Standard automotive relays , continuous operation?

[Jake Royd]

I have a fairly typical mid price security and immobilisation system on my 2008 X250 based motorhome.
There is a Cobra immobiliser but I also have the ability to remotely prevent it starting by energising a relay inserted into the power feed from the ign switch to the starter solenoid.
This is a perfectly standard automotive relay where of course the current normally passes through the relay via the normally closed contacts.
Once energised I assume the coil holds these open, or maybe it does then does not need power again until energised the opposite way ?

When we go away (not in the motorhome) I want to immobilise it using this process but I am concerned about the relay being energised continuously. I do not worry about any current consumption (it is suggested this will be around 100mA), I have plenty of solar , I'm thinking more of heat and degradation of the relay.

Doing some research via Mr Google most sources of info suggest this is not a problem. They all nearly always point to the relay service life being more limited by the number of operations.

Can anybody advise further? It seems it's OK to do this.

And yes I know I should have a Growler etc.

TIA

 

[Nedge68]

If the relay coil does draw 100mA @ 12V that would be 1.2Watts,
I wouldn’t expect it to be a problem, relays are normally rated by the the number of operations (cycles) and the current rating of the contacts, If you are using the relay to open when there is a high current flowing it causes the contacts to arc , causing pitting and burning of the contacts.

 

[Nedge68]

you will find some useful info here…

Automotive Relay Guide | 12 Volt Planet

Read our guide to relays found in vehicle electrical systems. How they work, why they're used and some example applications

www.12voltplanet.co.uk

 

[Jake Royd]

If the relay coil does draw 100mA @ 12V that would be 1.2Watts,
I wouldn’t expect it to be a problem, relays are normally rated by the the number of operations (cycles) and the current rating of the contacts, If you are using the relay to open when there is a high current flowing it causes the contacts to arc , causing pitting and burning of the contacts.

Thank You.
Normally the current to energise the starter solenoid will be passing through the closed contacts , maybe 10A , so no problem with sparking. Once open no current will flow , so ok there as well. It's more the continuous operation of the relay coil I am concerned about.

 

[Ranger]

You could use a normally open contact relay so it is only closed when the ignition is on so whilst using the camper.

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[Gromett]

You could use a normally open contact relay so it is only closed when the ignition is on so whilst using the camper.

Was just going to say that myself.

N/O contacts means you are not using any current to disable when the engine is off.
Means you only need to energise the coil to start the engine.

 

[NicM]

A relay will be fine, after all, the ones in motorhomes are on all the time the12Vs are on, and that can be weeks/months.

 

[autorouter]

A latching relay has two stable states, and is flipped between the two by short pulses from two momentary-acting switches, one for set, the other for reset. They are used for situations where the power drain of a relay coil is unacceptable. For example the main power on/off control relay in most Schaudt Electroblock distribution fuseboxes. Also called a bistable relay.