12Vac with 3V voltage sag

[roadto198]

Hi,

Can anybody help me with my problem? I need to check if an equipmment in our lab does operates when voltage sag occurs in our mini power system. Therefore, I need to have a voltage sag generator, I've been able to do now a circuit that has input 230Vac to 12Vdc in now need to use this to have a 12Vac with a 2 cycle voltage sag (3volts sag maybe) in between. Is this possible? I have read some papers that uses pwm h bridge inverters to do this but i was unsuccessful. can anybody help me with this?

kenneth

 

[kappa_am]

A simple way is using a transformer to convert 230Vac to 12Vac, and putting an 3Vdc in series with appropriate bi-directional switches. just inverse terminal of the DC source according to sign of the Vac.


Good Luck

 

[KlausST]

Hi,

Can anybody help me with my problem?

If you give important informations like current...
Pictures,, schematics, waveform.....

Klaus

 

[kappa_am]

A better idea is using of a transformer with two output terminal 12V and 9V and selecting one of them according to your desire output. something like solid-state tap changer.

Good Luck

 

[BradtheRad]

I need to have a voltage sag generator, I've been able to do now a circuit that has input 230Vac to 12Vdc in now need to use this to have a 12Vac with a 2 cycle voltage sag (3volts sag maybe) in between.

Is the goal to blackout a couple cycles of AC?
A simple method to do this is with a relay. Wire it so it normally conducts.

A capacitor is charged from the existing supply. Push a switch, and it momentarily energizes the relay coil.

It releases when the capacitor has discharged to the point where it cannot hold the relay in. It releases even if you keep the switch held down.

Simulation showing how to arrange components (with scope traces):

 

[kappa_am]

Sag is not complete lack of voltage (Long time:Black-out or short time: Interrupt). it is reduction in amplitude of the AC voltage and the amplitude define by CEBEMA or ITIC curve.
using capacitor is good idea you can use proposed circuit by Brad and a transformer with 3-end secondary winding.
By using brad suggestion you do not need any MCU or complicated control system.

Good luck

- - - Updated - - -

P.S: use a relay with very low traveling time, or go with solid-state switches.

GL

 

[chuckey]

You do not say what current your sagging 12 AC line has to cope with. If you wire the secondary of a low voltage transformer in series with your 12 AC and put a short on the primary of the transformer, you will get only the leakage inductance in series with it. If you open circuit the primary (Beware high voltage), you will get the reflected primary impedance in series with the 12 VAC. So you could put a triac across the primary, switching in a suitable load, to get your 3V drop.
Frank