AC/DC adaptor output in series with rectified mains output

Status
Not open for further replies.

Thread Starter

Arjan-Q

Joined Sep 20, 2021
7
Dear all,

After reading this thread: https://forum.allaboutcircuits.com/threads/ac-to-dc-adapters-in-series-or-parallel.130515/ I think I have found my answer but I'm not sure enough.

My aim is to charge a capacitor to about 330 / 340 V. I want to do this by rectifying 230Vac, giving me about 325Vdc. Next, I would like to place the output of an AC/DC adaptor (230Vac to 10Vdc) in series with the output of the rectifier. Doing so would give me eventually an electric potential of 325 + 10 = 335Vdc (see figure below). I think I'm allowed to do so but I'm unsure whether I'm doing the internals of the AC/DC adaptor any harm... Could you help me out?

Additionally, if you know better ways to achieve my aim or if you see improvements in the schematic, feel free to comment.

Looking forward to your findings.

Kind regards,
Arjan

23Vac_rectified_in-series_with_10Vdc.jpg
 

DickCappels

Joined Aug 21, 2008
7,836
In many places the peak mains voltage can fluctuate more than 10V our of 350. Why do you want to do this?

By the way, if you end up trying this, do an investigation to make sure that you don't create a shock or fire hazard by elevating the secondary of the power supply to around the line voltage. The designer of the power supply might have had a different idea of how it should work when they designed than you have now.
 

Thread Starter

Arjan-Q

Joined Sep 20, 2021
7
Why I'm looking for this:
in my PhD group one of the PhD's has issues with a piece of measurement equipment (I'd rather not mention the name of the company as it's one of our main financial supporters of one of the PhD's). We figured out it gives false readings due to the presence of voltage spikes on the mains power feeding the equipment, however, the manufacturer is not convinced. As a side project we are now trying to show the equipment's weak spot by a coordinated experiment (not a necessity but more because we like these kind of little challenges).

The idea is to expose the equipment to short voltage peaks on its line voltage powering the equipment, which are slightly higher than the current mains voltage. Eventually a) the amplitude, b) the timing and c) the duration of the peak will be controlled; every Pi cycle (i.e. at 100Hz for 50Hz mains) a peak is to be inserted. This makes that the capacitor is continuously charging to the desired voltage potential and every xx ms it briefly discharges.

With the use of a ZMPT101B we'll be detecting:
1. amplitude of the mains voltage (based on which we'd adjust the DC voltage, staying 'safe' below 240Vac, i.e. max. allowed mains deviation is 10% giving max. 253Vac, we have to stay below that to prevent damage)
2. the zero crossing of the AC-signal (for timing purposes of the signal)

I planned to discuss the overall schematic & aim in an upcoming different thread.

By the way, if you end up trying this, do an investigation to make sure that you don't create a shock or fire hazard by elevating the secondary of the power supply to around the line voltage. The designer of the power supply might have had a different idea of how it should work when they designed than you have now.
OK, I don't think it's wise then to pursue this way. Would you have another method in mind? Getting a capacitor at the required potential? I have considered using a voltage multiplier circuit but then I have less control over the voltage output as the steps are more discrete...

With no Regulator You will have no idea of what the Voltage is going to be.
That's true, the idea is to monitor the line voltage and vary the DC voltage accordingly.

Thank you for the replies so far.

Arjan
 

Ian0

Joined Aug 7, 2020
3,463
Wouldn't it be an awful lot easier to use a variac? If you're working in some sort of lab environment, there will always be a variac available!
 

DickCappels

Joined Aug 21, 2008
7,836
If place the pulse source in series with the neutral line it will lower your risk considerably.

This is equipment made for exactly this kind of test. You probably rent one if you have a budget for it, not only would that be safer, but you would probably have pretty good control of the type of transient to which you subject the equipment.

Incidentally, I designed a generator of this type for testing power quality instrumentation a few years ago. I would recommend it but it is not capable of driving a load. Worst case you could use something like that followed by a linear amplifier.
 

Thread Starter

Arjan-Q

Joined Sep 20, 2021
7
Wouldn't it be an awful lot easier to use a variac? If you're working in some sort of lab environment, there will always be a variac available!
I considered using a variac but my main concern was that the voltage then is a function of the 50 Hz is, whereby I can't arbitrarily time the release of a pulse at max. amplitude. However, at second thought, when using a variac for charging a capacitor the timing of the pulse is again decoupled from the 50Hz ac.... Thanks Ian0 for bringing up the variac again, these are certainly somewhere nearby!

This is equipment made for exactly this kind of test. You probably rent one if you have a budget for it, not only would that be safer, but you would probably have pretty good control of the type of transient to which you subject the equipment.
We PhD's like to do everything low budget... I think when using a variac, rectifying its output for charging a capacitor to the set voltage (i.e. manually set at the variac), we have a simple construction for the source of our pulse generator.

I'll start a new thread shortly (something like: 'pulse insertion into 230v mains') to ask for your insights about the next steps.

Thank you again for all the input.
Arjan
 
Status
Not open for further replies.
Top