Solar power dc solid state breaker

[robint]

This has been partly addresses in https://www.eevblog.com/forum/renewable-energy/solar-system-with-dc-failover-and-storage/msg4977091/#msg4977091 ca 1 year ago and tech moves on quickly.

What I have been researching is whether there is a reliable master circuit live disconnector to be used to cut Solar panel input before the inverter.  Unfortunately Ive seen a lot of very ill informed armchair opinions on the subject of dc current circuit breakers on the web that utterly fail to recognise the nature of high current dc source from a Solar panel array - know what I mean

In the Solar dc world a little knowledge is a very dangerous (burn your house down) thing

I hope we are all aware of the limitations of MCB type switches on Solar current so skip over that can of worms.

I have seen the prospect of using an array of power mosfets (as used in BMS's)  however I read that they are not always reliable sufficient for a Master Breaker (in my oldschool mind - a knife switch as used in heavy current industrial applications - traction, electrolysis, UPS (telecom) etc prewar.

The switch has to accommodate > 50Vdc  100 - 200A live disconnect and must not have any inclination to turn on (as per FET problem and potential spurious EMI).  I gather these SSR's have a heat dissipation problem and also a reverse leakage issue also generating significant heat.

I am considering a dual method approach, namely to use an SSR mosfet switch in series with a robust solenoid relay (as used in a fork lift for example) BTW most Auto offerings are not suited for continuous operation. The relay can be time operated to trip after the SSR in say x ms.  Ive even seen to old school bimetallic switch used as a timer with reliable proven duty.
This save wear on contacts.  I believe the reverse operation can be used when powering on (relays are more robust at handling inrush)

Might even be useful to put a relay across the SSR once power is established - reduces heat generation?  or is this getting Mickey Mouse?

400Adc  100V+ with little M6 phillips head screws  $15  Cheap Charlies is 'avin a giraff

Well thats my starter for 10

Whats your opinion guys

[ahbushnell]

I'm confused.  Do you want a circuit breaker or a disconnect?

[floobydust]

Safety agencies want a true physical disconnection. They don't accept semiconductor or polyfuse etc. interruption.
There is significant cable inductance present and the semiconductor will be subjected to that back-EMF.
There are latching relays for solar, smart meter, inverter, and EV use that work.

[jbb]

A cautionary tale that Robint apparently knows but others may benefit from.

TL;DR: carefully check the specifications for any DC switch gear!

A couple of jobs ago, my colleagues got a DC rated circuit breaker with a MINIMUM current rating. We thought this was odd, so we connected it to our big (7kW linear regulator!) PV (solar) emulator and a load resistor. The load was less than the specified minimum current.

When we opened the breaker manually, it arced internally. It arced and arced until we turned off the external power some seconds later.

If we hadn’t turned off the power I’m sure the breaker would have continued to arc and eventually broken apart in a hazardous manner.

[Gyro]

...
When we opened the breaker manually, it arced internally. It arced and arced until we turned off the external power some seconds later.

If we hadn’t turned off the power I’m sure the breaker would have continued to arc and eventually broken apart in a hazardous manner.

Ok, it's a big one, but solar arrays will arc and arc until the Sun goes down, or the gap gets big enough...

(I've been looking for an excuse to link this video! )

[robint]

I'm confused.  Do you want a circuit breaker or a disconnect?

Indeed there's a lot of misconception about the concept of a circuit breaker because Average Joe tends to take its position for granted thru basic ac domestic installation practice.

eg

It originated  with Utility suppliers insisting on this order of precedence "Source - Main fuselink(Utility access only) - Main Isolator Switch (maybe lockable often combined within Consumer Unit) - Distribution Board (aka Consumer Unit) Main Switch - MCBs - subcircuits - fused plugs( power) or switches (lights).

There are those designed for:

manual disconnect under load
auto disconnect under overload
disconnection under fault current
switches intended for isolation
emergency stop PBs
Selector switches
No Volt lockouts
etc

The use of "Circuit Breaker" by itself can be misleading in dc use

eg  I have often seen say battery (bank A to B) selector switches (rotary cam type) used without any warning about switching under full load (with the inevitable arc wear or worse that occurs). Where are the interlocks?

I believe the NEC insists on an exterior "Firemans Switch" for Roof panels

The last thing a Fireman needs is to be presented with a complex distribution cabinet somewhere in a basement
 
Here's the answer - the ubiquious preware Siemens pattern knife switch still used in millions of houses thru far east (a larger one rated for 60A is available ca 150% bigger ca $15 perfectly ok for ELV <50Vdc, just wear gloves and cover you eyes.  The Switchgear mafia dont want you to know about this
And below here is the proof it works - a 600Vdc prewar switchboard for the London Underground


I finally to bore you all stupid here is a demo of my hypothesis that a 48Vdc panel array needs a separation gap between contacts (and fuse links) of 50mm or 2" to break an arc flash reliably
If it still persists then use a plant water mister to douse the flame
Whats not to like?

[fourtytwo42]

I think a lot of people are using unsuitable equipment not rated for the job.
In my case I always use IMO operator independent (meaning make/break speed) gear such as https://technical.imopc.com/imo-solar-range.pdf with arc suppression.
I would never trust semi-conductors as an on-load fault breaker, in some cases the fault is actually caused by failed semi-conductors!
Fork-lift equipment is not rated for operation at anything like 600V or more that is fairly common in PV installations.

[floobydust]

[...] I finally to bore you all stupid here is a demo of my hypothesis that a 48Vdc panel array needs a separation gap between contacts (and fuse links) of 50mm or 2" to break an arc flash reliably
If it still persists then use a plant water mister to douse the flame
Whats not to like?

The video using DeWalt goatskin driving gloves for an arc flash (hand-hand) demo, I do find that funny.
There's no info about that show voltage/current/inductance other than three panels are in series. Would be very interesting to recreate it because it shows present DC disconnect/breaker spacings may not be enough. Although they do incorporate a blowout magnet.

Telsa Motors invented "electronic fuse" for their EV's, its some mosfets and a little lithium battery power system. There is a patent for it. Regular HV fuses are crazy expensive.
Not that overcurrent is really possible with PV but it shows their method to disconnect using semi's.

[NiHaoMike]

Seems the simplest solution would be thermal fuses rated to break the full string voltage, install one at every connection between panels. Don't think that exists off the shelf but it theoretically shouldn't cost much to make.

[uer166]

You're mixing up Tesla eFuses with the HV pyro disconnects, they're 2 unrelated systems:

The eFuses are just normal high-side-drive type of silicon for 12V and 48V systems, some are discrete, others integrated. They don't provide safety isolation, only fault/over current protection of the harness.

The HV pyro fuse with the lithium battery is an older type that is used to physically disconnect HVDC from pack. There are no silicon switches here. That use a cool trick where the main pyro is rated to 12V only, and then some small HRC fuses take the main 400V arc.

Finally the new HV pyro disconnect has no batteries, and is triggered from another ECU. It has arc quench plates that take the 400V arc after the explosive separates 2 metal plates by about an inch.  It's actually very similar in construction to mains breakers, just bigger arc quench plates than normal.