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AC-AC SSR Solid State Relay

This is a AC Control Input AC Output SSR Solid State Relay. When a Process Controller has an AC output or a system generates an AC signal of above 100V AC to signal the load to turn on, this device can be used. A BTA40-600 and MOC3041 are used in this.

Fire Retardant SSR Enclosures

A high voltage plastic cap limits current to a bridge which generates a small DC from 230 V AC, this drives MOC3041. The rest is the same. It is better to use a DC control SSR where possible. This AC control SSR is used where only an AC control signal is available. The BTA series has the heatsink tab insulated from the Triac chip inside. The BTB needs electrical insulation to the heatsink.

ac-ac-ssr

Electrical Control Panel Wiring

These devices BTA40600 and MOC3041 make SSR’s very simple. They have proved very reliable and rugged in the field, overrate your designs, use heat sinks and seal the SSR with thermally conductive epoxy. Alumina with ciba araldite without any other filler or dye is the best way to hermitically seal.

Drive SCR thyristor with 555

This circuit gives a burst of pulses to fire 2 SCRs, when pin 4 is taken to 12V the SCR is turned on, to use this circuit you need 12V short pulses phase shifted with respect to AC sine wave on bridge, like this you can control the bridge from near 0% to near 100% ON.

Drive or Fire Thyristors SCR with Pulses

Drive SCR thyristor with 555

Learn about Thyristors here Power Electronics

That way battery banks can be charged, electroplating can be done, current and voltage can be controlled with opamps, thyristors are very rugged compared to transistors and MOSFETS in that order.

Solid State Relay – Common

This is a DC controlled Solid State Relay which can turn 230V AC equipment on and off. The output is like a NO normally open contacts of a relay and have to be in series with the Load like any other switch.

Solid State Relay - Common
This should not be used for large inductive loads like big motors. The Q1 transistor limits the current thru the LED by providing an alternate path for more current. The DC input can be from 3V to 20V.

The Triac can be chosen depending on current in the load. Look for datasheets and applications at STMicroelectronics for BTA41600 triacs. MOC3041 zero crossover opto-diacs.

Read more at my main page – Solid State Relays – SSR I used to make them long ago.

Solid State Relay - Common

Triac based Lamp Dimmer power control

This is a phase angle control of a Triac which is a evolution from an SCR. The 50 Hz or 60 Hz Sine wave of mains can be turned on at any point after the Zero Crossing.

Design Notes – Power Electronics – 03

Triac based Lamp Dimmer power control

The Voltage ramps up in the sine wave which gives a near “Linear” slope which can be used to trigger the ON at a time delay after zero crossing when the voltage is zero. This is like a PWM but works on low frequency only. Some of the early SMPS(HV for TV and Mains Inverter) by Siemens were built around SCRs. Turning off a SCR is a difficult job for a designer, MOSFETS and IGBT are now used for PWM drive stages.

High Energy Circuits

You can use it with a bulb to vary brightness of bulb, this is a live circuit it can give a shock, enclose in plastic box, the pot should have a plastic knob, use a fuse, you can also use it for temperature control of soldering irons.

The Source file in CadSoft EAGLE format is here del00004.zip

Connection Diagram of AC Control SSR

SSR or Solid State Relay or Electronic Relay Connection Method. This is a Thyristor Based Normally Open 230V Switch that can be turned on / off at a fast rate. This switches at Zero Crossover .Built In Snubber reduces EMI and protects the SSR. USE SAME PHASE FOR I/P & O/P.

AC-AC-SSR Solid State Relay

AC-AC SSR Wiring

  • No moving parts hence no wear and tear.
  • Dissipates Heat when in On Condition.
  • Use adequate Heat Sink or SSR will fail. ( 10g / Amp)
  • Dissipation is 1.5 Watts per Amp thru Load.
  • Input to Output is optically isolated 2kV.
  • This one is AC 230V Control AC 230V N.O. Output.
  • Off state snubber Leakage is around 5 mA.

Notes –

The Termination’s of High Current Lines going to Load must be very tight and crimped. Loose contacts will Spark and cause Fire. Fuse Rating of HRC Fuse – High Rupture Capacity (HRC) Fuse is Safe and Reliable. 5kW Heater at 230V is 5,000 / 230 in Amps of Fuse Rating.

2N2646 based Voltage controlled SCR Pulser

A Center tap 50Hz Step Down Transformer with two diodes is used to get a train of Positive Sine Pulses at 100Hz which is applied to Q6 base via R51. 2N2646 is a unijunction transistor(UJT) in a TO-18 metal package. The control voltage or voltage proportional to error is fed to R56-Q3, The UJT drives a pulse transformer which provides isolation from the Load which the SCR bridge is controlling. This phase angle control gives a near Linear closed loop control for a SCR bridge which may be used in Electroplating or a Preregulator of a big power supply.

2N2646 based Voltage controlled SCR Pulser

Normally Closed AC SSR

This is a Normally Closed PCB Mount SSR. That means when DC Control input is low, the triac is ON, the output passes the load current to turn on small heater-motor-lamp or a bigger contacter-drive etc.

NC Solid State Relay or SSR

When input DC is high the output is OFF. This is also Optically Isolated from Mains. A Microcontroller output which is buffered by some driver can drive this relay. It is better that in big systems these SSR Modules can be on another PCB, to avoid mains wiring near Logic circuits. But this cannot be used for medical electronics, or critical applications. More reliability and visual isolation of voltages may be required for such equipment.

NC AC Load SSR DC control