L.E.D Bulbs, deabte . . .

(RIP) PLANK · 10-10-2012, 12:06

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

96terrano · 10-10-2012, 12:16

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

(RIP) PLANK · 10-10-2012, 12:59

Quote:

Originally Posted by 96terrano

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

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?

Fez_uk · 10-10-2012, 13:09

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

Paul · 10-10-2012, 13:41

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 · 10-10-2012, 13:43

Quote:

Originally Posted by Fez_uk

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

Fez_uk · 10-10-2012, 13:55

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.

briggie · 10-10-2012, 16:54

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

rustic · 10-10-2012, 17:06

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 · 10-10-2012, 20:34

Rustic - for some reason the quote button isn't working but cheers for that! As i really need to drop my power consumption now the nights are drawing in

edgerton19 · 10-10-2012, 23:07

To answer the original question it depends on the type of lighting fitted in your caravan. If you have fluorescent lights fitted the LEDs will be only very marginally more efficient as their efficacies are similar (but the latest LEDs win).
If you drive them via a resistor to control the current you are on a looser as the resistor just converts the excess voltage (and hence power) to heat. If you buy switch mode LED drivers the conversion efficiency should be over 90% and you can series LEDs, work on each LED needing around 3 to 3.3V at their rated current.
The big problem with home construction is getting the heat out of the LED body, at work we build high power LED light engines on PCBs with an aluminium substrate and these are then mounted on aluminium heatsinks. Small low power LEDs can be mounted on FR4 but you still need to back the assembly with some form of heatsink.
In your position I would look at a ready made solution, Labcraft got a good write up in RadCom for their 12V LED lamps and no I don't work for Labcraft but I do work for a UK company that manufacture 100,000 LED drivers and light engines a month!!

(RIP) PLANK · 11-10-2012, 14:14

Quote:

Originally Posted by edgerton19

To answer the original question it depends on the type of lighting fitted in your caravan. If you have fluorescent lights fitted the LEDs will be only very marginally more efficient as their efficacies are similar (but the latest LEDs win).
If you drive them via a resistor to control the current you are on a looser as the resistor just converts the excess voltage (and hence power) to heat. If you buy switch mode LED drivers the conversion efficiency should be over 90% and you can series LEDs, work on each LED needing around 3 to 3.3V at their rated current.
The big problem with home construction is getting the heat out of the LED body, at work we build high power LED light engines on PCBs with an aluminium substrate and these are then mounted on aluminium heatsinks. Small low power LEDs can be mounted on FR4 but you still need to back the assembly with some form of heatsink.
In your position I would look at a ready made solution, Labcraft got a good write up in RadCom for their 12V LED lamps and no I don't work for Labcraft but I do work for a UK company that manufacture 100,000 LED drivers and light engines a month!!

Interesting stuff but! my intention was/is always to use something ready made i.e. the ready made Led "bulbs" available to for use in cars. My point was that these all seem to use resistors that, as you say, waste the extra power as heat. In the case of indicators they would have to do this to work! So while there are benefits to LED replacement bulbs is energy saving one of them or is it just an assumption we all make.

So if i buy these for example:

http://www.ebay.co.uk/itm/2-x-LED-Li...true&forceRpt=

note the seller makes no claims regarding their efficiency! They can't use less power as they must use a ballast resistor to make the flasher unit in the car work and therefore use the same power in total!

(RIP) PLANK · 10-10-2012, 17:07

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.

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

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

Moochin · 10-10-2012, 18:27

18 years ago I completed a National Diploma in Electronics, I have just read through this and decided I haven't the first clue how I managed to pass.

96terrano · 10-10-2012, 18:28

Quote:

Originally Posted by Moochin

18 years ago I completed a National Diploma in Electronics, I have just read through this and decided I haven't the first clue how I managed to pass.

10-10-2012, 12:06	#1
(RIP) PLANK Senior Member Join Date: Mar 2006 Location: Central England, in the Heart of the Black Country Vehicle: T2 2004 TDI SE LWB Posts: 7,740	L.E.D Bulbs, deabte . . . 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

10-10-2012, 13:41	#5
Paul Senior Member Join Date: Jul 2007 Location: North West Vehicle: 2002 Terrano 3.0 Di LWB Posts: 1,961	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.. __________________ 2002 Terrano 3.0 Di LWB..

10-10-2012, 17:06	#9
rustic Senior Member Join Date: Feb 2007 Location: Staffordshire Vehicle: Maverick Mk I 2.7 TD LWB Posts: 7,825	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. __________________ Ford Maverick GLX 1995 2.7TD LWB in illusion silver, 98k miles. Owned since new, for 22 years. Best car I have ever owned. Just wish I could drive it more.

10-10-2012, 12:16	#2
96terrano Senior Member Join Date: Jun 2010 Location: Dumfries and Galloway, Scotland Vehicle: Nissan Terrano 2.7TD LWB Posts: 8,024	why don't you just get replacement bulbs for the 12v fitting? saves messing about with ballasts and step-down transformers

10-10-2012, 13:09	#4
Fez_uk Senior Member Join Date: Sep 2010 Location: Mid-Wales Vehicle: Maverick 2.7 - Patrol 4.2 Posts: 5,645	alot of the leds are wired to accept 12v or near enough. With very little or no ballast resistor.

10-10-2012, 13:55	#7
Fez_uk Senior Member Join Date: Sep 2010 Location: Mid-Wales Vehicle: Maverick 2.7 - Patrol 4.2 Posts: 5,645	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.

10-10-2012, 16:54	#8
briggie Senior Member Join Date: Mar 2010 Location: peoples democratic republic of west yorkshire Vehicle: " alice " Posts: 10,473	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

10-10-2012, 20:34	#10
(RIP) PLANK Senior Member Join Date: Mar 2006 Location: Central England, in the Heart of the Black Country Vehicle: T2 2004 TDI SE LWB Posts: 7,740	Rustic - for some reason the quote button isn't working but cheers for that! As i really need to drop my power consumption now the nights are drawing in

10-10-2012, 23:07	#11
edgerton19 Member Join Date: Jan 2011 Location: Yorkshire Vehicle: Terrano 3.0 SE Posts: 99	To answer the original question it depends on the type of lighting fitted in your caravan. If you have fluorescent lights fitted the LEDs will be only very marginally more efficient as their efficacies are similar (but the latest LEDs win). If you drive them via a resistor to control the current you are on a looser as the resistor just converts the excess voltage (and hence power) to heat. If you buy switch mode LED drivers the conversion efficiency should be over 90% and you can series LEDs, work on each LED needing around 3 to 3.3V at their rated current. The big problem with home construction is getting the heat out of the LED body, at work we build high power LED light engines on PCBs with an aluminium substrate and these are then mounted on aluminium heatsinks. Small low power LEDs can be mounted on FR4 but you still need to back the assembly with some form of heatsink. In your position I would look at a ready made solution, Labcraft got a good write up in RadCom for their 12V LED lamps and no I don't work for Labcraft but I do work for a UK company that manufacture 100,000 LED drivers and light engines a month!!

10-10-2012, 17:07	#13
(RIP) PLANK Senior Member Join Date: Mar 2006 Location: Central England, in the Heart of the Black Country Vehicle: T2 2004 TDI SE LWB Posts: 7,740	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. 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 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

10-10-2012, 18:27	#14
Moochin Junior Member Join Date: Oct 2012 Location: Staffordshire Vehicle: 1999 Terrano 2.7 Tdi Posts: 12	18 years ago I completed a National Diploma in Electronics, I have just read through this and decided I haven't the first clue how I managed to pass.