AC relay using light bulb to switch on/off ! will it work >

[paulwalldall]

Hello. first post. hope in right section.
Farmer friend has a hen brooding pen. (large enclosed box with 240watt heat lamp) with one lamp. when lamp fails the chicks get cold and soon die which is sad but also costly in birds. thought there must be a failsafe device somewhere to turn on an alternate bulb but he says not.
Thought that wiring his one bulb in series with the coil of a 240v 16amp relay would work and when bulb fails, relay de-energised and goes to normally closed and switches a second reserve bulb on would do the trick. wired this up , switching reserve bulb on/off by removing and replacing first bulb works fine but first bulb will not light at all. anybody know why. current must be flowing through first bulb to energise relay but bulb wont light. tested all components individually and all ok. only thought is the coil has a resistance of 7kila ohms and the bulb only 260 ohms. measured over each bulb and coil and all read 240v when they should. am i being a bit rubbish or am i missing something fundamental. this was just a mock up at home so no dead birds yet but has anybody any ideas. or suggestions to achieve the ' one light fails and another comes on goal'

thanks Paul.

 

[Silly Sausage]

Coil and relay coil in series, most of the voltage will be dropped across the relay coil, check that with a meter.

(Deleted this bit, not thinking straight!)

 

[telectrix]

i would use a photocell to activate a warning sounder and strobe when the lamp fails and it goes dark.

 

[ruston]

If it gets dark enough use a photocell to switch on auxiliary lamp and incorporate a warning device in the circuit.

 

[ruston]

i would use a photocell to activate a warning sounder and strobe when the lamp fails and it goes dark.

Takes me to long with the mobile broadband lol.

 

[Knobhead]

Use the same set up that you have now but change the 230V relay to a current sensing relay.

Remember this set up is only good as long as the lamp is changed ASAP after the first blows.

 

[Knobhead]

A photo cell would have the lamp flashing on and off like a disco light.

 

[ruston]

With a latching relay.

 

[Robotstar5]

I'd go with the same advice as Tony, fit a current sensing relay and fit an alarm/sounder in parallel with the back-up lamp to warn the main one has failed.

 

[telectrix]

A photo cell would have the lamp flashing on and off like a disco light.

i meant to use a photocell to activate the alarm. the photocell reacting to the light, and activating the alarm when the light went out. probably require a relay.

 

[Geoffsd]

Or a thermostat to turn on the second lamp.

 

[Swicade]

Instead of an alarm/sounder i'd install an outside indication light (a red bulkhead fitting for example) that shines when the main bulb has gone out......main reason being a sounder going off might effect the birds and annoy any neighbours if the farmer was out when a failure happened (he would however see the exterior bulkhead alight)

 

[RobWansbeck]

Since there seems to be room for a second lamp could you use two 120W ( or 4 x 60W ) in parallel?

 

[D Skelton]

Coil and relay coil in series, most of the voltage will be dropped across the relay coil, check that with a meter

Swap them round so the relay comes after the light. Make sure the light is lit before you drop the voltage across the coil. Simples!

Since there seems to be room for a second lamp could you use two 120W ( or 4 x 60W ) in parallel?

Thank god you said it, I was thinking it but didn't really have the cojones to say it through fear of seeming too simplistic. Surely this is the best solution? Maybe even go one step further and have the two/four lights on seperate circuits incase the overload caused by a bulb blowing trips the breaker then you still have three functioning.

 

[grantr37]

why not just put a couple of hens in beside them as nature intended......they will sit on top of the chicks and keep them warm.....

 

[paulwalldall]

thanks for the replies. dont know anything about 'current sensing relays' and price searches make them a little dearer than normal ones, though it seems they draw little current when active so seems a good solution. as for making sure light comes on first before relay, does that actually work ? cant get a hen with a big enough bottom as hes looking at getting 150 day olds soon. stick with 2 lights in parallel for now but will be looking at a photocell or bimetal switch as a cheprer alternative if i can get them switching on/off reliably.

 

[D Skelton]

as for making sure light comes on first before relay, does that actually work ?

Unfortunately not, I was trying to be funny, seems like it failed miserably leccy doesn't work that way I'm afraid.

IMHO, the best option here is to stick with two lights although I would make sure they are supplied from seperate RCBO's to ensure one light going down can't cause the circuit supplying the other one to fail.

Alternatively you could use Tonys suggestion of a current sensing relay, however I can't see the point really. The simpler you can make the solution to a problem, the less there is to go wrong.