Hi, I'm trying to add protection to some SSR's, I think I have everything sorted out but would like some input if possible.

This is a power bar that will have 8 relays total, I only drew up 2 as they are all the same.

The SSR is a Hoymk SSR-D3808HK, it has 1.5kV isolation, internal snubber and rated at 8amps up to 380VAC.

The input of power bar will be 120-240 VAC and load could also be between 120-240 VAC.

For the TVS's I selected 1.5SMC300A (click for datasheet)

The fuses will be slow blow 5SF 5-R



Should MOV's be added?

Thanks

 

I wouldnt use a MOV, just consider the option of using an input bidirectional TVS instead of unidirectional

 

Hi, I'm trying to add protection to some SSR's, I think I have everything sorted out but would like some input if possible.
This is a power bar that will have 8 relays total, I only drew up 2 as they are all the same.
The SSR is a Hoymk SSR-D3808HK, it has 1.5kV isolation, internal snubber and rated at 8amps up to 380VAC.
The input of power bar will be 120-240 VAC and load could also be between 120-240 VAC.
For the TVS's I selected 1.5SMC300A (click for datasheet)
The fuses will be slow blow
Should MOV's be added?
Thanks

Are you sure the TVS should be wired in "series" ?
I thought the TVS is added in "parallel" across the Load and/or SSR.

 

I wouldnt use a MOV, just consider the option of using an input bidirectional TVS instead of unidirectional

Oh thank-you! I knew to get bi and thought that was bi but yes I now see it was the uni version, the bi part number is 1.5SMC300CA.

Would you put the TVS on both sides of SSR like I have in diagram or only on load side? My thought is the first TVS would protect SSR from grid surges and the 2nd TVS would protect SSR from inductive loads.

Does everything else with that TVS look suitable for this?

Are you sure the TVS should be wired in "series" ?
I thought the TVS is added in "parallel" across the Load and/or SSR.

Sorry that diagram doesn't show that, I made up a schematic, is this correct? TVS goes across AC Hot and AC Ground and direction doesn't matter because its bi-directional?



The 12 amp fuse doesn't make sense in schematic but there are 7 other SSR's on the fused side limiting overall to 12 amps and only 5 amps to each SSR.

Thanks

 

Move D11 to be in parallel with / directly across the Inductive Load at far tight, do not connected to Ground Wire.
Move D10 to be in parallel with / directly across Pins #1 & #3 of the Opto-Isolator.

This should clamp the voltage across the device.

I don't understand 7 times 5 amp branch fuse = 12 amp total main fuse.

 

Sorry I'm not sure about D11, this is the changes I made but I think now I have D11 in series?



The 12amp fuse insures the 8 SSR's can't draw more than this all combined, for example if 4 SSR's had 4 amps on each that's 16 which is more than I want flowing so the main fuse would blow.

The secondary 5 amp fuses are to limit the load to each SSR to a max of 5 amps. The SSR's are rated for 8 amps but I don't want to push past 5 so if load is higher the 5 amp fuse will blow.

Am I doing something wrong?

Thanks

 

Remove D11- that's not how TVS diodes are meant to be used.

Also note that a typical "5A fuse" is glacially slow relative to protecting a semiconductor, like a triac.
A direct short may destroy the triac, long before the fuse can clear.

There are special fuses for this application.

http://www.mouser.com/ds/2/240/semi-26357.pdf

 

Remove D11- that's not how TVS diodes are meant to be used.

Also note that a typical "5A fuse" is glacially slow relative to protecting a semiconductor, like a triac.
A direct short may destroy the triac, long before the fuse can clear.

There are special fuses for this application.

http://www.mouser.com/ds/2/240/semi-26357.pdf

Thanks I didn't think D11 should be used like that but can't see how it goes parallel without connecting other end to Ground or Neutral. But now I see D10 in place maybe I only need one and it'll protect from inductive load and grid surge?

I looked up that fuse, wow expensive, for a 250v 5amp $35 a piece, yikes... If there's a direct short I'm ok with SSR being damaged as that should never happen, it's deserved if it does. I only care that the load doesn't go over 5amps. 30 cent fuse I can afford.

 

Per your Drawing in Message #6 .... D10 is OK, but ...
No, do NOT put D11 in SERIES with the Load.
Show the Inductive Coil / Load on your schematic
Now, connect D11 DIRECTLY to the two contacts of the Inductive Coil / Load,
which would be between "Switched-Hot" and "Neutral", not the "Ground" wire.

 

Per your Drawing in Message #6 .... D10 is OK, but ...
No, do NOT put D11 in SERIES with the Load.
Show the Inductive Coil / Load on your schematic
Now, connect D11 DIRECTLY to the two contacts of the Inductive Coil / Load,
which would be between "Switched-Hot" and "Neutral", not the "Ground" wire.

Ah, I see, thank-you!