I have installed 8 x 30 watt 12v led floods in my garden which are powered directly from a leisure battery but they don't work??

[Harry Bloomfield]

the cable is 2.0mm twin flat 25 amp rated cable is here (no earth as the lights only have pos and neg for 12v) There is only one independant PIR. The lights themselves do not have a pir. The switch is this one illuminated switch. I have broken my multimeter but have one on order. Cheers

Current rating is not the only thing you need to take into consideration, when ordering cable, volts drop is equally important. It is especially important, where very low voltages are concerned, delivered over long lengths of wiring.

You have already stated you have used 2mm, which will suffer extreme volts drop, at 12v/20a, even over just a matter of a few feet. Post on here the actual measurements cable, between each light, and someone will surely work out the volts drop for you.

 

[SeawolfGB]

Thanks Harry. The distance between each light is around 3.5 metres

 

[bernardgreen]

The other thing to consider is the in-rush current when lamps are switched ON

Almost all LED lamps have an in-rush current. The only exception is low power lamps with a simple resistor controlling the current through the LED element(s)

From Technical Support at a supplier of 12 Volt 1 Watt lamps with a capacitor controlling the current through the elements.
Please note that the inrush current in the LED lamps can go up to 10 times of the standard current value.
The inrush current lasts for about 10ms, but it takes between 40--50 cycles for the current to stabilize to the normal operating value.

Switch mode drivers controlling the current through the LED element(s) may power up erratically if inrush currents cause significant voltage drops along the cable.

 

[Why Not Indeed]

"cycles" of what? This is DC, right?
There won't be a switch mode driver if they're powered from a DC power source.

 

[Harry Bloomfield]

Thanks Harry. The distance between each light is around 3.5 metres

I'm too busy to work it out to each lamp position, but just to give you an idea of the problem you face....

Your most distant lamp position is 28m, assume all of them are mounted/co-located at that position, that is 20amps (240w/12v) along that wire.

28m; 12v; 20amps

Volts drop is around 11.5v

So you will have 12v-11.5v = 0.5v at those lamps.

 

[bernardgreen]

There won't be a switch mode driver if they're powered from a DC power source.

There will be a driver, Constant 300 mA current output to the LED element(s)

As in this 10 Watt 12 Volt floodlight

 

[Why Not Indeed]

Fair enough. What about the "cycles" thing then, does it do DC->AC->DC inside the driver?

 

[SeawolfGB]

I'm too busy to work it out to each lamp position, but just to give you an idea of the problem you face....

Your most distant lamp position is 28m, assume all of them are mounted/co-located at that position, that is 20amps (240w/12v) along that wire.

28m; 12v; 20amps

Volts drop is around 11.5v

So you will have 12v-11.5v = 0.5v at those lamps.

Blimey. What size cable would I need then? Maybe the under water cable from the nethelands/france that provides 5% of UK power! LOL

 

[Harry Bloomfield]

Blimey. What size cable would I need then? Maybe the under water cable from the nethelands/france that provides 5% of UK power! LOL

That's why they use high voltages, for long runs - it reduces the amps, and along with it, the voltage drop.

 

[SeawolfGB]

Looks like I will need to remove some of the lamps from the installation!

 

[SeawolfGB]

Looks like I will need to remove some of the lamps from the installation!

Or get some very low wattage lamps?

 

[SeawolfGB]

Hi Everyone. It sounds like I may have messed things up with my setup due to issues with voltage drop along the length of cable. Based on what kit I have got (see my previous diagram) can anyone advice (in simple terms) what would work with regards to a 12v DC setup? Thanks guys.

 

[Harry Bloomfield]

Hi Everyone. It sounds like I may have messed things up with my setup due to issues with voltage drop along the length of cable. Based on what kit I have got (see my previous diagram) can anyone advice (in simple terms) what would work with regards to a 12v DC setup? Thanks guys.

You could try individual wires, from the source, to each light, rather than daisy-chaining. Your PIR switch, would need to operate a relay with contacts, able to support >20amps and DC rated. Depending upon distance between the battery, and the relay/contactor, you may need to beef up that cable too - I would suggest 6mm, even for a few feet.

Cars run on 12v, lorries use 24v, simply because of the longer cable runs, and greater volts drop.

 

[SeawolfGB]

That would be very expensive for me. I need to try and use what I have but reduce the number of lights to an acceptable level. Cheers

 

[bernardgreen]

Fair enough. What about the "cycles" thing then, does it do DC->AC->DC inside the driver?

My apologies, my error... the 1 Watt lamps were 230 Volt AC. and not 12 Volt DC