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solid state relay on dc

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muhammadali_16

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hi to all.

i have to switch a surge current of 100A for micro second to burst a resistor. i generated 600V and stored in capacitor
i want to use ssr to switch. for that purpose i bought a relay. the output section of the relay is 240VAC.
i tried to switch the dc voltage from that relay but it didnot work.

can anyone tell me what should i do to pass surge DC current through a AC SSR


thx in advance
 

crutschow

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If an input control current is supplied, an AC SSR should turn on to pass the DC pulse from the capacitor. Of course it won't turn off until the current through it stops. Show your circuit diagram and the part designation.
 

FvM

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AC SSR means that the load can't be disconnected before the capacitor is fully discharged. I guess that's no problem.

Secondly the SSR must not have zero crossing switching logic, otherwise it would never trigger with DC voltage applied. Most AC SSR are equipped with zero crossing logic, however.

Finally, the SSR should have sufficient peak current and I2t rating for the expectable discharge current. I presume, you have checked this.
 
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Electro nS

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i will never switch DC load , this is an AC relay probably with zero corssing logic like FvM said .

if you want it to work , try to disconnect the load wire then connect it after the relay has been switched on , but again to turn off the relay you should disconnect the wire (forcing the current passsing to reach zero )

what you really need is a DC solid state relay . (by the way it is quite expensive)
 

betwixt

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Inside most SSR is two SCRs connected in parallel, head to tail, one for each half of the AC cycle. There is usually also a circuit that blocks the trigger pulse if a voltage of either polarity is present across the terminals (zero crossing detector). So for DC you need a circuit that only has one SCR and no zero crossing detector. In other words an SCR! If it needs an isolated input just use an opto-coupler.

Brian.
 

Electro nS

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Inside most SSR is two SCRs connected in parallel, head to tail, one for each half of the AC cycle. There is usually also a circuit that blocks the trigger pulse if a voltage of either polarity is present across the terminals (zero crossing detector). So for DC you need a circuit that only has one SCR and no zero crossing detector. In other words an SCR! If it needs an isolated input just use an opto-coupler.

Brian.
what you said is true , but how would you suggest turn off the SCR before current threw it reaches zero ? (assuming turning on is relativly simple)
i suppose that would be hard , or you will need a GTO. what do think brain ??
 

godfreyl

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Wouldn't a MOSFET or IGBT be more suitable for this?
 

betwixt

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It depends on how much charge is in the capacitor and what the resistor value is. Dumping 100A from a capacitor will surely discharge it very rapidly anyway.

I worked on a design a few years ago that discharged super-capacitors into ni-cad cells (don't ask why!) and I used a bank of parallel MOSFETS, each rated at 300A peak Id. Aparently if worked but but dimmed the building lights as it operated :shock:

Brian.
 

Electro nS

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Wouldn't a MOSFET or IGBT be more suitable for this?
yes offcourse , but as you know both need drivers and that compicates the circuit if you are designing the relay.

actually DC solid state relays contain mosfets with Optoisolated drivers built in .. check www.crydom.com/
 

FvM

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Everything is correct for DC solid state relays in general. For the problem addressed in the original post, a SCR switch will be probably the best solution.
 

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