Newbie needs to power LED Rope w/ Deep Cycle Battery- Tips?

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charliebrowniest
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Newbie needs to power LED Rope w/ Deep Cycle Battery- Tips?

Post by charliebrowniest » Tue Aug 05, 2008 3:48 pm

Hello kind people :)

My small camp of newbies has come across a great deal of LED rope lighting (~150ft) on the cheap. I've volunteered to figure out how to power it and have a couple of questions. Any advice is greatly appreciated!

- The rope came without power connectors. Is there a straightforward approach to connecting it to a deep cycle battery? A link to a part perhaps?

- After researching a bit, I think I may have overestimated the number of hours that a battery within our budget will run the light rope. Is there an easy way to recharge the deep cycle battery by connecting it to the battery of a running car? Would I need a charge monitor of some kind?

Again, any info is deeply appreciated!!!

Cheers

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Token
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Post by Token » Tue Aug 05, 2008 3:57 pm

You need to list some specifics

Rope Light:
Is it designed for AC or DC operation?
What voltage does it expect. (12V DC; 120V AC ...)
How much power does it draw (Watts or Amps would help)

Battery:
How big is your battery (Amp-hours)
How long do you expect to run the lights per day

Recharging from a car is not the most efficient use of gas.

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Marscrumbs
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Post by Marscrumbs » Tue Aug 05, 2008 4:01 pm

Fully recharging your battery off your car will be lengthy make sure you have enough gas. It would almost be as strange are running your lights off your car.

I've literally spent hundreds of dollars coming up with a solution not involving a gas generator.

charliebrowniest
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Post by charliebrowniest » Tue Aug 05, 2008 4:08 pm

-The rope light is 12v DC
-It draws about 1 watt / ft (we'll be using maybe 75ft? We may use less and cut it down depending on how my tests go)

-The battery I'm looking at is 115 amp-hours
-I expect we'll run it about 8 hours a day.

Sorry for being vague in my first post. I know that the car recharging isn't the greatest idea. Would a solar cell be a better idea?

Thanks!

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Token
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Post by Token » Tue Aug 05, 2008 4:32 pm

12 feet of rope will suck down 1A from the battery.

6 x 12 = 72, so 72 feet of rope will drain 6A from the battery.

Running for 8 hours, 6 A x 8 Hours = 48 Ah.

You would have to put that much back into the battery each day.

Realistically, if you can reduce your consumption to 10 Ah per day, say running 24 feet of lights for 5 hours ... you could go all week without recharging.

If you had a 10W solar panel charging 10 hours a day, that would let you double the load before your battery drains.

As you can see, the flexibility here becomes endless ...

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AntiM
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Post by AntiM » Tue Aug 05, 2008 4:36 pm

And if all else fails, check this out:

http://eplaya.burningman.org/viewtopic.php?t=25127

As a back up to your own resources, of course.

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phil
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Post by phil » Tue Aug 05, 2008 4:48 pm

_Generally_, DC circuits perform work measured in amps, and AC circuits perform work measured in watts. I'm confused, then about a DC circuit in watts.

Be that as it may, to convert watts to amps,
Amps = Watts/Volts
Amps = 75W/12V = 6.25 Amps. (For LED ropes, this is probably correct; it is not likely to be a 75 Amp rope, i.e., 1 Amp per foot for 75 feet.)

115Amp-hours / 6.25 Amps = 18.4 hours of power in the battery. If you'll be running the rope 8 hours per day, you'll have basically 2 days of power.

If you draw only 1 Amp, you'll get 115 hours out of the battery - about two weeks of 8-hour days. Two Amps gets you 57.5 hours, about a week's worth of 8-hour days. See the formula? You can either divide 115 Amp-hours by the number of Amps you'll be running in the cord (number of feet in the LED rope / 12V gives you the amps), or you can decide how many 8-hour days you want to run the lights, and back into the length of the rope.

Number of hours you want to run the lights = 8-hours times number of days = H

115 / H = Amps
Amps x Volts = Watts (1 per foot)

So if you want to run the rope for 3 days at 8 hours, H = 3 x 8 = 24

115 / 24 = 4.8 Amps

4.8 x 12 = ~ 57 feet

Hope I've got this right. If not, I'll be corrected pronto. :->

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Token
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Post by Token » Tue Aug 05, 2008 6:19 pm

The only thing I would change is the fact that you really do not ever want to drain a battery all the way. So in the math, I would do something like having a goal of 50% capacity on the battery drain.

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Post by LeChatNoir » Tue Aug 05, 2008 6:30 pm

As I understand it, typical automotive batteries will deteriorate the plates if discharged completely, but deep cycle batteries are made to withstand numerous complete discharges without harm.

Correct me if I'm wrong, though.
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Token
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Post by Token » Tue Aug 05, 2008 7:07 pm

I think that is true for real deep cycle batteries, like the ones from golf carts or the gel-cells used in solar systems.

The Pep Boys, Kragen etc. Marine/RV batteries are hybrid cranking + deep cycle designs. They must have a trickle charge on them to act deep cycle. At least mine do.

T

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capjbadger
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Post by capjbadger » Tue Aug 05, 2008 9:46 pm

Couple corrections:

1) While you can discharge a deep cycle battery more than an auto battery, draining it WILL still kill it. You don't want to go below about 20% of the total capacity.

2) In your math, remember the drain rate is not 1 to 1. As you drain it, you get a diminishing returns effect. Get about 50% more Amp Hours than the straight math says you need in your battery.

3) Golf cart batteries are deep cycle. If the battery says anything about "cold cranking amps", it's NOT a true deep cycle battery. It's a auto or some hybrid battery.

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phil
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Post by phil » Wed Aug 06, 2008 9:33 am

Token wrote:The only thing I would change is the fact that you really do not ever want to drain a battery all the way. So in the math, I would do something like having a goal of 50% capacity on the battery drain.
Thank you! I'd totally skipped over that. See
http://www.cieux.com/bm/batteryWreck.html
for more information on how not to totally wreck your battery.

Instead of guessing when you battery is half-discharged, use a voltmeter and measure the battery's voltage. A 12V battery will read 13.2V (or a little more) when fully charged, and it should _not_ be discharged below 10.5V. So either keep the meter attached and watch it like you would a gas gauge, or read the battery on some schedule so that you know you're not wrecking it.

Gel cells, lead-acid, and AGM batteries all contain acid and lead, so ruining your battery means it's going to the great recycler in the sky sooner than it has to. Vulcan is not happy when he sees batteries that have been abused.

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gyre
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Post by gyre » Wed Aug 06, 2008 2:00 pm

All power is measured in amps and watts.

Batteries are typically measured in amp/hours.

I have seen deep cycle batteries with cranking amps rated.

Optima is essentially a deep cycle design to start with.
Their deep cycle is identical except for heavier plates.
I have often had better luck using cranking batteries instead of deep cycle.
I ascribe this to the difference in sophistication of design.
Because of the radically higher power, I was drawing a smaller percentage of power.
But these were not low grade cranking batteries- 1200 A.

On the other hand, I use two Optima deep cycle batteries for starting in one car.

Very important to match multiple batteries.
Buy them from the same box and lot when you can.

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