Only getting a fraction of battery capacity

[angelakelly]

Hi!

I'm new to the forum and also new to Solar (though I've done a good bit of research and testing for my system). I was wondering if you guys might be able to provide a little insight into something that has me scratching my head.

_specs_
Everstart (walmart) 24DC Marine batteries x 2, wired in parallel.
Each is rated at 105 AH @1a (which I find out later isn't standard. They're probably about 85 Ah when set to a 20hr rating.)
I don't take these below 12.1V (my usual current draw lowers the voltage by about .1 v, so at 12.1, I'm really at 50%)

Dokio 100W portable and foldable solar panels x 2
Practically speaking, I get about 100W total from these in the pacific NW, depending on the time of day. Input Amps during bulk charge tends to range from 8A-10A.

Dokio PWM 10A charge controllers x 2 (they came with the panels. I have both hooked up, as I was worried about exceeding the 10A rating if I did both panels with one controller.

_monitors_
I've three ways of monitoring power usage. I've the Voltage and Current readings on each of the charge controllers. I've a simple hall-effect monitor (not usually hooked up), and I've got A multi-function battery monitor that basically goes through a 100A rated shunt to give me Voltage, Amp, Watts and accumulated Wh as well as Ah. All three of these monitors agree on the amount of usage (within tolerances).

I'm running my laptop from this battery bank. On any average day I will use between 110-135 ish Wh, or 8-11 Ah, and the voltage will drop to between 12.1 and 12.3 normally, sometimes 12.4. I've tested the system to see how much my typical usage lowers the voltage just from the draw- ie... getting up at six am and looking at the voltage, then comparing it to what it had been the night before. Typically it will have raised by .1V to .2V depending on whether I was playing my game at the time I went to sleep. When recharging, it typically takes about 30% more power than I used before the controllers go to float charge. This actually seems about right, considering inefficiencies and how the recharging is accomplished, etc.

So all the numbers balance out within reason, and they've been confirmed seven ways from sunday. I even ran some tests using only my laptop battery over a period of time to confirm the wattage being drawn by the device. I wanted to make sure that the issue wasn't systemic.

You might already be able to see the issue. I'm only using about 10ah.. maybe up to 12, and I'm draining the batteries down to 50-70 percent.With two batteries in parallel, I should be getting about 100 Ah before I hit 50% (Considering that my laptop usage is about 1.5A on average). Even accounting for Wallmart's deceptive labeling, I'm not getting anywhere near close to what I should, and it's far enough off that I don't think the issue is with my numbers. I think I am missing something conceptually. 10 percent of the capacity I am expecting is just too far off.

Can any of you see where I am going wrong? If I had to guess, I would think that my assumption that the battery is charged when the controller switches to float is incorrect, and that the battery isn't actually being fully charged, and then this compounds over a couple of days. I -have- done tests to let the battery rest after the panels went to float, and that dropped nicely down to 12.7 after six hours or so, but I don't test that every time. I tested it once to confirm that what I expected to happen, was actually doing so.

In truth, I just can't think of anything else. I appreciate very much any help you might provide.

Sincerely, Angela

[5foot2]

Right off I wonder if you've purchased the wrong type of battery. Meaning a starting battery vs a RE type or golf cart type. Could you post the specific make and model of battery?

[angelakelly]

Right off I wonder if you've purchased the wrong type of battery. Meaning a starting battery vs a RE type or golf cart type. Could you post the specific make and model of battery?

Yes, they're the Everstart 24DC, Walmart brand. They are marketed as a marine deep cycle, but it lists MCA (Marine Cranking Amps), and I believe this battery is really sorta a hybrid, more suited to deep discharge than a staring battery, but still made to be able to deliver those bursts charges for starting as well. It's supposedly designed for trolling, etc.

[5foot2]

I looked at the walmart web page for this battery, and didn't see a listed ah rating. Given the battery is called EverStart, and it lists cold cranking amps, I still feel confident that your issue is with the batteries. Meaning they are an engine starting battery. If your holding to a budget, buy a pair of GC2 batteries from Sams Club. They are 6v 215ah @ 20h batteries and cost $90-$100.

[angelakelly]

I appreciate you doing that and your replies. It's kind of you to look the battery up. The website doesn't list the capacity, but it prints the numbers on the battery 101 Ah @1a. I'd put this information in the _specs_ section of my post. I found out after the fact that that @1A is a little marketing ploy (though I typically only draw 1.5A give or take), and the real Amp Hour rating @20H tends to be around 85Ah. That's these batteries in a nutshell; I wish I'd seen the Sam's Club ones, as I'd have much more faith in the posted rating.

Even worst case though, the batteries being 85Ah, I've got two of them in parallel, and I'm only getting 10-12Ah before I'm nearing the 50% discharge.

If I were to take the actual usage, say about 12Ah before I get down to 50 percent, that means I really only have 12Ah batteries and that just doesn't make sense. It's why I think I'm missing something big conceptually. I'm just not sure what.

[Bala]

If your batteries are as the photo looks when I google them you should be able to use a hydrometer to check for SOC.

It is quite possible they are not getting properly charged.

What Voltages do the regulators charge to?

What time of day do they go into float?

How many hrs a day of good strong sun do the panels get?

Are you using power from the batteries while they are charging?

[angelakelly]

If your batteries are as the photo looks when I google them you should be able to use a hydrometer to check for SOC.

It is quite possible they are not getting properly charged.

What Voltages do the regulators charge to?

What time of day do they go into float?

How many hrs a day of good strong sun do the panels get?

Are you using power from the batteries while they are charging?

1. The regulators have (supposedly) four stages-though I've observed three. The bulk charge, which is at full Amperage. The controllers will keep pushing the voltage up to 14.2, which is where it will stay for an hour or so until it goes into float charging. Over time at 14.2, the current tapers off until by the time it goes to float, it's about 1.0A or so of current going in. Upon switching to Float, it will drop down to 13.7

2. I don't always charge them the same time during the day, It will take from 2.5-4.5 hours to switch to float charge.

3. At least three hours of good sunlight, generally. Most often 5-6, but I seldom need that long.

4. Generally no, and certainly I did not when I was doing my tests. I tracked both usage and how much was put back over a series of a few days to get at my numbers. During that time specifically, I was careful not to do anything that would convoluate the numers, so the usage, for example, was read at the end of day, and then reset the next day for the charging sequence, and that sequence was only begun once the sun was high enough in the sky to give a decent charge rate. No other devices at all were drawing during those times, save for the controllers and the monitor.

[Bala]

I suggest that are just not getting enough charge.

I would be trying to keep the charge V at over 14 all day and move the panels to chase the sun to get as much charge time as possible.

When you take a cap off they should be bubbling and as long they they dont get hot they will be fine.

Ideally they need a mains charger and a hydrometer to get them to known full charge.

[angelakelly]

I was wondering about that as well- that perhaps the controllers switching to float doesn't imply what I think it does (ie that the batteries are fully charged). I tested that one time. I let it go to float, I then let the batteries rest for six hours and looked at the voltage. It read 12.7V, which is exactly what it should have. I also just looked at the controller, having only now started my nighttime computer use. It also reads 12.7. If it wasn't getting charged, I would expect the voltage to be lower in both cases.Also, when I compare usage from one night with how much charge goes in during the charging cycle, they're within reason. about 10Ah going out, about 12-15Ah going in.

If I'd been using the laptop half an hour or so and looked and saw 12.3V, then yeah, I'd be inclined to think that they hadn't fully charged, but that hasn't yet been the case.

[Bala]

How long has this set up been in use??

Going into float is not full charge, it may be 95% but it depends on the charge controller.

You are using budget batteries and controller so as I suggested I would be looking to get a hydrometer and get them to a known full charge and go from there.

I have a folding panel I use for camping, its controller does not do bulk well.

The hydrometer will also tell you if you have a bad cell or uneven cells.

Also disconnect the two batteries after charge and see if they hold the same V overnight.

Sunking has suggested for years that battery manufacturers have gone away from multistage charge profiles to what he has, or is, termed max smoke. I think there is a sticky on it.

I put new batteries in last yeas and a new controller. The new controller hardly ever goes into float, it just holds absorb unless they are very very charged.

[angelakelly]

You know, you may have something there. I had noticed in the horrible manual for the chargers that it will go into float after a certain amount of time has elapsed beyond getting up to 14.1V, and I had one experience when this was verified. One of my panels had come loose about halfway through that hour or two that it took to go from 14.1 to float, and the one that had come loos and been reconnected didn't to go float four about half an hour after the other. And thinking about things, while I haven't noticed a really low charge starting out, there could be enough of a charge on the batteries that I simply don't notice that it goes from 12.9 to 12.7 to 12.4 much more quickly than it should.

I'm a little intimidated at the idea of taking a hydrometer reading. I have a hydrometer from brewing, but...eh, it's acid and all that.

Let me ask you this though, if not getting fully charged is the issue, wouldn't my recharge be a good deal less than discharge? After all, there would be more juice going out than was coming in, and eventually, the battery simply wouldn't have a charge at all. Every time I compare, my charge in comes out to about 30% more than the charge that went out the night before.

[Bala]

For hydrometer use, glasses at least, face mask, gloves, whatever makes you feel safe. Just be careful and precise when doing it and you should have no problem. if you get acid on you water is your friend. if you get it on your clothes they will get holes in them.

I have used a saying for many years in that, " You can theorize till the cows come home and still be wrong"

I have not tried to work your math.

From what you have posted I just see a unknown start point, you dont know if the batteries are actually getting fully charged. Because of the size of battery and the amount of panel wattage you have and as little as 3 sun hrs I doubt they are.

You need a mains charger and give them an equalize charge separately and ensure they are actually fully charged and in good condition via hydrometer readings.

[angelakelly]

Alright, I'll take that advice. It has seemed to me as well that 2-3 hours of charging doesn't make sense with the two batteries I have and as low as the voltage went. In fact, that's part of why I'm posting here, the numbers I have no matter how many ways I've verified just do not fit logic. It make sense to go back to the beginning and find a more reliable way to check charge and see if the batteries are getting fully charged. Can always pick this back up later if needed.

Just to to clarify, I"m checking each of the cells to make sure that the pH indicates a 14.7 charge at the end and also checking that the batteries will hold that charge overnight, wouldn't the charge have dropped overnight to the resting 12.7 volts?

[Bala]

The hydrometer needs to measure SG, Specific gravity. The reading will vary depending on what the manufacturer did, SOC and temp.

You are looking for each cell to be the same.

SG will tell you SOC at any time, no need to rest batteries. it can be done while charging.

Have a read of this for what to expect for SG and its relationship to temp.

https://batteryuniversity.com/learn/...tate_of_charge

[angelakelly]

Awesome, I'll do that, and thank you both for all your help. I appreciate you taking the time to work with me.