High DC voltage relays

lazza

HI

This is linked to my posts on the net-metering problem in Spain. Where we have to avoid grid-feed at all costs (literally cos they charge you!)

So I'm thinking that maybe we could switch the PV system on and off with an in-line relay, depending on the sum of production minus consumption. The problem is that as the grid-tie inverters are high DC voltage, and any relay/switches, will have to work up to 400Vdc..

Does anyone know of high DC voltage relay and switching products/ manufacturers?

Thanks
Larry

NorthGuy

Re: High DC voltage relays

There are very many.

For example, this.

tallgirl

Re: High DC voltage relays

NorthGuy wrote: »

There are very many.

For example, this.

That's a 12 volt relay. The OP needs something in the 600 to 1,000VDC range.

NorthGuy

Re: High DC voltage relays

tallgirl wrote: »

That's a 12 volt relay. The OP needs something in the 600 to 1,000VDC range.

12 VDC is a coil voltage.

This relay can switch up to 400 VDC. That is exactly what OP asked for. I don't know where you got 600 to 1,000 VDC range.

Cariboocoot

Re: High DC voltage relays

Well if you're going to switch standard line power (240 VAC 60 Hz or 230 VAC 50 Hz) and meet code the contacts need to be rated for 600+ Volts just like wiring. They'd also have to be able to switch whatever current could be involved.

The relay NorthGuy linked to would work, but would it be code-compliant? Would that actually be necessary in this application? Good questions in search of answers.

NorthGuy

Re: High DC voltage relays

Cariboocoot wrote: »

... need to be rated for 600+ Volts just like wiring.

I looked at several ROMEX cables (14/2, 14/3, 10/3) that I had, which are all CSA listed, and they're all rated for 300V. I'm sure they meet the code for 240V wiring.

tallgirl

Re: High DC voltage relays

NorthGuy wrote: »

I looked at several ROMEX cables (14/2, 14/3, 10/3) that I had, which are all CSA listed, and they're all rated for 300V. I'm sure they meet the code for 240V wiring.

I checked Southwire's website and the voltage rating for Romex wire is 600 volts. My NEC is at the office, but I seem to remember that NM has 600 volt insulation as a requirement. If someone can quote Code, that might help.

(And to answer the question about thinking the contacts were rated at 12 volts, I saw "automotive relay" and read no further. My bad.)

Cariboocoot

Re: High DC voltage relays

Hmm. I have some cable here (standard 14 AWG wiring) and it's 600V rated (it's actually insulation rating of course). Never seen any with 300V rating.

NorthGuy, you've got to stop buying your wire from that guy on the corner in the trench coat.

niel

Re: High DC voltage relays

300v wire may break down under the peak ac voltage presented by 240vac as 240 x 1.414 = 339.36v. often times that 240vac is closer to 250vac anyway making the peak even higher. not sure if the voltage ratings are for rms or peak from nec, though the peak rating makes more sense to me.

NorthGuy

Re: High DC voltage relays

tallgirl wrote: »

I checked Southwire's website and the voltage rating for Romex wire is 600 volts. My NEC is at the office, but I seem to remember that NM has 600 volt insulation as a requirement. If someone can quote Code, that might help.

The NMD90 cable that is sold here for residential wiring in all hardware stores made by Southwire and Nexan is rated for 300V. I'm totally incompetent in codes, but I don't think they would sell the wire if it was illegal.

inetdog

Re: High DC voltage relays

niel wrote: »

300v wire may break down under the peak ac voltage presented by 240vac as 240 x 1.414 = 339.36v. often times that 240vac is closer to 250vac anyway making the peak even higher. not sure if the voltage ratings are for rms or peak from nec, though the peak rating makes more sense to me.

The 300 volt insulation is the nominal AC voltage rating and already takes into account the difference between nominal (RMS) and peak.

stephendv

Re: High DC voltage relays

lazza, apologies if I've posted this already, but there is a commercial grid tie inverter available in Spain that will prevent grid feeding: http://powerrouter.com/products/powerrouter-solar-inverter
I can't remember whether you have to use the battery version if you don't want to grid feed... anyway they have a ton of docs on their download pages which describe the different configs.

With regards to your original question, why do you want to switch the high voltage DC instead of just switching the AC output of the inverter?

inetdog

Re: High DC voltage relays

tallgirl wrote: »

I checked Southwire's website and the voltage rating for Romex wire is 600 volts. My NEC is at the office, but I seem to remember that NM has 600 volt insulation as a requirement. If someone can quote Code, that might help.

NM-B is 600 volt.
NMD90 ,"old Romex", is 300 volt.
Both types are recognized in the NEC.
Individual conductors and cables of various types are covered in Table 310.104(A) (2011) and are all 600 volt rated, and one of those types must be used for the insulated current carrying conductors in NM. And we have the lovely Informational note:
"Informational Note: Types NM, NMC, and NMS cable identified by the markings NM-B, NMC-B, and NMS-B meet this requirement."
This recognizes that NM produced before a certain date did not have to meet the 600 volt requirement.
Southwire's NMD90 does not have to meet the 600 volt requirement because it is not NM. (I know, your first guess would have been that NM90D would be a subtype of NM) And NMD90 cannot be used in all the places where the code allows use of NM.

lazza

Re: High DC voltage relays

Hi, thanks for the replies, but does anyone have any more links for those types of relays.

I also have had a couple of thoughts:

1. If I put a kind of by-pass with a relay for one panel in a series of 6 panels (i.e. it short-circuits only that panel in question.), what will happen to the current... i presume it will just cut out the production from that particular panel and the rest of the series will continue to operate normally?

2. If the aforementioned relay is a by-pass in the series for just that one panel... then will the voltage it needs to cope with be just the Voc for that panel, or will it need to cope with the whole string voltage??

Be very grateful for answers to these questions

Larry

ps in reply to Stephen, yes all these types of solutions are ok, but they push the financial viability for an installation out of the window--- the idea is to make systems financially feasible whilst avoiding any problem with the Family (Endesa).

Cariboocoot

Re: High DC voltage relays

If you are bypassing one panel by shorting across it the relay has to carry the Voltage of the remainder of the string.
If you are bypassing one panel by switching it out of the string (using both NO and NC contacts) it has to carry the full Voltage of the string.
If you are bypassing one p0anel by switching it out of a parallel connection it has to carry the Voc of the single panel.

NorthGuy

Re: High DC voltage relays

inetdog wrote: »

NMD90 cannot be used in all the places where the code allows use of NM.

NMD90 is the only kind of ROMEX sold in Canada in Home Depot, Lowe's, Rona and by guys in trenchcoats.

Perhaps code requirements in Canada are different from the US.

NorthGuy

Re: High DC voltage relays

lazza wrote: »

ps in reply to Stephen, yes all these types of solutions are ok, but they push the financial viability for an installation out of the window--- the idea is to make systems financially feasible whilst avoiding any problem with the Family (Endesa).

Switching individual panels may be even more expensive. For every panel you would need a relay with MC4 connections and control wires. All this needs to be installed outside, which means you need weatherproof boxes. That's really expensive.

Using diversion load resistors, or even incandescent light bulbs (if they're not banned yet) on AC side is much cheaper than this.

inetdog

Re: High DC voltage relays

NorthGuy wrote: »

Perhaps code requirements in Canada are different from the US.

They definitely are, and they get updated out of sync with the NEC as well.

NorthGuy

Re: High DC voltage relays

inetdog wrote: »

They definitely are, and they get updated out of sync with the NEC as well.

That's puzzling. How the same thing may be safe in Canada and unsafe in the US (and vice versa)?

Safety is in the eyes of the beholder

Cariboocoot

Re: High DC voltage relays

NorthGuy wrote: »

That's puzzling. How the same thing may be safe in Canada and unsafe in the US (and vice versa)?

Safety is in the eyes of the beholder

It sure is.
When the beholder is John Wiles, and we sometimes think he needs glasses.

westbranch

Re: High DC voltage relays

NorthGuy wrote: »

Safety is in the eyes of the beholder

Safety is from the eyes at the border

tallgirl

Re: High DC voltage relays

NorthGuy wrote: »

NMD90 is the only kind of ROMEX sold in Canada in Home Depot, Lowe's, Rona and by guys in trenchcoats.

Perhaps code requirements in Canada are different from the US.

That's because Canada is not (yet) a part of the US.

(Canadians don't think this is funny. Many Americans don't think it's true.)

Cariboocoot

Re: High DC voltage relays

The big box stores sell what is most often used. They can't stock everything. But we do have electrical supply stores that have a wider variety and greater range of product available.

When I was still working down on the coast I needed a particular, out-of-the-ordinary cover plate. HD and Revy didn't have it. Came home to 100 Mile and bought one at Garth's. Kind of added to the cost with that 850 km trip, but I was making that anyway.

In short, don't expect the Big Guys to be the ultimate source of everything. They're in business for volume sales.

inetdog

Re: High DC voltage relays

tallgirl wrote: »

That's because Canada is not (yet) a part of the US.

(Canadians don't think this is funny. Many Americans don't think it's true.)

Oddly enough (or maybe not given the state of our educational system) inhabitants of New Mexico have the exact opposite problem.

westbranch

Re: High DC voltage relays

Geesh, the War of 1812 is only 200 years ago, The anniversary is just over 8), (we endured a year long :grrset of TV ads about the battles) the Mint even stamped out a commemorative coin set to keep the memory alive, but it seems some ideas die hard.

NorthGuy

Re: High DC voltage relays

westbranch wrote: »

Geesh, the War of 1812 is only 100 years ago ...

I think it's 200 years ago

westbranch

Re: High DC voltage relays

my bad...

the silence on the tube is great now!

lazza

Re: High DC voltage relays

errr about High Voltage DC relays?

ggunn

Re: High DC voltage relays

I have to tell a story on myself. A while back I was touring an inverter company whose gear uses internal DC contactors, and when my guide pointed them out to me I remarked at how small they were. He told me that they were sealed and evacuated to prevent arcing. No arc in a vacuum. Duh.

inetdog

Re: High DC voltage relays

ggunn wrote: »

I have to tell a story on myself. A while back I was touring an inverter company whose gear uses internal DC contactors, and when my guide pointed them out to me I remarked at how small they were. He told me that they were sealed and evacuated to prevent arcing. No arc in a vacuum. Duh.

All you have to worry about is eroding some metal from the contacts (since at a short enough distance and high enough voltage you can have electrical conduction even in a vacuum) or creating an arc based on vaporized metal.

stephendv

Re: High DC voltage relays

lazza, a Spanish company has built and is selling a device that will prevent grid feeding by diverting excess power into a resistive load: http://revosolar.com/solar-shop/es/accesorios-/188-inhibidor-inyectar-en-la-red.html The price to installers is about 150 euros.