Two power sources, one LED light 🤔

[Chris Evans001]

So I am installing a drip led light above the sliding door today. Basically the type of drip channel that stops you getting a shower every time you open the sliding door in wet weather. It also has a smart LED strip built into it.

To wire it, I want to take a feed from the existing van wiring that is above the sliding door already, and this goes live for a time when the sliding door is opened. Simple enough.
But, I also want to take a switched supply from the leisure side, think of it as an override for awning use etc.

So I suppose my question is, if I connect two sources of power to one item, can they cause a mischief to each other?
Will power from one side or the other go somewhere it shouldn't? What about when they are both live?

Hmmm all opinions appreciated! Not sure about this one.


Cheers
Chris

 

[wildebus]

So I am installing a drip led light above the sliding door today. Basically the type of drip channel that stops you getting a shower every time you open the sliding door in wet weather. It also has a smart LED strip built into it.

To wire it, I want to take a feed from the existing van wiring that is above the sliding door already, and this goes live for a time when the sliding door is opened. Simple enough.
But, I also want to take a switched supply from the leisure side, think of it as an override for awning use etc.

So I suppose my question is, if I connect two sources of power to one item, can they cause a mischief to each other?
Will power from one side or the other go somewhere it shouldn't? What about when they are both live?

Hmmm all opinions appreciated! Not sure about this one.


Cheers
Chris

if you had two 12V supplies into the same light connection, then the light would be on when EITHER supply was live, of course.

In your example above, I would think the courtesy light power is from the starter so you would have a situation where if the switch to the awning light was ON, and the door is opened (or maybe the courtesy light was turned on?), you are connecting the Starter and Lesiure Batteries together and you will get a current flow on that circuit as the two different batteries try to equalize their voltages. If there is a big mismatch, you could get a relatively high current that could be above the capability of the wiring (especially if you happened to try and start the engine at that point).
What you could do to get round it is feed the Light only with the Leisure Battery for power, but instead of using the Courtesty Light power to drive the Awning Light, use that signal to switch on a relay that allows the Lesiure Battery power to turn it on.

So ...
Leisure Battery 12V goes to Awning light on two parallel circuits:
Circuit 1 has a dedicated manual switch to allow the light to go on and off
Circuitr 2 has a relay that is turned on and off by the Courtesy Switch

 

[Chris Evans001]

Makes sense to me.

Thanks for this.

Can you link me to a suitable relay please? Had a quick look on Amazon but I'm finding it a bit confusing if I'm honest.


Thanks

Chris

 

[wildebus]

Any 5-pin relay will do -
I would do the circuit like this (blue box is Relay) ....

Courtesy Light Switch activates (closes). Pin 85 Goes high and Relay turns ON, connecting pins 30 and 87 and Awning Light goes on, powered by Lesiure Battery
Courtesy Light Switch deactivates (opens). Pin 85 Floats and Relay turns OFF, connecting pins 30 and 87a, sending power to Awning Light Switch. If Awning Light Switch is ON, light is on, otherwise light is off.

You may have to adapt the circuitry depending on how the courtesy light circuit works (e.g. on VWs, it works by switching the -ve, not the +ve so you would control on the relay -ve not the +ve), but the principle still holds.

 

[Chris Evans001]

Thanks so much Dave. Exactly what I needed. Will order a relay now and let you know how I get on.

Thanks

Chris

 

[PeteS]

You could just use a couple of 10A solar blocking diodes, one in each feed to stop one battery feeding the other

 

[xsilvergs]

Or perhaps a SPDT switch with centre OFF.

 

[st3v3]

.

 

[wildebus]

Wait and see what polarity the courtesy light circuit is .......

 

[Dilbert]

You could just use a couple of 10A solar blocking diodes, one in each feed to stop one battery feeding the other

You do not need 10A solar diodes. That is overkill!

Check the maximum current of the Led light strip and use 2 diodes rated above that. Led lights will not notice the 0.7 Volts drop. It will cost pennies and not pounds.

 

[MarkJ]

Check the maximum current of the Led light strip and use 2 diodes rated above that

I would have thought you'd need diodes rated just above the value of the fuses in the circuits. Isn't that so?

 

[PeteS]

You do not need 10A solar diodes. That is overkill!

Check the maximum current of the Led light strip and use 2 diodes rated above that. Led lights will not notice the 0.7 Volts drop. It will cost pennies and not pounds.

I used those diodes as I thought people could relate to them and to be honest they are 69p on Amazon when in a pack of 10. But you are right if there is only a handful of leds then a lower value could be used

 

[wildebus]

I used those diodes as I thought people could relate to them and to be honest they are 69p on Amazon when in a pack of 10. But you are right if there is only a handful of leds then a lower value could be used

Sometimes finding the "right size" can be more effort than it is worth. This is why I would have used a 30A relay when all that is needed is a 5A one - the smaller ones are harder to find, harder to connect up and more expensive as less popular.