24V lamp maintenance resistor

Good day all. I'm looking to flash a 24VDC status tower light via a plc's relay output contacts. In an attempt to prolong the life of the lamp and contacts, I want to maintain a low idle current into the lamp, ie. across the contacts. I don't have a stock of resistors to play with, or even a variable psu so I wondered if any of you had a "recommended" value for a 6.5W signal lamp.

Cheers, Steve.

Why don't you look for for an LED light system if you are interested maximizing life? If you were to drive it with an SSR, contacts also shouldn't fail. I have seen them advertised but have not priced them out as I have not had an application for using them yet.

Others have experience with these type of lights?

I have used only LED's on 'stuff' for the last 2 years...a little more up-front cost, but we have not had any of them fail, so no upkeep, just put in a stack light on a cube rotator conveyor, it signals the status of the machine...now this thing doesn't cycle for 3 or 4 min, just sits there, so I put in an extra counter that strobes the lights in 'random' order, very fast, when it's been idle for more than 2 min...the operators are sure that it means HURRY UP...oh, and I am recording the number of flashes of each color...too much time on my hands???
David

LEDs are my first chioce too, but I'm stuck with stock equipment.

If they are standard lamps, you can purchase LEDs to replace them. I use IDEC (IZUMI). They have bi-directional diodes built in (24vac/dc). Filament lamps are for the birds these days. See if there is some way you can replace them with LEDs. Perhaps replace the transformer in the light with a 24VAC secondary version. The lights I use are happy with AC or DC.

By the way, I now use 240VAC direct versions as well. No transformers.

The 24VAC/DC types I normally drive straight from the transistor card in the PLC. Have not had a lamp or PLC output failure in 5 years.

...back in the day..

When faced with this problem in days of old, we just
replaced the 24V lamps with 28V lamps, of the same
lumens and base size.

They'll last longer, and you don't need resistors.

With a small resistave load electrical wear on the contacts wont be the issue, but the mechanical wear on the relay armature/hing springs etc.. If your flashing the light frequently go with a solid state output and led lamp. You can buy LED lamps for just about any size base and voltage from a number of sources. The minute it outlives an incendesent lamp it's paid for it'self 5 fold.

If you REALLY don't want to go to LEDs (best bet) then you can put a HOT source to the lamp, in parallel with the PLC Output.

HOWEVER... run that HOT source through a POT. Apply just enough voltage to the lamp to keep it warm without illuminating it.

Once you find the right Pot-Value (resistance), replace the POT with a resistor, or resistor bridge, of similar value.

Install the same resistor, or resistor bridge, on other lamps of the same wattage.

It's up to you... but I recommend the LEDs. They will more than pay for themselves.