How to properly charge lead acid batteries from solar with a load

[mhanna]

Hello all, I am hoping that someone could help me with a lead acid battery charging issue that I have been having. The way I have configured my charge controller & load does not seem to allow for the batteries to get to full charge.

I am not looking for specific device settings, more for the theory of how to properly charge a lead acid battery correctly to near full capacity (if possible) while there might be an automated on/off load connected.

For information on what I am using: the items include a Victron 75/15 MPPT CC, a phoenix inverter, a Victron BMS 712, a new 100A/h deep cycle lead acid battery and 3-100W solar panels. I have the CC set for 14.5 absorption, 13.6 float. I have the inverter set for a charge detect of 14.6 and dynamic disconnect of 11.5-12V (about 50% of the battery via Voltage). The 100A/h battery at 50% should give me ~600W/h usable. I actually had more of the same deep cycle batteries in parallel but for the purpose of this testing reduced it to one battery.

I started out with the MPPT charge controller, Phonix inverter, a fully charged battery and solar. The load via the inverter is my office equipment and is fairly static at 70Watts and got approximately 8 hours of run time until the inverter disconnected at ~12V (approx. 550 W/h). After several days I found I was only getting about 3-4 hours of inverter run time.

I bought a Victron BMS712 to better understand how the amp capacity worked and found I was pulling more amps from the battery than I was putting back via solar (as the inverter attached was turning on automatically).

There are hundreds of articles on how to properly charge a lead acid battery, but they all are done with a standalone battery and charger (no load on the battery during the charging). Most articles say that 80% of putting back the capacity is done in the bulk phase and the other 20% done in absorption phase that will take hours.

My inverter turns on when the voltage gets to the absorption phase 14.5v and on some days, there is not enough solar power to run the load directly, so it uses the battery thus never allowing the battery to get to 100%.

If I just let it run this way the battery will most likely cycle between 50%SOC and ~85%SOC, maybe hitting 100% on the very sunning days, obviously ruining the life of a lead acid battery if not brought to 100% often. If I add more solar than I moved the problem from not filling up the batteries to not using all of the solar capacity (I could just put a smaller battery in to achieve that result).

You would think the first option is to not turn on the inverter until the battery reaches the float stage (using the remote connection on the inverter and load output on the MPPT connected), but #1) The Victron inverter does not have this as an option in the load settings (really Victron...?) and #2) I would not like to use this anyway as hours of strong solar time might go by not being used during the absorption hours that pull little amps to charge the battery.

Another option is to use the relay output of the BMS and trigger the inverter on when the battery has a good SOC (% of full) but again if I start at say 90% the battery still would not be full and the above would still happen. If I wait too long ~99% I am wasting solar energy during absorption.

Sorry for this long description but wanted to get out what I am dealing with. Hoping I am not overthinking this, there are years of use of lead acid batteries doing the above and hoping someone can help me understand if I am doing something wrong / not understanding something.

Thanks in advance,

Matt

 

[sunshine_eggo]

Hello all, I am hoping that someone could help me with a lead acid battery charging issue that I have been having. The way I have configured my charge controller & load does not seem to allow for the batteries to get to full charge.

I am not looking for specific device settings,

You're going to get them.

more for the theory of how to properly charge a lead acid battery correctly to near full capacity (if possible) while there might be an automated on/off load connected.

Step 1: make sure load does not exceed solar.

For information on what I am using: the items include a Victron 75/15 MPPT CC, a phoenix inverter, a Victron BMS 712, a new 100A/h deep cycle lead acid battery and 3-100W solar panels. I have the CC set for 14.5 absorption, 13.6 float. I have the inverter set for a charge detect of 14.6 and dynamic disconnect of 11.5-12V (about 50% of the battery via Voltage). The 100A/h battery at 50% should give me ~600W/h usable.

Not quite. Since you're pulling more than 5A, you'll get less than 100Ah.

I actually had more of the same deep cycle batteries in parallel but for the purpose of this testing reduced it to one battery.

Have you gone through and confirmed every single crimp is good and every single connection is properly torqued.

The above causes more charging problems than any other reason.

Set MPPT to:

Absorption 14.5V
Fixed time, 4 hours
Float 13.6V
Tail current 2A

Set BMV to:

charged voltage: 14.3V
tail current 3%
Peukert 1.25

I started out with the MPPT charge controller, Phonix inverter, a fully charged battery and solar. The load via the inverter is my office equipment and is fairly static at 70Watts and got approximately 8 hours of run time until the inverter disconnected at ~12V (approx. 550 W/h). After several days I found I was only getting about 3-4 hours of inverter run time.

What does your MPPT report as daily yield on the detailed tab?

I bought a Victron BMS712 to better understand how the amp capacity worked and found I was pulling more amps from the battery than I was putting back via solar (as the inverter attached was turning on automatically).

There you go. You need more solar.

There are hundreds of articles on how to properly charge a lead acid battery, but they all are done with a standalone battery and charger (no load on the battery during the charging).

It doesn't really matter. The result is a net current flow to or from the batteries. The MPPT sees the voltage and the current it's providing. Your battery isn't fully charged until 14.5V AND 2A. If you're using loads, it can never reach this point; however the fixed absorption time of 4 hours ensures you get really really really really close.

If you truly use consistent loads during absorption, you can refine the tail current to reflect 2A + XA loads, but that's later. The above should get you to 100% even if it stays in absorption for the full 4 hours.

Most articles say that 80% of putting back the capacity is done in the bulk phase and the other 20% done in absorption phase that will take hours.

Close enough, but it depends on starting charge current.

My inverter turns on when the voltage gets to the absorption phase 14.5v and on some days, there is not enough solar power to run the load directly, so it uses the battery thus never allowing the battery to get to 100%.

Yep. More/better solar needed. Better means properly oriented with 100% solar exposure from sunrise to sunset.

If I just let it run this way the battery will most likely cycle between 50%SOC and ~85%SOC, maybe hitting 100% on the very sunning days, obviously ruining the life of a lead acid battery if not brought to 100% often. If I add more solar than I moved the problem from not filling up the batteries to not using all of the solar capacity (I could just put a smaller battery in to achieve that result).

You can't avoid having more solar than you use. Period. The absorption phase is voltage limited meaning you are literally wasting available solar power. Every single solar power system has this characteristic.

Another option is to use the relay output of the BMS and trigger the inverter on when the battery has a good SOC (% of full) but again if I start at say 90% the battery still would not be full and the above would still happen. If I wait too long ~99% I am wasting solar energy during absorption.

Welcome to solar power systems. You may want a 10,000lb truck to get 100mpg, but the universe says you can't. No difference here.

IT'S POSSIBLE THAT THE ABOVE TAIL CURRENT SETTINGS MIGHT ADDRESS YOUR ISSUE COMPLETELY. UNLESS YOU HAVE TRASH SOLAR OR TRASH ORIENTATION, THE DEFAULT CHARGE TERMINATION CRITERIA AREN'T GOING TO WORK WELL FOR YOU.

If the above tail current settings don't work, you need MOAR SOLAR!

 

[mhanna]

Thank you for the reply sunshine_eggo, I have read your responses and appreciate the time you took to break out and reply to several items and that I think your overall sediment is "I need more solar".

I thought about that more and built the below graph for one average day in January to plot out what I was producing and then using. What I think I found was you are correct I need more solar but not in solar capacity but in solar time. I am actually generating about 3 times what the inverter is using but not for long enough to charge the battery to full (including absorption stage).

The panels are on my roof and tilted so they face south but my neighbor has large trees right on the property line and I only get good sun in the middle of the day, it may actually get worse once the leaves come in :-(

From the graph below I start the day with slightly higher than a 50% capacity battery, then solar gets me through the bulk stage to absorption but I do not have another 4+ hours for absorption to get the battery to a full state. After the sun goes down, I run the battery down to ~50% in the evening, the inverter shuts off and then the next day starts again.

After thinking about it more, who cares that the battery gets to full (other than for the life of a lead battery), I'm going to pull it down to about 50% by nighttime anyway...right ?

From the below day my CC identified ~750W/h of solar, the load (green line below) runs @ 65Watts from 11:30am - 10 PM (65W*10.5h= 682 Watt/h), so actually using most of what I generated.

The absorption stage below did not complete, the CC went back to bulk probably due to the quick drop in voltage.





The downside of this (for the lead battery) is that it never gets full and stays at 50% most of the time, but even if I had more solar time and got the battery closer to 100% I would plan on doing the same thing and run them down to 50% and get more hours of inverter...

I guess I could experiment with shutting off the inverter at say 75%, then the next day the bulk time would be less giving a little more time for absorption, this might get the battery closer to cycling at a higher voltage and add some battery life?

If anyone is using lead acids for storage, do you run them down this far?

I think the efficiency of the system would decrease if I spent more time at absorption and did not use the full power of the panels at that time, then we would start a topic on dump loads to use everything we can but that's for another time.

I know this is small scale, but I am trying to learn before buying more solar hardware.

Thank you for any inputs.

Matt

 

[sunshine_eggo]

I'm not parsing out your message again. You're talking yourself into something based on belief, not facts. Your expectations are clouding your interpretation. Data are missing from your analysis - inverter idle consumption and inefficiency losses.

Your graph SCREAMS that you have insufficient solar due to poor solar conditions.

Have you made the following changes?

Set MPPT to:

Absorption 14.5V
Fixed time, 4 hours
Float 13.6V
Tail current 2A

Set BMV to:

charged voltage: 14.3V
tail current 3%
Peukert 1.25

Your array is underperforming because of conditions.

1. Unless you have a steep pitch, your panel angle is suboptimal for this time of year, so you get poor performance.
2. Shading is devastating to production. You clearly have a narrow window in which you can get good, unshaded sun, and that is destroying your ability to harvest energy. The plummet at about 1:15 or so in the afternoon is the killer.

Guess what you do when you have poor solar conditions?

MOAR SOLAR!

Are you generating 30-50% MORE kWh in solar than you are using? If the answer is "no", then MOAR SOLAR!

Inverters are most efficient around 30% of their rated max continuous output. It can drop DRAMATICALLY at low power. My "idle" load is about 77W, and my Quattro is barely 65% efficient at that level. If your 70W is less than 30% of the unit's rating, you're using more than 70W.

From a qualitative perspective:

You need to move your solar harvest to capture as much as possible in the earlier hours of the day. Some ways:

More solar in the current location
More solar in an East of South orientation to get more from the morning sun
More solar in a location that has less shading and/or the ability to better tilt the panel (ground array).
Reorient the existing array so it's facing East of South to capture more morning energy.

Until you get more solar, I recommend you cut inverter sooner - about 1.5 hours before the chart indicates. Maybe 12.1V?

EDIT: If you don't have unshaded solar exposure from sunrise to sunset, your array is going to be crippled. The only question is "how much?"

Here's a day in November. It is optimally tilted for year-round performance, and they are unshaded from sunrise to sunset (except for clouds). 1 hour after solar, my array is at 50% of rated (1.5kW vs. 3kW rated):



Clearly I had some clouds mid morning and on, but I sketched a red line indicating my actual potential solar profile, i.e., what it would have looked like if there had been no clouds while I was using/charging with every Watt the array would yield.

My panels are oriented at 165° for this exact reason - I want to catch a little more of the morning sun because this region tends to have clouds in the afternoon. You can kinda see how my bell curve is skewed to the left.

 

[mhanna]

I have checked my settings and they are already very close to what you recommended.

Here is the MPPT:


For My BVM I do have Peukert set to 1.25 and charge efficiency to 85%, but I have the charge voltage set to 16V on purpose, I do not want the battery monitor to reset to 100% by itself until I am ready to do that, this way I can graph a few days of current in and out.

The solar is what it is for now, so I have to work with that.

I will be changing the inverter disconnect to something closer to 65% and see how that goes in getting the battery closer to a full absorption.

After understanding more of the details of lead acid with slow absorption, needing to put in 15% more current than what you get out... for my needs this kills me that there as this is a huge waste too... Honestly if I did not already have these new lead acid batteries, I would go straight to Life Po and from what I understand run them between 20-90 % all the time with no bad effects (maybe top balance once every few months).

Thanks

 

[sunshine_eggo]

For My BVM I do have Peukert set to 1.25 and charge efficiency to 85%, but I have the charge voltage set to 16V on purpose, I do not want the battery monitor to reset to 100% by itself until I am ready to do that, this way I can graph a few days of current in and out.

I don't see a logical reason to fail to permit a sync. All you're logging at that point is ever increasingly inaccurate SoC.

The solar is what it is for now, so I have to work with that.

Then you MUST tailor your usage to your conditions.

I will be changing the inverter disconnect to something closer to 65% and see how that goes in getting the battery closer to a full absorption.

Recommend you terminate all loads until you can truly get back to 100% with a legit sync before you continue forward.

After understanding more of the details of lead acid with slow absorption, needing to put in 15% more current than what you get out... for my needs this kills me that there as this is a huge waste too...

Your voltage profile shows that you fall short of absorption most of the time and the limit is your ~200W of solar. You're not losing that much due to "long absorption" with lead.

Honestly if I did not already have these new lead acid batteries, I would go straight to Life Po and from what I understand run them between 20-90 % all the time with no bad effects (maybe top balance once every few months).

Yep.

As an experiment, consider shifting your usage earlier in the day. Turn on the Phoenix at about 13.1V as the solar is "accelerating." You're using loads more during the period you can pay for it with solar, and you can finish the day at a higher state of charge. You will obviously need to cut-off at an even higher voltage, but you can have the battery sitting overnight at a higher state of charge rather than a lower one - better than nothing.

I actually handle my idle loads in a similar way (it's an off-site property we visit a couple times a month). I power an RV absorption fridge that uses 5kWh/day if I let it run. I don't care to run it all the time because there's nothing in it that can spoil, but I do want to keep it cool to prevent mold. As such I run it about 8-10 hours/day. My fridge + idle loads are about 450W, so as soon as the array is producing about that amount, I'm turning on the fridge with a WiFi outlet on a timer. I get fully charged powering these loads and then before the array cuts below 450W, I cut off the fridge. This ensures that I start the non-charging period at 100%.

It would be better for your batteries to follow a similar schedule. Based on the chart, If you just use power between 9:30 and 2:30, everything in between goes to charging the battery. You can then shift your limit outside that range. Unfortunately, you would need to devise a different means of on/off as you go further out. I don't think assistants would do it since there's no time value on the Phoenix.

 

[12VoltInstalls]

After thinking about it more, who cares that the battery gets to full (other than for the life of a lead battery), I'm going to pull it down to about 50% by nighttime anyway...right ?

If you are going down to ~12.1 to 12.2V that’s not good use of the batteries. It will reduced their service life in my opinion.

anyone is using lead acids for storage, do you run them down this far?

No. 12.1V is my ‘absolute’ low and I prefer 12.2+

cIf I add more solar than I moved the problem from not filling up the batteries to not using all of the solar capacity

That is a dichotomy problem.

You are and would be using all of the capacity- the “extra” or overpaneling are the one-time cost of accommodating for your site conditions.

3-100W solar panels.

In my location a year or so back I didn’t get sun exposure due to trees until 12:30pm. And I lost sun an hour before sunset. I optimized two panels that “lost” a bit at peak but made more moderate watts for a longer period of time.

In your situation, I would maybe buy 3 more like-spec’d panels and arrange them one of two ways: 2S3P, 3S2P. If 2S3P I’d mount them in a shallow arc
This will spread your harvest over a longer time with the overlap acting sorta like 300W of panels for 4 panels at a time.
Alternatively two series strings of three could be positioned two geo directions instead of three.

Secondly: that your one battery voltage goes low but your use seems consistent, adding a second battery in parallel theoretically would make your overnight voltage not go to as low (harmful) a voltage. The risk here is that you’ll have more capacity and if you use it the extra 3 panels may not do anything better than what you are doing now.

For me, facing parallel strings to different compass points improved my harvest substantially. I don’t know your lot but unless it’s “impossible” the above suggested $400+ may -or should- get you going better.

 

[Mike Mas]

If you're looking for solar storage, you should consider lithium, flooded and AGM are more for starting and not really designed nor have any real capacity to store much solar, unless you have many many of them.

Thanks Mike

 

[12VoltInstalls]

flooded and AGM are more for starting and not really designed nor have any real capacity to store much solar, unless you have many many of them.

This isn’t really true.
Lead acid batteries are designed for many things including deep cycle backup by the phone company, and solar power since the 1970s. AGM batteries exist in millions of UPS systems and more fire alarm systems.
Starting batteries are not the only lead batteries.

 

[time2roll]

You would think the first option is to not turn on the inverter until the battery reaches the float stage (using the remote connection on the inverter and load output on the MPPT connected), but #1) The Victron inverter does not have this as an option in the load settings (really Victron...?) and #2) I would not like to use this anyway as hours of strong solar time might go by not being used during the absorption hours that pull little amps to charge the battery.

Another option is to use the relay output of the BMS and trigger the inverter on when the battery has a good SOC (% of full) but again if I start at say 90% the battery still would not be full and the above would still happen. If I wait too long ~99% I am wasting solar energy during absorption.

The best option is to get more solar. Minimum should be 20% to 50% higher than the continuous load.
This will get the inverter started earlier in the day and continue charging while the load is present.

 

[Mike Mas]

Thanks for the reply - Regretfully because of the extreme high amperage of a 12 volt system, they are not the best choice for continuous high amperage since it heats the components like fuses cables etc. creating losses and voltage sag. Making matters worse a 100 ah flooded battery can only store 50% or around 50 amps. Therefore if yyour looking to have a battery to store solar energy duringthe day, you need a higher capacity lithium battery.

To be clear - I'm not saying there are not good flooded battery solar systems - I'm just saying if you plan to run an AC unit or heavy loads there are better choices than 12 volts and flooded batteries.

Thanks Mike

 

[12VoltInstalls]

I'm just saying if you plan to run an AC unit or heavy loads

Oh! I thought you said, “flooded and AGM are more for starting and not really designed nor have any real capacity to store much solar”

Therefore if yyour looking to have a battery to store solar energy duringthe day, you need a higher capacity lithium battery.

Lithium battery options have a number of beneficial features. Getting better all the time!

I store solar energy during the day using lead batteries ??

best option is to get more solar. Minimum should be 20% to 50% higher than the continuous load.

Yup. That’s how I wound up with 800W. The days getting longer is a noticeable improvement right now.

 

[mhanna]

Followup from my tests with my group 31 100 Ah LA deep cycle Interstate battery for solar use.
BTW I have 2 of these and got the same results with both of them but only testing 1 at a time.

With further testing of the lead batteries, I allowed the battery to get to its fullest by manually shutting off my loads and give the battery its 4 hours of absorption via solar. When the sun went down, I turned on the loads and monitored via my Victron smart shunt. I was getting <20 ah of capacity when the inverter shut off (shut off at ~11.9 and then the battery would float back up to 12.2 within minutes). This was slightly above 50% capacity via voltage measurements but only 20% of the rating of the ah of the battery.

I bought a good stand-alone charger and ran it in 'heavy' mode, This allows some higher voltages and disulfates the battery as well. This process took almost 10 hours before the charger said it was done, I never had 10 hours of sun to charge the battery this way. After this 'heavy' charge I ran it on my system and then got 27-28 ah, I did this two times.

As the batteries were only 6 months old, I documented this and brough it back to my local Interstate dealer to say, 'do I have a bad battery'?

The manager was very nice but said leave it with them to test, they kept the battery to charge and test, I got a call the next day to say it's fine and to come pick it up. When I came to pick them up he said it should be good to go and only needed a charge, when I asked if they checked the Ah capacity, he said it just needed a charge. When I asked if I would get 50ah at 50% battery capacity he said that would be under ideal conditions.

I took the battery home, hooked it up and got 35ah out of it, better than what I was getting before but not what I expected. I am guessing they used a higher voltage charger to really put a top on it. After this one time, even with my wall charger I never got more than 27-28 ah after that one time.

I did soooo much research on flooded lead acid batteries and found that they need ~10-15% more charge put in than what you are going to get back, they will lose capacity when cold or when discharged fast and that they will self-discharge in a few months. One article described it as a pitcher with pinholes all over it and you have to maintain the batteries, or you will come back to an empty pitcher one day. And this is when the batteries are new, give them 2-3 years and they will naturally wear more. Also, with my use, leaving the batteries at ~50% soc overnight would not help them with their life.

After trying so much to make these batteries work for me and not getting what I needed I bought a 100 ah lifepo4 Chins battery from Amazon just to try. Chins just happened to be the lowest price and available to ship right away. I am not promoting any particular battery brand, this just happened to be the one I bought.

I got it within 1 week, charged it up with my wall mounted charger and put it in my system, I reset the shunt and turned the loads on and on the first night the shut indicated 101 ah's of discharge before I shut off the inverter. I charged it back up and according to the shunt and charger it only needed the 101 ah of recharge until it was 'full' where the charger shut off. I disabled the 100% sync portion of the shunt so that I could see how it does over several days.

I researched the absorption time for Lifepo and found that depending on the absorption voltage set it may only take 30 - 120 min to top and that except for some top balancing BMSs they don't even recommend or need this. Many articles recommend running them between 20 - 95 % soc regularly.

I have been using it for a few weeks now and love the fact that it will take all the amps allowed to charge from the solar almost right up until the very end and if I don't get it charged to the top its still ok. Tracking the amps via the shunt for discharging and charging seems to be right on.

I have been running it from 25% soc to just shy of 100% and getting 75 ah of usable capacity every day after good solar the prior day. That would be equivalent to 2-3 of my deep cycle lead batteries, and I should not have to worry about damaging them when left at 25% overnight.

Of course, I don't know how long this new lifepo battery is going to last me, but the lead acids are going back on my boat soon and I have never had the lead deep cycles on the boat last more than 4-5 years. With solar use and almost daily cycles I'm sure they would not have even lasted that long.

I'm sure with better lead acid or AGM's these issues could be lessened but I wished to close out my post with what I have learned for me and that from my lead acids to lithium this has been a game changer.

Thanks

 

[Zil]

Longer sunshine hours or more solar panels. If you don't want more solar panel watts, I guess you got to move south.
I successfully ran my microwave, computer office and some other stuff with 6 GC2 batteries connected for 12 volts. I used four 100 watt Renogy panels with a TriStar 45 amp controller. 40 degrees north.