Wiring up Footwell lights

[steve_earwig]

Use an ammeter in series with the coil side, which will be between your existing lighting feed and earth. The other side will need a power feed and a wire away to your new lights with an earth on the other side of them, which will be switched by the existing lighting feed.

Loads of diagrams on Google:

(Ignore 87a)

[FarmerPug]

no bother ill give it a go tommorow, i assume my multimeter has an ammeter function, will any relay out of any car do the trick i have some pug ones lying around

[steve_earwig]

More or less, so long as you know which terminal's which.

[FarmerPug]

yip my multimeter will let me figure that one out, but anyhow i had a play on livewire which is a circuit creator you can test things out to see if they will actually work but it doesnt seem to simulate blowing bsi units very well, but anyhow it helps explain what i did the first time:

And after finding a relay i think this would keep the thing from blowing up the bsi:

The question is then would it stop it killing the bsi, and what size should the fuse be.

[Doggy]

Please, please use a coil suppression diode if you're planning to drive your relay from the BSI.

[FarmerPug]

whats a coil suppression diode, is it a reverse bias diode to prevent back EMF caused by the magnets in the relay from sending a high voltage back into the bsi, and after asking an ebay seller about a relay i was told the input side resistance is 85ohm and using ohms law that means 0.16amps or 160miliamps is that ok for the bsi?

[Doggy]

whats a coil suppression diode, is it a reverse bias diode to prevent back EMF caused by the magnets in the relay from sending a high voltage back into the bsi,

That's essentially correct.

and after asking an ebay seller about a relay i was told the input side resistance is 85ohm and using ohms law that means 0.16amps or 160miliamps is that ok for the bsi?

Don't know. I think the BSI uses relays as the switching device, (it definetely does for a/c clutch, hrw, etc. but clearly can't for interior lights as they fade in/out), so we can't be sure.

Steady state current will be as you suggest, but the inrush current will be many times this value. In normal circumstances, you'd just try it and see, but with the cost & complication of fixing a BSI, caution is essential. Ideally you want galvanic separation of the two systems, (opto-isolators or similar). If you can't easily do that, see if you can find a transistorised relay - RS used to do an 11-pin, 12V one, maybe still do.

[steve_earwig]

This is getting too complicated

What about swapping the puddle light bulbs for LEDs and using LEDs in the footwell lights? Would this drop the current enough to keep the BSI happy? Or wouldn't they be bright enough?

[modified406]

This is getting too complicated

What about swapping the puddle light bulbs for LEDs and using LEDs in the footwell lights? Would this drop the current enough to keep the BSI happy? Or wouldn't they be bright enough?

yes mate as the normal bulbs use alot more current for them to work so if using leds both ways then it should even out the current

[FarmerPug]

Is this the transistorised relay
http://uk.rs-online.com/web/search/sear ... &R=0348245
i dont quite understand its concept but does it simply require much less power to switch on and off, and when i think about the puddle lights there isnt any dimming effect from them they just turn straight on when the doors are opened, go off straight away if the doors or closed or after a certain time delay they go off they dont dim down at all. As for optoisolators i have only learnt of them in theory they are just a chip with a led and a phototranistor, something powers the led and the phototransistor acts as a relay swithching something on and off heres one:
http://www.maplin.co.uk/Module.aspx?ModuleNo=2198

now i have took a look at the cars instructions peugeot doesnt reccomend adding any electrical accessories that use 10miliampres of power

[Doggy]

Yep, that's the RS beastie, (which works as you described). Only doubt over this is it's meant for 12V and your car probably gets to 15V or so. If you can download a data sheet & check this point, you're sorted.

The opto coupler IC's in the Maplins link could form the basis of a solution, but you've got the hassle of making up a circuit board with stable supply(s) for the electronics, protection etc. Maybe someone does a ready made solution - for industrial stuff you can get DIN rail mount terminals with built-in opto couplers for example, though they tend to be 24V.

[FarmerPug]

That rs unit is quite expensive and then there is an awful lot of connectors on the back, what is the maximum power useage i can add onto the door lights without causing harm my target is 10mA but thats very low, as for maplins i suppose id need a voltage regulator because i think IC chips need 5v to work, who makes PCBs for the job or do they supply breadboards, but ive started thinking again about LDRs coupled to a vairable resistor as the switch

[FarmerPug]

i did some reading on that RS big yoke, and here is the bit which sounds good:

if this is correct the input voltage (the switching bit i assume ie from the door lights) it can be between 3.5 to 50v and then that table is that bit i have highlighted correct in that at even 15v there is only 760 some units of amps i cant remember that symbols purpose but i assume its lower than a miliamp, so 760 of them is lower than 10mA, is it?
And then i also produced a plan B:

i did the simulation on livewire and the ldrs, and the transiors didnt explode only the bulbs as it cant simulate ones capable of 12v, but i forget the potential divider formula could i actually do it this way, and would it be possible to set it up right with adjustments to the vairable resistor to make it turn off fully when there is no light from the door light because if it didnt then the footwell lights would stay on and run my battery down?

[Doggy]

The advatages of the RS gadget are:
- very low current required to switch it on, (760 uA is, as you say, less that 1 mA) 1000 uA = 1 mA
- no reverse voltage spike on de-energising, so you can gaurantee it won't hurt the BSI.

The input voltage range is fine, but you need to be sure the car's nominal 12 V supply won't exceed the maximum power supply voltage.

'Plan B' might well be OK, but you would need to ensure your cct didn't get triggered by sunlight etc especially when the car's parked. It feels a bit uncertain to me, but I've never tried anything like this. The principle of separating the two circiuts is good. You should consider what happens if a lamp fails partially short cct, (you know the way they sometimes get real bright before they go) - could this take out Q1? what protection do you need should Q1 fail short cct?

[FarmerPug]

well i sent RS a message about the maximum power supply voltage, but just so im sure the power supply voltage is the voltage that the device will be supplying out to the footwell lights direct from the battery