russbost
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| posted on 18/3/15 at 01:53 PM |
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One for electrical experts - LED knowledge
As some of you may already know I have recently started stocking led lighting modules - household stuff, brilliant product & ticks all the
environmental friendly & energy saving boxes 
However as with anything I sell I always want to fully understand the product & what makes it tick, hence I have been testing the modules with
various different drivers, both constant current & constant voltage. With the constant voltage stuff things go pretty much as you'd expect
in that the more of the 3 led modules you use the current goes up hence overall wattage goes up.
However when using the constant current drivers, for instance a constant current 1320mA, 22 - 38V driver if you drive 20 modules, they draw 1.32A
@11.2V, which would imply a total draw of 14.8W (W = V x A) or 0.74W per module (the units have a nominal power of 1.5W each as given by the
manufacturer). But if you drive 40 modules you get 1.32A @ 9.5V implying a total draw of 12.5W or just 0.31W per module - the light output of each
unit remains very similar in both situations.
What am I doing wrong in terms of calculation? I am measuring voltage across all the units which are simply daisy chained in series; & current in
line with all the units, how can 40 modules draw less wattage than 20 with the same power of light output??? It doesn't make sense! I simply
want to be sure I am recommending people correctly in terms of which driver will be best for a particular application.
I have done similar tests with the lengths of flat led strip & similar results, more lights = lower overall power drawn - it appears to be
contravening the laws of physics!
Please put me out of my misery & tell me what I'm doing wrong with the calculation or measurements! 
I no longer run Furore Products or Furore Cars Ltd, but would still highly recommend them for Acewell dashes, projector headlights, dominator
headlights, indicators, mirrors etc, best prices in the UK! Take a look at http://www.furoreproducts.co.uk/ or find more parts on Ebay, user names
furoreltd & furoreproducts, discounts available for LCB users.
Don't forget Stainless Steel Braided brake hoses, made to your exact requirements in any of around 16 colours.
http://shop.ebay.co.uk/furoreproducts/m.html?_dmd=1&_ipg=50&_sop=12&_rdc=1
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coozer
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| posted on 18/3/15 at 02:18 PM |
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Quantum physics is way out of my ever decreasing area of non expertise...
The more I think about things the more I realise the amount of stuff I know...
1972 V8 Jago
1980 Z750
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theprisioner
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| posted on 18/3/15 at 03:17 PM |
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LED's light o/p is proportional to current and is usually set by the manufacturer of the LED. You can run them off a constant voltage but you
need a resistor in series. The power supply however (to provide a given constant current) is at it's maximum internal dissipation when the
voltage on the output is minimum (depends on the technology however). The voltage vs current of an individual LED chip is non linlear. It has a knee
point (maximum efficient light output) about 1.2V so if you stick 10 of these in series you get approx. 11V. If the current source maximum voltage is
12V then that is the maximum number of LED's you can put in series.
To calculate dissipation for the load it is I x V. To calculate the load dissipation for the power supply is more complex it depends on the technology
employed.
I hope this helps.
http://sylvabuild.blogspot.com/
http://austin7special.blogspot.co.uk/
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tegwin
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| posted on 18/3/15 at 06:04 PM |
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Id also comment that a constant voltage driver is not a bright idea for powerful LEDs. As they get hot they draw more current which makes them
hotter.....
If you use a constant current driver you don't get the same temperature spiral....
Also worth noting that the human eye is terrible at discerning the difference between brightnesses of objects... so even if something is infact
considerably brighter than the other...you might not actually be able to tell...
There's another consideration for LED's runnin of a rectified AC supply... they tend to flicker inline with the phase changes... a decent
switched mode power supply should smooth that out somewhat
[Edited on 18/3/15 by tegwin]
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Would the last person who leaves the country please switch off the lights and close the door!
www.verticalhorizonsmedia.tv
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russbost
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| posted on 18/3/15 at 06:20 PM |
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I should have said these are manufactured using the 5630 chip, 3 x 0.5W (nominal) chips to each LED module.
theprisioner - you obviously know what you are talking about - is it likely that any 12v constant voltage led drivers would already have the resistor
mentioned built in or that the led modules would have? As the ones I've been testing so far seem fine running anything from 1 module up to 22
for a 24W driver or up to 30 for the 36W driver - neither supplier of the driver or the led modules (different suppliers/manufacturers) has mentioned
any requirement for a resistor. Also when driving the led's from a 12V battery there appears no limit to the no. you can daisy chain together
(within reason!) without affecting light output - they simply draw more current - again, no resistors involved.
Are you saying that with the constant current drivers you can actually have the situation that I appear to be seeing that you can actually have less
power drawn whilst getting the same light output from more chips as you approach this "sweet spot" - the knee point you mention - or am I
misunderstanding?
And when you refer to 1.2V per chip as being around the ideal, then I assume that with a 3 x 5630 chip led module the ideal voltage would be around
3.6V, so, say, a 24 - 36V driver would drive 10 x modules each with 3 x led chips?
" To calculate the load dissipation for the power supply is more complex" - you're telling me!!! 
I no longer run Furore Products or Furore Cars Ltd, but would still highly recommend them for Acewell dashes, projector headlights, dominator
headlights, indicators, mirrors etc, best prices in the UK! Take a look at http://www.furoreproducts.co.uk/ or find more parts on Ebay, user names
furoreltd & furoreproducts, discounts available for LCB users.
Don't forget Stainless Steel Braided brake hoses, made to your exact requirements in any of around 16 colours.
http://shop.ebay.co.uk/furoreproducts/m.html?_dmd=1&_ipg=50&_sop=12&_rdc=1
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NOTE:This user is registered as a LocostBuilders trader and may offer commercial services to other users
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theprisioner
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| posted on 18/3/15 at 07:05 PM |
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Yes I do think you are suffering inconsistent measurements due to the knee point.
There a number of pitfalls using LED's in cars. The biggest problem is the vast majority of cheap automotive LED bulb replacement devices have
built in resistors and are "designed" to work across 12V. My experience is this is not always a reliable way to design a product. The
worst offender are the festoon type for internal lights. As you say they put several LED chips in series then connect whole lot in series with a
resistor. The problem doing that is that the Alternator in a car varies from 11.5V to 14.5V this either under stimulates the LED producing a light
that is not in the (designed) spectrum or it overheats the chip when the alternator puts out 14.5V. This produces a product that is less reliable than
a filament bulb. I have experienced this, it is not just a theoretical possibility. The best way to run the festoon type LED replacement bulbs is to
use a 12V - 12V regulator and put it in your lighting circuit for internal lighting.
I have had some LED type products that last extremely well especially the higher power LED ones in running lights etc. I assume the chip is either
better cooled or they have a constant current chip built in.
http://sylvabuild.blogspot.com/
http://austin7special.blogspot.co.uk/
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russbost
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| posted on 18/3/15 at 07:30 PM |
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Just to clarify this is household lighting running from rectified AC, everything I have works, I'm just having difficulty in getting my head
round what I see!
As the manufacturer of the chips says they are 1.5W nominal I had expected that a 3W driver, say, would only drive a couple of modules, however in
practice this defo isn't how it is working & in fact I have 9 modules in my understairs cloakroom being driven very satisfactorily with a 3W
driver, it has been running without issues for 3 months now. I just wanted to be better able to have an understanding of what wattage driver should
sensibly be used for what no. of modules/chips - it would appear trial & error is going to be the only accurate way - all very confusing.
I don't like selling a product I don't fully understand, I like to be able to give people sensible & accurate information &
recommendations!
Any further info much welcomed!
I no longer run Furore Products or Furore Cars Ltd, but would still highly recommend them for Acewell dashes, projector headlights, dominator
headlights, indicators, mirrors etc, best prices in the UK! Take a look at http://www.furoreproducts.co.uk/ or find more parts on Ebay, user names
furoreltd & furoreproducts, discounts available for LCB users.
Don't forget Stainless Steel Braided brake hoses, made to your exact requirements in any of around 16 colours.
http://shop.ebay.co.uk/furoreproducts/m.html?_dmd=1&_ipg=50&_sop=12&_rdc=1
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NOTE:This user is registered as a LocostBuilders trader and may offer commercial services to other users
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theprisioner
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| posted on 18/3/15 at 08:03 PM |
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The problem is what is the 3W referring to. Is it the total load or is it the maximum the driver is allowed to dissipate.
The only example I can find quickly
eBay item number:400614227266
It says 2 - 12V 0.3A 3W PSU
This means when the output voltage is 2V (1-2LED chips in series) output power = 0.6W
when the output voltage is 12V output power is 3.6W (10 LED chips in series).
In other words the power unit is delivering 1 - 3.6W if it is a switching technology and is in the order of 80% efficient then the consumed power will
be 3.6/0.8 = 4.5W
Simples
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http://austin7special.blogspot.co.uk/
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02GF74
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| posted on 18/3/15 at 10:11 PM |
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Back to first post.
What exactky is this module.
Any electrical item is specified by its operating voltage and current it draws.
Find the current vs voltage graph via google for a led and y ou will see it being non linear. At low volt, hardly any curtent flows then it increase
hugerly for smaller steps.
Constant current source does just that, and you would connect leds in series, no drop resistors are needed as there is a sense circuit to keep the
current fixed.
It is not a good idea to connect doides in parallel as you cannot guarantee the share the current equally unless they are matched devices.
Constant voltage is for connecting leds in parallel. they need a drop resistor to limit the current.
Im guessing the modules you are selling are specified for a constant curruent, they wilk be specified for a minimum voltage so you know how many can
be connected in series.
Or they are soecified for fixed operating voltage and current drawn, the latter allows you to work out hke many can be connrcted in parallel.
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russbost
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| posted on 19/3/15 at 09:56 AM |
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quote:
Originally posted by 02GF74
Back to first post.
What exactky is this module.
Any electrical item is specified by its operating voltage and current it draws.
Find the current vs voltage graph via google for a led and y ou will see it being non linear. At low volt, hardly any curtent flows then it increase
hugerly for smaller steps.
Constant current source does just that, and you would connect leds in series, no drop resistors are needed as there is a sense circuit to keep the
current fixed.
It is not a good idea to connect doides in parallel as you cannot guarantee the share the current equally unless they are matched devices.
Constant voltage is for connecting leds in parallel. they need a drop resistor to limit the current.
Im guessing the modules you are selling are specified for a constant curruent, they wilk be specified for a minimum voltage so you know how many can
be connected in series.
Or they are soecified for fixed operating voltage and current drawn, the latter allows you to work out hke many can be connrcted in parallel.
These are the 3 led modules,
L
ink they are specified by the manufacturers as being 12V working voltage 15V max - this doesn't appear to tie in with 1.2V per chip. The
modules will run perfectly reliably & giving good light output from a 12V car battery or similar whether you connect one unit or a string of 20 or
40, when running from the various drivers we have I have found by experimentation what sensible minimum & max units per driver works, but still
don't understand what's going on electrically "behind the scenes" as when I record voltage & current drawn it simply
doesn't appear to make sense!
Going back to the driver situation, we stock a driver identical to the one given above, but why would you specify a driver as being 3W when it's
actually 3.6W (12V x 0.3A)??? I can see customers being confused by this because I certainly am! I guess as long as we can tell customers what works
with what & how many modules to drive with a given unit it is straightforward enough, I just hate not understanding WHY they work as they do!
I no longer run Furore Products or Furore Cars Ltd, but would still highly recommend them for Acewell dashes, projector headlights, dominator
headlights, indicators, mirrors etc, best prices in the UK! Take a look at http://www.furoreproducts.co.uk/ or find more parts on Ebay, user names
furoreltd & furoreproducts, discounts available for LCB users.
Don't forget Stainless Steel Braided brake hoses, made to your exact requirements in any of around 16 colours.
http://shop.ebay.co.uk/furoreproducts/m.html?_dmd=1&_ipg=50&_sop=12&_rdc=1
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NOTE:This user is registered as a LocostBuilders trader and may offer commercial services to other users
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gremlin1234
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| posted on 19/3/15 at 11:49 AM |
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although the modules appear to be in series when daisy changed, you are actually running them all in parallel, (+ & - ) both going to the next
board.
the constant current limits the total current to 1.32A, shared between 20 modules, and the driver finds it can push that current at just 11.5v
if using 40 modules in parallel the driver can push that current at just 9.5v
if you were to connect 2 x20 modules in series
ie one string going to plus, the minus of that going to plus on the second string, and then back to the driver,
you should then find a current 1.32A, and a voltage of 23V
as others have said, brightness is difficult to judge, so you may need to get a light meter.
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russbost
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| posted on 19/3/15 at 12:04 PM |
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quote:
Originally posted by gremlin1234
although the modules appear to be in series when daisy changed, you are actually running them all in parallel, (+ & - ) both going to the next
board.
the constant current limits the total current to 1.32A, shared between 20 modules, and the driver finds it can push that current at just 11.5v
if using 40 modules in parallel the driver can push that current at just 9.5v
if you were to connect 2 x20 modules in series
ie one string going to plus, the minus of that going to plus on the second string, and then back to the driver,
you should then find a current 1.32A, and a voltage of 23V
as others have said, brightness is difficult to judge, so you may need to get a light meter.
Top man! Yes, that makes perfect sense, tho' still slightly mystified that it can apparently take less power overall to run 40 units rather than
20, am I measuring voltage in the wrong place? - I am measuring direct across the source/load, I can only see one place you could ever measure
current, inline on either + or - supply
I no longer run Furore Products or Furore Cars Ltd, but would still highly recommend them for Acewell dashes, projector headlights, dominator
headlights, indicators, mirrors etc, best prices in the UK! Take a look at http://www.furoreproducts.co.uk/ or find more parts on Ebay, user names
furoreltd & furoreproducts, discounts available for LCB users.
Don't forget Stainless Steel Braided brake hoses, made to your exact requirements in any of around 16 colours.
http://shop.ebay.co.uk/furoreproducts/m.html?_dmd=1&_ipg=50&_sop=12&_rdc=1
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NOTE:This user is registered as a LocostBuilders trader and may offer commercial services to other users
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theprisioner
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| posted on 19/3/15 at 02:26 PM |
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These LED substrates are configured for constant voltage, not the most efficient way of running multiple modules. You can see the series resistors in
the images. The series linking of the design is just passing on the +12 to the next substrate.
As each module consumes 1.5W then 10 modules will consume 15W. Any variation will be due to the non linear nature of the diodes and the supply
voltage.
Assuming 1.5W is correct and three chips. The current will 0.125A Total drop across resistor is 8.2V therefore there is 1W lost heat per substrate
(10W for 10off). Hardly a green design.
If you were to remove the resistors you can run 10 modules off a power supply 1/3 the size.
http://sylvabuild.blogspot.com/
http://austin7special.blogspot.co.uk/
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russbost
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| posted on 19/3/15 at 05:06 PM |
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Been doing some more testing with these today & also with the flat "ribbon" led strip, I've more testing to do & then
results to compile, but they don't draw anything like 1.5W per module unless using them with a 12V battery rather than an LED driver, if used
with constant current then there definitely appears to be a "sweet spot"where the power drawn drops significantly despite the fact that
you are powering more modules. This was the main thing I was finding so confusing, but from the info you guys have supplied does in fact make more
sense now. Many thanks for your input guys!
If this is an inefficient way of using LED's then I don't know what they are doing with LED bulbs in mass manufacture, I would say that
comparing these with LED replacements that I've got for halogen bulbs then the actual lighting capability watt for watt is very similar to the
mass produced bulbs
I've actually made a DIY LED "Bulb" which works brilliantly - I will post a youtube vid up at some point - should be of interest to
Locost peeps!
I no longer run Furore Products or Furore Cars Ltd, but would still highly recommend them for Acewell dashes, projector headlights, dominator
headlights, indicators, mirrors etc, best prices in the UK! Take a look at http://www.furoreproducts.co.uk/ or find more parts on Ebay, user names
furoreltd & furoreproducts, discounts available for LCB users.
Don't forget Stainless Steel Braided brake hoses, made to your exact requirements in any of around 16 colours.
http://shop.ebay.co.uk/furoreproducts/m.html?_dmd=1&_ipg=50&_sop=12&_rdc=1
|
NOTE:This user is registered as a LocostBuilders trader and may offer commercial services to other users
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gremlin1234
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| posted on 19/3/15 at 08:02 PM |
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quote:
Originally posted by theprisioner
These LED substrates are configured for constant voltage, not the most efficient way of running multiple modules. You can see the series resistors in
the images. The series linking of the design is just passing on the +12 to the next substrate.
As each module consumes 1.5W then 10 modules will consume 15W. Any variation will be due to the non linear nature of the diodes and the supply
voltage.
Assuming 1.5W is correct and three chips. The current will 0.125A Total drop across resistor is 8.2V therefore there is 1W lost heat per substrate
(10W for 10off). Hardly a green design.
If you were to remove the resistors you can run 10 modules off a power supply 1/3 the size.
some modern LEDs run at about 3- 3.3V, and about
120mA
http://www.lumichip.com/Lumichip/Aurorics_files/LC_5630XXPN_G1X.pdf
they can also manage over 100lm/w
[Edited on 19/3/15 by gremlin1234]
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theprisioner
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| posted on 19/3/15 at 08:17 PM |
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That is interesting, I am however retired now so I guess there have been some further developments in 10 years. Thanks
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http://austin7special.blogspot.co.uk/
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02GF74
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| posted on 20/3/15 at 06:56 PM |
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quote:
Originally posted by gremlin1234
some modern LEDs run at about 3- 3.3V, and about 120mA
http://www.lumichip.com/Lumichip/Aurorics_files/LC_5630XXPN_G1X.pdf
they can also manage over 100lm/w
These are what i was referring, usaully called LED emitters. Pretty sure some of these are driven at 1.0 A, as used in bike and car headlamps.
You would use a constant current driver to avoid i2r losses in the drop down resistor.
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