how to stop smsps working when there is no neutral?

[Mokthar]

Hi,

I have Designed a 3phase 4wire smps with neutral. The output of the SMPS is 12v 1Amps. When there is no neutral i want my smps output to go off.

I achieved this by altering the diode bridge rectifier arrangement.

But there is a capacitive power supply that shares the input of 3phase 4wire smps which is used for sensing phase presesnce.

Now with these to combined when neutral connection is terminated, the return current from the phase of the capacitive power supply runs into the neutral. As both the neutral points are tied together this flows into smps and makes it to power up.

Kindly suggest how to discharge this return current into the neutral when there is neutral termination. so that both capacitive and smps power supplies can turn off..

With Regards,
Mokthar

 

[FvM]

There are good reasons why any three-phase power supply on the market doesn't use neutral...
Otherwise you need to measure phase-to-neutral voltage and define an acceptance window.

 

[c_mitra]

When there is no neutral i want my smps output to go off.

What exactly you mean by the phrase "when there is no neutral"? If you have a 3phase 4 wire input, there will be always a physical neutral present.

If your 3 phase load is not nicely balanced, there will always be some current into the neutral.

If your load is not using the neutral line and is not nicely balanced, the phase relations will not be symmetrical.

It will be better to research why the three phase load is behaving unbalanced.

 

[Mokthar]

What exactly you mean by the phrase "when there is no neutral"? If you have a 3phase 4 wire input, there will be always a physical neutral present.

If your 3 phase load is not nicely balanced, there will always be some current into the neutral.

If your load is not using the neutral line and is not nicely balanced, the phase relations will not be symmetrical.

It will be better to research why the three phase load is behaving unbalanced.

Yes u r correct. The smps load is balanced. When the phase sense circuit comprising capacitive power supply is used with smps it goes unbalanced.

At this point if my neutral wire is disconnected or goes fault. Some voltage builds across the neutral with return current from capacitive supply. This voltage inturn makes the smps power up even if neutral is not present.

Actually my application is to take out single phase out from three phase input with automatic change over. So without neutral my total circuit has to go off.

Because of this return current in neutral its not happening.