Relay rating for lightbulb

[Plummet]

Hi

I'm just finishing a PIC project where I am driving 3 relays to control 3 bulbs (1 relay per bulb) in a traffic light. The bulbs are 240v 25w incandescent (SES E14). The relays are Shinmei RSB-5-S, and on the contact side are rated at 1A @ 125VAC nominal, with a max voltage of 250VAC and max current of 2A.

So..with a 25W bulb I'm only pulling about 0.1A - should be fine I thought, but then I remembered the issue of inrush current on indandescent bulbs and read that this can be around 12x the normal current when the bulb is cold. This takes me up to 1.25A for a short period of time when the relay is switching.

What do you think - good enough, or have I underrated the relays? I've actually tried it with 40W bulbs and it all seems fine, but I want to be sure

If I am underrated then the solutions I have thought of are:

- Go for 15W bulbs (0.75A inrush) - but still over the 'nominal' voltage
- Bigger relays (but I have a space problem)
- Use LED 240v bulbs - but not sure these are suitable for regular relay switching?
- Use LED 12v bulbs - again, not sure these can be used with relays

Thanks in advance for any help!!

 

[BeeBop]

Hi

I'm just finishing a PIC project where I am driving 3 relays to control 3 bulbs (1 relay per bulb) in a traffic light. The bulbs are 240v 25w incandescent (SES E14). The relays are Shinmei RSB-5-S, and on the contact side are rated at 1A @ 125VAC nominal, with a max voltage of 250VAC and max current of 2A.

So..with a 25W bulb I'm only pulling about 0.1A - should be fine I thought, but then I remembered the issue of inrush current on indandescent bulbs and read that this can be around 12x the normal current when the bulb is cold. This takes me up to 1.25A for a short period of time when the relay is switching.

What do you think - good enough, or have I underrated the relays? I've actually tried it with 40W bulbs and it all seems fine, but I want to be sure

If I am underrated then the solutions I have thought of are:

- Go for 15W bulbs (0.75A inrush) - but still over the 'nominal' voltage
- Bigger relays (but I have a space problem)
- Use LED 240v bulbs - but not sure these are suitable for regular relay switching?
- Use LED 12v bulbs - again, not sure these can be used with relays

Thanks in advance for any help!!

If this is a 'novelty' or 'one off' hobby project I wouldn't worry about it, it should be fine.

On the other hand if it is commercial, you may want to find relays rated for 250V nominal....

 

[Plummet]

Thanks - it's a one-off so I guess I'll just go with it (or maybe get some 15W bulbs just to be a bit more in spec).

 

[Hero999]

It's normally the breaking current that's more critical than the making current so it's probably alright.

 

[crutschow]

It's normally the breaking current that's more critical than the making current so it's probably alright.

The making current is also important because of contact bounce which momentarily opens the circuit.

The worst that can happen is that the contacts will prematurely erode and the relay will fail to make contact (or weld together) at some point. But that depends upon how often the relays are operated and could be well past the lifetime of his project.

LEDs can be switched with a regular relay. LEDs operate with current just like any light bulb. The relay doesn't know the difference.