Further info.
I never did get the failed Victron isolator back.
The blue sea 9004E on the inverter (10kW) got warmish maybe 50C at 100A? However the replacement to the Victron (a no-name 9004E) which was taking perhaps 110A was essentially stone cold.
I replaced the Blue Sea, as I knew it had been used (perhaps 3 to 4 times) with a turn-on arc. I was surprised at the damage, particularly as the switch really wasn’t excessively hot. Quite impressive that that much damage has a relatively modest effect. I wouldn’t like to trust it though.
This totally confirms my belief that potential equalisation is essential to maintain isolator integrity. It is an isolator, NOT A BREAKER, and the capacitance charging compromises its life and may be a fire hazard if in an isolated location.
Personally, I would use a 75 ohm resistor for charge/discharge. I used a 25W, but probably a 5W would suffice. Now some pix.
The latter a crude but effective charger/discharger. Normally, the probe would be plugged into a multimeter to check the residual voltage before actuating. Cockup with lead and croc clip colours, hey-ho…
Impressive, but also expectable. This “sparks” of hot metal shoot out of the contact area tells the story. Very likely this was few 1000A for microseconds, but this is what destroys your contacts.
Hopefully everyone building such high amp aplication is seeing this pictures.
I have a fixed installed pre charge circuit in parallel to the breaker. I just push the button switch with a ~48Ohm resistor for 5 seconds before switching on the breaker.
I have marked your post as the solution. Professionally, of course, it is, probably with a label describing the required actions.
I very much doubt this will go much further, save for a few teckky installers.
Ideally, isolation would be built into the MPPT/inverter/charger and arranged such that arcing is prevented (eg by delays).
You are right, - a kind of soft-start would help to avoid this inrush currents, but this has to be added in every component (MPPTs, Multiplus,…) that has big capacitors instead of a central unit.
And every additional component is another source of problems… so it is up on us DIY guys or the installers to know this and to prevent this.
Yes and you still need the isolator to isolate the component for (eg) replacement, so actually not solving anything.
It needs a specific switch for high capacitance devices.
I note that in each damaged isolator only ONE contact is burned. I presume that the first half contact to make contact does so at zero potential difference, as the second is yet to make contact. When the second one does, it arcs and appears to plate copper from one contact to the other leaving the other contact undamaged.
A solution is to have two pairs of contacts. One pair that makes first and gets the arc damage but equalises potentials, then the second does so at zero amps (eg 35 deg and 45 deg). The working current will go through the second pair as it will be a lower impedance and the switch will stay cool. This is simple and cheap. More complex methods with delays etc will be more expensive and perhaps prone to other failure modes.
Anyway a thought. All avoided by knowledgeable installers and users.
