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Topic: 12 A relay shield for 230 volt ac home appliances  (Read 2489 times) previous topic - next topic


Hi All,

Can I use 12 A relay shield for home appliances which operates on  230 volt ac  ?


It depends on the relay contacts rating and the appliance you are wanting to switch, and of course this depends on what relay shield you are using.


The relay contact ratings are their maximum.   For example, a 230V, 12A relay can be used to switch 1 Amp at 120V.   

If know the wattage rating of your appliance but not the current, power (Watts) is calculated as Voltage x Current.  ...A 230V 1200W hair drier is drawing 5.2 Amps.

The relay's coil ratings are "exact" ...A relay coil that takes 12V @ 100mA, needs a 12V power supply/soruce that can supply the required 100mA.


No shield as such can be used safely for mains - there is not enough physical separation between
mains and low voltage stuff possible on a shield.

A separate relay board with adequate spacing and/or PCB cutouts to protect low voltage from
the mains side would be the right technology.  It ought to be conformally coated too really...
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]


Jan 23, 2016, 10:30 pm Last Edit: Jan 23, 2016, 10:31 pm by CrossRoads
I have a relay shield, with 250A, 5A rated relays.
Here's a youtube video of it controlling LED light strings.
and close up is attached.

I've also done a standalone version that could connect to any card, with more separation between the line that gets switched, closeups also attached (not assembled one yet tho).

For 12A, you need much wider, and/or thicker traces, to handle the current and not just become fuses.

Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.


At some point, a contactor might be a better choice.
He's not stated if he needs it to handle an inductive load.


No shield as such can be used safely for mains - there is not enough physical separation between
mains and low voltage stuff possible on a shield.
I agree with that.

These days there are low-cost relay boards like  THIS:that have built-in Optical Isolation. The board linked here has a relay rating of 10A at 230V.

There is also a 30A rated relay with optical isolation  HERE:

There is some relay How-To on the ArduinoInfo.Info WIKI HERE: See the page  HERE:

If you need to switch inductive loads or have EMI (ElectroMagnetic Interference) problems see the page  HERE:

DISCLAIMER: Mentioned stuff from my own shop... but you can find these relays on Ebay etc...
Regards, Terry King terry@yourduino.com  - Check great prices, devices and Arduino-related boards at http://YourDuino.com
HOW-TO: http://ArduinoInfo.Info


I need to on off below mentioned devices

1. RS Water heater 200 watt AC 220/240V 50-60Hz
2. SOBO air pump 2.5 watt AC 220/240V 50/60Hz
3. SOBO WP-850F filter 4Watt AC 220-240V
4. Aquarium Bulb 15 watt  AC 220/240V

And i have below show Relay with  Toshiba  ULN2803APG


Jan 26, 2016, 04:21 am Last Edit: Jan 26, 2016, 04:24 am by Boardburner2
One other thing worth mentioning.
While a shield may well be suitable for domestic control of mains.

If it does not have UL and CE ratings your insurance may be invalid.

Also connecting it to your domestic supply will likely need a certified electrician to meet local electrical codes.



You have data on the top of relays. Important value for you is 7A 250V ~. All your devices are under max. switched current (7A). In case of higher current need you can add auxiliary relay (let say for 16A) with ~250V coil driven by shield relay.

1. You have already similar topic. To create another one is useless.
2. You can drive ULN2803 directly by Arduino ports (ULN2803 is good for inductive load also), no additional components are needed like opto-isolator.
Arduino clone with ATmega1284P   http://forum.arduino.cc/index.php?topic=277260.0

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