Will an SPD protect my charge controller?

[48Rob]

My off grid system produces a max of 142 volts. It is being fed into a Victron 250/85. The closest SPD is 300 volts.
All indications are that if I feed more than 250 volts to the SCC, such as by over paneling, I will destroy it.
If that is the case, then will the SCC be destroyed by surge voltage over 250v volts, before the SPD clamps it at 300 volts?
In the case of a nearby lightning strike causing a major surge, the SPD should protect most of my equipment, though I will probably lose the SCC. Is that correct?
Or does the SCC allow a surge, just not continuous voltage ? If so, where can I find those numbers?

 

[Bluedog225]

You can over panel amps, not volts.

 

[48Rob]

Thank you for that clarification!

 

[JRH]

My off grid system produces a max of 142 volts. It is being fed into a Victron 250/85. The closest SPD is 300 volts.
All indications are that if I feed more than 250 volts to the SCC, such as by over paneling, I will destroy it.
If that is the case, then will the SCC be destroyed by surge voltage over 250v volts, before the SPD clamps it at 300 volts?
In the case of a nearby lightning strike causing a major surge, the SPD should protect most of my equipment, though I will probably lose the SCC. Is that correct?
Or does the SCC allow a surge, just not continuous voltage ? If so, where can I find those numbers?

Ya know that’s a good question I have never thought about the way it’s presented…

I have 85 +/- volt pv system… I have several MS SPD 115 DC …I am in the same boat if that’s a problem that actually exist…. I don’t know…..I do know the SPD reacts very quickly so perhaps that’s the key to this scenario…

I know of no easy way to fix it if it is a problem.. so it may just a thing that is what it is…

I have a hunch if it were a common problem across the land there would have been plenty of squawking about it ..

J.

 

[48Rob]

Great response!

I try to consider if these “problems” I sometimes feel a need to correct, really are a problem…

My basic research found this question in various forms, with the real concern voiced numerous times, that there is a range between the SCC voltage, and the SPD voltage, where there is no general surge protection.

How big a concern I am unable to determine.
If a damaging surge of any size only comes around once in a hundred years, then the concern isn’t so great.
However, I suspect that there is a lack of information and education available, regarding the need and use of SPDs, at least in the DIY community.

I think spending a hundred dollars to protect my equipment is not a bad deal, but the big question is; will it actually protect anything, with such a wide band of unrecognized/unprotected voltage.

 

[JRH]

Great response!

I try to consider if these “problems” I sometimes feel a need to correct, really are a problem…

My basic research found this question in various forms, with the real concern voiced numerous times, that there is a range between the SCC voltage, and the SPD voltage, where there is no general surge protection.

How big a concern I am unable to determine.
If a damaging surge of any size only comes around once in a hundred years, then the concern isn’t so great.
However, I suspect that there is a lack of information and education available, regarding the need and use of SPDs, at least in the DIY community.

I think spending a hundred dollars to protect my equipment is not a bad deal, but the big question is; will it actually protect anything, with such a wide band of unrecognized/unprotected voltage.

Well ,it will be better protected with it , than without it… I have a similar but larger MOV device that protect my RV and it has worked several times shunting lightning voltage in a gradient form and once with a surge over the incoming grid power.

The lightning surges have caused the death of two horses 100 ft from my RV just standing in the pasture…and the death of my internet router( out in my shed) and much of the associated gear 3 times ..( yes , get the insurence they sell ..7 bucks a month) . The phone tech opened up the boxes and showed me the burned wires the surge caused in the various boxes..


Nothing has ever made it to the RV though….I’m not saying it can’t next time , but it always trashed the unprotected stuff I had and leaves the RV alone and it’s all connected together..

That was a very good 300 dollars I spent on that SPD device…


I do not think the gap of voltage coverage I have , will hurt the my CC …I think it would be a discussed thing if it was a danger and the free market would be making more voltage variations of the SPD’s to accommodate this need in the solar market ……like they do fuses….

Again , and maybe I’m wrong , I think the extremely fast clamping time plays into the protection issue…

Finally , I don’t want to loose any of my victrons to a surge , but if that’s all that get killed in a close surge event then that’s better than the whole system ..

J.

 

[efficientPV]

Your controller will likely have some short term protection devices. The majority of the protection will be from the power FET. These have internal avalanche diodes which can take quite a bit of power short term from a lightning event. In effect these are zeners about 7% higher in voltage than the FET rating. They do shunt that power into the output capacitors and the battery. Again these are short term events. The FET can not take a long event like panel overvoltage.

 

[JRH]

Your controller will likely have some short term protection devices. The majority of the protection will be from the power FET. These have internal avalanche diodes which can take quite a bit of power short term from a lightning event. In effect these are zeners about 7% higher in voltage than the FET rating. They do shunt that power into the output capacitors and the battery. Again these are short term events. The FET can not take a long event like panel overvoltage.

Thank you …I will have to take your word about some of that but I am happy to hear there is some protection built into the CC… maybe that and the SPD and bit of luck is all we can do…

 

[seneysolar]

Perhaps one of the folks at Midnite Solar could weigh in here? I have wondered this myself but always just assumed it happened fast enough to not cause harm.

@SpongeboB Sinewave

 

[JRH]

Perhaps one of the folks at Midnite Solar could weigh in here? I have wondered this myself but always just assumed it happened fast enough to not cause harm.

@SpongeboB Sinewave

I have spent a lot of time talking with the friendly techs at MS and we discussed many many things about SPD’s and ways to protect things and this has never come up … I have read and watched a ton of things on SPD’s and learned all I could ……and again I have never heard of this topic, …

but then there is alot I haven’t heard of…

J.

 

[seneysolar]

I have spent a lot of time talking with the friendly techs at MS and we discussed many many things about SPD’s and ways to protect things and this has never come up … I have read and watched a ton of things on SPD’s and learned all I could ……and again I have never heard of this topic, …

but then there is alot I haven’t heard of…

J.

Yeah i have the 115v spd installed on my Victron 100/30. Seems close enough to give me some confidence.

Then for my Midnite Classic 150, the only one that could handle it would be the 300v spd. Thats a big jump... but i dont know enough on the engineering side of things, just have to trust them.

The blue lights are very comforting.

 

[JRH]

Yeah i have the 115v spd installed on my Victron 100/30. Seems close enough to give me some confidence.

Then for my Midnite Classic 150, the only one that could handle it would be the 300v spd. Thats a big jump... but i dont know enough on the engineering side of things, just have to trust them.

The blue lights are very comforting.View attachment 222554

I have taken flack here for commenting on how much I like blue lights on my system…
I got em all over … I’m considering a small blue neon beer sign to with them…
Be careful with mentioning likening blue lights..
Jus sayin…
J.

 

[SpongeboB Sinewave]

Hi guys.
Sometimes there is a misconception about how regular lightning protection with SPDs (MOVs) work.

An SPD does NOT protect the voltage across the PV+ and PV- lines (differential). This CAN be done but not with a lightning arrestor/SPD.

Most electronic devices have what's known as a "Hi-Pot" voltage which is designed into and tested on each and every product going out the door. (common-mode). This is tested by connecting all of the power lines together and is one connection to the hi-pot machine voltage generator. The other line is connected to the GND or chassis of the unit under test.

This voltage is usually much higher than the actual operating voltage of the unit. Charger controller or inverter or whatever.

The voltage from lightning is typically known as common-mode which is applied from say, the PV or AC grid (the "antennas") and the unit's ground or chassis. When this voltage is applied to both PV wires (or AC grid) and chassis, the insulation system inside that unit is rated for some high voltage. Lightning can far exceed this common-mode voltage Hi-Pot rating and arc over from components through that insulation to chassis ground and can hurt the unit. This is why an SPD or the MOVs inside the SPD clamp that voltage at somewhere between the operating voltage and the hi-pot voltage. A MidNite Classic, for instance has a hi-pot rating that we test to of around 2100 volts DC.

So, the SPD would start clamping and protecting at some hundreds of volts. The SPD-300 clamps at around 500 volts and a SPD-600 at around 800 volts.

Lightning is a very a short lived over-voltage and so can be clamped usually by the SPD.

The Classic and some other controllers and products have small-ish MOVs inside that can help in certain situations but not necessarily the bigger lightning strikes. Close or direct lightning strikes. But an MOV clamping voltage depends somewhat on the strength or current coming from that lightning strike. Higher current raises the clamping voltage between those hot-lines (eg. PV+ and PV-)

At some point, (direct strike on the PV array ?) the current can become so high that it blows the MOVs. Every lightning strike that the SPDs get hit with can/will reduce the voltage clamping ability so might want to be replaced once in a while (years ?) if there is a lot of close lightning strikes.

It is correct though to say that the FETs have an intrinsic avalanche diode that can help high differential voltages with low-ish current capability but must also be a short duration. I don't ever like to count on that though.

So, this is why an SPD clamps at a higher voltage than the unit's operating voltage ratings. It's to help keep that insulation system from breaking.

The differential voltage exceeding the component breakover voltage would usually be a long-ish term event and that power would have to be big enough to dissipate that energy over a much longer time. This is what our "Clipper" does for wind turbines. They contain large power resistors for that purpose. MOVs that everybody uses are just too small to handle a power source like a PV array or grid power to an inverter/charger.

Battery cables are normally not great antennas to the outside world like PV or grid so SPDs on the battery lines are not normally needed.

boB

 

[seneysolar]

Hi guys.
Sometimes there is a misconception about how regular lightning protection with SPDs (MOVs) work.

An SPD does NOT protect the voltage across the PV+ and PV- lines (differential). This CAN be done but not with a lightning arrestor/SPD.

Most electronic devices have what's known as a "Hi-Pot" voltage which is designed into and tested on each and every product going out the door. (common-mode). This is tested by connecting all of the power lines together and is one connection to the hi-pot machine voltage generator. The other line is connected to the GND or chassis of the unit under test.

This voltage is usually much higher than the actual operating voltage of the unit. Charger controller or inverter or whatever.

The voltage from lightning is typically known as common-mode which is applied from say, the PV or AC grid (the "antennas") and the unit's ground or chassis. When this voltage is applied to both PV wires (or AC grid) and chassis, the insulation system inside that unit is rated for some high voltage. Lightning can far exceed this common-mode voltage Hi-Pot rating and arc over from components through that insulation to chassis ground and can hurt the unit. This is why an SPD or the MOVs inside the SPD clamp that voltage at somewhere between the operating voltage and the hi-pot voltage. A MidNite Classic, for instance has a hi-pot rating that we test to of around 2100 volts DC.

So, the SPD would start clamping and protecting at some hundreds of volts. The SPD-300 clamps at around 500 volts and a SPD-600 at around 800 volts.

Lightning is a very a short lived over-voltage and so can be clamped usually by the SPD.

The Classic and some other controllers and products have small-ish MOVs inside that can help in certain situations but not necessarily the bigger lightning strikes. Close or direct lightning strikes. But an MOV clamping voltage depends somewhat on the strength or current coming from that lightning strike. Higher current raises the clamping voltage between those hot-lines (eg. PV+ and PV-)

At some point, (direct strike on the PV array ?) the current can become so high that it blows the MOVs. Every lightning strike that the SPDs get hit with can/will reduce the voltage clamping ability so might want to be replaced once in a while (years ?) if there is a lot of close lightning strikes.

It is correct though to say that the FETs have an intrinsic avalanche diode that can help high differential voltages with low-ish current capability but must also be a short duration. I don't ever like to count on that though.

So, this is why an SPD clamps at a higher voltage than the unit's operating voltage ratings. It's to help keep that insulation system from breaking.

The differential voltage exceeding the component breakover voltage would usually be a long-ish term event and that power would have to be big enough to dissipate that energy over a much longer time. This is what our "Clipper" does for wind turbines. They contain large power resistors for that purpose. MOVs that everybody uses are just too small to handle a power source like a PV array or grid power to an inverter/charger.

Battery cables are normally not great antennas to the outside world like PV or grid so SPDs on the battery lines are not normally needed.

boB

Thank you for the detailed response!

 

[48Rob]

Thanks, Bob, and all, for your help. It is appreciated!

 

[Hedges]

SpongeBob would be more the product expert than me, but:

1) SPD can't protect against over-voltage from PV array. It clamps thousands of amps but only for microseconds, can't pull down a continuous power source. It would quickly overheat

You could develop a circuit which detects over-voltage and shorts it (two zero volts), although MPPT input capacitors may not like the current spike. Once pulled to zero the power is dissipated in PV array, which is large enough to handle it.

2) Even differential mode spikes, I think SPD will help. Electronics can take some duration of over-voltage, in many cases it is just deposited energy causing heating. Capacitors have inductance and store energy, may not see a brief high frequency spike but let it get through.

A transistor designed for 200V might withstand a small brief 2kV spike, be damaged by higher or longer spike, so SPD that clamps to 1000V can help by absorbing some of the energy and limiting voltage.

(I've seen test data showing this, voltage and current way over spec but surviving a certain amount of energy.)

I would put 3 MOV, PV+ to GND, PV- to GND, PV+ to PV-.
There is a large loop formed by PV+/PV-, which can pick up differential mode.

https://www.midnitesolar.com/pdfs/SPD_Installation_Manual.pdf

"SPD300AC -LED indicators when voltage is present between L1+Ground and L2+ground
SPD115, 300DC and 600- LED Indicators when voltage is present between DC+ and DC-"

Not sure if the Midnight SPD have MOV only between DC+/ground and DC-/ground, or have additional SPD between DC+/DC-.
If only to ground, differential spikes would be clamped to 2x what common-mode are clamped to.

 

[SpongeboB Sinewave]

Hedges, there are only 2 MOVs in each SPD. Good for PV+ to ground and PV- to ground OR AC L1 to ground and neutral to ground. Another 1/2 SPD for L2 to ground.

Shorting the input could work for full differential protection. That would be called a crowbar as is on some power supplies.
The crowbar would have to take the charge of those caps too. That tends to break a FET. I think they used to use thyristors for that ? Triacs and SCRs.

PV+ and PV- to ground (etc) places the two MOVs in series. But that is going to differentially conduct at twice the MOV turn on voltage.

boB

 

[Hedges]

Why neutral to ground? They are hard bonded at my first disconnect.

A diode (or FET) would be needed to block backfeed from caps.
Unless a load could dissipate that energy and what comes from array during the time it took to discharge.

All to protect against installation error.
Measure twice, cut once.

Years ago, not all PV inverters had reverse protection diodes.
Some brands had high failure rate at install.

Swapping PV array from one inverter to my bench test area (MC3 connectors) I inadvertently connected one inverter's 480V charged MPPT input capacitors to another's, discharged but reverse polarity. Blew string fuses. Inverter survived, Ethernet communication card didn't work (don't know if DOA or I killed it) and SMA replaced that.

 

[SpongeboB Sinewave]

"Why neutral to ground? They are hard bonded at my first disconnect."

Good point ! You are correct. As long as the ground bond point is where the SPD would be located.
The PV negative are often grounded and we put a MOV on PV- to GND as well as PV+. But those lines can be long and accumulate a good amount of common mode voltage during a strike.

boB