Shunt trip breaker

[Dave Festing]

Hi Dacian,

In another thread you mentioned shunt trip breakers.

I had a quick look at shunt trip breakers and stopped looking
when I saw some prices.  It would be cheaper to use 3 more DSSR20s
as a protection against failure to stop charging.

Would a unit like this 60A DC SSR work?  I assume breaking 60Amps DC is OK for a SSR.

The down-side is that you need a heatsink to dissipate probably somewhere around

40A * 40A * 0.007 Ohms = 10-15Watts, in my case.

It seems that using a mechanical relay that can handle both the continuous
current and to break high DC current is also a challenge.

Thanks,
Dave

[Dacian Todea]

Dave,

Not sure if those SSR are Mosfet based or IGBT but in any case they will have around 1V maybe even over drop so you can expect 60W at 60A maybe 40W at 40A and that will require a significant heatsink and a fan.

Have I not listed the prices for the shunt trip breakers ? They are not that expensive and they are a mechanical disconnect so a different type much more reliable than having a fail safe that is similar.

One of the breakers I think TAXI is rated for 25kA but you will likely disconnect less than 100A just normal operating current as they are a failsafe in case charger or Load fails to disconnect so it will be normal operation current that will be disconnected.  

[Dave Festing]

Found the thread where you tested some shunt trip breakers, no prices but I will do my own search on Aliexpress.

Thanks,

Dave

[Dacian Todea]

For example the Taxi TXCM1Z 2 pole 125A was 59CAD + I paid extra 13CAD to get the trip coil so around 72CAD in total and I consider that a good price as there are two separate contacts one can be used for Loads and one for charge sources since they need to be separated.  https://www.aliexpress.com/item/4000537721228.html  this is the link I used but there are other sellers.

[Dave Festing]

Thank you for the link I had searched Aliexpress and could not find it.  BTW, it is TAIXI.  Don't see any mention of the trip coil.

Just an idea for a simple solution to ensure that PV would be switched off in case of DSSR20 failure ... either using a PV breaker or a suitable fuse place the contacts of a 24V 200Amp starting relay to ground, driven by a relay driver and EXTIO ... between the breaker/fuse and the DSSR20s.

For a possible once in a lifetime event, it might cost a fuse and a relay.  Main issue is that the relay survives long enough to ensure the fuse blows.  I'll conduct some tests.

[Dacian Todea]

:) Yes is my interpolating brain that seen TAXI instead of TAIXI.

You need to contact the seller and he will provide you with a way to pay for that separately.

I do not have time now to check more option it will be nice to find one that already has the trim shunt integrated by default and be 24V or at least have that as a separate option you can add directly.

Fuse or breakers can not protect against a failed DSSR20. If a DSSR20 where to faill meaning not stop the charging current will not be abnormal it will just not be able to stop the charging and significantly overcharge the battery.

If the DSSR20 fails as open circuit then there will be no charging but again no current so fuses or breakers will have no role.

A relay if I understand you correctly will be more expensive than a trip breaker and will require a few Watt to keep the contact closed circuit.

I'm only aware of one failed DSSR20 and that was because it was installed outside and rain water got inside.  If installed correctly I doubt the DSSR20 will fail unless maybe some direct lightning.

One or two people have damaged the connector by forcing the lever way above 90 degree and breaking the plastic but that is just a mechanical failure.

[Dave Festing]

Contact seller, OK ... if I go this route.

If in a million to one chance that a DSSR20 failed and the battery voltage raises to the high over-voltage value then activate a normally open relay that will place a "dead short" on the junction between the PV circuit breaker.  The resulting 1000s of amperes from the battery will blow the fuse thus disconnecting the PV from the battery.  Effectively, a "crowbar".

Or am I playing with fire here?

[Dacian Todea]

Dave,

I see what you mean now but that relay will need to be powerful enough to generate the current needed to blow the fuse or trip the breaker else if the relay contacts fail fist nothing is done.

Also type 5 is normal close and fault condition open circuit as all the other types that means that if you disconnect the SBMS0 for any reason you will damage a fuse unless you disconnect that first or disable the relay.

If you use a circuit breaker then why not just get one that has trip switch coil like the one I mentioned as is only $10 extra for that trip coil.

The coil since it requires up to 6A (short period) needs a small normal close solid state relay that in turn is controlled by the EXT IOx set as type 5.

[Dave Festing]

A 200Amp 24V starter relay might be enough.

It is not the extra $10 it is the initial $70 as I currently do not have a fuse or a circuit breaker :)

I have the skills to interface a type 5 normal open to control a BIG relay.  Those relays are less than $10 on Ali

[Dave Festing]

Before doing any tests I did think of one potential problem.  If the relay contacts did not release you would have a short circuit on the PV wiring and panels.  Doing that for an extended period might compromise your PV wiring and connections to the panels.  Maybe, even compromise your fire insurance on the house :(

Went ahead and did the test with a 40AMP fuse and a 20/30AMP horn relay.  Fuse blew within a second and the relay still works.

Shunt trip breaker sounds the better choice.  Thanks again for your input.