Can I rectify this simple AC dimmer circuit/module to make adjustable dc voltage regulator?

Thread Starter

myall

Joined Mar 7, 2018
12
Can I simply rectify this AC dimmer circuit/module + add a capacitor on the DC side to make adjustable DC voltage regulator?
My understanding is that AC dimmer switch just cuts off the AC peak voltage so it should work right?

 2024-04-25 at 3.59.17 PM.png  2024-04-25 at 4.03.08 PM.png
 

crutschow

Joined Mar 14, 2008
34,817
My understanding is that AC dimmer switch just cuts off the AC peak voltage so it should work right?
No.
It reduces the voltage by turning of for only part of each AC cycle, so the peak voltage can be the same, but the average voltage is less.

But note that there is no isolation with that circuit so it can have lethal voltages at the output.
And the voltage will be adjustable but won't be regulated for changes in the load current.
Unless you are in the running for the Darwin award, I wouldn't mess with that circuit. :rolleyes:
 

MisterBill2

Joined Jan 23, 2018
19,366
Can I simply rectify this AC dimmer circuit/module + add a capacitor on the DC side to make adjustable DC voltage regulator?
My understanding is that AC dimmer switch just cuts off the AC peak voltage so it should work right?

View attachment 320768 View attachment 320769
The short answer is :"Yes, BUT." A more useful answer is that you can create an adjustable DC power source that is not regulated, nor isolated from the AC mains. And since your mains voltage is 230 volts AC, 50 Hz, it will be a supply quite easily able to deliver lethal shocks if you make any wrong error.
So unless you are experienced in working with such dangerous electrical systems. I suggest not doing it. The potential hazard is real, and totally non-forgiving if you make a mistake.
I am not peddeling fear, just providing a caution that I am obligated to provide you with, as I did state that it can be done.
 
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Thread Starter

myall

Joined Mar 7, 2018
12
Wouldn't 50% and under duty cycle (potentiometer adjustment) start dropping the voltage?
It wouldn't be a very accurate nor good voltage regulator but wouldn't it be able to do 30~170 VDC
Im just talking theoretically here again. I'm more curious about electricity in theory

And @crutschow I know this isn't isolated and can be dangerous. I've been shocked by 220vac back in Europe as a kid a feeew times, I know the pain lol. PS been on this side of the pond at 110vac for a while
.
 
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Pyrex

Joined Feb 16, 2022
296
Hi,
adding a capacitor after the bridge is not a good idea. The SCR will burn down because of huge current pulses .
And, in addition, what kind of a DC load you want to power up? If a motor to be powered, take in mind it's impedance is active-inductive . A special dimmer need to be used for this kind of load
 

MisterBill2

Joined Jan 23, 2018
19,366
The need for an inductor depends on the load and the capacitor. If there is a load drawing current then the voltage will start to drop when there is any reduction in the conduction angle. At no load the voltage will be rather high. As for regulation, there is no regulation because there is no feedback to provide regulation. and the capacitor charging current will depend on the size of the capacitor. Most dimmers are designed to work with a tungsten lamp load, which also has a low initial resistance.. If the load is a DC motor then there is no need for am special dimmer made to control AC motor speeds.. Also, if the load is an AC motor, it will not work on a rectified filtered DC supply.. (Why would anyone try to run an AC induction motor on a filtered DC supply?????
 

LowQCab

Joined Nov 6, 2012
4,290
A Triac-Dimmer is a very crude devise that can reduce the POWER, not necessarily the Voltage,
that will be transferred to an AC-Load, like an Incandescent-Light-Bulb.

They have only limited usefulness otherwise, and may be very dangerous.
.
.
.
 

MisterBill2

Joined Jan 23, 2018
19,366
A Triac-Dimmer is a very crude devise that can reduce the POWER, not necessarily the Voltage,
that will be transferred to an AC-Load, like an Incandescent-Light-Bulb.

They have only limited usefulness otherwise, and may be very dangerous.
.
.
.
The Triac Dimmer is safe when correctly used for the purpose of dimming incandescent lights. Other uses may not function as desired and certainly some will be unsafe. That applies to a great number of common devices and materials. But some of us could safely use it for an emergency power supply, because we would fully understand what we were dealing with, and how to safely use it. The problems begin when the unknowing folks grab into that which they do not at all understand. Thus that ancient adage:"Fools Rush In".
 
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Ian0

Joined Aug 7, 2020
10,232
The circuit depends on the current through the lamp when the triac is off in order to function.
If the lamp is replaced by a bridge rectifier and a capacitor, then when the capacitor remains charged between cycles, it will block the current needed to charge the timing circuit.
 

DickCappels

Joined Aug 21, 2008
10,245
Did that once, It was actually for a 400 watt electromagnet power supply -what a pain that was. A pair of SCRs was used as a full wave controlled rectifier which provided a poorly regulated voltage what was used by the next circuit, which had a high loop gain and a temperature controlled voltage reference to provide a 0.01% regulated current.

In other words, even is you use a transformer (don't do it!) to isolate the power line from the load, you still have to add a lot of circuitry to make it useful.
 

Ian0

Joined Aug 7, 2020
10,232
I use a controlled full-wave bridge and inductor for 216V lead-acid battery chargers. It is possible to get very accurate control of voltage and current, but the response speed of the control loop is SLOW!
 

Thread Starter

myall

Joined Mar 7, 2018
12
Reasons why this came across my mind is...

In the past I've had to charge different voltage LARGE polar/dc capacitors and without buying special equipment I was using 110vac/mains --> 10a 12vdc adapter --> adjustable step-up 0-400v to do this. I've also used this circuit for other experiments when I needed the voltage to be dialed in.

But obviously this setup I had was very slow and very ridiculous... but it was what I had around the house. At the time I didn't have a variac and good full bridge.

Just recently I thought about this circuit and wondered if it would have helped back then especially since its a $2 module
.
 
I also employed SCRs to charge a large SLA battery bank. But you require something more complex than a Diac and an RC time constant.
We used a variant of a circuit published in GE’s SCR Manual, and required some UJTs in addition to other components.
 

boostbuck

Joined Oct 5, 2017
562
Here's a circuit from Jim Williams LT AN32, using phase angle switching to control the power delivered to a linear regulator, which is sort of what the suggested dimmer circuit is. The SCRs are switching low voltage in this case:

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Ian0

Joined Aug 7, 2020
10,232
Here's a circuit from Jim Williams LT AN32, using phase angle switching to control the power delivered to a linear regulator, which is sort of what the suggested dimmer circuit is. The SCRs are switching low voltage in this case:

View attachment 320876
That's very much in the discontinuous mode. It needs 30mH for a 24V 2.5A battery charger to keep the current continuous.
 
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