What kind of 12v relay do I need?

[Jokani]

I would like to install a low wattage deck light connected to a photocell, but I would like it to be automatically turned off if I switch power on to my nav lights panel.

I think I can do this with a relay? But I'm confused by the terminology and unsure which kind I would need?

 

[Rum Run]

Bog standard automotive 12v relay, which is single pole double throw will do fine and cost buttons off eBay. They are available in waterproof too. This is the 5 connector type. Normally has 1/4" spades for crimp connectors.

 

[Jokani]

Bog standard automotive 12v relay, which is single pole double throw will do fine and cost buttons off eBay. They are available in waterproof too. This is the 5 connector type. Normally has 1/4" spades for crimp connectors.

Thanks for the advice Rum, I am glad I asked, I was looking at something totally different.

I've Googled wiring diagrams for this but I can't see an example of how to wire, when I need to switch off the light if another switch is switched on, can you point me in the right direction?

 

[PaulRainbow]

Thanks for the advice Rum, I am glad I asked, I was looking at something totally different.

I've Googled wiring diagrams for this but I can't see an example of how to wire, when I need to switch off the light if another switch is switched on, can you point me in the right direction?

http://www.12voltplanet.co.uk/relay-guide.html

85 and 86 are for the coil, connect one to 12v - and the other to the light 12v +

Your light positive is wired via 30, then 87a.

 

[Jokani]

http://www.12voltplanet.co.uk/relay-guide.html

85 and 86 are for the coil, connect one to 12v - and the other to the light 12v +

Your light positive is wired via 30, then 87a.

Thanks Paul, so I need the 'Make and break' 4 pin relay, no need for a 5th pin?

 

[William_H]

The coil and so the relay needs tohave power or pull in when the nav lights. So this will present a bit more current to the nav lights circuit. (not a concern) The contacts on the relay need to be those that are made (connected) when the relay is quiescent ie no coil power. But contacts which open when the relay operates. This contact is wired in series with the deck light.
Or if you wanted to be a bit smart use a p channel Mosfet like IRF540 with +ve supply for deck light going to the source and +ve supply to the deck light going from the drain. The gate is connected to -ve via a 220k ohm resistor. This will make the deck light work. If you then feed from the nav lights +ve via a 10k ohm resistor to the gate this pull up the voltage on the gate to near 12v so stopping the Mosfet from conducting turning lights off. PM me if youwant to try this last option olewill

 

[PaulRainbow]

Thanks Paul, so I need the 'Make and break' 4 pin relay, no need for a 5th pin?

No Gary. The 4 pin only makes a circuit when the coil is energised, the 5 pin makes one and breaks another. You need to break the deck light circuit, so you need the 5 pin.

 

[Jokani]

Many thanks for all the advice, I'll let you know how I get on.

 

[Jokani]

Relay on order, can I ask, is this the correct way to wire the relay for my needs?

Just to recap what I am trying to achieve. Security light will be on all the time, except when the nav panel isswitched on, then the security light will be switched off:

 

[bedouin]

It would be simpler if you could use a switch rather than a relay - could you replace the switch that you want to use to switch the relay with a DPDT one that directly switches the other circuit? Or just add a separate switch to disable the deck light in case you should want that and the nav lights on at the same time

 

[Jokani]

Hi Bedouin, thanks for the advice.

I would prefer to go with the relay for two reasons:

1) The switch to power the nav panel will be in a ready made 12v switch panel so I cannot swap the switch.

2) I could add a second switch to disable the security light, but I know I would forgot to switch it back on, so would prefer to automate if possible.

 

[rogerthebodger]

Relay on order, can I ask, is this the correct way to wire the relay for my needs?

Just to recap what I am trying to achieve. Security light will be on all the time, except when the nav panel isswitched on, then the security light will be switched off:

Don't think that id correct if I understand what you are trying to do

You wish to have your security light to be able to operate when there is no power to your navigation light panel. I assume you have a master power switch that only feeds the nav panel and the nav panel controls which nav lights are on when the master switch is on.

If that is the case
85= nav panel power from output of master switch. If its only when one of the navigations light configuration is on it from the output of that switch
86= negative DC system 0 volts line.
87a = + from battery
30 = to securite light
87 = nothing
87a and 30 could be reversed

My reading is that when the nav light is off you wish the security to operate so when the relay is deenergized you wont power to the security light. When the nav light is on and the relay is energized you wont no power to the security lights system.

Hope I understood what you wanted.

 

[PaulRainbow]

Relay on order, can I ask, is this the correct way to wire the relay for my needs?

Just to recap what I am trying to achieve. Security light will be on all the time, except when the nav panel isswitched on, then the security light will be switched off:

Correct relay, wrong wiring Gary.

85 12v -
86 + from nav light switch
30 12v + This should be fused, rated for the security light.
87a To security lights

When you turn the nav lights on the circuit between 30 and 87a will be broken and the security light will go off, terminal 87 will become live (make sure it's insulated, an insulated spade will do the job).

 

[Jokani]

Roger and Paul, I really appreciate you taking the time to correct me, thank you.

 

[Jokani]

terminal 87 will become live (make sure it's insulated, an insulated spade will do the job).

This could likely have saved me from a bit of a shock, maybe even the boat, I would have left it bare! Thanks again!

 

[VicS]

This could likely have saved me from a bit of a shock, maybe even the boat, I would have left it bare! Thanks again!

If by "live" PR means at +12 volts then the same comment about insulation is valid for all except 85. Even the unused 87

 

[rogerthebodger]

Correct relay, wrong wiring Gary.

85 12v -
86 + from nav light switch
30 12v + This should be fused, rated for the security light.
87a To security lights

When you turn the nav lights on the circuit between 30 and 87a will be broken and the security light will go off, terminal 87 will become live (make sure it's insulated, an insulated spade will do the job).

True but if 12V positive goes to 87a and the security goes to 30. 87 cannot become live so no need to insulate.

 

[bedouin]

When you turn the nav lights on the circuit between 30 and 87a will be broken and the security light will go off, terminal 87 will become live (make sure it's insulated, an insulated spade will do the job).

Or you could swap the connections on 30 and 87a

 

[PaulRainbow]

True but if 12V positive goes to 87a and the security goes to 30. 87 cannot become live so no need to insulate.

Or you could swap the connections on 30 and 87a

Indeed