Extendng the life of a car indicator relay?

Hello,
We are using the following relay to switch incandescent car indicators (21W) on a 12V car…

JSM1a-12V-4 Relay datasheet
https://www.farnell.com/datasheets/1702843.pdf

This relay is rated for 10A contact current, and we only have about 2A contact current.
However, the relay will obviously last longer if it has less contact current. Therefore, would it not be a good idea to put in a 'contact-current-limiter' comprising a power resistor in series with the indicator bulb, which gets shorted out by a FET 30ms after the relay has closed?

Also, the datasheet doesn't say what is the contact bounce time, do you know? Does it depend on the current being contacted/broken?

Hi,

If you consider using a FET, then don't use the relay anymore.
The FET shouldn't wear out.

Or you could use an automotive high side switch. It has several protection circuits inside.

Mind: Your incandescent bulb might draw 5..10 times the nominal current at start up.
I recommend to add at least overvoltage protection and maybe short current protection with a single FET.

Klaus

thanks, sorry we cant have fet as they have leakage current...wow an automotive indicator bulb has 5 to 10 times the current when cold...?...I didn't know that...thanks.

how do you know that automotive incandescants aren't made with carbon filaments?

https://en.wikipedia.org/wiki/Incandescent_light_bulb#Current_and_resistance

carbon filament lamps resistance gets more as they get colder...opposite to tungsten

???

I just used IRFZ46 is a similar application. Leakage current is specified as max 250uA at 44V Vds and 150C temperature. At 13.7V and 25C I measured < 25uA. That's magnitudes less than internal discharge current of a car battery.

Brian.

Cars do not use old fashioned incandescent light bulbs anymore. They also do not use old fashioned relays anymore.

Thanks...

Cars do not use old fashioned incandescent light bulbs anymore. They also do not use old fashioned relays anymore.

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many cars still use incandescent indicators, and relays to flash them on and off.
LEDs powered by switch mode led drivers are not wanted for car indicators because of the repetitive inrush that you get into the input filter capacitance of a switch mode led driver's input capacitor. -So its either relays flashing incandessant lamps, or relays flashing leds powered by linear led drivers (linear led drivers have very little input capacitance).

Its the same with automotive brake lights to an extent..they can be going on and off and on and off...and the inrush (every time they come back on) into switch mode led drivers input capacitance is too much...so they get done with linear led drivers or incandessants.

I just used IRFZ46 is a similar application. Leakage current is specified as max 250uA at 44V Vds and 150C temperature. At 13.7V and 25C I measured < 25uA. That's magnitudes less than internal discharge current of a car battery

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FET leakage current is very low, but you still don't want it.....what if the car is left in the garage for a long time?....if the leakage is the same as the car battery self discharge, then by using the fet, you have effectively doubled the discharge.

Despite of the imagined leakage current problem, modern cars replace mechanical relays with smart power switches, except for a very few cases, e.g. main "ignition" switch or starter motor. A serious calculation of battery capacity reveals why even a mA sum of bias and leakage currents won't be a problem, actual smart power switches have 10 µA maximum and probably < 1 µA typical leakage current.

Reinventing the square wheel?

Modern cars have an ultrasonic car entry alarm that consumes a watt or so. According to the AA who charged our battery in a airport long term car park, most modern cars quiescent battery drain flattens the battery in under three weeks. so the leakage current of a few extra FET switches can be ignored.
Even with filament bulbs the life of the electromechanical flasher relay is a lot longer then of the bulb it drives. I have never changed one in forty years of driving old cars, but I have changed perhaps 10 bulbs. As said its the inrush current that sees them go open circuit. So drive the bulb supply with a constant current source. This will also over come overrunning the bulbs when the battery is over 14V.
So go ahead, design a CC circuit that can be switched on and off with an inbuilt multivibrator, so you have the modern "flasher" unit. as a goody put in a current monitoring circuit that will detect that a bulb has blown. For a 100% replacement, put in an audio "ticker"
Frank

Hi,

For a 100% replacement, put in an audio "ticker"

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For this a cheap piezo disc could work.

Klaus

most modern cars quiescent battery drain flattens the battery in under three weeks

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I left my year 2000 Peugeot 106 in leeds white rose shopping centre for three months, and the battery was still ok..the car still started. I was just wondering if anyone had the datasheet for one of these "smart power switches" that gets used to blink car indicator bulbs?

do you mean like this...?...

**broken link removed**

Wow, that's impressive, has it got an internal ultra sonic car alarm? the car we had a problem with was a Cavalier a lot older then 2000.
I wonder if there is a proper spec. on this or its model dependent, the more expensive the car, the more gizmos, the higher the quiescent current? I know my Passat has a flashing LED in the drivers door, say 20 mA on for 20 %, so mean current = 4mA, which is the same as 1000 FET leakage currents?
Frank

The problem is your SMPS. It should have a surge limiter then use a FET with appropriate timing dwell times.