EEVblog® Electronics Community Forum
Electronics => Projects, Designs, and Technical Stuff => Topic started by: classified on July 20, 2022, 07:40:30 pm
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hi there now for me safty is #1 so for a battery i am building i will have 2 contactors a side (mostly for safty incase one or more weld closed) but to test if there closed i can not see how this couldgo wrong its simple raily useing a optoisolater going from usaly open side of the contactor to the opasit pole useing a resistor to avoid blowing up and leds so dose this seem like a good way to do it and if there better ways i am open to ideas
F.Y.I i know in the picture it shows relays but i couldent find a contactor sch item but a contactor is just a realy after all
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Well, I think you could do it this way, although for me this is close to paranoia.
There is also a special type of relay, Dold calls them Safety relays with forcibly guided contacts, which could spare you the additional circuit.
As far as those type of relay are suitable for your application demands.
Is there a specific reason why you use the NC contact on the negative side?
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as i stated i used what i could find to do a quick schematic of what i was thinking the relays will be replaced with contactors that are NO when i build it
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If u1 welds, but u2 doesn't how will you know? I don't see a current path for the LED in U5 when the contactors are deenergized with U1 welded. I'm assuming they all turn off at the same time. I think you would need to turn the contactors on and off sequentially while monitoring the optos for faults.
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Use a "shunt trip" circuit breaker as the backup disconnect. That way, a fault that the main contactor is not able to break would require a manual reset.
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If one arc welds shut so might the other, it will have to try and disconnect the same load current.
RC snubbers are essential. The capcitor slows the di/dt and the resistor limits the peak current in the cap.
see section 4-2 of https://sound-au.com/articles/relays2.htm.
You might want to consider using IGBT(s) or MOSFET(s) to make a solid state contactor. SiC MOSFETS would be my first choice.
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Model sailplane flyers who use a 12V DC winch to get the planes to altitude will often use two solenoid switches in series for safety. It does happen that a single switch will weld in the on position. That creates a problem.
The solution we used was just an LED with suitable resistor across the contacts for each switch. Both LED's on = OK; otherwise, not safe.