question

Hallo

Do you unterstand what happends now? Or do you still need some explanation?

ohhh yes, I removed the 275A VICTRON Battery switch, no desire to burn

This is also a solution :D
It is because of the contact resistance. The 275A Switch has a contact resistance. This causes a power loss, heating the switch.
But 100A and 67°C is ok for me .... I'd say I have the same ...

I also use the Victron 275A switch with my Multiplus-II 5kva and even with 100A+ running through it, it doesn’t heat significantly.

HOWEVER, as I have commented in other threads on this forum, these switches can be very easily damaged either by turning the switch off while under load or, more commonly, turning the switch on with the Multiplus internal capacitors discharged and thus causing a current surge and associated arc which damages the internal contacts. I went into more detail on the correct power up/down sequence in this thread if you’re interested: https://community.victronenergy.com/questions/313922/what-is-the-correct-order-to-power-up-a-mp2.html

Another thing that’s important is to ensure that the bottom nut is tightened up before the crimp lug is fitted along with the spring washer and top nut. This bottom nut ensures that the internal contacts are correctly positioned in relation to the switch wiper. I don’t think there is a torque spec for the bottom nut but the top nut is 12.5NM (IIRC) so I’d suggest something like 6-8NM for the bottom nut. It’s important to check it every time because the bottom nut tends to loosen slightly when the top nut is removed.

I’ve gone through three of these switches and my latest one has never been switched so has pristine contacts. If you want to check yours, you can remove the 4 screws on the back of the switch and take a look. It’s not a complex assembly so just take care how it comes apart and don’t over tighten those screws. I posted a photo of the inside of one of my switches on the forum but I can’t remember which thread it was on.

HTH

Edit: This is the thread - look for posts by me on December 8th 2023 and you’ll find the photos of my switch (old and new). I tried to upload the pictures to this thread but I’m getting an error from the website so can’t.

https://community.victronenergy.com/questions/247351/what-happened-to-this-cable.html

I didn't know the term "jean-muller" in France they call them "knife disconnectors" and indeed there is nothing better. These are the ones I put and no overheating since :)

I want to comment on this. We have stopped using this switch after too many dangerous situations - the switch was totally destroyed many times.

The switch is poorly designed and its rating is WAY too high. All our problems with complete destruction were with currents BELOW 200 A. All the current is transferred on a few mm2-sized contact.

If something has 275 A rating for continuous duty cycle, then it MUST be ensured that heat is dissipated so that there is no risk of thermal destruction - given the internal resistance.

We have had multiple switches fail with only one start-up (during commissioning) - so the idea that this can be caused by the wrong start-up sequence is FLAWED.

Also, in none of the cases were terminals too loose or too tight - terminal failure was never the case.

I have reported this many times via our distributor, but it has never been reflected nor properly explained by Victron.

Problems with this switch are:

- poor construction

- overrated amperage

- resulting in overall bad quality

Period.

My advice (with all due respect towards good Victron products) -> don't use this if you want to be safe and have a good night's sleep. Knife disconnectors/fuses by Jean Muller for example are a good solution. If you can't use them, don't use the switch at all.