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Deep cycle battery won't run LED lights very long...why not?

 
Posts: 21
Location: Catskill Mountains, NY
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WOW - a lot of info to wade through! Thanks everyone, for your time, interest, and knowledge!

Just to reiterate - everything in the system is new. The battery has never been drained below about 11V, because the inverter (which IS a "pure sine wave inverter) will indeed alarm right around there. The generator doesn't seem to very effective at charging the battery when it is so close to fully charged, which makes sense? Almost like there's a certain amount of "electrical pressure" like a balloon gets harder to fill the more you fill it...

And yes, I fully get that it's a wasteful way to charge a battery, but the alternative is lugging that beast back and forth to house power, until I set up a solar array. Until then, I'll burn some dinosaur bones in the interest of ironing out some kinks like this....


Thanks again,

Joe

INVERTER: https://www.amazon.com/Power-TechOn-Inverter-Outlets-PS1002/dp/B0131L8NLM?pd_rd_w=FHYv3&pf_rd_p=a92e0124-cfa8-4f1e-82b5-a4a348d97008&pf_rd_r=YYNBWAFFFJBJ5M6TFG04&pd_rd_r=0dab872e-2bd4-417c-a899-3b7ca40b8895&pd_rd_wg=XEDJL&pd_rd_i=B0131L8NLM&ref_=pd_bap_d_rp_35_t&tag=pfa12-20

GENERATOR: https://wenproducts.com/products/1250-watt-gas-powered-inverter-generator-carb-compliant

BATTERY: https://www.amazon.com/Universal-Power-Group-100Ah-Battery/dp/B00S1RT58C/ref=sr_1_1?dchild=1&keywords=Universal+Power+Group+12V+100Ah+Solar+Wind+AGM+SLA+DEEP+Cycle+VRLA+Battery+12V&qid=1606916290&sr=8-1&tag=pfa12-20

ROPE LIGHTS: https://www.lowesforpros.com/pd/Utilitech-48-ft-LED-Clear-Rope-Light/1000330329

 
Joe Krein
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Location: Catskill Mountains, NY
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OH YEAH, AND HERE'S THE CHARGER: https://www.amazon.com/gp/product/B00KNMKRU8/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
 
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I have had a tiny solar system at our hunting cabin, starting with a single deep-cycle flooded lead-acid battery like you would use for a trolling motor (rated at 74 Ah) from the local farm supply store and a 100W polycrystalline solar panel from a big box store,.  Our first inverter ran my husband's CPAP all night long the first year, but since the panel was wired direct, it continued shoving voltage in after the battery was fully charged, so it hydrolysed electrolyte, not so good for long life, and wouldn't run the CPAP all night the next year, so I added a second battery.  Time passed, I bought a charge controller (Bogart Engineering SC-2030) that is still sitting in the box.  My current setup has 2 100W panels and 3 of the same batteries (one of which I managed to boil dry-it took over half a gallon of distilled water to bring it back up), but when I bought a new, larger inverter (not even pure sine), it would alarm after a couple hours.  Rearranging cable connections did not help. Finally for whatever reason, when I put the CPAP on an extension cord with no other changes, it worked fine. So there is something about the way the inverter draws current from the battery that makes it dip into a state it thinks is low voltage, and maybe the cord sort of evens things out so the draw isn't as deep.  I suppose if I dragged my $10 used oscilloscope up there I could find out...

The other thing is, the SLA and AGM batteries I have had experience with are not robust when it comes to solar or other practical uses. We have replaced my husband's AGM ATV battery at least 3 times, and he has only run the ATV a handful of times. PITA. But he got it cheap, used, so that met his standards.

If you really want to learn about making a solar system and how it responds to loads, you can get far with just your multimeter, with the caveat that VOLTS only tell half or less of the story.  You must know the amp draw in order to correctly understand your battery state of charge. And to measure amps, you need a known resistance to measure voltage across, so you can use our old friend V= I*R.  A Radio Shack 1/4 watt resistor will not do the job, for that you need a "shunt" (see this page for description. Other places sell them too). All a shunt is, is a resistor that can pass all the current while not heating up or reducing the voltage drop very much, and you put it in line with the positive line from your battery, so all the current passes through it. A good analogy is a water meter-water comes from the supply, all of it passes through the meter, and then to the various loads.  Every amp you use has to be replaced, AND a little more, by your charger. Put in the shunt, measure the amps going into the battery from the charger, and out to your loads.  

The other key thing to understand about lead-acid batteries is that the temperature affects the voltage. And for the long-term life of your battery, you should not discharge deeper than 50% state of charge. According to this chart, 11V is 10% state of charge, and this is not too good for the life of your battery.  Make sure you understand, though, that the chart shows OPEN CIRCUIT voltage (no loads) and you can't measure this accurately until after AT LEAST an hour has passed since you drew a load.  

It seems like a lot to learn, but you can really get very far indeed with good, concise information. I highly recommend Handy Bob Solar, as this guy is a retired electrical engineer who has written pages about setting up a usable solar system for RVing or small off-grid cabins, and he shares his actual experience with the components he recommends.  I haven't found any information there that did not work as he said it would.

Good luck, and enjoy your system!
 
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I agree with what is posted here.  We have been totally off the grid since 1986 and it is still a learning curve.  The big message here is that the right box of tricks must be used for the job or it will not work in any way shape or form.  A conventional car battery charger will not charge deep cycle batteries.  The amount of energy required to get those poor struggling electrons from one side to the other is simply insufficient.  You will need a proper "solar battery"charger with multiple stage charge manager.  If you can access the electrolyte in the battery check the pH.  It is likely that with multiple deep discharges, you battery is far from healthy and may need a good deep charge to reinvigorate it.  I agree that the best way forward is 6 X 2 volt batteries.  Without going into the electro-chemical stuff, the batteries fair better than a single 12 volt battery.  But set your battery cutout at 11.8 max unless they are lithium (which I would not waste money on).

With your LEDs, they need a driver to make them work.  The bottom end LEDs have an under powered driver that will burn out and cause issues.  We buy a good quality LED light or string then match the driver, ensuring it has 10 - 20% more available power than required.  Our LEDs are 10 - 15 watt but the drivers are all 22 watt so they do not get hot.  Strings of LEDs can be bought ex Asia and you can make your own string by buying coloured (Aussie - we still use the 'U')  tube.  Seal one end and run wires from the end.  12 volt strings are available. so there is no DC > AC > DC and hence no power conversion losses that can be as much as 80% on top of the nominal draw.  So 50 watt lights would use 75watts of draw.  For every 110 volt appliance/ item you have, take the wattage and add the value that your inverter says will be used as well as resistance in the wire.  You will be surprised how much power is lost to heat (resistance)

We have just upgraded our system by buying the components as we could afford them and now we have them all have done the job.  You will never be up with the latest technology so don't try.  Get what works for your intended power load and go for it.  Just one note of caution, make sure that your regulators/ charge controllers have only about 80% capacity going through them.  A work around and way cheaper option is to use a Solid state relay (SSR) run by your regulator.  We have a 10 amp regulator and 100 amp SSR to manage 5 X 200 watt panels (20% spare capacity).

Best wishes for your system
 
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Joe Krein wrote:Hi, everyone! Thanks for letting me pick your collective Brain!

I recently purchased a deep cycle battery, a pure sine wave inverter, and a battery re-conditioner/trickle charger. I intend to build a small solar array in the spring. In the mean time, I am experimenting with charging the battery with my 1250 watt generator => trickle charger => battery. I know that this is a terribly inefficient way to go about things, but it's just a temporary way to begin the learning process about battery power and a way to avoid having to transport the battery back and forth to charge it from house power, so please forgive the transgression!

In any case, all that I typically power with the battery is a 50' run of LED rope lights out at my yurt. They are 110V plug-in type lights, plugged right into the outlet on the inverter. I believe the draw is pretty low (approx 33W) but even once the battery is fully charged to 12.5 or 13V, I can not run the lights very long (approx 45 minutes) before the inverter begins to alarm, indicating that the voltage of the battery has dropped below some critical threshold. (I think at that point the battery is down to about 11 - 11.5V).

Does this make sense to anyone with more than my very rudimentary electrical understanding (i.e. me)? I had hoped that the lights would just keep running until the battery was fully drained... what gives?

Looking forward to where this leads,

Joe



A 50ft string of led lights running on 120vac is going to be closer to 100-200w depending on the number of LEDs it has. The Battery is draining fast because you are running them through an Inverter, and then back through another inverter to change the 120vac to dc voltage. If you divide the actual wattage by 10 that will give you an idea of the number of amps it takes to run those lights for 1 hour. Probably 15amps. The inverter you have has an alarm that warns you when the voltage gets too low basically meaning you have drained your battery to about 85% in that 45 minutes. One way around this is to join more batteries in parallel to give you more amp hours and thus letting you run lights longer. I would ditch these lights and go with lights that are designed to be powered by USB which is 5vdc you can simply wire up a dc to dc converter to your battery and these lights here will drain your battery after 400 hours, and you don't have to use that inverter with the annoying alarm.

lights
https://www.amazon.ca/Twinkle-Waterproof-Remoted-Christmas-Decoration/dp/B082TYJKJP/ref=sr_1_11?dchild=1&keywords=usb+string+light&qid=1613713602&sr=8-11

USB dc to dc converter.
https://www.amazon.ca/Keenso-Waterproof-Converter-Charger-Motorcycle/dp/B07GC1NB43/ref=asc_df_B07GC1NB43/?tag=googleshopc0c-20&linkCode=df0&hvadid=335051411962&hvpos=&hvnetw=g&hvrand=836330529893563377&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=1002283&hvtargid=pla-739651023743&psc=1
 
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Gentlemen, have we a solution yet?
 
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Maybe I missed it reading through, but nobody mentioned that a 12v battery at a 12v state-of-charge (SoC) is seriously depleted. You normally want to avoid going beyond 50% depth of discharge (DoD) to avoid damaging the battery, and for most 12v batteries that's over 12v:


Joe mentioned "the battery was never drained below about 11v" which is more like fully discharged, to the point of permanent battery damage. A 12v, 100ah battery has a total of 1200wh but only 600 is usable to avoid that long term damage which can kill the total possible cycles. I start to get concerned when my batteries hit 24.5v (24v system) and adjust my use accordingly. Maybe I missed that this was a LiFePO4 battery and not lead acid, then this is a moot point.

For sure if the battery is lead acid it should only be charged and not used until the voltage reads over 12.5v at rest to get out of the voltage hole, IMO. Then see if the SoC can be kept above 50%.
 
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So an LED drawing 1mA would last from 45 to 100 hours. Many LEDs are very dim at 1 mA. According to Duracell, the standard CopperTop AA cell has a capacity of between 2000 and 3000 mAH depending on how it is used and how end of life is determined.

Hopefully the point and the problems would be cleared after the information above mentioned posted for the user
 
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When you see the amp hour (AH) rating on a battery, it can be deceiving. The amp hour may not apply to the full voltage listed but on an individual cell.
For example, I recently purchased a 12v lithium battery listed as 20 AH. However, the battery also listed as 76 watts. That means the AH rating is based on a 3.8v cell which equates to two of the lithium cells at 1.9v each. Note: this means this is actually a 11.4v battery but lists as 12v. So for the full 11.4v, the actual AH = 76/11.4 = 6.6AH. Next you have to apply the DoD (depth of discharge) that a battery can handle before the voltage significantly drops. For a lithium battery, this is ~ 80%. So the actual amount available is 6.66 x 80% = 5.3AH. I applied this battery to an 8 watt, 12v led light bulb (800 lumen output). Amps = 8 watts / 12v = 0.75amps. So the battery should last 5.3AH/ 0.75amps = 7.1hours. That is exactly what I got.
Now, applying this to an SLA (sealed lead acid) that you are discussing, the DoD is 50%. You also need the watt rating for the battery to
Correctly calculated the AH rating for the entire 12volts. Each cell is 2volts so the actual AH for the battery @12volts may be 100/6 x 50% = 8.3AH. If you are getting 45 minutes of run time, that would mean you have a 8.3AH/(0.75) = 11.1 amp load. Or 11.1amps x 12v = 133 watts.
By the way, when your 12v to 120v converter gets an input voltage below about 11volts, it will shut down to protect a lead acid battery. The converter wants a 14v input +/-. On my lithium battery that is not a concern so I added a buck boost electronic voltage regulator. I could the boost my voltage to 14v, hook it into a converter, and power a 120v load. The regulator and converter adds about 0.4 amps to the load so the equivalent 120 volt, 800 lumen bulb, my battery life reduced 50% to 4.5 hours. That is why using 12v loads with no converter is a more efficient way to use battery power.
 
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