How may lights from one relay?

[Bowhunter]

I've recently mounted some spotties on my roof but am yet to wire them up.

Before I do it, I was wondering though, is it possible to wire 4 lights to the one relay or is two lights the limit?

Apart from drawing higher amounts of current and therefore having a negative effect on the performance of each light is there any other negative that might come from doing this (ie, will it melt the relay, blow bulbs or fuses etc?)

cheers,

Luke

[DamTriton]

100 watts = 12 volts @ 8.5 amps. Being safe about it allow 10 amps per light

Normal single throw relay is about 30 amps continuous so you could do three, but again being very conservative two would be preferrable.

The coils on the relays (driving the contacts) don't draw too much so they are able to be paralleled together with minimal risk of overloading anything but the dickiest of switches.

Short answer: 2 lights per relay.

Use a decent guage of wire (4 or 8 Ga ricer boombox stuff, FUSED AT THE BATTERY!!!) to get the power up to the roof bar and mount the relays up there. Run a decent earth too (often overlooked).

[drivesafe]

Hi DAMKIA, that’s a novel idea and I can see your wiring advantages to mounting relays with the lights.

One question though, how do you fuse the set-up.




Hi Bowhunter, if you use headlight relay, they are already set up to handle two lights at a time by having to two separate output terminals and this makes wiring up the system easier.

Headlight relays are rated at 30 amp and this is sufficient to power two 130w lights without going anywhere near the maximum current limit of these relays.

Cheers

[6.5 rangie]

easiest way to figure it out is:- watt/volts = amps.
so 120w / 12v = 10a

[DamTriton]

Hi DAMKIA, that’s a novel idea and I can see your wiring advantages to mounting relays with the lights.

One question though, how do you fuse the set-up.

Main power fuse it at the battery end using one of the 60 amp large glass fuses they use for ricer "audio systems". Inline fuse near the switch for the trigger if you have to go through too much metal when routing the trigger cable Good thing is you are running 2 heavy cables for "bulk" power (+ve and earth), and two "signal" wires for relays, one if you only want all on/all off (parallel the trigger to both relays). If you want to add work lights/rock lights, it's only a matter of running a seperate trigger for the relay, and taking you power off the existing heavy cable on the roof, much easier....

Hi Bowhunter, if you use headlight relay, they are already set up to handle two lights at a time by having to two separate output terminals and this makes wiring up the system easier. Some are 5 pin double throw (87 & 87 pin "outputs", typically rated at 20-22 amps per "throw") others are changeover (87 & 87A pins, typically 30 amps) and others are single throw 4 pin (single 87 pin, typically 30-40 amps).

Headlight relays are rated at 30 amp and this is sufficient to power two 130w lights without going anywhere near the maximum current limit of these relays. 260 watt = 22 amp at 12 volts, agreed, but the full 400 wats from one 30 amp relay is asking for trouble (~34 amps)

Cheers

[Shadow]

You can get a 70amp relay and possibly higher they are about $20-$25

They use a larger than normal spade connector though, which will be sold by the same people you get the relay from.

I wouldnt recommend running more than 4 130watt lights on one though.

2 normal headlight relays would be simpler in that they take normal spade connectors and are available everywhere fairly cheaply ($5ea?)

[r0ck_m0nkey]

I would be using 55W bulbs aswell. There won't be a huge visual difference in light output, but you will cut down majorly on cable size needed and current draw. There isn't really a need to run high wattage, reflector quality and bulb quality play a bigger part in brightness.

[The Gimp]

Good to see this topic up as I was going to ask the same question. Ive only got cheap shit supercheap specials I believe, 2 wired up already on the front bar, and two on the roll bar that arent wired. Will I be able to run these cheap shitters off the origional relay or will I have to rewire another relay in?

Note: It is more likely for me to set fire to the car, then wire it properly.

[V8 Middy]

Use a decent guage of wire (4 or 8 Ga ricer boombox stuff, FUSED AT THE BATTERY!!!) to get the power up to the roof bar and mount the relays up there. Run a decent earth too (often overlooked).

So if the wire is the same guage all the way through a continuous circuit, what difference does it make having the relays up on the roof?

Imagine a hose pipe with a tap. Turn on the tap and water flows out at a certain rate. Put a trigger on the end of the hose and water still flows at the same rate.

Definitely fuse as close to the battery as possible (ie. centimeters!!) From there, mount the relays wherever is most practical... probably in the engine bay. 8Ga wire will be enough for 400W of lights. If you like, you can even connect 1 length of 8ga wire to both relays. Otherwise, if its easier the run 2 lengths of slightly thinner wire.

[DamTriton]

Use a decent guage of wire (4 or 8 Ga ricer boombox stuff, FUSED AT THE BATTERY!!!) to get the power up to the roof bar and mount the relays up there. Run a decent earth too (often overlooked).

So if the wire is the same guage all the way through a continuous circuit, what difference does it make having the relays up on the roof?None, but the idea is to use a very heavy guage wire to get the "bulk" power up to the roof then tap off that with smaller wire to the lights.

Imagine a hose pipe with a tap. Turn on the tap and water flows out at a certain rate. Put a trigger on the end of the hose and water still flows at the same rate.

Definitely fuse as close to the battery as possible (ie. centimeters!!) From there, mount the relays wherever is most practical... probably in the engine bay. 8Ga wire will be enough for 400W of lights. If you like, you can even connect 1 length of 8ga wire to both relays. Otherwise, if its easier the run 2 lengths of slightly thinner wire.

Ok, the idea is to feed one mofo power cable up there (capable of handling 50-80A over its length with minimal voltage drop), and then tap into it at the roof level, instead of running several smaller wires for each light (carrying med-heavy current 10-16 A or so). In effect it is a buss bar system that most sparkies would be well familiar with. Would also suggest a 2 pin Anderson power connection and Molex trigger wire connector to be added under the bonnet if you want to remove the lightbar in the city (police reasons...) or at least disconnect it for safety.

The only wires will be a 8 Ga +ve, 8 Ga earth, and one light duty 18-22 Ga trigger cable for each relay, versus a seperate med-heavy power wire for each light and an 8 Ga heavy earth return. Much easier to have to deal with one heavy +12v wire than 4 medium +12v ones, heavy one is more rigid and less susceptable to vibration. One 8 Ga power line for 4 x 100 watt lights, one earth return, and one relay trigger for all on/all off operation, or two triggers for 2x2 on/off. Trigger wire have 5 amp fuses, all that is really necessary.

The other issue is about the voltage drop along the power cable. With lights, about 20% of their brightness comes in the last 1-1.5 volts of their operation (compare headlight brightness at 12.8 v engine off, then with 14 volt fast idle) The main idea behind the buss bar approach (in any electical application) is to minimise the voltage losses, therefore reduce heat generation in the cabling, and reduce the possibility of shorts ocurring due to softening/failing insulation.

This also gives the option of peeling off an external 12v socket for campsite light/power, or seperate line for adjustable worklight/overhead reversing light without having to run yet another heavy cable carrying switched current from under the bonnet.

[Goatse.AJ]

What Damkia said x2

[DAZZ]

What about a dual headlight relay (New Era type) these can handle a fair amount of current.

[Shadow]

running a current supply would be a very good idea IMO.

How do people actually get power to the roof though?

Drill a hole in roof?
Run up external A pillar?
Run up isnide door and then go through gap in door rubber? (wouldnt work i dont think?

I was thinking running it up behind the snorkel would be a good idea.

[chimpboy]

running a current supply would be a very good idea IMO.

How do people actually get power to the roof though?

Drill a hole in roof?
Run up external A pillar?
Run up isnide door and then go through gap in door rubber? (wouldnt work i dont think?

I was thinking running it up behind the snorkel would be a good idea.

I ran a hole through the mudguard that emerged under the snorkel. There was an indent in the snorkel designed to allow for the antenna, so there was a bit of room there.

Then I ran the cable up behind the snorkel as you've suggested, to a sealed box containing relays for the roof lights which was tucked under the roof rack. The roof rack itself was custom made by me with a light bar at the front. Cabling for the lights ran inside the light bar to the same relay box, and the light bar was made so that you can pull a pin and drop the lights down (ie so that they are lying face down towards the roof instead of pointing forward) to (a) keep them legal on-road and (b) allow the roof rack to be used as a roof rack.

I should add that this was on my SWB. I've since transferred the same roofrack to my LWB, but I don't plan to repeat the wiring. I'm going to pull off the lights and put them on the front bar. I don't think roof lights are worth the stuffing around except on a ute.