Go Down

Topic: can you power ac relay of an arduino (Read 983 times) previous topic - next topic

Joes

hi there is it possible to power an ac coil of a relay from an arduino ?
if so how and what with?

Krodal

Yes, with a transistor (or darlington transistor) or a mosfet.

Transistor: you need a resistor to the base of the transistor (value has to be calculated), and a flyback diode over the load.
Mosfet: you need 1k to the gate, and a flyback diode over the load.

Joes

ok what sort of transistor would you recommend?

CrossRoads

Relay with an AC coil?  Do you have a part number?
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.

jackrae

In general terms,NO you cannot power an AC relay from a DC supply.   Basically the DC coil resistance of an AC relay is only a fraction of that of a DC unit of equivalent size.  It will therefore draw excessive current and probably end up either damaging your power supply or burn itself out.  When used on an AC supply the coil is inductive and it is its inductive reactance (Xl) which limits the coil current.   One other factor to be considered is that DC relay armatures (the magnetic core) often have a little non-magnetic buffer (copper or plastic) for the moving blade to contact onto.  This prevents any residual magnetism from holding the relay closed when the power is disconnected.  AC relays do not need this facility since residual magnetism is minimal - it being eliminated each half cycle of the AC waveform.

Joes

lol no no no a AC relay being powerred by a AC supply
this is the sort of relay i was thinking of : http://uk.rs-online.com/web/p/non-latching-relays/0376830/

ChuckJaxFL

You can use an Arduino to control a SSR w/ no other components involved. Must your relay be mechanical?

Krodal

For a 24V AC relay at DC, you might want to start with 12V.
If you use the AC relay with the same DC voltage, the coil could get too hot.

CrossRoads

That relay comes in both AC coil versions and DC coil versions.  See the last page of the data sheet.
http://docs-europe.electrocomponents.com/webdocs/0027/0900766b800270d6.pdf

The specific part you linked to has a 24VDC coil:
Coil Voltage 24V
So you'd need a 24VDC source, and Arduino controlling a transistor to sink current thru the coil to control the contacts.
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.

Joes

i think i havent explained myself correctly i want to power an ac coil or a relay using ac controlled from an arduino the link was for a 24V ac coil would prefer to have a mechanical type

jackrae

If you are adamant that you want to operate an AC relay then what you need is a DC "interposing" relay.  Your arduino drives (via a transistor) a DC relay.  A set of contacts from the DC relay are used to control your AC relay.  Messy ? yes, but that's how you operate an AC coil from a DC system.  There is no way you can use an arduino directly to drive an AC device.  But no doubt others may come up with alternatives.

Joes

ok so us a PCB SSR to power a AC relay

jackrae

#12
Aug 06, 2012, 10:41 pm Last Edit: Aug 06, 2012, 10:44 pm by jackrae Reason: 1
Arduino drives this directly via a 220ohm resistor and this then switches your AC relay.  The device output current is a maximum of 100mA but this is more than enough for your titchy little AC relay
http://www.farnell.com/datasheets/73794.pdf
Be aware that you have low voltage DC on one pair of terminals and your AC drive voltage on the other

Joes


Grumpy_Mike

Quote
The device output current is a maximum of 100mA but this is more than enough for your titchy little AC relay

Not much more, as it takes 75mA so it s close to being not high current enough.

Go Up