150V Mppt surge protection

[Rotary]

What size surge protector should i be using for my 150/85 victron Mppt. I originally ordered a 100v SPD but the supplier sent me a 150v SPD instead. The SPD will be mounted within my PV combiner box.

Can i get away with the 150v ? Just wondering how others size their SPD.

 

[Samsonite801]

What size surge protector should i be using for my 150/85 victron Mppt. I originally ordered a 100v SPD but the supplier sent me a 150v SPD instead. The SPD will be mounted within my PV combiner box.

Can i get away with the 150v ? Just wondering how others size their SPD.

150v is the DC circuit Voc rating, should be fine (depending on your circuit Voc number). I went with some MidNite Solar 300v surge protectors since I calculated around 201v max Voc on mine..

 

[crossy]

As a minimum I'd go for your max Voc + 30%.

It's important to remember that MOV surge suppressors do actually wear, each time they catch a surge the trigger voltage goes down slightly, eventually they end up being "on" at your normal solar voltage and swallowing your energy.

Of course they get hot at this point, they "should" have an overheat mechanism (which operates the "fail" flag in the window) but that usually relies on solder melting so a spring can pull contacts apart, primitive but reasonably effective.

 

[Rotary]

Thanks for the replies. Everyday a school day, I wasn't aware of the fact that SPD wear

 

[tellingson]

As a minimum I'd go for your max Voc + 30%.

It's important to remember that MOV surge suppressors do actually wear, each time they catch a surge the trigger voltage goes down slightly, eventually they end up being "on" at your normal solar voltage and swallowing your energy.

Of course they get hot at this point, they "should" have an overheat mechanism (which operates the "fail" flag in the window) but that usually relies on solder melting so a spring can pull contacts apart, primitive but reasonably effective.

Sorry. I realize this is an old thread. I have a Victron system and a 450/100 MPPT. Would I want to get the 600v SPD? I currently have panels that generate 380 VOC. My concern is that my MPPT may get fried before the 600v SPD kicks in.

 

[crossy]

There's nothing to stop you using a 450V or 500V arrestor other than that they will possibly be "failing" (clamping "on") sooner than the higher voltage ones due to them wearing.

Also, these trigger voltages aren't very tightly controlled at manufacture, don't go too low or you may be replacing them rather often.

Are you in a particularly high-lightning area?

 

[tellingson]

There's nothing to stop you using a 450V or 500V arrestor other than that they will possibly be "failing" (clamping "on") sooner than the higher voltage ones due to them wearing.

Also, these trigger voltages aren't very tightly controlled at manufacture, don't go too low or you may be replacing them rather often.

Are you in a particularly high-lightning area?

Not really. I just really don’t want a lightning strike to blow up my system. If a 600V arrestor will prevent a lightning strike from killing my system, then I’m fine doing that. I was just concerned that it wouldn’t clamp soon enough (max VOC 450) and that it would fry my MPPT anyway.

 

[crossy]

The Voc max figure for your MPPT is the "continuous" rating, don't exceed it for "long" periods (10s of milliseconds).

Lightning surges are very, very fast (often sub-microsecond) but also very big (several kV) meaning they actually carry a lot of energy.

It's these fast pulses that can punch through the internal workings of your semiconductors turning them into lumps of plastic with legs

The MOV reacts fast enough (<10 nanoseconds) to clamp the pulse for its duration, the energy is dissipated in the MOV and not in the gate of your semiconductor.

See what's available in 30kA DC suppressors and make an educated choice (you may be forced by a limited range anyway).

 

[tellingson]

The Voc max figure for your MPPT is the "continuous" rating, don't exceed it for "long" periods (10s of milliseconds).

Lightning surges are very, very fast (often sub-microsecond) but also very big (several kV) meaning they actually carry a lot of energy.

It's these fast pulses that can punch through the internal workings of your semiconductors turning them into lumps of plastic with legs

The MOV reacts fast enough (<10 nanoseconds) to clamp the pulse for its duration, the energy is dissipated in the MOV and not in the gate of your semiconductor.

See what's available in 30kA DC suppressors and make an educated choice (you may be forced by a limited range anyway).

I’m looking at the Midnight Surge Arrestor. On the 300v SPD, their chart shows that it clamps at 470v at 1mA so maybe that is the way to go rather than the 600. Thanks for the feedback and thoughts.

 

[crossy]

I’m looking at the Midnight Surge Arrestor. On the 300v SPD, their chart shows that it clamps at 470v at 1mA so maybe that is the way to go rather than the 600. Thanks for the feedback and thoughts.

I wouldn't go that low. The "300V" is the operating voltage, keep that above your max panel Voc at least.

EDIT why not consult with Midnight for their recommendation?