# [EVDL] Driving LED Christmas lights off Pack (DC)?



## EVDL List (Jul 27, 2007)

I don't have a solution and hope someone will.


But I do have past experience of doing something similar (oh Bruce, 
you were a youthful, wild and crazy guy, way back when ...)

Back in the early 1990's, strings of xmas led lights were not on 
shelf for the public to buy. In fact buying leds were still not as 
inexpensive as they are today.

Since it rains xmas time here near Silicon Valley (S. of SF), I 
decided to keep my light display inside my vehicle and in a manner 
that would not give the police an excuse to bag me with a ticket 
(EVs were still new to them back then, thus a target for a 
pull-over/ticket-bait).

So, I strung the strings around my rear side S10 Blazer windows, and 
made an ELECTRIC sign out of leds for the center lower part of my 
rear window (positioned so the police could not claim my vision was 
blocked).

I also used some circuitry I had recovered from some light-show boxes
I got when I was stationed over seas (hey, it was the 1970's and 
having a light show was cool ... even without deleterious herbs or
libation).

So, while I had a continuous lower level ambient light level from the 
strings, they would also pulse brighter to any music I had going on 
in the vehicle.

Talk about drawing attention to my EV ... It worked pretty good. But 
I could only have it up for the holidays. It was fun while it lasted.

Today, pulsing led lights around door speakers are common place, but 
back then ... 




{brucedp.150m.com}





----- Original message -----
From: "Jay Summet" <[email protected]>
To: "Electric Vehicle Discussion List" <[email protected]>
Date: Sun, 30 Oct 2011 22:21:06 -0400
Subject: [EVDL] Driving LED Christmas lights off Pack (DC)?

As the holidays are coming up I wanted to light up my truck with some
Christmas lights I bought on clearance last New Years... 
I was wondering if somebody had already figured the solution out?
Jay
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## EVDL List (Jul 27, 2007)

You can probably split the string and parallel the halves, as you propose. 
You might want to consider though that the lights may have been designed for 
a less than 100% duty cycle (they are off for half of the 60 Hz waveform). 
Operating on DC may result in a shorter life. 

Lee Hart or one of the other EEs on the list may have other thoughts about 
this. OTOH, that would get rid of the annoying 60Hz flicker.

I don't know of any government-sponsored reference design for LED festoon 
light strings (as there are for other more complex Chinese products such as 
inverters). I wouldn't think they'd be very expensive to develop.

(It occurs to me that a QND way to fix your problem would be to get one of 
those cheap $20 50 watt mobile inverters and just plug the light string into 
that. Run the inverters from your acc battery or 12v DCC. True, it'd be 
less efficient than running right from the pack, but when you look at the 
tiny amount of energy those lights use, the effect on your range would be 
negligible.)

Though I've never used them on DC or in an EV, I have several strings of LED 
festoon lights that I bought back when they first began to decline in price 
(around 2002, IIRC). They are straight series strings of 35 LEDs with no 
resistors or other current limiters. One string has failed so far. I was 
able to get it working again by replacing the open LED with one from my 
junkbox. By experimentation, I picked one that had about the rated forward 
current without a series resistor. 

David Roden - Akron, Ohio, USA
EVDL Administrator

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## EVDL List (Jul 27, 2007)

Hi, Jay,
I have worked with LED circuits before. I would suggest splitting the
wiring in mid string (30 LED on each string.)
As you say, "I think if I reverse the polarity on the 2nd half of the
string and make
sure it's in parallel with the first half the voltage will be correct
and they will all light up....but following all of those wires around is
getting hard... 120v and 30 "bulbs" is 4v per bulb...which is possible
for white LED's but sounds a tad high...perhaps that is where the
(resistors?) come into play."
I would agree with this methodology, but the two bulges are
propably a current regulator, perhaps a "three lead regulator" and a couple
of resistors, and perhaps a diode to increase the PIV blocking to protect
the regulator IC hopefully one is in each half and it limits current to 30
or 40 ma.OR a tungsten fillament lamp of about 7 watt at 120 vac rating as
that makes a very inexpensive regulator of current at abour 60 ma. Either
way seperating the string int two 30 LED strings should work quite well.
Please tell us all when you get it working si we can emulate you. PS or
skip all that and buy a 120 vac inverter that plugs into the cigarette
lighter socket for 12 volts DC input and supplies up to 100 W (80W
continous) I bought several on sale last month but even regular price is
under $20 here and you need do consider how much your time is worth.
besides I use mine for recharging several cell phones and other items
without having to pay $7 to $15 for a "Car Cord" for each one.
Regards,
*Dennis Lee Miles* (Founder)
*"**Electric Car Service Shop"*
*[ the Forgotten Infrastructure ]*
*[email protected] <http://www.e-v-t-i-inc.com/> *
(Adviser)* EVTI-EVA Education Chapter*
++++++++++++++++++++++++++++++++
The number of EV on USA roads has doubbled this year.
But, who is fixing problems for Major Brand Purchassers ?
+++++++++++++++++++++++++++++++++++++++++++++


> Jay Summet <[email protected]> wrote:
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## EVDL List (Jul 27, 2007)

Hi - I don't want to poop your party but it might be worth running 
your idea by your local law enforcement office as you may fall foul of 
the, no doubt, numerous bits of legislation concerning displaying 
lights on moving vehicle - assuming it will be moving, of course. MW




> Jay Summet wrote:
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## EVDL List (Jul 27, 2007)

> On 31 Oct 2011 at 11:57, Dennis Miles wrote:
> 
> > the two bulges are propably a current regulator, perhaps a "three lead
> > regulator" and a couple of resistors, and perhaps a diode to increase
> ...


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## EVDL List (Jul 27, 2007)

Dear David,
Did you miss the next sentence where I said".OR a tungsten fillament
lamp of about 7 watt at 120 vac rating as that makes a very inexpensive
regulator of current at about 60 ma." ??? At least I Thank You for your
kind comment at the end of your message, but I note that was a suggestion
you had made and I was reinforcing it and mentioning how inexpensive that
solution was.
Regards,
Dennis Miles



> EVDL Administrator <[email protected]>wrote:
> 
> > On 31 Oct 2011 at 11:57, Dennis Miles wrote:
> >
> ...


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## EVDL List (Jul 27, 2007)

Jay,
Not only the first and the last bulb have only 2 wires,
also in the middle (after about 30 lights) you will see
one section of only 2 wires.
If you cut the string there and swap the two wires,
then you can light the whole string on DC.
Since you cut anyway, you can just as well treat it as
two half strings and wire each directly to our pack,or
take care of the strings by the following:
Since your pack voltage may fluctuate more than the grid,
you may want to see if you can get the brightness of
the LEDs stabilized by adding a series resistor, in case
your string does not already have some regulation
(The string I have here does not and has already blown
1/4 of it, probably from a spike that blew a LED open...)
The LEDs are typically 20mA contant current, so each
string should get its own resistor (or more complicated device)
to regulate it to 20mA, they they essentially live forever.
(Well, 10,000 hours or so, but that is pretty darn close to
forever for a Christmas display)
20mA means 50 Ohms for each volt dropped, so say that you
want 3.5V per LED, 30 LEDs = 105V and your pack is an
average 130V then you need to drop approx 25V with a 
1200 Ohm resistor (this value will give 24V drop).
The dissipation in this resistor should be 20mA x 25V = 1/2W.

Make sure you use appropriate fusing and insulation to connect 
strings to your pack, it sounds like a fun application!

Hope this helps.

Cor van de Water
Chief Scientist
Proxim Wireless Corporation http://www.proxim.com
Email: [email protected] Private: http://www.cvandewater.com
Skype: cor_van_de_water XoIP: +31877841130
Tel: +1 408 383 7626 Tel: +91 (040)23117400 x203 

-----Original Message-----
From: [email protected] [mailto:[email protected]] On
Behalf Of Jay Summet
Sent: Monday, October 31, 2011 7:51 AM
To: Electric Vehicle Discussion List
Subject: [EVDL] Driving LED Christmas lights off Pack (DC)?

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

As the holidays are coming up I wanted to light up my truck with some
Christmas lights I bought on clearance last New Years... They have 60
"bulbs" total, but unlike regular incadesent lights, when I run them off
of 120 volts DC only half the string lights up (the first 30 of the
lights) (If I reverse the polarity, the other half lights up.) If it was
every other bulb I could live with this, but it's the front/back half of
the string.

It seems to me that each half of the lights are running on half of the
AC current, (LED's are diodes, right?) and my DC current is only getting
half of them to light up. Unfortunately, the lights are keyed, so I
can't (easily) reverse a dark LED to see if that is all it would take.
(And besides, it may just cause it to blow up....)

The first and last bulb have two wires going to them (from the plugs)
but have three wires leading away from them (one from the left, two from
the right). It looks sort of like how an incadesent system would be
wired such that one bulb could burn out without taking out the whole
string....but almost all of the other "bulbs" only have two wires
connected. (the other two exceptions are the bulbs at either end of the
"middle" break where the lights start/end depending upon polarity.)

They also have two "bulges" in the wires covered with heat shrink
tubing. I believe the fuses are in the plug, so I'm not sure what these
are (a large power resistor that limits current is my best guess...)

I think if I reverse the polarity on the 2nd half of the string and make
sure it's in parallel with the first half the voltage will be correct
and they will all light up....but following all of those wires around is
getting hard... 120v and 30 "bulbs" is 4v per bulb...which is possible
for white LED's but sounds a tad high...perhaps that is where the
(resistors?) come into play....

Anyways, before I hurt my brain thinking about polarity and diodes and
LEDs some more, I was wondering if somebody had already figured the
solution out?

Jay
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## EVDL List (Jul 27, 2007)

> On 31 Oct 2011 at 12:58, Dennis Miles wrote:
> 
> > Did you miss the next sentence where I said ...
> 
> ...


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## EVDL List (Jul 27, 2007)

Dear David, Thanks for all you do!
In reply: No offense taken I was merely attempting to call
attention to the suitability of using the tungsten light bulb as a current
regulator. but for the hobbyist with a few spare parts in their stockbox
adding the three terminal regulator, as a constant current regulator might
be a satisfying sophistication, personally I used to be that way but now I
use the simplest solution as the best. "There are many alternatives" My
choice would be a small (100 w. ) inverter to 120vac and just plug it in
and save time for other more satisfying activities like watching the
Blinking Lights...

Regards,
*Dennis Lee Miles* (Founder)
*"**Electric Car Service Shop"*
*[ the Forgotten Infrastructure ]*
*[email protected] <http://www.e-v-t-i-inc.com/> *
(Adviser)* EVTI-EVA Education Chapter*
++++++++++++++++++++++++++++++++
The number of EV on USA roads has doubbled this year.
But, who is fixing problems for Major Brand Purchassers ?
+++++++++++++++++++++++++++++++++++++++++++++


> EVDL Administrator <[email protected]> wrote:
> 
> > On 31 Oct 2011 at 12:58, Dennis Miles wrote:
> >
> ...


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