Battery voltage

So what is the problem? What you described is perfectly normal operating voltages. It charged at 13.1 volts, and when you turn off the charger, what you see is the RESTING voltage of the batteries at 100% State of Charge. Exactly what you want to see. 12.8 volts is 100% SOC

Power goes in a battery at higher voltages than going out of the battery. Just the law of physics. Think of it like a river and water flowing. To charge a battery, you have to have a higher state of energy to transfer power into the battery at a lower state of energy like water flowing down and cannot go up hill. When dark comes turns off all charging and now you see a resting voltage on the battery which is always lower than charging voltage.

Ok Thanks I've been trying to read as much as I can. I just don't wanna do any harm to what I have! & thanks for answering what probably seemed like a stupid question!

Mike

If you are really pulling juice from that inverter, it is going to pull a good 100 amps from those batteries.. Keep that in mind. If you are powering lighter stuff, then not so much of a problem.

Thanks, My goal is to power my tv with is pulling 275w and my xbox 1 and home reciever. Which they are all total pulling 436w. Right now I have 2 100ah batteries and 2 100w solar panels installed. My goal is to power that setup for about 5-6hrs a day through the week. Maybe more on weekends weather depending. I'm pretty sure I will need at least one more battery.

From what I've read most suggest that you don't take your batteries below a 75% monthly average, does that sound right? I'm trying to get the most life out of the batteries. Can anyone shed a little more real life experience or knowledge on this for me?

Mike

Do the math, 436 watts AC @ 120v = about 45 amps DC + / - @ 12V. For best life pulling your batteries below 50% dod is a short life. A 100 amp hr battery would be depleted in 1 hour. Charging the battery is another issue. The battery voltage needs to be brought back up to 14.2v -14.4v ( with 10-15 % of it's amp hr capacity in charging current ) for at least 2 hrs with a tapering charge until the amps drop to 2 % are you'll be in a deficit and the batteries will sulfate and be unusable.

Guess again Mike.

436 watts x 6 = 2600 watt hours.

That requires a 1200 watt solar panel and a 800 pound battery. The batteries you have now will be destroyed shortly with the abuse you are giving them. Your little system can only generate a fraction of what you want. You want 2600 watt hours per day, and you can only generate 500 watt hours per day. You are bankrupt and insolvent.

Thanks Willy and Sunking for the great info! I haven't used them for that purpose yet but that was what the goal was. Till now I have only charged our cell phones and tablets. So what is the most important thing to consider when building a system? Is it the Watts or Amps per hours. I know you gave this (436 watts x 6 = 2600 watt hours.) What does the 6 represent? Feeling stupider by the post but am learning that's a plus.....

Mike

Your math needs a lot of work 436 watts / 12 volts = 36 amps.

Why don't you hook up your Inverter and see what the draw actually is with losses instead of some theory out of you head. I posted a + /- to account for differences in Inverter and wiring efficiency.

What theory and good 90% inverter draws 436/12/.9 = 40 amps.

Ok I have bought a Kill-a-Watt meter and have been testing all my house hold items to see what they draw. I've also heard that the inverter while in use will draw .9amps as well. Help me out here! So do I take my house hold items and find out how many amps or watts they draw? Then convert those numbers to amp hours?

Mike

Everyone will differ, but I like to do the battery capacity necessary first so I can see what equipment I need and system voltage indicated. To do that I need the total load and the expected time it's to be used. Some reserve is necessary for differences on the choices you intend to use. So do it in watts and in the end you have to use amp hrs to be consumed.

Real simple Mike.

Watt Hours = Watts x Hours.

So take each device and determine the wattage they use with your watt meter. Say 50 watts. How long do you want to run it? 5 hours? If so 50 watts x 5 hours = 250 watt hours or .25 Kwh. Do that for everything you want to run everyday and total them up. Say it is 2600 watt hours. I already showed you how.

For the battery decide on a battery voltage. Say 12 volts for boys and toys. You need a 5 day capacity to maximize battery life and get the most value from your money 5 days x 2600 wh = 13,000 watt hours.

To find Battery AH = Watt Hour / Battery Voltage or 13,000 wh / 12 volts = 1083 AH or a 800 pound $2500 batter is what it takes. You get to replace it in a few years.

To find panel wattage you need to know daily watt hours usage (2600 wh for you) and your winter Solar Insolation Sun Hours. Winter Sun Hours depends on location but say you have the national average of 3 Sun Hours. Panel Wattage = (Daily WH x 1.5) / Sun Hours, or (2600 wh x 1.5) / 3 sh = 1300 watts of panel.

If operating at 12 volt battery requires two very expensive 6 amp MPPT Charge Controllers costing around $1100 total for the controllers. Or you could be smart and use 24 volt battery and only need one 40 amp controller.

Bottom line it is going to cost you around $6000 to play with your toys, and roughly $2500 every few years in battery replacement cost. Ready to get started burning money? If not you could just the mean old electric company $90/year to run your toys. A lot cheaper.

Read This, it answers all your questions.

Great - very handy tool. Maybe this will simplify things. Why don't we stick to the WATTS measurement on the kill-a-watt and go from there.

How many watthours will my battery support? (Hint- P/I*E formula coming).

1) 12v battery * 100ah capacity = 1200 watthours.

2) BUT, since we don't want to drag a battery below 50% DOD, we have to cut that in half, soooo... ONE of those 100ah batteries will really support 600 watthours. Obviously if you parallel two, we are back to supporting 1200wh of your loads.

Lets use the TV as your load. 275 watts - fine! But the 6 million dollar question is "how long?". Lets use just ONE battery that can only handle 600 wh.
600 / 275 = 2.18 hours. Again, if you parallel your other one, that would extend it to 4.2 hours.

BUT this is a big oversimplification but at least gets you in the ballpark.

Now, armed with your kill-a-watt sitting on the output of the inverter, see how many watts it pulls. What does it pull?

Take THAT measurement, and multiply it by 12, which is basically the voltage of the battery. TADA - you can figure out the amps being drawn from the battery ALONG with the loss from the inverter if you you are interested.

Do the same with your xbox and see what it pulls. Add that to your total.

In reality, with all your stuff going, the Peukert effect of drawing a heavy current may also be making your voltage sag prematurely as well as normal discharge. You've got to either beef up the system, or conserve energy.

One way to conserve with your television, is with an Led-backlight tv, turn the backlight down as far as you can comfortably go. You may end up cutting your power draw in half by doing that.

Right now I'm doing just that with nothing but a honking big Optima battery and a pure-sine-wave inverter powering my directv receiver and tv just for kicks. About 8 hours before I want to recharge it without killing the battery.