LED, blinded by the obvious!?

[snoopy64]

Ok, spent the weekend helping a mate fit replacement LED lights here and there on his std Mk2(not headlight), soooo what is it about the online brake switch that causes all manner of odd things to happen with lights going off when they should stay on(tails and number plate) and go on (pilot light) when you press the brake pedal.... I'm even starting to wonder if there's enough current in the fluid to do it!!

No bad earths... Just bad tempered banter as s result!

Ideas?

[mk1]

As LEDs draw very little current sometimes it upsets older systems & you have to stick resistors inline to balance things up again.

M

[ianh1968]

The LED's drawing a low current would imply a high resistance...

Don't the resistors go in parallel so that the electrical system sees
something like the load it would do under normal conditions?

It's usually just the indicators that play up, because the flasher units
are electro/thermo/mechanical and rely on a sufficient current draw
to work.

... unless you use one of these...
http://www.carbuildersolutions.com/uk/3 ... sher-relay
http://www.carbuildersolutions.com/uk/2 ... sher-relay

For indicators, having the resistor to sort the load out would surely
totally negate one of the reasons for having LED's, ie, low power
consumption? They would probably last longer, however...

The other thing about LED's is that they are DIODES - You need to wire
them up with the correct polarity or they won't work. I would also
imagine that if you have a mixture of LED's and traditional lamps on
the same circuit, there may well be "bad earth"-style problems.

The side-lights, tail lights and number plate lamps would be a good
example of stuff being on the same circuit. The brake lights share
a common earth with the tail lamps, so it's all getting a bit messy.

A few years back, I built a new dash for my Mini - It had an on-override
switch to the fan and a panel lamp to show when the fan was running.
This stuff was all earth-return, so the lamp had to have a permanent
feed. The clock also has a permanent feed and when I needed to
change the clock because it was fast, I thought that pulling the fuse
would do the trick...

WRONG - The clock continued to work, pulling its positive feed through
the filament of the panel lamp for the fan, or at least I think that is what
it was doing... I put a diode in the clock circuit and this cured it.

My conclusion was that putting in fancy wiring could have quite easily
turned out to be a right pain-in-the-arse.

Sometimes a circuit will find a supply or earth via the easiest path
which might not always be the intended one. Your earths might not be
"bad", but the LED's might find it easier to pull an earth through the
filament of another lamp rather than the correct route.

Ian

[Tim]

I suspect that's the issue. The resistors are only needed to make the bimetallic strip get hot enough in the old flasher cans, at least in theory, they shouldn't be needed for anything else.

My guess would be the old 'bad earth' problem. Either taking away the filament globes has removed a dodgy earth path that was present before, or having a mix is providing an unexpected earth path. The dual filament globes, e.g. brake/tail or on some models the front park/indicator or reverse/indicator are usually the cause.

Tim

[mk1]

OK, I was close, but no cigar. My original comment was based on one overheard conversation in the pub

[Frogeye61]

I used these for the turn signals, though one per side.
http://www.ebay.co.uk/itm/Electronic-LE ... SwpdpVeSZN

They cost very little and are adjustable.

I bought doide "bulbs" off the bay and found they were wired wrong. Normally a dual filimant bulb will have two power sources and a ground. ALL the ones I got out of china had both power sources wired together. I had to put "supply" diodes in to prevent all the turn signal lights and brake lights to come on when the parking lights were lit.

[snoopy64]

Hi, some great pointers folks thanks.., going to have another bash at it this weekend ....

[ianh1968]

OK, I was close, but no cigar. My original comment was based on one overheard conversation in the pub

Mark, it was close enough to be a very valid point here
- Yes, resistors, and yes you have to wire them up correctly.

I was thinking about getting some of these myself, but am having
serious second thoughts now. I'm not overly fussed about power
consumption as I have a 70 amp alternator and I'm even less fussed
about the theoretical "extra" fuel that it would take to generate the
electricity to power the traditional type of lamps.*

I also don't find changing a bulb, probably on average once a year,
too onerous. Now a "CREE" headlamp conversion at a sensible price
would be another matter...

I hope that this gets sorted out on snoopy64's project because
otherwise it may turn out to be money down the toilet!


Ian
* Energy saving domestic lamps are another of my favourite gripes.
It is said that an 11 watt fancy lamp is equivalent to a 60 watt
traditional lamp - By definition, therefore, they say you are "wasting"
49 watts of electricity, on each one, no less!

"That's perfectly true", I hear you say, "Are you some kind of dim-wit
that cannot subtract 11 from 60?".

Well, yes, I can do that, but why do they consider the 49 watts of
electricity to be "wasted"?

"- Because it's just producing heat and not light, you idiot...
... and obviouly, this is totally bad under all circumstances."

OK, Mr Smart-Arse expert, you consider this then:
1) I have my central heating on for approximately 7 months of the
year, these are the coldest months, and also the darkest, when I
use my lights the most.

2) When it's dark, it's also generally colder, mostly because it's
night and the Sun has set. (Can you see where this is going, yet?)

3) My central heating system has a thermostat on it which detects
heat and turns the boiler on and off.

4) The thermostat is unable to tell the difference between heat
generated by the central heating, and heat generated by my
un-environmentally friendly collection of traditional light-bulbs.

Conclusion - During the winter months when my central heating
is running, the 49 watts of "wasted" electricity is saving 49 watts
worth of gas used to heat the house... Only during the 5 months
of the year when the heating is not on would the electricity be
"wasted", but during these months the lights are not being used
half as much anyway.

Go figure!


... It's all a scam!

[Tim]

Ah, but if you used a heat pump/reverse cycle air conditioner, they harvest around 4 times as many watts of energy as they consume. So the 49 watts that you saved could be used to deliver 196 watts of heat.

Tim

[mk1]

You make a good point Ian,

As an electrical wholesaler I sell a hell of a lot of LED lamps.

On more than one occasion I have had customers complaining that when they switch over to LED they have to turn the central heating up to compensate for the reduction ion heat given off by traditional incandescent lamps. So you do end up "Robbing Peter to pay Paul".

M