want to know technical reason abt relat

Hi
I am connecting a relay (AC) parallel with the AC bulb. When i am connecting it to supply the bulb is glowing and the relay is not energizing means almost all the current is diveritng towards the bulb not in the relay and when the the fault bulbs get faulty (burns out) than the currnet is enerzing the relay and show that the bulb get faulty. I want to know the reason that why this is happenig. Can any one tell me. THANKS

It sounds like the AC power source is being overloaded so the voltage is too low to activate the relay.

What voltage are you using?

Is it a transformer or being powered directly from the mains?

What is the AC source, the power mains or a transformer?

Ken

i am using 24V AC supply. 24v Bulb and Relay

if you parallel the two, the bulb has lower resistance, and hogs all the current. Only a fraction of the current goes through the relay, dictated by ohms law of parallel resistances.

When the bulb burns out, all the current is diverted to the relay causing it to engage.

mike you mean that bulb filament has low resistance that the relay coil???????

No, the bulb filament has too lower resistance from the transformer.

Use a lower wattage bulb or a higher VA rating transformer.

Does the bulb glow brightly or is it dim?

What's the VA rating of the transformer and wattage of the bulb?

ranariaz said:

mike you mean that bulb filament has low resistance that the relay coil???????

Click to expand...

yes, I believe it is the low resistance that causes them to heat up and GLOW... relays, on the other hand, aren't being used properly if they are glowing...
he's probably seeing a voltage drop due to the limited source current of the transformer... that would be the only reason both the relay and the bulb don't come on... 24V and this resistance dictates this current, but since we can't supply that much current and we can't change the resistance, the voltage would have to go down to compensate...

sounds like a lab experiment where the two components were picked to do just that, demonstrated, and then the instructor said "now, why did it do that?"

Good point. If this were a real life situation then I'd expect the transformer to start smoking if the power was connected for a significant length of time.

ya, you would think that, wouldn't you.

I once shorted 12V to ground on my timer board and burned the damn thing in for 4 days before I noticed (why isn't this one's LEDs on?). When I removed the short (supposed to be on the enable jumper to ground, not the 12vout to ground) it came back up and worked perfectly... I use a series resistor in line to remove half the power from the regulator so I don't have to heatsink. The 12v supply only had a zener since it wasn't critical (so I didn't have a 7812 to save my butt). But this resistor was not rated to take the full load across it, something like 6 watts or so on a 3 watt resistor, for 4 days! I think the poly fuse on the ac input to the transformer maybe saved the day.