Reed Switch / Relay Circuit

[DAH1]

Hi,

Sorry if this is a very basic question - pretty new to electronics.

I am looking to but a 2-channel circuit board to switch off a pond pump when a level sensor triggers - then switch on a lamp.

I need to switch 240vac for the pump via the normally closed contacts on one relay and 12vdc to the lamp via the normally open contacts on the other relay.

Both relays will be triggered by a level sensor (essentially a reed switch). Should I fit a resistor in series with the reed switch so I am not connecting the switch across the 12vdc supply?

Thanks
David

 

[D.A.(Tony)Stewart]

Reed Relays have specs for many different coil voltages like 5V or 12V and generally rated around 0.5A where the coil resistance is around 1K for 12V and 0.5K for 5V
Power Relays are the same and are generally rated up to 2A for signals and >2A for power.

Since 12V Reed Relays can activate at 9V, if you actually have 13 or 14V, one might put a 3V White LED in series with the coil to indicate active power Relay.

A lamp with tungsten has a surge cold current 10x hot current which can stress reed relays so LED is better with direct drive from logic up to 20mA for 5mm types.

Relay coils must have a reverse signal diode across coil to suppress voltage spike or transient when opened.

 

[DAH1]

Hi

Thank you for your reply. It's not a reed relay as such but a reed switch connected to the coil connections of a 12vdc relay - just wondered if I need a resistor in series?

Thanks again
Dave

 

[kam1787]

If it is a 12V power supply [12V across the reed relay] then do not put 'anything' in series. The relay is designed to work off 12V.