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.

[jrnymn7]

In my experience, with my four 6v GC-2's, it takes several days for a good surface charge to dissipate on its own. Checking resting OCV an hour, or even a day later will give a higher than actual reading. Moreover, higher top charge voltages (15+V) result in lower resting/ocv readings, even though SG readings improve.

There seems to be a sweet spot, where both SG and OCV's max/equalize out... in my case, in the 14.6-14.8Vabs (TC) range. So I find it best to do a good top/desulfation charge, in the 15+V range, followed by a "normal" 14.6-8v Abs charge. I notice this with EQ'ing, as well. The resulting individual OCV's go crazy, but then level/equalize out, once followed by a normal charge cycle.

The OP's % SOC monitor is clearly not reliable... SOC cannot change at the flick of a monitor switch. And no, checking OCV cannot be done while under ANY load, or it's simply not an OCV... OPEN CIRCUIT means just that. And the same load will have a different peukert effect at a different SOC. So, for a simple, basic indication of when to charge, OCV may be fine, but for trouble shooting, it is very unreliable.

[5erToyHauler]

^^^^
Agreed. That's about all I've been using it for the last couple of weeks. Monitoring the current coming from my panel and monitoring the battery voltage. It gives me a good enough idea as to where everything is at. All of my batteries turned out to be just fine. My panel has no problem restoring my battery bank to 100%. Boondocking with 2 toddlers is easy with this setup along with a 5500 watt Onan. I'm trying to keep my stress level to a minimum during my camping time. Afterall that is why we do it. Thanks everybody for your help. You've all been a wealth of knowledge.

[MEXICOWANDERER]

Amp hour meters have to be "zeroed" occasionally or they become worse than useless.

I lost track decades ago of the number of people who complained...

"The batteries were full tip-top last night then at four AM the heater quit. There's a short!"

A battery charged to 12.75 volts resting may have half the capacity it used to. I wish folks would understand this. Trends and tendencies volt and amp wise with a real amp-hour meter is very handy. Danged tough to stare at a battery and psyche it into coughing up it's amp hour capacity. .It can be done only one way and you know what that way is...

Panel meters are useful to detect delivery anomolies. And that is it.

[Harvey51]

Maybe you have a battery monitor like mine that calculates the % charge from an initialization to 100% when fully charged, the battery capacity you enter when setting it up, and the amp hours it senses going in and out. Mine works quite well for a day or two after a full charge and setting it to 100%. It doesn't take into account losses so accuracy fades over time and the reading becomes meaningless.

With solar charging, the only time you get a useful voltage reading is just before dawn when the surface charge from the day before has settled in overnight.

[MEXICOWANDERER]

Actually this sounds like a monitoring meter measurement issue. Ampere hour capacity of the bank has to be factored and AH capacity degrades. Charge Efficiency Factor is reduced both by cell aging and sulfation.

Net numbers especially kWH in and out will be infinitely more accurate and reflect what is actually going on. Percentiles are a dirivitive and can be skewed so easily it isn't funny. Eighty percent of sixty-six percent tells a user little if anything. Percentage values should not be incorporated into a battery charge monitoring system IMHO.

[Vulcan_Rider]

NinerBikes wrote:

Nothing else matters.

Well it kind of does.

It is possible for the battery to be fully charged but due to a corroded internal connection or some other fault, it might not be able to DELIVER that charge.

That is why they test automotive batteries with a LOAD test.
Specific gravity is important but voltage and current are too.

[5erToyHauler]

I agree with a lot of what has been said here. The meter that I have does calculate AH In/Out. However that is only accurate to anything plugged into the "Load" output on my controller. As with many controllers that have this feature, the draw on a 5th Wheel can far exceed what the rated output is at that terminal. So needless to say, my power source does not come from that output. So I do stand corrected..... There is no way that my meter and controller can actually sense an accurate SOC. Therefore the SOC that it is giving me is likely based off of the current Voltage that it is seeing at any given time. As stated before, the voltage reading on the solar meter/display is accurate. The only thing that still confuses me is why last year my SOC didn't seem to drop permanently and not recover to where it should as soon as I put a load on the batteries. Maybe that wasn't the case and my memory is failing me here. But it's weird that the voltage will come back up to 12.8V (which is 100%) but the SOC only comes back up to 50%-60%. It doesn't make any sense to me. I put 2 x 6v's in on the weekend and the result still seems to be the same. But at the end of the day both sets of batteries seem equally as strong. So I believe that my lesson learned here is to not pay attention to the SOC and just worry about my voltage reading on my solar display. I don't think that my issue has anything to do with weak batteries. The batteries which I removed from the camper have settled for well over 24 hours now and are reading 12.68V. I did however have some corrosion starting on a couple of my jumper wires. I replaced the corroded cables with new. I'm sure that didn't help matters. I ran my onboard generator for a bit and the converter seems to be working as it should. I'm still going to take a hydrometer to the batteries as recommended many times over in this thread. As long as that test checks out, I think that I'll just gauge my battery life off of my voltage reading. Unless anybody thinks that isn't a good idea. I know that I can install a proper Xantrex or equivalent battery meter that measures current In/Out. But to be honest, I really don't have the time to be messing with one and keeping it calibrated. I want to keep my time spent in my Toy Hauler as leisure time with my family and the least amount of work possible. Our first camper was a 1979 Kustom Koach. The only fancy meters that it had was an analogue battery meter. We didn't have any generators or solar power. Boondocking on weekends was a breeze. That was only a few years ago. My what whimps we've turned into.

[NinerBikes]

I've learned that someone should make battery caps with built in temp corrected SG readings.

Nothing else matters.

[MEXICOWANDERER]

I like politico speak. It's all about indecipherable percentages. Sorta like buying and selling dirivitives...

[time2roll]

Probably need to separate the charging systems and batteries so they can be tested separately.

All the % had me confused. If all those % were replaced with voltage and amp reading we could get someplace on this.

[Almot]

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

He said "display/meter for my solar setup". Sounds like a built-in AH counter present in some mid-range controllers. Not much different from expensive toys like Trimetric or Victron battery monitors that people here are using ;)... I don't have AH counter on my controller, and would not rely on it.

The only real measurement is by hydrometer.

Open circuit voltage of battery rested at least 24 hours is the second best. It has to be Open Circuit, i.e. no loads, and even then it won't tell the whole truth if battery can't hold the voltage under load.

Too little info to guess, it could be either failing battery or failing AH counter.

[3_tons]

Question, how old are the batteries??

[littlemo]

We were having same issues. Our Converter was bad. Getting new one solved "lots" of problems.

[MEXICOWANDERER]

HYDROMETER STORAGE

Go to a large plumbing supply house with your hydrometer. Choose BLACK pvc tube big enough to hold your hydometer inside. One end of the tube gets a cement-on cap
Permanent.

The other end gets a threaded flange collar that is also permanently cemented to the tube. Then a threaded plug is screwed into the collar. The bulb protects one end of the hydrometer while the rubber nipple cushions the other end. Two large hose clamps and a length of 1/2" nylon rope makes a great handle. A smear of electronics silicone grease on the plug and collar threads makes the fit glide like butter.