How do I know how full my batteries are?

[riffraff]

My setup has 2x 125ah deep cycle batteries powered by 200w of panels and the alternator. I have heard the letting them drop below 50% is bad (reduces the total amount of times they can be recharged). Seems like they never go above 13.9v on the control's display and I've had them down to about 12.0 or so. How full is 12.0?

 

[Optimistic Paranoid]

Assuming you have flooded lead acid and not sealed batteries, you need a battery hydrometer to really know what your state of charge is.

Anything above 12.8 volts is not the battery voltage, it's the voltage of the charging source. (Voltage is pressure. The charging source must have a higher pressure than the battery in order to push electrons into it.)

12.0 volts is VERY low - about 30% or so.

Regards
John

 

[riffraff]

They're sealed AGM batteries. Im surprised that just charging my laptop, kndle, mifi stuff once in a while and running a fan for 1/2 the night drops them that much. I wonder if shortcuts were taken and I'm not getting the amount of volts I should have (mostly thinking about the wiring from the panels to the controller might be a bit thin). I've been looking at the controller most of the time to try and determine how full they are, but also the inverter has a voltage reading which usually is close to what's on the controller.

When it's sunny the controller shows about 6.0 on the "charge" setting. Seems weak? Dunno what it should be with 200 watts and an MPPT controller.

 

[Optimistic Paranoid]

Thin wires could definitely do it.

Google "Handy Bob Solar" and read your way through some of his posts to get a better handle on this.

Regards
John

 

[DC Fuse]

If your panels are in full sun you should be getting at least twice the amps you currently are. Somethings not done right. Wire size? Connections?

 

[DC Fuse]

RiffRaff, at the risk of earning your wrath i'm going to tell you some things.
Your solar wattage for your system is too low. You need another panel (100 watts).
Your AGMs when depleted that far are hungry for voltage in the 15 volt area for a length of time as agms have little resistance compared to wet cells and they respond well. For every amp/hr you use 1.3 amp hrs. need to go back in to charge correctly.
You said 13.9 was the highest voltage you've seen on controller. This is too low. You need to find out why it's not in the 15 volt area regardless of amps going in. You stated you have a MPPT controller which should give you optimum voltage/amperage from your panels but it's not. Your panels charging if tested directly off panel is 20 volts. To right before charge controller will be 17 volts. This is why a charge controller is used to bring it to 15+ volts @ initial charge for bulk charge w/ mppt controller sensing when voltage can drop for safe charging to completion.
W/those 2 panels and your MPPT you should be getting upwards of 16 amps when charging.
With your two panels in good sun you will be getting 70-80 amps per 5 hrs. of daily sun.
Knowing that you can add up whatever draws you are using to see your daily total. Example - Fan @ 2 amps ran for 8 hrs. equals 16 amp hrs.
Do not get discouraged as their is a learning curve. I myself have gone thru 2 sets of 6 - 6 volt GC batteries and just recently discovered something i did that was totally wrong and is now corrected so we're all learning as we go. Research. Then research some more. Then............

 

[riffraff]

Thanks dc fuse. I tried to make sure my setup was correct by posting here what equipment I was getting ahead of time. It does look like I have room for another panel on top. Last time I saw Gary he said the 13.7 I had at the time was very good. This sort of confirms my suspicions that even though he's been doing this stuff for 40 years he may be weak in the solar knowledge. I suspect the wiring of the panels to the controller are too thin but don't know how to confirm this exactly. Perhaps I'll open the battery box take some pictures and share

 

[DC Fuse]

Riff, You don't have to get another panel but you will need to correct whatever is not right and limit your daily use to 70-80 amp/hrs a day. That might work too for now. Seems your current needs are'nt that much and you can always add capacity later.
Let us know what you find is the problem.

I bet it's wire size. Remember, those panels are putting out 20 volts initially

 

[riffraff]

How would be the best way to go about diagnosing the problem? I don't feel comfortable tAking it back to personalized vans at this point. I'll take it easy on those power use. If I can charge my electronics at the library or storage I will. Or maybe only use power during the sunniest times. There is a tremendous amount of Sun in this area. If I owned a house it's roof would be covered in panels.

 

[DC Fuse]

If this system were mine i would cover panels w/a blanket and pull wires going in at charge controller. Take off blanket and test voltage here w/voltmeter and see if it's higher than 13.9 volts. If it is you have a bad charge controller. If not measure voltage at panels which should be 20 volts. If this checks out you have either bad/loose connections or too small wires.
I'm thinking wires are too small.
When this system is working right you'll have 70-80 amp hrs. a day to work with.

 

[SternWake]

How much load was on the battery when it read 12.0 volts?

ONLY if there had been zero load on the battery for an hour or more, and then you saw 12.0, would you be in the 30% range, And this voltage equating to specific states of charge is also inaccurate. Especially on AGM batteries. Applying flooded battery voltage state of charge percentages to an AGM battery is just ...unwise. AGM's range is generally wider and they will hold much higher voltages in the 60%SOC + range than the same size flooded battery at the same level of depletion.

LOaded voltage readings are not, NOT indicative of state of charge. Only resting voltages. With time and observation, then one can see any given voltage estimate how long they have been running electronics, and then make a semi educated guess as to their battery's State Of Charge, but just seeing any given voltage, while still discharging the battery, and declaring a SOC percentage is unwise.

When All loads are removed from a battery, voltage will rebound, and can rebound significantly! Only rested voltage, only rested voltage and only rested voltage is indicative of state of charge. Can;t remove all loads from the battery long enough to take a rested voltage? Then don't think any voltage is indeed indicative of state of charge.

As batteries recharge, the voltage will rise.

When the battery is low, and the solar is doing all it can, you are NOT going to get 14.4+ volts on the output terminals of the charge controller until the battery is nearing full charge.

I recently was applying 38 amps to a depleted battery, battery voltage 13.13, charger terminal voltage was only a volt more. 38 amps! nearly 4 times what you can expect from 200 watts of Solar. You are not going to get 15 volts from a solar charge controller output on 10 amps, on 38 amps, on 58 amps when on a depleted battery.(But the 58 amps will get it there much faster)

UNless your AGM manufacturer recommends 15 volts, YOU DO NOT want your AGM battery at 15 volts. To my knowledge, only LIFELINE AGM lists anywhere in their rather impressive AGM charging PDF, list a 'conditioning' cycle in which 15+ volts are allowed, if monitored closely.

Too long and too thin of wiring leading to the charge controller really impacts the effectiveness of MPPT controllers. I used to have 12awg for my single 130 watt panel. When I swapped this with 8awg, output increased about 10 to 15%. But I also moved the solar controller closer to the batteries at that time.

Most every paid installer out there is going to underwire panels. Thinner wire is cheaper and easier to work with. Once again, in this day and age, the appearance of completion is more important to the installer than actually ensuring best performance. Minimum voltage drop on PANEL to MPPT Controller is very important.

70 to 80 amps hours a day is only possible, this time of year, in the SW desert, with 200 watts of panels re aimed at least twice a day, perhaps 3 times a day at the sun, and a well wired operating system. NOT flat on the roof and unmoved. Any loads on the system while the sun is shining is eating up the Amp hours returned.


YOur AGM is going to need a few hours at a safe 14.4v each and every day. 13.9v for twice as long is not going to do it. You might need to turn more things off Midday to allow the controller to achieve 14.4 at the battery terminals. An hour or 2 after it holds 14.4v you might be able to turn some things back on, but if it cannot hold 14.4v, give it more time.

You should be expecting about 11 to 12 amps at noon from 200 watts of solar in the desert southwest with panels flat on the roof, at this time of year.

Not knowing your exact AGM batteries I say 14.4v,, but there are some AGM which will list higher absorption voltages in Cyclic duties. If it has a range of 14.7 to 15, feed it 15v when the batteries are cool, 14.7 when it is hot. most all charging voltage specs are at 77F or 25c and Ideal absorption voltages are tweaked depending on battery temperature.

As batteries heat up when charging and while discharging, Ambient air temp sensors on charge controllers are NOT as effective as temp sensors on the battery itself, but is better than no temp sensor at all.


Somebody with a Digital clamp on Ammeter should be able to put this tool over one wire from a single panel and see if it is in the 4 to 5 amps range around noon. If both panels are not the same, investigate the open circuit voltage of both panels. It is certainly possible you got a DUD.

 

[riffraff]

ok I'll get a voltmeter tomorrow thx

---

Wow just got knowledge bombed by sternwake the controller and inverter usually read about 12.7 or thereabouts after 1/2 night running the tornado fan (once or twice I had it on all night). I am often charging the kindle or mifi also but most of the time there is no load or just the standby load of the inverter for the few hours between when I shut off the van and start the day (which is usually when I'm paying the closest attention to it)

Will reply again after reading the rest of your post.

 

[riffraff]

These are the batteries I got:
http://www.ebay.com/itm/QTY2-VMAX-S...es-/271491772027?ssPageName=ADME:L:OU:US:1120

I've seen the controller read over 14 Only a couple times. I'll try and not use the fan at all tonight or my fantastic fan tomorrow and see how charged they get.

 

[SternWake]

I'll be interested in how long these batteries last. I always suspected that they are just Universal Battery with a fancier sticker put on them.

http://www.batteryplex.com/universal.cfm/m/12V_110AH

I am suspicious of these batteries because of shelf life. "Universal' batteries do not have the very low self discharge rates of some other high quality AGM batteries, barely better than flooded batteries.

Since they have to come over on the slow boat from China, then sit on a shelf waiting for somebody to buy them, they could be sulfated and have lost some percentage of their capacity before they even got to the end user.

These batteries might need a high amperage, a fast recharge from 50% to "Wake them up"

I think Universal battery says not to exceed 30 amps for a 100 amp hour battery. If you can take these batteries to 50% or less, and then feed them together, about 65 amps for 2 hours, they might respond nicely there after.

I had to do a 50% discharge and a high rate recharge before I could get my Northstar AGM to hold the 13.06V fully charged open circuit voltage. northStar says OCV on a fully charged battery is 13 volts.

A clamp on AC/DC Ammeter might be a good investment for you.
Clamp it over any one wire in a circuit, and it will tell you how much current is flowing through it.

http://www.amazon.com/gp/product/B0...d_t=201&pf_rd_p=1535523722&pf_rd_i=B001VGND88

---

This universal battery has the threaded inserts closer to the Ebay vmax batteries. Dimensions appear just different enough i guess that are not just rebranded UB batteries.

http://www.batteryplex.com/universal.cfm/m/UB121100-B2-GP-30H

 

[akrvbob]

Nearly all solar controllers come factory set from the factory to float at between 13.8 to 14.4. I've never heard of one set to float at 15 or over. Never. For most batteries, that's certain death.

They may get that high (or higher) during equalization, but not daily.

Better controllers let the user adjust the float point. Your controller may have come preset to 13.8 but if your battery wants more you might can set it up higher. Read your manual to see if it's user adjustable.
Bob

 

[SternWake]

Float is usually 13.2v to 13.6v
Absorption is usually 14.1v to 14.8v
Bulk charging is maximum available current until absorption voltage is met. After absorption is held for X amount of time, controller then reverts to float.

The Higher the bulk current, the lower the state of charge of the battery is at when absorption voltage is met. Once absorption voltage is met, less and less current is required to hold battery at Absorption voltage.

Reaching Absorption voltage daily and holding it for at about 2 hours is the pretty much what is needed on a nightly cycled battery, AGM or flooded. More time might be needed. Some batteries like US battery list a 'Finishing charge' where after 2 hours or so at absorption voltage, the controller will do a higher voltage to shoehorn in that last 5% or so. This can be considered a topping charge on batteries that need it.

How do you know if your flooded battery needs it? A hydrometer will tell you. A flashing green "full charge" light does not. It means very little. it only really means the charge controller has completed the programmed charge algorithm. it has no idea if the battery is fully charged. it cannot. Each battery is different and changes as it ages.

Equalization can be upto 16 volts on some flooded batteries. 15.3v will not do it on my flooded group 31. AGMs should not be equalized.

Battery manufacturer charging specs should be sought out and followed as best as possible. If you cannot find charging specs/ recommendations from the manufacturer, I'm move onto a battery which does.

Beware of the word equalization where chargers/ controllers are concerned. Their marketing departments have done studies that have determined this word can add 30% to their bottom line.

Equalization is a forced overcharge with voltages at least 15.2v and up to 16 volts.

The time needed at these voltages is to be determined by a temperature compensated hydrometer. When specific gravity no longer rises, end EQ cycle.

 

[VanLifeCrisis]

When my inverter squeals like a pig getting slaughtered for more than a few seconds when the fridge kicks on i know its time to charge

 

[DC Fuse]

I'm finding that research on these AGMs is all over the map for clarity. For instance, several sites tell me that if you have a low amperage charging source relative to total amp/hrs of AGM bank to set at 15 volts for bulk which does'nt stay there long where it would then go down to 14.2-14.4 volts for absorption period tapering further to float rate. This is explained as an advantage of the AGMs.
Then it goes the other way where i read not to ever go over 14.2 regardless of amperage rate applied. What is one to believe?

 

[SternWake]

You gotta find the manufacturer of the AGM, and use their specs.

AGMS are sealed, but have valves. At certain PSI the valves open. The batteries can recombine the gasses upto such and such a PSI. It is different for each AGM.

There is no One AGM profile which will meet all AGM batteries. Most every AGM one size fits all controller is set to the lowest AGM voltage parameter you can find. Far from Ideal for the ones which want 14.7v ABSV, like Odyssey.

Adjustable charge controller set points will pay for themselves in longer lasting batteries.
A better controller which allows user adjustable setpoints only costs more until the first set of batteries fails prematurely.

Blindly trusting a cheaper controllers charge algorithm is actually doing the job it claims to do is....Unwise.

Better than nothing, but unwise still.

 

[DC Fuse]

SternWake, What charge controller would you recomend i use for a 450 watt system using AGMs as a bank including battery temp sensors.Would like to use a Blue Sky product. Thanks.