Pixels on a battery

bert-nc

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I have a pixel tree that is 250 pixels and only stands about six foot tall
Was thinking about placing it at the end of our driveway that is probably 300 feet from any power outlet
Was wondering how long I could power the tree off of a 12 volt car battery
Was going to use a pixel tester to run the pattern on the tree, so no adjustments for brightness
If I calculate at solid green that should give me a max amount of time I can run the lights
I do not plan on solid white
What is the equation that I would use for this question
Thanks in advance
Bert-nc
 

merryoncherry

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You might be tempted to think that the 12V car battery has 50Ah (Amps * Hours) in it (some more, some less, depending on battery size), and that a string of 250 resistor pixels on full white could take almost 5A, meaning that it would run 10 hours (or a lot longer, 2-3x longer, if just on green). Do bear in mind that the car battery will start at around 14 volts and gradually work its way toward 8V, and that a little bit of capacitance should be present in any battery circuit (added, if not already in something else). If you used 5V pixels and a DC converter you'd get the same amount of light for double the time, and this would likely correct for the gradual voltage change of the battery also.
 

Indigogyre

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Hello,

Not sure how long you plan to run it daily or how often you want to recharge the battery. I have heard that people can run a led panel tune-to sign for days off of large battery recharger packs. They're smaller and would be easier to move back and forth for charging. Not to mention you might get a pair and keep on charged and just swap them out.

I'm sure someone will chime in on the right formula for calculating draw and such.
 

merryoncherry

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Keep in mind regular car batteries are not meant to be discharged by a large amount and then recharged. You will kill the chemical makeup pretty quick if you do that.
A deep-cycle battery is designed for this type of work.
Ahh, right. This problem is particularly exacerbated if you let the battery freeze when it is fully drained. You should plan not to cycle it too deep, and certainly don't have it discharged all the way when the occasional December polar vortex hits. (Maybe less of a concern for Bert or Sky than it is for Indi or I.)
 

bert-nc

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Ahh, right. This problem is particularly exacerbated if you let the battery freeze when it is fully drained. You should plan not to cycle it too deep, and certainly don't have it discharged all the way when the occasional December polar vortex hits. (Maybe less of a concern for Bert or Sky than it is for Indi or I.)
All valid points
Had prefer to stick to 12 volt pixel since that is what I have
My intentions would be to power the tree for about five hours (5-10 pm)
Then go remove the battery, bring back to the garage and recharge the battery with a trickle charger until next evening
 

merryoncherry

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My intentions would be to power the tree for about five hours (5-10 pm)
Then go remove the battery, bring back to the garage and recharge the battery with a trickle charger until next evening
I think your odds are really good on this, but you might measure it first to verify the assumption about power draw.
 

TerryK

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To answer your question directly, there isn't really one or even several (formulas) that will produce a good result. Partly due to your post including few specifics and also that some if not most of the variables are rather difficult to accurately determine.

An easy part even though you did not indicate the type of pixel or drive intensity, if drive = 100% and WS2811 bullets are assumed, amperage will be pretty close to 4.5 Amp.
Batteries though complicate things somewhat. Batteries are typically rated in AH (Amp Hour) so one can somewhat consider that a 100 AH battery will produce 100 Amp for 1 hour or 10 Amp for 10 hours. Problem is though that a flooded lead acid battery produces only about 80% of that and a AGM 50% without significantly shortening battery life and in addition the higher the discharge and lower the temperature the less (dis)charge/power that the battery will produce. That 80% can easily (and quickly) drop to 60% or less.
However, to give you an idea (and working backwards) if you want to keep the tree lit through the night, say for 10 hours and as mentioned at 4.5 Amp, the battery will need to be 45 AH at the reduced percentage and if we use a conservative 40%, the battery's AH rating should be somewhere at or above 120AH.
Not a formula as such but that's [250 * .055 * .33 * 10 / .4].

But actually, if you are not picky about colors or intensity, 16AWG 100 foot extension cords can be had for about $30. Daisy-chain 3 of them to a small enclosure with a 150W Meanwell supply and a SP-105 or similar controller. Rather simple, easy to implement, economical (somewhat, likely cheaper than battery, charger, and all that), and almost certainly fewer/less headaches/stress keeping it running.
 
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bert-nc

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Well, I was trying to use what I already have and avoid to much extra cost Planning on small mega tree and that is taking most of the funds for this year
I am sure that I can run extension cords to the site for ac and it would work
Think I am going to do a test and see how long I can run the pixel tree, before voltage drop becomes a concern
I have access to deep cycle battery from the boat during the winter
If it does not do as I hope then will need to rethink ac option
I think my biggest issue will be if I get lazy or forget to go bring the battery back in before bedtime and tree runs all night
That may be part of the testing. Turn the tree on in the morning and let it run during the day and keep observing during the day
 

TerryK

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The use of a deep cycle battery will not necessarily make much difference. Differences exist between the types of deep cycle batteries amongst various manufacturers. Some deep cycles shouldn't go under a 50% discharge, others can go lower. A reason I mentioned specifics previously; allows one to research discharge curves for the particular battery you intend to use and give a more relevant answer.
Voltage drop too isn't 'exactly' what you need to look at. It's semantics somewhat, but rather look at the voltage range of the battery when fully charged and at the proper percentage of used charge (the 50% or whatever). For a 12 Volt battery I would expect this to be approximately 10.5 Volt or higher.

Knowing the range will tell you if the electronics will work properly and how much lifetime you will take out of the battery.
 

bert-nc

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The use of a deep cycle battery will not necessarily make much difference. Differences exist between the types of deep cycle batteries amongst various manufacturers. Some deep cycles shouldn't go under a 50% discharge, others can go lower. A reason I mentioned specifics previously; allows one to research discharge curves for the particular battery you intend to use and give a more relevant answer.
Voltage drop too isn't 'exactly' what you need to look at. It's semantics somewhat, but rather look at the voltage range of the battery when fully charged and at the proper percentage of used charge (the 50% or whatever). For a 12 Volt battery I would expect this to be approximately 10.5 Volt or higher.

Knowing the range will tell you if the electronics will work properly and how much lifetime you will take out of the battery.
Done some searching on google yesterday and better understand what you are saying about DOD and its effect on battery life.
The controller you mentioned is also something to research more
Thanks for the info
 
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