Battery SOC Low - Voltage Normal

[5erToyHauler]

Hi All.

I'm new here so go easy on me. I've Googled for hours but can't find any solid answers. My setup is in my signature. So here's my issue....

Whether plugged into shore power, running my generator, or charging with my solar setup under the sun on a good day, I can't get my SOC up on my batteries. I'm monitoring my vitals through my display/meter for my solar setup. When we were out boondocking 2 weekends ago, I couldn't seem to get my batteries up past 60%. I could run my generator for many hours. It would only bring them up to the low 60's and than hover there. With the generator running, the SOC would drop when using lots of 12v power. Not by a lot but it would drop. I will note that the converter was working. During the day when the panel was charging at 10-16amps it would bring the SOC up to the 90's. But as soon as the sun disappeared it would drop back down to that 58%-61% range. Here's the kicker, my battery voltage readings seemed to be dead on. Exactly what they were last season when my solar display would show my batteries charging right up to 100% and staying there. There is no abnormal drop in voltage (according to my display) when 12v power is being used. I can't say that I've experienced any noticeable loss in capacity. The furnace ran all through the night. The batteries were drawn down in the morning as per the norm. Than they charge back up to the recent norm of 58%. I can't get them to show past 61% no matter how long the generator runs or the shore power is connected. And again, when the solar panel is going strong it will bring the SOC up into the 90's. But once the sun goes away it will go back down around 58%. My best guess would be that the converter can't get the high SOC readings because of the low amperage it charges at compared to my solar setup. All voltage readings on my display seem to match the numbers I get when taken directly off the batteries using my multimeter. Last night I went and checked out my readings again. The trailer had sat in good sun for a few days with the main battery disconnect off. My display was showing 94% SOC @ 13.0V. When I turned the main power disconnect to "On" It went down to 78% SOC @ 13.0V. There would be next to nothing for load at this point. I turned my kitchen lights on and it went down to 50% @ 12.8V. Shut them off and I went to 58% @ 12.9V. Than I cut the main disconnect and things stayed the same (58% @ 12.9V). SOC never recovered more than that.

So it seems that once a load is applied, the SOC/ Capacity doesn't hold up but the voltage stays where it should. In my research the only situation that I could come up with was that I may have a case of Sulphation. My Solar Charge Controller has multiple stages of charging. It is supposed to equalize when necessary. How it knows when to do so...... I am not sure. If my voltage was dropping and the batteries were draining quickly than it would be an easy diagnosis. But, the fact that the voltage seems to fluctuate on a normal scale while the SOC is all over the place, has me scratching my head. So I'm calling out all experts to see what gives?

Thanks in advance for your help.

[Vulcan_Rider]

5erToyHauler wrote:

- My display measures SOC as well as Voltage. It does take into account the battery capacity

That voltage doesn't seem to drop abnormally when loads are placed on the system. It's just the SOC that does.

There are only TWO ways to know (or estimate) the state of charge:
Testing the specific gravity
OR
Measuring the voltage after a good rest or under a very small (known) load.

So.....if the "display" doesn't have a probe into the acid (unlikely), then all it REALLY knows is voltage.

The ONLY way for it to make an educated guess at SOC is go measure the voltage while a known load is applied. It can't do that when ANYTHING else is drawing power: NOTHING.

Bottom line: your SOC numbers are varying wildly because the test conditions aren't right or the "display" has gone haywire.
To repeat (this is important): The "display" can't give you an accurate SOC number under varying loads.

The more I read this thread, the more I think that the SOC number you are seeing is really more like a "time remaining" approximation assuming that the current load continues as is.

I think you should ignore that fake SOC number and just watch the voltage and use the provided chart. It is similar to the one I have and assumes no load or a real small one.

[consumeratlarge]

I think the EP controller can only guess at state of charge if you use the dedicated 'load' outputs, (most wouldn't on an RV because you already have a distribution system for 12v). The remote tells you the voltage at the charger output, which is virtually paralleled to the DC converter output as well as the battery, with fairly large wiring. Plus, as somebody pointed out, if you add energy with other charging, the EP can't know that you did. Only the type that has a shunt bolted at the battery can monitor everything coming and going, and those are a great tool to learn how much everything uses.

Meanwhile, I think you can get 14.8 equalizing charge out of your solar controller, just turn off the dc converter, and don't use the lights or any dc loads while you'r doing it, since the voltage is a little high. Start when you've got good sun, of course. I would do one at a time, since the equalization really overcooks the good cells in the hope of adding current to the cell that's sitting low, and your set up will be a kind of low amperage with 3 batteries, I think, for that operation.

[5erToyHauler]

Good input guys. Maybe I'll try that hydrometer. I'll do some reading on the equalization charge. I know they are harder to do nowadays since all of the newer charges have all of these "Smart" features built into them.

I have to get the make and model off of my Monitor and the Controller. I don't have them handy. Pretty sure they are both EP Solar.

[MrWizard]

Lots of good advice posted above
I would start by manually charging the batteries with a portable charger until the acceptance is ONE amp or less
Then reset your meter/counter..and take SG readings with a hydrometer
Be advised the solar amp h4 counter is not going to count the amp hrs from the converter
There for, the more you run the generator, the more you throw the solar counter off the count, acceptance will be down, voltage will be up, but the amp hoor counter, will be out of wack
Only counters that are mounted at the battery, inline with all charging sources can come close to be being correct

[westend]

Yes, please list the gear.

BTW, Freas Glass Hydrometers, might as well get the industry standard. They are not that much more than the $20 you mentioned and will last a lifetime if you take care of it.

[NinerBikes]

you use a hydrometer you are looking for a reading of 1.275 or better for specific gravity on each cell you want to minimize the spread to .010 or less. An equalization charge set of sessions is in order. Do a search here on equalization charging by mexicowanderer.

[time2roll]

Exactly what equipment is giving such accurate percentages of battery charge level?
Need make and model number.

Charging on generator/converter or solar should get voltage in the 14.2 to 14.8 range at some point. If not the converter or controller should be updated.

[5erToyHauler]

Thanks everybody for all of the great responses so far. You have all given me a good list of issues/corrections to consider. I'll add a few things for clarification that I missed in my original post.

- I did top up the water in my batteries before I started monitoring this issue. They took a bit but weren't that low. No cells were exposed.
- When I say that I took readings from my display/meter, I am referring to the display unit that is hooked to my solar controller. Not the useless LED battery meter that comes standard on all campers.
- My display measures SOC as well as Voltage. It does take into account the battery capacity (which is setup based on the amount of AH I set in the controller)
- In all tests that I've done, the voltage on my display seems to directly match up with what I get on my voltmeter with everything disconnected from the batteries.
- When I spoke of seeing 13.0V the other night, I should add that this was just after sun down. So the controller was in "Night Mode" (Not Charging) but the batteries hadn't had time to properly settle. But when they do settle they settle around the 12.6-12.8V mark (which is 100%). That voltage doesn't seem to drop abnormally when loads are placed on the system. It's just the SOC that does.
- I have definitely not ruled out the idea that my display/monitor has gone defective. The only reason that I'm not jumping to that conclusion right away is because it did charge to 100% SOC and rest there in the past with the same setup. Of course, there is no telling when things will go defective.
- The hydrometer test is something that I have not done yet. I guess I don't trust the cheap testers that you buy for $20. And I don't really want to fork out the amount to buy a proper tester as they are not cheap.
- When I completely disconnect all 3 batteries and measure them, they all give the same voltage reading (they only differ by a matter of hundredths of Volts).

In the past I have read that sulphated batteries can show a proper voltage, but will read at less capacity (which my monitor is likely capable of reading) or a lower SOC. Can anybody comment on this? I'm okay with buying new batteries if that is in fact the issue. But on the same token I don't want to replace good batteries with good batteries. If I wasn't getting good battery life anymore than it would be a no brainer. My battery bank was more than sufficient before, so it is possible that I have lost capacity but haven't realized it. But the fact that they still seem to last pretty good is what has me confused. I guess one easy way to test would be to take a known good battery and hook it up in place of the others and see what happens.

[red31]

My battery maker provides a warning on using OCV! note its many digit accuracy :Z and precision :B

[Matt_Colie]

5er,

You have some issues. (Big news flash - Huh?)
First is that your instruments do not agree. This is not uncommon, but you have to get into the wrestling match to find out who is right. For starters, I suspect everything.

Your instrument that reads SOC is suspect because the SOC can't change as fast as you have reported without a disaster.

Your voltmeter is inadequate to the task. A lead/acid (LA) batteries entire life is between 12.0 and 12.6(~7). You really need to be able to read 12.XX to know how things are really working.

Your converter/charger is either out of calibration or inadequate. It should be able to bring the house bank to 90% in less than three hours from the 50% (12.00V) mark.

Your house bank may also be in trouble and this will be difficult to diagnose with jars in parallel. When anything gets wrong about one cell in one jar of a parallel bank, the whole set will go down. So, you have to break it up and find out who is the problem. You cannot replace one jar of a parallel bank.

My simple suggestions are that you first buy/borrow a meter that can do 12.XX, then get a way to measure electrolyte density (the true measure of SOC) and that can be a real hydrometer or a refractometer. The car store cheapy hydrometer with floating balls will be useless or worse. It it does not have a thermometer to indicate the temperature correction, then you can only use it at the stated temperature. This is why I carry a refractometer.

Your problems are not original or unique. Before the depression, I did a lot of this work on expensive pleasure boats and they all had problems.

Good Luck Guy

Matt

[RoyB]

This is the one I use...

[Vulcan_Rider]

5erToyHauler wrote:
My display was showing 94% SOC @ 13.0V. When I turned the main power disconnect to "On" It went down to 78% SOC @ 13.0V.

I haven't read the rest of the answers yet but there really is only ONE explanation for your dilema: The monitor that is showing your SOC is defective.

The no-load resting voltage is directly related to SOC in a healthy battery.

It is impossible to have 13 V indicating 94% and then later having 13V indicating 78%.

Actually both figures are off a bit but the first one is close.
The second one is WAY off.

Either your electronics has gone bad or the connections just need to be cleaned up and re-tightened to get a better reading.

I monitor my house batteries with a simple voltmeter that plugs into one of the 12 V outlets and don't worry about it until it starts staying a bit below 12 with a nominal load.


I have a SOC table but don't know right off hand how to post it here.

[RoyB]

X2 on the simple % METER that comes with the trailers. I have never found them to give good readings. Only ball park readings...

I go with the DC VOLTS readings backed up by how long they last over night. My setup and usage gets my three 85AH batteries down to 12.0VDC by 8AM each morning when I start my battery recharge for around three hours using smart mode charging procedures.

If this happens the same each morning I know I am in the ball park of cycling my batteries from appx 50% to 90% charge state.

One of these days I may purchase a HYDROMETER to prove my charge state...

My 85AH batteries were purchased in 2008... I just measured them yesterday sitting in their outside battery trays on my POPUP trailer and they read 12.5-6VDC after sitting disconnected all winter long... Looks like I will get another camping season out of them this year.

I do not reply much on the built-in % of Charge meter that came with my two trailers...

Roy Ken

[dclark1946]

MEXICOWANDERER wrote:
Your meter showing state-of-charge could be off-it's-rocker.

Use a hydrometer to see where the batteries are really at charge wise. Meters are as reliable as using a Fortune Teller. A hydrometer dip will indicate if any of your cells need equalization.

I agree with MEX if you are saying that your voltage is holding up under load. Not sure how these battery monitoring systems determine SOC but you need to verify SOC independent of you monitoring system if voltage is holding up normally.

Dick

[wa8yxm]

IF you are using VOLTAGE to monitor SOC then one of two conditions must exist.

1: NO Current flowing save for the flea power needed by the volt meter..If you have a light on, or any other load..or if you have a converter on charging, the reading at the panel WILL BE FALSE

The other condition.

Meter at the batteries..NOT thew wires hooked to them but the batteries themselves.. Again,, Stopping ALL CURRENT (use disconnect) is needed for most accurate measurements.

Finally: SOC as measured with a hydrometer

IF that is low, but voltage is good.. EQUALIZE Battery may have stratifid.