Led Lighting Question

[The_Lad]

Hi all,

I need a bit of help here, I have fitted some led strip lights in the rear of the van but the behaviour is a little strange.

I have connect a perm 12v from the leisure battery and a switched ground through a 2 way switch which switches either perm ground from the leisure battery or door ground from the factory fit ceiling lights.

Behaviour I see is

1. Switch set to switched ground, I open the door, the lights flicker but don’t come on

2. Switch set to off ie no ground I open the door and move the switch to switched ground the lights come on

Why is this? And how do I get 1 to work? My led boot lid light is wired the same way and works so I’m guessing maybe my controller is pulling too much current? Can I fix this?

3. With the engine running Or within a few min of switching off if I switch to perm ground for the lights the controller shuts down, I’m guessing over voltage? Any ideas?

Cheers
Justin

 

[travelvolts]

When you say controller, to what are you referring?

 

[The_Lad]

It’s the controller for the led strips colour changing and remote control this sort of thing but 12v

https://www.amazon.co.uk/dp/B01KLDC...t=&hvlocphy=1006567&hvtargid=pla-562798224451

 

[travelvolts]

I think you will struggle to power that from the switched negative directly. You will need to use a relay to control them when you open a door. Something like this https://www.travelvolts.net/product-page/door-switching-option-2006-2017

 

[The_Lad]

Thanks Martyn

So your thought is there is too much current through the BCm module?

As I already have all the wiring in place I presume the kit you linked to is a bit overkill all I would need is a 12v switching relay to switch the leisure battery ground to the lights when the bcm ground is seen on the relay? So just one of these Halfords (HEF554) Relay 12v 30amp 4 Pin

Cheers
Justin

 

[travelvolts]

It's not due to excess current. It's the way the BCM outputs the negative. A relay on its own won't work. You will also need a diode and a capacitor to stop the relay from buzzing on switch off. The relay also needs to have a fairly high impedance.

 

[The_Lad]

Ok so if I bought the kit you linked above could I dissect it easy enough to fit it to my existing wiring so I wouldn’t need to strip the roof panels out.

My setup is all in the cubby box by the drivers mirror, I have the door switched neg feed from the roof light in the rear, and a perm neg direct from the leisure battery. I can also easily pick up a 12v from the leisure batt to power the relay

Could I just crimp my existing wiring to your kit easily enough?

 

[The_Lad]

This thread seems like a good explaination

Led Rear Interior Lights - How I Done It.

But I still don’t understand the “it’s the way the bcm outputs the neg” how is the BCM neg different to say the chassis neg or direct leisure battery neg? Other than its timed?

I’d really like to get my head around how this works before messing with it further so I don’t mess it up or damage the bcm

 

[Dellmassive]

This is an interesting one, im not sure of the current capacity of the BCM switched neg. Though i believe its transistor switched and may have a current limiting resistor internally in the BCM.

the set of LED strip lights i have come with a 5amp DC power brick, so i know they can draw some power when running.

the rear lighting circuit is fused at 10 or 15amp or something, and as per the other thread is relent on the +12v BCM timer. (incase you leave the lights on)

dont forget that when the van is not running the leisure battery +12v is isolated from the starter +12v.

might be time to get your multimeter out and start testing things.

varify that you are getting the:

-VE via the BCM

+12v from leisure battery

good chassis ground on leisure battery

take the switches out for now and just test with a bit of terminal block.


(on our setup we have a relay directly -ve switched via the BCM for the factory leisure battery so you wouls assume that it would just work . . . . . . but I've not tried it out on the rear LED circuit yet)

saying all that @travelvolts knows his stuff and im sure would have tried your hookup before suggesting the relay work around above.

 

[The_Lad]

I’ll get out with a multimeter over xmas, it seems to be working now, but not with the engine running or just after switching off but after being parked for a while it works as expected

 

[Dellmassive]

I wonder if there is a internal pull-up resistor on the BCM -ve causing your issue. That may explain the working after a time and BCM sleeping?

 

[The_Lad]

Yeah that’s possible, I can’t seem to find any info on how the BCM works.

Regarding using a relay with capacitor and diode has anyone done this? And is there any info on what size cap and a wiring diagram to save me working it out myself?