Low voltage disconnects

[Sceadwian]

Does anyone know of low voltage disconnects made from solid state devices that are relatively affordable? Or even decent electromechanical modules that don't cost an arm and a leg?
Our zinc plating line is based off of an 8-12 volt three phase DC rectifier that supplies about 3000-4000amps total over 9 cells. Which is 300 or 400 amps per cell continuous. We need the disconnects to delay the application of the power supply once the barrels have contacted in order to control the total plating time. This is to provide variable plating thickness over varying loads with the barrels being in the cells the same amount of time total. Believe me when I say altering ANY part of the system aside from these disconnects is not possible to make the situation easier.
They're currently using air operated solenoids which contact large copper block together, they're basically massive custom made relays, and they cost upwards of 700 bucks each. I was hoping to find some kind of Mosfet or snubber based SCR switching modules or cheaper relays that have snubber to prevent arc welding (primary cause of failure obviously)
Google's not being helpful, can anyone else?

 

[Analog]

Do you need to disconnect all at the same time (4000A) or per cel (400A)??

It wasn't clear to me.

BTW, WTH are you plating? I used to work at GM decades ago and I remember the bumper line - we plated steel with copper first, then chrome.

 

[stevez]

30 yrs ago or more I helped upgrade a plating line and we purchased equipment similar to what you are describing. I'd encourage you to look closely at commercially manufactured equipment for this purpose to see how they are doing it. As you suspect, there are likely to be better ways of handling it.

 

[Sceadwian]

400amps per cell, I'm going to want to derate it a bit probably 150-200% or so. I'm having diffculties finding companies that supply high current disconnects like this. I'd be very intersted if you could provide a few suggestions.

It didn't occur to me until after I'd wrote the post that a simple high current SCR might just work. The SCR's won't turn off under load, but there's no problem with the hoist picking up a barrel while it's under load so that would allow the SCR to reset when the load was removed. The gate current would be off at that point so it's not going to go into it's on state when the next barrel was placed into the cell untill the hoist controller. The hoist enables a 120volt line which would be easy enough to put through a transformer and rectifier to provide 5 or 10 volts to drive the gate when it's enabled, and a simple pulldown on the gate would prevent accidental triggering.
All the SCR's I've found that handle currents this high are in an puk package though. Need to find more information about it.