[RE-wrenches] DC power for LED lighting

Dan Fink buckville at hughes.net
Fri Dec 16 16:02:02 PST 2011


Jeff;

I finally had to chime in.

There are plenty of nice DC power supplies out there that will do the 
trick. I have used them in the past for small sensitive electronics that 
can't take high equalize voltage. you can get them right from Digikey 
and elsewhere in many capacity ranges, $20 and up.

But it sounds like they haven't given you any info on how the individual 
LED series strings are arranged and regulated. Do you need one DC supply 
for each, or just one for the whole thing? Your assessment is correct I 
think -- parallel connections are BAD with LEDs, and the string with the 
most voltage will eventually fail first, so best practice is regulate 
every string.

And the words "void the warranty" sound extremely ominous, with scary 
music playing in the background.

Why not just a Morningstar SureSine inverter? You keep your warranty, 
and it's just down into the amperage range that there are some PV 
controllers that could switch it via a low voltage disconnect, or you 
could add a small extra relay. Wouldn't have to be big. From what I see 
in your post, you'll be at 120 watts from LEDs max. The SureSine is 
cheap, compact, low standby draw, and if you interrupt DC input via the 
controller LVD and bring it back, it just turns right back on again with 
no operator resett needed. I'm not sure about what you'd need for the 
timers, but I bet they are cheaper at 120VAC than at 12VDC. There are PV 
controller/LVDs that will do this too, though maybe not exactly how you 
need it.

just food for thought anyway!
-- 

Dan Fink
Executive Director;
Otherpower
Buckville Energy Consulting
Buckville Publications LLC
IREC / NABCEP accredited Continuing Education Providers
(970) 672-4342



On 12/16/2011 11:24 AM, Jeff Yago wrote:
>
> I have a local sign company that asked is to provide a solar lighting 
> system for a double sided sign they were building for a large 
> retirement community entrance.  We have provided many solar lighting 
> systems just like this over the years and sent them several examples.  
> All our systems have been turn-key in that we provided the 12 VDC 
> ground mounted LED flood lights with the separately pole mounted solar 
> module(S) and battery/controller box.   We "assumed" when we told them 
> our system includes the LED lights that they understood that we were 
> providing the lighting.
>
> Unfortunately, when we arrived on the site to install the solar 
> system, they said they did not need our LED lights, they wanted us to 
> power the LED lights inside the sign.  We opened up the signs and 
> found two 120 VAC electronic LED power supplies.  Each was clearly 
> labeled as providing a maximum of 5 amps at 12 VDC output, and each 
> powered a separate string of about 150 tiny plastic "blocks" and each 
> block contained 2 small LED lamps.   We immediately advised the client 
> that the solar  system was designed to power our two  12 VDC flood 
> lights and we would have to totally tear out what we had just 
> installed and go to a much larger system that included an inverter, 
> larger array, 120 VAC timing device, and replace the 2 conductor DC 
> underground wiring  with 3-conductor AC wire and all  this would 
> really increase $$$.
>
> I said as an alternative, why can't we just cut out the two 
> electronic120 VAC input  LED drivers since we are providing well 
> regulated 12 VDC power direct from the GEL battery.   He checked with 
> their LED lamp supplier and they said they strongly disagree and will 
> void warranty.  Since we are talking about almost 300 total LED 
> devices my client is afraid to give us the OK, even though we did run 
> them overnight and everything worked just fine.   As I recall, an LED 
> needs something in the circuit to limit the amp current, not the 
> voltage flowing through it,  or it will just get brighter and brighter 
> and then fail.  However, I thought almost all strings of separate LED 
> lights already had some kind of regulator built into each light block 
> otherwise those near the end of the string would be less bright than 
> those near the power source.    Is this correct??
>
> Finally, if strings of LEDs require some kind of voltage or current 
> regulator, I can't believe they all have to run on 120 VAC as 
> indicated by this LED manufacturer who offers no alternative.    Any 
> LED experts out there that can point me to some type of DC-to-DC 
> converter or current  regulator that can replace these 120VAC LED drivers?
>
> Thanks,
>
> Jeff Yago
>
>

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