replace relay with mosfet to switch ac loads

[mshh]

i want to replace a relay to switch Ac load(heater ) that will draw about 20 Amps . i used IRFP250 and bridge rectifier as in the picture . i still didn't do it . the voltage gate come from a plc (programmable logic controller) 24 Volt positive or negative .
will this circuit need any thing else ? will the mosfet need heat sink to act as a switch ?

 

[Easyrider83]

Damn, this gona blow ))) Man, don't even think about turn all of this on.
Use **broken link removed** if you want so, but please, don't show this schematic anybody else.

 

[mshh]

what a terrible comment ! but you didn't tell the reason for blow?

 

[Easyrider83]

You trying to supply AC current motor with DC current.
Your diode bridge (right one) will have to dissipate 20A*2*(~1.5V)=60W power in heat.
And somehow you should find isolated DC voltage source to open the mosfet.
I have no idea what will blow first, but it could be very impressive.

 

[mshh]

isolated DC voltage source is on the left. there i s optocoupler to isolate,isn't it?

 

[Easyrider83]

Again, where do you want to take '24 volt dc' to open the mosfet? And why 24? 9V will be enought.

 

[FvM]

The schematic makes no sense. You say "heater load", but the schematic shows a motor.

A heater could be possibly supplied with DC voltage, but why you should? AC switching is much easier with triac and triac optocoupler, you also get rid of the auxilary supply.

 

[mshh]

The schematic makes no sense. You say "heater load", but the schematic shows a motor.

A heater could be possibly supplied with DC voltage, but why you should? AC switching is much easier with triac and triac optocoupler, you also get rid of the auxilary supply.

there is no heater in proteus so i used motor, the heater is ac not dc. if i used triac i willneed big heatsink i want it small

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Again, where do you want to take '24 volt dc' to open the mosfet? And why 24? 9V will be enought.

as i said in the first post it s coming from plc so it is 24 v no more no less. 24 v will be applied on the optocoupler

 

[kappa_am]

The schematic has many vague points.
why you have add a full-bridge rectifier? (Right-side of the picture)?
in this configuration voltage over the heater is DC.

I recommend using solid-state relay. i have seen some in TE site which works with 24V command voltage.

you could also build one, yourself.

all in all, this circuit strongly is not recommended.

Good luck

 

[FvM]

there is no heater in proteus so i used motor

Really? A heater isn't but a power resistor, so it's surely available in Proteus.

the heater is ac not dc

1. Why? Most heaters don't care about AC or DC.
2. If so, your circuit is wrong, because it applies DC to the "heater".

as i said in the first post it s coming from plc so it is 24 v no more no less. 24 v will be applied on the optocoupler

Is the 24V supply floating (not connected to ground or other circuits) as required by a gate driver connected to 230V?

 

[schmitt trigger]

A phototriac, like the MOC30xx-series, plus a suitable rated main Triac, will accomplish the job easily.

To switch very high currents, a pair of anti-parallel SCRs may be substituted for the Triac.