30 x 3w high powered leds , power source 12v car batteries  - Page 1
Forum section: electronics / projects

author: wilko
author_rank: Newbie
timestamp: October 27, 2015, 05:24:01 pm
content: Hi allam building a installation for our anti fracking campaign to promote the use of green and new technologiesHaving real trouble trying to figure out a set uptrying to connect up 30 x 3w high powered leds , these will be run in parallel with 4-6 meters of cable between each lighti have 2-4 car batteries at my disposal which will be charged during the day by solar panels.the lights only have to light up for 2-3 hours per night

author: MikeW
author_rank: Regular Contributor
timestamp: October 27, 2015, 05:29:34 pm
content: Whats the vF across the LED?

author: JacquesBBB
author_rank: Frequent Contributor
timestamp: October 27, 2015, 05:30:24 pm
content: Assuming a battery of 40 Ah,it provides 12*40 = 480 wh, so with your 30x3 w = 90 wyou should be OK for 4 h on a battery.It is better to be on the safe side and if you have 2-4, take them.Now you need a regulator for the leds (current limit) , for the batteries (avoid deep discharge) , and for the solar panels ( avoid overcharge of the batteries).All these will add some overhead on the power consumption.What do you have ?

author: wilko
author_rank: Newbie
timestamp: October 27, 2015, 07:22:53 pm
content: forward voltage 3.5 - 4.5as regards regulators im outta my my depth in term of whats neededbought one of these but not sure if this right for jobhttp://ie.rs-online.com/web/p/linear-voltage-regulators/7044029/sorry for ignorance with all this , newbie yaknow

author: georges80
author_rank: Frequent Contributor
timestamp: October 27, 2015, 07:30:35 pm
content: 30 x 3W LEDs means you have 90W (nominal) of heat to dump. Wiring them in parallel is not really a good idea due to Vf mismatch. LEDs when possible should be wired in series.Linear regulators at those power levels will mean a lot of waste heat - hardly 'green'... unless you match the battery voltage to the LED string voltage closely. Regardless, you want current regulation, not voltage.LEDs are current driven devices. You want a constant current LED driver.I'd suggest 2 strings of 15 series connected LEDs each, so around 50V total Vf per string. Then use 2 current regulated boost drivers running from 2 series batteries (24V nominal input).Modern white LEDs should have a Vf around 3.3V for 3W devices (Cree etc). Of course if you are buying junk LEDs from China then anything is possible.Mount LEDs on an appropriate heatsink - you will have a lot of heat from the LEDs to dissipate.cheers,george.

author: wilko
author_rank: Newbie
timestamp: October 28, 2015, 03:01:25 pm
content: from what im gathering from all of your comments i was thinking of attaching 2 x 12 volt car batteries to this driverhttp://ie.rs-online.com/web/p/constant-voltage-led-drivers/6973027/and then run all 30 x 3w ( 750ma 3.5 Vf ) leds in seriesdoes this seem like would work ?cheers

author: georges80
author_rank: Frequent Contributor
timestamp: October 28, 2015, 03:08:02 pm
content: That's one stupid expensive driver... it also only has a 31V output (in the spec). In fact it's spec says 31V max and 1.4A max, not sure how it becomes a 180W driver, though maybe that is another model in the series.How would it deal with 30 LEDs at 3.5V each in series?cheers,george.

author: Kjelt
author_rank: Super Contributor
timestamp: October 28, 2015, 03:33:21 pm
content: Build this two times:2 car batteries in series +/-24V as voltage source.3x 1 string of 5 leds in series (+/-20V) with a LM317 as a currentsource of 900mA/1A on a heatsink. The LM317 will dissipate max the 4V's at 1A so 4W so should be cooled properly still without any risk or expensive driver you have a efficiency > 83% If possible (so measure the ledvoltage) use 6 leds in series and the efficiency >90%Alternative for a LM317 is to use a Fet in linear mode.

author: MikeW
author_rank: Regular Contributor
timestamp: October 28, 2015, 03:44:51 pm
content: You will have trouble finding an off the shelf driver that meets the slightly bizarre requirements you have.You'll have to use a combination of drivers and perhaps consider a series in parallel circuit to do the job.But for example using 4 of thesehttp://ie.rs-online.com/web/p/constant-voltage-led-drivers/6689886/and putting 7/8 leds on each driver in series would still be half the price of the one you found that can't even do the job.You can get a dimming variant of that if 1.2A is a bit much for your needs/drains the batteries too quickly. The LEDs will definitely need some sort of heatsink at that current level.

author: Seekonk
author_rank: Super Contributor
timestamp: October 28, 2015, 03:55:37 pm
content: Have you bought these LEDs yet? I would buy 10W LED for ease of mounting. There is no reason they have to operate at 10W and they are likely only good for 4-5W anyway. The 10W floodlights on ebay only draw 8W and that is about 5W to the LED which is probably excessive. Drop converters are often suggested. I think you are better off using boost converters. When a boost converter shorts it won't damage a LED. Search ebay for these little boost converters like the XL0009 something like that.These are $13 for ten, at least one will blow up. Unless you are very talented, you can not drive a 3W LED anywhere near 3W. I would keep it closer to 1W. My suggestion is constant voltage driving a string of 5 or 6 LED in series. These boost converters will start to self limit at about 10W. More LED at less power always look better.

author: Halvmand
author_rank: Regular Contributor
timestamp: October 28, 2015, 04:18:24 pm
content: You can use a cheap boost converter like this on off ebay:http://www.ebay.com/itm/DC-DC-10-60V-to-12-80V-Boost-Converter-Step-up-Module-Car-Power-Supply-600W-AWP-/111806632340?hash=item1a0831d194:g:pMkAAOSwgQ9Vk4lRConnect the 2 batteries in series and adjust to the desired current with a multimeter in series. Done.Edit:I have to add that you may want to connect the leds so you have 10 in series times 3 strips. connect the 3 strips in parallel.Start with the lowest current and adjust up from there.

author: MikeW
author_rank: Regular Contributor
timestamp: October 28, 2015, 04:27:41 pm
content: Quote from: Halvmand on October 28, 2015, 04:18:24 pmInteresting solution. You would need to wire the LEDs in 15S2P though as that doesn't quite meet the voltage requirements of 30 in series.

author: Halvmand
author_rank: Regular Contributor
timestamp: October 28, 2015, 04:29:14 pm
content: You beat my edit Mike.. You are right.

author: MikeW
author_rank: Regular Contributor
timestamp: October 28, 2015, 04:30:27 pm
content: Quote from: Halvmand on October 28, 2015, 04:29:14 pmThis is what happens when you have precisely zero work to do.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: October 28, 2015, 04:46:57 pm
content: You may have already bought the LEDs, but you might want to consider a packaged option. The off road vehicle market has packaged LED illuminators already set up for operation off of twelve volts, insanely bright and reasonably priced. You loose the learning from bodging something together yourself, but you gain reliability. You also loose green cred by buying in this market place, but maybe you can find somebodies truck that they have overturned and salvage something off of it.

author: richard.cs
author_rank: Super Contributor
timestamp: October 28, 2015, 09:35:48 pm
content: Quote from: Halvmand on October 28, 2015, 04:18:24 pmI have used that exact module for LED driving, with a couple of mods to suit my application. (I connected sensors to the controller enable pin, changes the pots to fixed resistors, up-rated the output capacitors and the diode, bypassed the input protection diode, con-coated the lot. None of that is necessarily needed).Mine drives two 10W LED floodlights in series. Each floodlight has a single LED package with 9 LEDs in series (same form factor is available with 3s3p). Original driver was 300 mA from mains input, I've adjusted the boost converter for 300 mA constant current, with a bit of cable resistance it puts out 68V. The voltage limit is set just over that to protect the driver from open circuit LEDs. Efficiency is pretty good, and now I'm not running at the very limit of it's voltage rating it's been very reliable.I would agree with 2 or 3 parallel stings off that driver in CC mode, adjust the current into a load first before connecting the LEDs (but don't try to adjust into a short circuit as there's no regulation at Vout less than Vin). I'd suggest dropping a few volts across balancing resistors to equalise the current between your strings.

author: wilko
author_rank: Newbie
timestamp: October 30, 2015, 10:21:02 pm
content: Okso with your help ive decided to go with 2 strings of 15 leds run is series powered by 2 drivers from 2 12v car batteries charging from solar panels (which ive been told there are plenty of high spec ones available)these drivers in facthttp://www.banggood.com/DC-DC-Converter-Step-up-Step-Up-Module-10V-60V-To-12V-80V-p-85660.htmlthe leds are 3w high power 750ma , 3.5 - 4.5 Fvim worried that the power will dissipate too much before the last few leds in the series but going to give a shot anyways because of the shape of the setup if i run smaller series , say 7-8 then would need another battery solar driver setupeach series ( 15 leds ) will be 70 meters long !!! so heres hopingthanks for all the help , ill be back hanging my head in shame if this all goes tits up : )