Tricky-Ricky Posted February 8, 2017 Share Posted February 8, 2017 Just run into a problem on my bike protect, the bike has to run a + earth system due to the nature oof the electronic ignition system fitted, but in my wisdom i bought a really nice LED rear light......now as we all know LEDs are current flow direction dependent, so i need to try and come up with some way of integrating both the brake light which would be relatively simple to use a separate circuit . But i also need to be able to run the the headlight on the + earth system (or do i?) and the rear on a - earth, and all running off a single ignition switch, now i guess it could be done with relays, but i am also very limited on space for things like that, as i have a small battery box that also contains all the coils ans electronics, and theres room for little else...so if any of you guys have an idea or solution i would be grateful Quote Link to comment Share on other sites More sharing options...
Style Posted February 8, 2017 Share Posted February 8, 2017 I guess you've already bought it, so may not be much use but do you get positive earth LED's especially for this sort of thing? Quote Link to comment Share on other sites More sharing options...
Hitbox Junkie Posted February 8, 2017 Share Posted February 8, 2017 Could you reverse the polarity of the light connection so connect the positive to your battery negative terminal and the negative of the lights to the positive of the battery. As older cars/bikes used the negative terminal as the live. Just me having a though as the the current would flow through the LEDS but I'm. Unsure if this would light them, kill them or work. As they are diodes so block current one way. Other than that run them from.your battery on the positive to negative in a separate circuit with its own switch and earth the negative to the chassis to make your own negative earth circuit system. Or switch out the switch to run a relay that energizes as you turn your ignition on. Quote Link to comment Share on other sites More sharing options...
Hitbox Junkie Posted February 8, 2017 Share Posted February 8, 2017 Only other thing could be to run a dc to AC converter then convert that back to DC. Maybe able to use 3 small bridge rectifiers to convert the negative dc to a positive dc. Quote Link to comment Share on other sites More sharing options...
stevie_b Posted February 8, 2017 Share Posted February 8, 2017 Naive question - could you just connect the LED light the "wrong way round"? i.e. connect the light's cathode terminal to the supply (not to earth, which will have a higher potential than the supply). Mixing +ve and -ve earth on a single vehicle sounds like bad news to me - would you have to make sure the two systems are fully segregated? Anything connected across them (maybe the rider, in the case of a bike) will get current flow. Quote Link to comment Share on other sites More sharing options...
Tricky-Ricky Posted February 8, 2017 Author Share Posted February 8, 2017 Current will only flow in one direction through LEDs, so far the only way i can think of is to run two totally separate circuits, one for the ignition system using + earth, and one fore the lighting, horn, stop light circuits, but the problem arises with trying to switch the two circuits as one, so its either two separate switches, or a relay for one that triggered from the ignition switch....unless i can find a dual circuit ignition switch? Or a micro relay of some kind that i can cram into the small battery box?? Quote Link to comment Share on other sites More sharing options...
stevie_b Posted February 8, 2017 Share Posted February 8, 2017 Current will only flow in one direction through LEDs... That's right. With a positive earth, current flows from the chassis to the load (e.g. brake light), and then to the -ve battery terminal. Could it work if you connect the cathode of the LED light to the battery side, and the anode to the chassis side? Quote Link to comment Share on other sites More sharing options...
Tricky-Ricky Posted February 8, 2017 Author Share Posted February 8, 2017 Sorry should have said that the current will only flow from + to -, so will only light if connected this way around, which is the opposite of the ignition system. Quote Link to comment Share on other sites More sharing options...
Hitbox Junkie Posted February 8, 2017 Share Posted February 8, 2017 [ATTACH=CONFIG]216923[/ATTACH] Smallest relay I could find in work shop Quote Link to comment Share on other sites More sharing options...
Tricky-Ricky Posted February 8, 2017 Author Share Posted February 8, 2017 LOL! that's tiny, mind you it would need to be able to handle 12-14V 10 amp. Quote Link to comment Share on other sites More sharing options...
Tricky-Ricky Posted February 9, 2017 Author Share Posted February 9, 2017 Think i may have found a solution, apparently the ignition system can have the polarity reversed, so i may be OK..i hope!...thanks for the input guys. Quote Link to comment Share on other sites More sharing options...
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