhippy on March 08, 2024, 02:14:24 pmIt is a phase control dimmer. They work for typical AC fan motors, but poorly with little control at lower speeds, and they are electrically noisy. I stopped using them for motor speed control long ago in favor of variacs.

author: Edison
author_rank: Frequent Contributor
timestamp: March 08, 2024, 02:32:08 pm
content: Yes, it looks like it, but it's not - this is a triac regulator with negative feedback - there is no significant drop in motor power.It's just another option to control the fan speed, the cheap inverter has already been mentionedThe classic dimmer has a different connection and this device can also take into account the motor capacitor

author: jonpaul
author_rank: Super Contributor
timestamp: March 08, 2024, 03:08:40 pm
content: https://www.ebay.com/itm/386842809817https://www.ebay.com/itm/266684203970https://www.ebay.com/itm/326032816573

author: tooki
author_rank: Super Contributor
timestamp: March 08, 2024, 03:18:19 pm
content: Quote from: jonpaul on March 08, 2024, 11:33:02 amPretty sure they meant that the fan motor has 3 windings. Not the variac. The variac is used to provide more granular control than the fan’s 3-speed motor control.

author: Edison
author_rank: Frequent Contributor
timestamp: March 08, 2024, 04:25:42 pm
content: Quote from: tooki on March 08, 2024, 03:18:19 pmI understood it to mean that it has a three-speed fan, but it needs even lower speeds than the first stage.