led rear light

[Marty ULC]

Planning to fit an led light to the back.
Looks like the same leds light up only brighter when power goes through the brake light wire.
my question is this.
If i use the ac to power the rear light can I use dc for the brake light switch?
It's only a small 1.2ah battery charged by a trickle feed so I won't be powering the main lights from it.

[Knowledge]

Hi Marty,

My initial reaction to your question was no, but then I thought about when I first got a Lambretta with traditional 6v electrics and a battery as standard. If the battery was flat, the horn, brake light and parking light wouldn't work, even though the lights (inc tail light) did work.

This was because the horn and brake light were DC and the main lights were AC. This is just the scenario that you describe Marty, so the answer would appear to be yes, unless there is something very clever in the ignition switch that allowed this to occur (I suspect not).

Good luck.

Martin

[Marty ULC]

Cheers Martin. I'll just give it a go with a temporary wire and see if it works.
I'm thinking earth should still be earth whether it's ac or dc. Be an interesting experiment to see how that setup works with a conventional bulb too. Be nice to be visible from behind as well as not dimming the front when I brake.
I'll let you know how I get on.

[Nelly]

It should work, make sure you have a fuse connected in line with the positive.
The only difference in the feeds to the led back light is the lighting circuit feed has a resistor in series to drop the voltage, so the leds are dimmer than when the brake feed is on. You will find the brake light is substantially brighter when using DC over AC.
I noticed quite a difference when I did the DC conversion.

[Jono]

Hi mate answer is yes , I run 12volt DC brake lights a horns on both my GP's with AC lighting.
I originally used LED bulbs in the rear light for both brake and rear lights however using AC they were not very bright.
Best of luck - jono

[pirate pete]

As posted above. It does work as mine was wired that way until I went the Wassell route.

[coaster]

The answers above have got me wondering, I have a BGM rear light in one of my scoots and a cheap ebay motorcycle led lamp http://www.ebay.co.uk/itm/MOTORCYCLE-RE ... 4d03be113c on the other (they will fit snuggly inside a s3 rear light with the reflector removed) and I think separate leds are used for the brake light on both I'll check at the weekend

[Marty ULC]

it works.
froze my nads off this evening getting it sorted but now I have a rear light that is just as bright as the old one (it was quite bright) my brake light is way brighter and there's no effect on the headlamp.
I have a fuse between the battery negative and the frame, should i add one to the positive side too?
If so where and what ampage?
I have three wires going to the positive side of the battery, one from the regulator/rectifier,one to the brake light switch and another to a cigarette lighter socket for charging the phone/satnav/camera etc.

[Nelly]

I always prefer to see a fuse in the positive side.
I would put a 2A or 5A fuse between the 3 feeds and the battery, it doesn't want to be too big as your battery is only 1.2AH.

[foremanbob]

I always prefer to see a fuse in the positive side.
I would put a 2A or 5A fuse between the 3 feeds and the battery, it doesn't want to be too big as your battery is only 1.2AH.

if you put the fuse in the ground side, an accidental short against the +ve terminal will not cause a big bang!!!

[Marty ULC]

Coaster that's the cheap Chinese eBay type I have in mine. It's the same LEDs for rear and brake lights.

[Nelly]

I always prefer to see a fuse in the positive side.
I would put a 2A or 5A fuse between the 3 feeds and the battery, it doesn't want to be too big as your battery is only 1.2AH.

if you put the fuse in the ground side, an accidental short against the +ve terminal will not cause a big bang!!!

This is very true.
It was always drummed into me as an apprentice electrician to have the live side fused, whether that be in a 240/415V circuit or in vehicle wiring. It's just the way we think, I suppose. It's natural instinct to fit the fuse to the positive side, particularly if there is more than 1 circuit to be protected
If we are going to have a belt and braces approach, fuse both positive and negative to be on the safe side.

[Marty ULC]

Update.
I decided to go D/C on the townlight, speedo bulb and rear light while keeping the headlight and horn A/C.
The casa ignition switch wouldn't let me do it as the purple wire only feeds the black (speedo and rear) and yellow (town light) in position 2 but nothing in position 3. The brown feeds nothing in position 2 and everything except the yellow in position 3.
Scratched my head for a while then decided to try the SIL switch in my 125 special.
Purple feeds black and yellow in both positions and the brown feeds only orange (headlight switch) in position 3.
Swapped the switches round and connected the trickle feed/battery/D/C to the purple and the simplified electronic A/C power to brown. Haven't got the engine running to test the A/C but the D/C works great.
Have ordered LED speedo and town light bulbs to give the trickle feed a chance to keep up with powering it all.

[dave411]

I am going to be using led rear lights on my re build,and will be using AC lighting.I just fitted some resistors to the feed wires,and it works a treat.