Solar not working right

chasegarland

I installed a solar system on my rv and it doesn’t seem to be working properly. Mainly, after the batteries are fully charged they drain much faster than I think they should. I have 560 watts of solar panels and four brand new 75 amp hour deep cycle batteries. The solar seems to charge them wonderfully especially on sunny days. One example of the battery drain: Batteries we’re reading 12.6v, turned on inverter ( 3000w pure sine inverter) to charge phone. After 1 hour the battery is reading 12.2v. This is with nothing else plugged in to draw power and with one led light on. I am a solar beginner and at a loss. Any help would be greatly appreciated!

Photowhit

What brand inverter? Inverters can have somewhat high self usage. Are they 75 amp 6 volt batteries? or do you have 4 parallel strings of 12 volt batteries? I take it this is at night and you don't have solar still connected to your system?

mike95490

Many inverters consume a large amount of power just being turned on.   I'd look into getting a Morningstar 300w suresine inverter for charging little stuff. 
Currently, you are using 10w for charging and likely 150w just having the inverter on.

chasegarland

Yes, the batteries are 4 parallel 12v batteries. My inverter is a windy nation vertamax 3000w. It is doing it at night but will also do it on very cloudy days. I mostly want to get it right before it gets hot so we can run a fan at night.

SupraLance

Take a look at the following generic inverter efficiency graph, and you will see why you should avoid using an inverter at less than 20% load.  The inverter you have is 85-90% efficient with a 500-3000w load, but it's efficiency drops on it's face when only used to charge a cellphone or run a single fan.  Buy a much smaller unit to run your fan, and/or better yet, buy a 12v fan and use a 12v cellphone charger and light to avoid the conversion loss altogether, only switching the inverter on for larger loads that require AC.
https://www.e-education.psu.edu/eme812/node/738

Estragon

560 watts of pv may or may not be charging "wonderfully". Ideally tilted, in most climates, you',ll see ~ 560w * .75 / 14.5v charging = ~ 29a. You have 75ah * 4 = 300ah of battery capacity. If run down to 50% state of charge, it will take about 3-4 hours with max pv output to reach ~80%, then another 2-3 hours with diminishing current to reach a "full" charge.

In a realistic rv installation, full sun and ideal tilt are unlikely, ,and very few locations will give you enough daylight year-round to fully charge available pv.

12.6v is not quite full, and may be showing a "surface" charge. A battery at 12.6v while still charging can be at a quite different state of charge than a battery at 12.6v having sat with no loads or charge source for several hours. While charging, when the battery reaches ~14.5v, it's ~80% full. It then needs another 2-3 hours or so to get full.

At 12.2v, the battery is about 60% full. My guess is the 12.6v you're seeing is a surface charge voltage from bulk charging, and the small loads are taking the surface charge off to reveal the true state of charge (~65%).

As noted by others above, a 3000w inverter can take a lot of power just being on, but my guess is what you're seeing is deficit charging. Left unchecked, the batteries will sulfate and lose capacity. As they lose capacity, they'll appear to charge fast, but will also discharge fast. Ideally, to prevent this, you should charge the batteries fully (get voltage to ~14.5v, and keep at 14.5v for 2-3hrs) once or twice a week (with a generator or shore power if necessary).

Photowhit

You are new here, and you have an RV so perhaps are limited to a 12 volt system voltage. there are many reasons to use a higher system voltage and also reasons not to buy such a high wattage inverter. Most people will see these within a week or to of following discussions on this and other sites.

It's is very hard to maintain equal resistance and hence load across multiple parallel batteries. If the load isn't shared equally you will use one battery harder than the others and not share the load. It would be better to have higher amp batteries and limit your self to 1 or 2 strings. If you must have multiple batteries in parallel here is a site that will help maintain equali resistance across the battery bank;

http://www.smartgauge.co.uk/batt_con.html

Currently you have a 4x75 amps = 300 amp hour 12 volt battery bank. Batteries are rated based on a discharge over a 20 hour period. If they are discharged faster than this they will have a smaller effective amp hour capacity. a 3000 watt inverter at90% capacity assuming a 90% efficiency will use 3000watts or 3000/12=250 amps. It is unlikely it would run at this output for long. Many lead acid batteries will simply not be able to deliver close to a 100% of it's capacity at a 20 hour rate for even a brief time, and as I said earlier their effective capacity would be greatly reduced.

Wire gauges to carry such high amperage are very large. Your manual suggests using a 1/0 wire no more than 4 feet from the battery bank. 

https://www.windynation.com/cm/VertaMax Pure Sine Wave Owners Manual_R2.pdf

Wire gauges for amperage carried would suggest heavier wire. This chart would recommend 4/0 wire; which is quite thick weighing about 1 pound for every 18". 

http://www.cerrowire.com/ampacity-charts

When you use undersized wire you have voltage drop, an undersized battery bank can also lend in this issue. This loss of energy is heating up the wire. It might be in noticed when it's small loads and 3-10%. But heavy loads can turn the wire into an effective heater, and be a real hazard.

mike95490

Estragon said:

......... As they lose capacity, they'll appear to charge fast, but will also discharge fast. Ideally, to prevent this, you should charge the batteries fully (get voltage to ~14.5v, and keep at 14.5v for 2-3hrs) once or twice a week (with a generator or shore power if necessary).

The best way to use your generator, is in the morning, on a day you know will have good sun.  Start the genset, start charging, and as the charge tapers off, save fuel, and shutdown the genset, Then you have batteries at 80% charge, and the sunlight can finish them for a good 3-4 hours

chasegarland

Thanks so much for all of the help. It does sound like my problem is it is not getting charged fully and the inverter is using too much power. I’ll try getting a 12v fan and a smaller inverter.