Relay or not?

[HCA]

What is the consensus amongst the electrical folk here:

A modern style light switch on end of indicator stalk, controlling two LED head lamps drawing 1.96A each - less than 4A total - could I wire without a relay without long term damage to the switch contacts? I do not know what these modern switches are rated for, but something tells me that they should be good for 4A..?

(Reason for asking, I am copying Vegantune on the Evante and using a Mk4 Escort column ind/wipers/lights switch arrangement)

[SimonH]

By the sound of that you could leave the relay out. I wouldn’t but you could do.
I’d go by what Ford did rather than Evante personally

[Slowtus]

What is the consensus amongst the electrical folk here:

A modern style light switch on end of indicator stalk, controlling two LED head lamps drawing 1.96A each - less than 4A total - could I wire without a relay without long term damage to the switch contacts? I do not know what these modern switches are rated for, but something tells me that they should be good for 4A..?

(Reason for asking, I am copying Vegantune on the Evante and using a Mk4 Escort column ind/wipers/lights switch arrangement)

Back in the day I wired up 2 spotlights and 2 foglights to my friend's Vauxhall Cresta...no relays were involved.

But I wouldn't recommend that method!!!

[Foxie]

A modern style light switch on end of indicator stalk, controlling two LED head lamps drawing 1.96A each - less than 4A total - could I wire without a relay without long term damage to the switch contacts? I do not know what these modern switches are rated for, but something tells me that they should be good for 4A..?

Now why would you want to leave out a relay ?

"Something tells me they should be good for 4A..?"

Are you hearing voices ?

[Andy8421]

Escort MK4? any chance you could post a link to the switch you have in mind, or the wiring diagram of the car it was used on? I can be a bit more specific if so.

[Craven]

Not completely sure on our stalk switch but many Head/dip switches were ‘make before break’ contacts so that for very short time both filaments are powered. This ensures there is no loss of illumination at change over. A little more difficult to arrange with relays. Probably not needed with fast LED’s
FWIW.

[HCA]

I am with you on this Craven. And for this it is my understanding that light switches of the day were rated at 20A+ I think you will find that the contacts in the Spitfire and Westinghouse switches on the +2 have pretty beefy contacts to meet this rating. Fast forward to the introduction of micro switches, the need for relays became a necessity. Fast forward more to today and LEDs, the theoretical need for relays diminishes. (I heard somewhere, but cannot vouche for its legitimacy, that switching LED lights is much less harsh on contacts than it is with incandescent lights, so that micro switches can be used more easily without relays...maybe someone can verify?)

Andy, the switch I will be using is illustrated here:
https://www.ebay.co.uk/itm/255618601380 ... R5DQ0rzaYA
I do not want to open it up and measure the contacts as no doubt there are a multitude of springs and indents that will pop out As to the wiring diagram - there are relays all over the place on the Escort Mk4, four for the headlights alone, BUT, this is expected as not only were the switches micro, it was about the time thinwall cable was introduced.

All this is a result of my lhd conversion. New dashboard. So I will take advantage of streamlining a few things - plumb in a satnav, bring main item switching up to the steering column etc. It is a nuisance that I will now need two relays for the wipers, but maybe I could balance it and ditch two from the lights...

Yes, I will probably keep them there as it might be more trouble than its worth to strip them out!
But still interested...

ps - I use the term 'microswitch' for the modern switch with small contacts - not sure what it is called in relation to the old bomb-proof ones - and not in the leteral meaning of microswitch...

[Andy8421]

Apologies for the slow response, as our antipodean members would say, “I’ve had a dose of the ‘rona”

I checked out the Mk4 escort. It does have relays on the main and dipped headlight circuits, so as a starting point, relays would be a safe bet in your application as the switch current carrying capacity is an unknown quantity.

LEDs are a much kinder load than normal bulbs as they don’t have the switch on surge that incandescent bulbs have as the filament warms up, but even so I would still use a relay - with a 12v (well, 13.6v really) system, you don’t have many volts to throw away, and keeping circuit resistance down will give you the brightest lights possible.

[Craven]

Voltage drop with LED’s is not a factor they are current driven devices, voltage across an LED is around 1.2 volts.

[Andy8421]

Voltage drop with LED’s is not a factor they are current driven devices, voltage across an LED is around 1.2 volts.

You are of course correct, but it rather depends what is in the circuit to drive the LED from the battery voltage. If it is some fancy constant current drive electronics chopping away at the battery supply, then it could well be immune to changes in battery voltage (within limits). If it is a bit more mundane, then supply voltage could have an effect. I think I would still lean toward a relay.