L.E.D Bulbs, deabte . . .

[(RIP) PLANK]

I am considering upgrading the interior lights in my caravan to L.E.D bulbs for power saving. But do they really save any power?

The caravan is 12v (obviously) and LEDs run at 3-5v (I think) so need some kind of ballast resistor to allow for this (I think?)

So whole the LED itself may only draw milli amps what does the whole 12v LED replacement bulb draw? has anyone put a meter in line and tested this? O do they have LED bulbs they could test for comparison?

This sounds like a job for 96Terrano to me :thumb2

 

[96terrano]

why don't you just get replacement bulbs for the 12v fitting? saves messing about with ballasts and step-down transformers

 

[(RIP) PLANK]

why don't you just get replacement bulbs for the 12v fitting? saves messing about with ballasts and step-down transformers

you have missed the point entirely :doh

I am talking about replacement bulbs! they have a built in ballast resistor as LEDs don't run on 12v! Therefore the resistor wastes power as heat. So are the replacement bulbs really that much more efficient than the old ones?

:thumb2

 

[Fez_uk]

alot of the leds are wired to accept 12v or near enough. With very little or no ballast resistor.

 

[Paul]

A mate of ours swears by them, abit on the dear side to buy but he says he can use them all on @ night and the batt lasts alot longer before needing recharge..

 

[(RIP) PLANK]

alot of the leds are wired to accept 12v or near enough. With very little or no ballast resistor.

yes that is my point, an LED bulb runs at 12v but how much current does it use as compared to the filament bulb it replaces, I was hoping someone who has LD bulbs could put an ammeter in line and compare :nenau

 

[Fez_uk]

What i mean is some are wired in series and some parallel to get it near to 12v.

It all depends on what LEDs are used. Some pull more amps than others. All i know is they use less and usually have a clearer light.

 

[(RIP) PLANK]

What i mean is some are wired in series and some parallel to get it near to 12v.

It all depends on what LEDs are used. Some pull more amps than others. All i know is they use less and usually have a clearer light.

What we all assume is that they use less! and to be fair the LED's would, but does the completed bulb use less? I was hoping for a tried and tested answer rather than the hype, I suppose I will have to buy some and try it (with a meter) myself :thumb2

 

[Lazy-Ferret]

Basically, the resistor is used to limit the current to the LED, which is in series with the LED, so apart from a bit of wastage in heat, there is very little lost by the resistor.


Think of it as a hose pipe running out of a water butt, if you put a kink (Resistance) in the hose, it slows the water down, so it takes longer to flow away, but ultimately there is no loss of actual water.

 

[(RIP) PLANK]

Basically, the resistor is used to limit the current to the LED, which is in series with the LED, so apart from a bit of wastage in heat, there is very little lost by the resistor.


Think of it as a hose pipe running out of a water butt, if you put a kink (Resistance) in the hose, it slows the water down, so it takes longer to flow away, but ultimately there is no loss of actual water.

the water analogy is interesting but the kink will have several effects! the most interesting one being and increase in water pressure!

The LED bulb question is a real one, example: take the bulb out of your indicator in the front (most cars) and the remaining bulb will flash twice as fast as the relay needs the resistance in m=bot to be equal to function correctly. SO now put in LED's wired in series/ parallel or both to make them run on 12v, the relay will still operate much to fast at the resistance is so low - the answer, put a ballast resister in the bulb, the equation is I=V/R (ohms law) so now the LED bulb is using the same current as the filament bulb!

In modern cars that use LED's as standard they have a lower voltage circuit for this so the current consumed is less!

So you see my point, LED's use less power YES! But do LED bulbs? Unless you compare with an ammeter you will never really know :nenau

example: http://www.ebay.co.uk/itm/2x-501-W5...arts_Vehicles_CarParts_SM&hash=item4845b7f1f0

Read it carefully, it claims the CREE LED is 1.5 watts, not that the bulb is 1.5 watt, it would be worth putting a meter in line!

 

[Lazy-Ferret]

the water analogy is interesting but the kink will have several effects! the most interesting one being and increase in water pressure!

The LED bulb question is a real one, example: take the bulb out of your indicator in the front (most cars) and the remaining bulb will flash twice as fast as the relay needs the resistance in m=bot to be equal to function correctly. SO now put in LED's wired in series/ parallel or both to make them run on 12v, the relay will still operate much to fast at the resistance is so low - the answer, put a ballast resister in the bulb, the equation is I=V/R (ohms law) so now the LED bulb is using the same current as the filament bulb!

In modern cars that use LED's as standard they have a lower voltage circuit for this so the current consumed is less!

So you see my point, LED's use less power YES! But do LED bulbs? Unless you compare with an ammeter you will never really know :nenau

example: http://www.ebay.co.uk/itm/2x-501-W5...arts_Vehicles_CarParts_SM&hash=item4845b7f1f0

Read it carefully, it claims the CREE LED is 1.5 watts, not that the bulb is 1.5 watt, it would be worth putting a meter in line!

Unfortunately, the Water analogy only works to a point:bow

We are off out, but I do have a few 12v LED bulbs here, so I will try and measure it later for you.

The main problem is, as you say, Indicators, and some CanBus systems require the bulb to draw a certain current, in order for them to be able to monitor the bulb is working, and if you look, you will see many LED lamps that say they contain a ballast resistor in order to fool the cars ECU into thinking it is a normal bulb. This Ballast resistor is fitted in parallel to the LED and it's resistor though, so the majority of the current then passes through that, and is totally wasted in heat.

Those would obviously not be the sort you put in a Caravan, as it would be pointless.

 

[arcascomp]

I have some 12v LED's that claim to be as bright as a 20W halogen and I'm fairly sure they are, perhaps a little less spread out, but the cree bulb used is 3W and the whole sheebang is rated at 4W so a little loss. but still way less than the halogen it replaces.

 

[(RIP) PLANK]

I have some 12v LED's that claim to be as bright as a 20W halogen and I'm fairly sure they are, perhaps a little less spread out, but the cree bulb used is 3W and the whole sheebang is rated at 4W so a little loss. but still way less than the halogen it replaces.

but the point is still misses, while the LED may be lower wattage is the lED plus resistors etc, that make up the 'bulb' actually lower wattage?

I = V/R: So if the supply V is 12 and the v needed by the LED is 4 and increasing R is used as a method of to make up the value of V then I would be the same :nenau

So has anyone actually put any of these claims to the test with an ammeter?


Example: http://www.ebay.co.uk/itm/2x-5-SMD-...arts_Vehicles_CarParts_SM&hash=item45ff46c137

These bulbs can't possibly use less power or they simply wouldn't work!

 

[arcascomp]

Nope but LED is 3W at 12V, Bulb is packaged and rated as 4W at 12V, light out is close to Halogen 20W at 12V.

So, the LED saves 17W but after losses in the bulb package it only saves 16W.

Have I tested, nope, but my bike lights run substantially longer on LED than Halogen with the same battery pack.

 

[briggie]

another equation you might be interested in for this debate ...

p= i x v

p ( power measured in watts ) can be dissipated as heat

i= current measured in amps

v= voltage measured in volts

 

[briggie]

you have pm plank :augie:lol

 

[rustic]

On my boat I converted the navigation lights to LED, they were originally 10 watts each, so less than an amp.

When I fitted LED's the power consumption dropped to 10 % of the original power..

I will find a note later and post it on the effect of putting 2 led's in series.

One string of LED's in series will take approx 20 mA 0.02 Amps.
Most LED bulbs are wired in series parallel so often have say 8 strings of 2 LED's

So current will be 8x 20 mA or 160 mA or 0.16 amps.

If that helps for now.

 

[(RIP) PLANK]

so, in transposing that equation if V = 12 and I = 10 then P = 120

so if a light is giving off 120 watts at 12 volts it must be drawing 10 amps regardless of it's filament or LED status.

In this case the 'missing' power is used by the resistors that are allowing the LED's to run at 12 volts. :nenau

even if one considers that LEDs of much lower wattage are used to produce the same quality of light (lumens/kelvins?) then by default some power must be being wasted by running LED's at 12v :nenau

I have ordered 10 Led "bulbs" and will do some measuring when they arrive, though they are on a slow boat from China so I won't hold my breath :augie

 

[briggie]

the pm i sent you explains it plank , if you dont fall asleep reading it :lol

 

[briggie]

i love a good debate , im often called a great mass debator ...... or i think thats what they said