Mains surge protection TVS voltage for 220V mains

[riccardo]

Hi, I want to add some basic surge protection on a PCB used to rectify the mains for use in a project.
I understand that I could use a TVS between L and N (after the fuse), but when I look up the parts, they all have a number of voltage ratings which can vary widely on the one part. (min/max breakdown voltage, clamping voltage, etc)
What voltage rating do I need to look for for protecting the circuit with a mains input of 220V AC ??

 

[Nigel Goodwin]

Where's it going to be used?, and why do you feel the need for a TVS? - particularly as you have a UK location (and we have excellent quality mains).

The mains here is also 240V, not 220V.

 

[riccardo]

The mains will be rectified to charge a bank of 400V electrolyitics (1000uF total) for use as a PSU. I just want to make sure that if a surge did occur, the capacitors are not damaged. I'm thinking for the sake of part probably costing <£1 I could add that little extra protection.
Should I should go higher than the 400V rating for the capacitors as rectifying 240V will be getting quite close to that.

 

[alec_t]

Are you aware that your PSU won't be elctrically isolated from the mains, so is hazardous? For safety's sake, use an isolation transformer. Even with isolation the charged electrolytics could KILL you .

 

[riccardo]

Yes, I am aware. How about the original question?

 

[Nigel Goodwin]

The mains will be rectified to charge a bank of 400V electrolyitics (1000uF total) for use as a PSU. I just want to make sure that if a surge did occur, the capacitors are not damaged. I'm thinking for the sake of part probably costing <£1 I could add that little extra protection.

Again, if you're in the UK there's no reason to - our mains is good enough not to require it (and commercial equipment often leaves them out for the UK market, but fits them for elsewhere).

If you're in Spain, them by all means fit them - it's a very common problem in Spain.

 

[riccardo]

It may well get used in Spain at some point actually . Would this one suit it?
1.5KE180CA-E3/5
https://www.farnell.com/datasheets/1719592.pdf

Clamping voltage is 246V, but max breakdown voltage is 189V so I'm concerned it would be conducting even in normal voltage conditions.

 

[Nigel Goodwin]

246V is much too close to 240V, as the permitted maximum is 230V+10%/-6% (so 253V in the UK). The 220V countries are 230V +6%/-10% - notice that BOTH allow all countries to keep their existing 220 or 240V supplies.

If your circuit is as crude as you mentioned, just a rectifier and caps, then using 450V ones would be a better idea. TVS's only give a limited degree of protection, and anything the TVS stopped probably wouldn't harm a big bank of caps anyway.

 

[Cicero]

I suggest using MOV's for AC surge protection. Something like this https://uk.farnell.com/epcos/b72220s0271k101/varistor-151j-275vac/dp/1004363?ost=B72220S0271K101 .

My general feeling is that MOV's are more suited for the higher voltages, and TVS transorbs are better suited for the lower DC side protection.

 

[Tony Stewart]

The Caps will suppress and line surge if a series RF and LF chokes are used in series.

More important is what is the ESR of your caps as line surge if not regulated by a ZCS and soft start metal oxide Inrush current limiter ICL ( pennies) will blow your fuse or caps.. Poof.

Add a 1uF film cap for insurance and ultra low ESR across bulk caps and any lightning transient will safely blow similar voltage rated fuse or breaker. But I suggest choosing an ICL to sustain your max holding current then start currents will be reduced /10 and ZCS reduces stress on ICL if frequent power cycles or rapid power cycles are anticipated which can occur from supplier. A hot ICL and low cap during peak voltage will trigger nuisance fuse blows.

If you anticipate unregulated overvoltages on line, choose operating voltage of MOV above worst case normal voltage, but less than 400V

Obviously ICLs will be in series with fuse before MOVs. gas Tubes are better for SCR like clamping high energy impulses but generally LC filters attenuate 6KV 10 us spikes by >30 dB with carefully selected chokes.

Use 1 MOV per cap if used in series as they are cheap and aging can cause serious imbalanced voltage splitting if used in series.

 

[riccardo]

Thanks again guys