LED tail lights

LJ said:
I ve put LEDs in the GT for flashers,permanent side light and tail, remember they can act as a dam if there is a bad earth and can fry your wiring , unlike a standard bulb which the fault would probably pass through and blow your fuse. I ve used them as its a dynamo and just lowers voltage,
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Sorry LJ, I don't follow your meaning. I don't understand how a LED can act as a dam, or how a dynamo can lower the voltage in that situation. Maybe I'm misunderstanding what you're saying.
 
OK. Now I think the misunderstanding is with you. You're correct in saying that LEDs can blow fuses (although they shouldn't fry your wiring if your fuses are correctly sized) but your theory as to how they do it is incorrect.

Current can't back up at a LED. It'll either conduct or it won't. It has zero capacitance, so no way of piling up electrons like water against a dam.
However, LEDs can fail in short-circuit mode which can blow a fuse - unlike incandescent globes which fail in open circuit mode.
 
However, LEDs can fail in short-circuit mode which can blow a fuse - unlike incandescent globes which fail in open circuit mode.
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Knew there was a reason why I stayed with incandescents.
 
I'm using this bulb in tail light led.

http://www.ebay.es/itm/1-x-710LM-White-1157-Bay15d-21-5730-SMD-LED-Car-Brake-Tail-Signal-Light-Bulb-/221288420426?pt=Motors_Car_Truck_Parts_Accessories&hash=item3385d1544a&_uhb=1
 
So! Is my house going to burn down or not Cam? (I have a few LED'S).

Although I believe my modern circuit breakers trip out on high load as well as earth leakage.
 
Circuit breakers, including the RCD type, have current overload trip, so you won't fry the wiring in your house. I'm sure you know that.
A shorted-out LED won't trip a circuit breaker in your house anyway. It'll more likely overload the little transformer that drives the LEDs, and that'll catch fire  ;)

Seriously though, a LED that fails in short circuit generally won't do any harm. The series resistors that are nearly always connected to them will limit the failure current.

 
Cam,  the reason I said a "dam" was I had a bad earth to the frame,(powder coating wasn t all off) sent live down the brake wire to the LED and backed up and melted the plastic wire sleeving,the electrical wholesaler said the current won t pass through an LED bulb so never got to the fuse.I may have misunderstood him but it"s fine now the bikes properly earthed.
 
Hi Shaun

It sounds like a load of codswallop to me. But I've never walloped a cod.  And I'm not a mechanic, so what would I know?  ;) 

I'm only an engineer (mechanical/electrical).

Your electrical wholesaler may be correct in saying that electrical current won't pass through a LED, but only if the LED is wired in reverse polarity. LEDs are diodes (that's the D bit in L.E.D). They're like non-return valves. Electricity will only flow one way. If they're connected arse-about, nothing will happen. It's like not being connected at all.

In very general terms, it may be helpful to use the flow of water in pipes as an analogy to electricity, with the following equivalents:
Voltage = pressure
Current = flow rate
Resistance = flow friction
Capacitance = reservoir storage, but let's not worry about that.

Fuses blow when there is too much current. They simply overheat and melt.

If there's a blockage in the system somewhere, whether it be a diode (including LED) or a switch in the off position, no current can flow. Pressure (or voltage) can't build up any more than is available from the battery. Nothing is going to blow up. 

If the current never got to the fuse, how could it blow? If you had blown fuses, it wasn't the LEDs that caused it. You probably fucked up the wiring somehow.

Cheers,
Cam


 
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