Author Topic: Variable Voltage AC supply- Not a Variac  (Read 19988 times)

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Offline PurduephotogTopic starter

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Variable Voltage AC supply- Not a Variac
« on: February 29, 2024, 08:34:05 pm »
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-
 

Online Faringdon

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Re: Variable Voltage AC supply- Not a Variac
« Reply #1 on: March 01, 2024, 08:20:43 pm »
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 the
neg 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!
« Last Edit: March 01, 2024, 09:15:52 pm by Faringdon »
'Perfection' is the enemy of 'perfectly satisfactory'
 
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Offline David Hess

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Re: Variable Voltage AC supply- Not a Variac
« Reply #2 on: March 01, 2024, 10:13:48 pm »
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.
 
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Offline NiHaoMike

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Re: Variable Voltage AC supply- Not a Variac
« Reply #3 on: March 02, 2024, 12:30:27 pm »
Replace the motor with a variable speed BLDC one? (They're known as "ECM" in the HVAC industry.)
Cryptocurrency has taught me to love math and at the same time be baffled by it.

Cryptocurrency lesson 0: Altcoins and Bitcoin are not the same thing.
 
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Offline PurduephotogTopic starter

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Re: Variable Voltage AC supply- Not a Variac
« Reply #4 on: March 03, 2024, 04:55:28 am »
That would take all the fun out of rebuilding the fan .. but I'll take a look at the HVAC surplus place near me

I'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.
« Last Edit: March 03, 2024, 04:59:05 am by Purduephotog »
 

Offline David Hess

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Re: Variable Voltage AC supply- Not a Variac
« Reply #5 on: March 03, 2024, 09:21:04 pm »
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.

« Last Edit: March 03, 2024, 09:25:03 pm by David Hess »
 

Online BrokenYugo

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Re: Variable Voltage AC supply- Not a Variac
« Reply #6 on: March 03, 2024, 09:23:43 pm »
Maybe hack an inverter for variable voltage?
 
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Offline Jeroen3

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Re: Variable Voltage AC supply- Not a Variac
« Reply #7 on: March 04, 2024, 07:18:33 am »
What I'd love to find is some electronically controllable variable AC voltage supply.
But you probably don't want to pay for them. They're expensive. Eg: GW-Instek ASR-2050R.
 
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Online Faringdon

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Re: Variable Voltage AC supply- Not a Variac
« Reply #8 on: March 04, 2024, 10:30:41 am »
Quote
But you probably don't want to pay for them. They're expensive. Eg: GW-Instek ASR-2050R.
Too right
This is why the post #2 above is the way forward...nice and simple.
'Perfection' is the enemy of 'perfectly satisfactory'
 
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Offline Jeroen3

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Re: Variable Voltage AC supply- Not a Variac
« Reply #9 on: March 04, 2024, 01:08:50 pm »
Did you build one yet Faringdon?

@Purduephotog, do you know single phase motors are very poor with speed control?
 

Offline mag_therm

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Re: Variable Voltage AC supply- Not a Variac
« Reply #10 on: March 04, 2024, 01:50:24 pm »
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 the board 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.
 

Offline Stray Electron

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Re: Variable Voltage AC supply- Not a Variac
« Reply #11 on: March 04, 2024, 02:07:12 pm »
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.


    Have 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. 
 


Offline boB

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Re: Variable Voltage AC supply- Not a Variac
« Reply #13 on: March 04, 2024, 07:52:21 pm »
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=1

I don't know what they mean by LCD module though cuz that isn't part of this PCB AFAIK.

boB
K7IQ
 
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Offline jonpaul

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Re: Variable Voltage AC supply- Not a Variac
« Reply #14 on: March 08, 2024, 11:33:02 am »
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 controls 

Jon
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Offline Edison

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Re: Variable Voltage AC supply- Not a Variac
« Reply #15 on: March 08, 2024, 12:30:53 pm »
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 - 1kW
I made it myself, but a lot of commercial speed regulators are sold - especially for fans that require a running capacitor to run.
Everything works as the weakest link in the chain
 

Offline PurduephotogTopic starter

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Re: Variable Voltage AC supply- Not a Variac
« Reply #16 on: March 08, 2024, 01:37:48 pm »
*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.
 

Online langwadt

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Offline Edison

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Re: Variable Voltage AC supply- Not a Variac
« Reply #18 on: March 08, 2024, 02:10:43 pm »
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.
Everything works as the weakest link in the chain
 

Offline themadhippy

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Re: Variable Voltage AC supply- Not a Variac
« Reply #19 on: March 08, 2024, 02:14:24 pm »
Quote
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.
That looks more like a dimmer switch and not a variable frequency drive
 

Offline David Hess

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Re: Variable Voltage AC supply- Not a Variac
« Reply #20 on: March 08, 2024, 02:31:12 pm »
Quote
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.

That looks more like a dimmer switch and not a variable frequency drive

It 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.
 
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Offline Edison

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Re: Variable Voltage AC supply- Not a Variac
« Reply #21 on: March 08, 2024, 02:32:08 pm »
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 mentioned

The classic dimmer has a different connection and this device can also take into account the motor capacitor
« Last Edit: March 08, 2024, 02:34:30 pm by Edison »
Everything works as the weakest link in the chain
 

Offline jonpaul

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Offline tooki

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Re: Variable Voltage AC supply- Not a Variac
« Reply #23 on: March 08, 2024, 03:18:19 pm »
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 controls 

Jon
Pretty 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.
 

Offline Edison

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Re: Variable Voltage AC supply- Not a Variac
« Reply #24 on: March 08, 2024, 04:25:42 pm »
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 controls 

Jon
Pretty 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.

I understood it to mean that it has a three-speed fan, but it needs even lower speeds than the first stage.
Everything works as the weakest link in the chain
 


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