Easy way to prevent overcharging of FLA or AGM battery bank?

[OTG 4 LIFE]

Hi, this is my 1st post so plz 4give if I'm asking a dumb question but, I have researched the problem exhaustively to the best of my ability and I'm on a time crunch, any help is GREATLY appreciated!

I have installed a solar system in a small RV so I'm not a total n00b, and I've read a lot but I think my problem is somewhat unique because of my situation.

I bought an off-grid cabin for my family and am LOVING it, it's been my life's dream. Previous owner had a DIY system that was built without really understanding, he just copied the system his dad built to the best of his ability using cheap and OLD parts.

I plan on redoing the whole thing AFTER I get back from a business trip that will require me to be gone for months. Meanwhile I need a quick solution that will keep my family from going w/o power while I'm away...

The battery bank I inherited is flooded lead acid, which worked fine until now (I think they are just at the end of their life cycle).

I have a bunch of LiFePo batteries for the big overhaul but, the current charger controller is a dinosaur. I'm sposta already be in Texas and every day I put off leaving is $ lost. SO...

I want to just replace the old batteries with another type of lead acid battery for now, so I don't have to change anything else. I'm thinking of using AGM cuz they're low maintenance and I think the old FLA ones may still be working if my wife had added water while I was away over the last few months, or they may have been overcharged - which brings me to my point.

Is there anything I can EASILY install on the input line into the battery bank to prevent overcharging? I have LVDC to prevent damage from overdraining on my systems, but the ancient charge controller doesn't have anything like a "high voltage disconnect" feature and, the diesel generator we use for most of our current power needs (there's only 2 solar panels currently on the roof - many more in the garage that are going up when I get back but, not nearly enough for now) is something my wife will likely forget to turn off many times while I'm gone.

So, is there a simple way to install a "HVDC" (High Voltage Disconnect) for the battery bank to prevent overcharging from the generator if it gets left on while I'm away?

I figure replacing the FLA with SLA batteries will take care of her forgetting to add water while I'm gone. But I've read that SLA batteries are vulnerable to overcharging, and I need a quick and easy way to make sure that doesn't happen while I'm away over the winter.

Thanks for reading all this and thanks in advance for any helpful suggestions that would be quicker and easier than replacing the charge controller with something not made in 2003 (yes, I know it's what I need to do eventually... I just need a quick fix for the battery bank until then).

 

[Solarcabin Channel]

What is the brand of the old controller and how many watts and volts is your current battery bank?

I can't imagine it has just a shunt controller and it probably has high voltage cut off.

 

[Hedges]

Failure to fully charge is said to be the primary way lead-acid batteries get killed.
Charge controller should limit voltage so not over-charged.

Need to check on balance between cells or batteries occasionally. Or at least resting voltage, if several cells are combined in one battery. If FLA, check specific gravity. In the event some cells get to lower SoC, other cells will be over-charged. The low cells will proceed to die. Separately charging (if accessible) or equalization, can be used to get all cells to similar SoC.

What is between the generator and the batteries? Inverter/charger? Stand-alone battery charger? What kind?

 

[OTG 4 LIFE]

It occurred to me that I should probably post pics of the current setup so my question (maybe) doesn't sound quite as retarded.

The pic showing the entire setup has the charge controller on the top left (a 60A PWM), and in the top right there's a thick line running into a box labeled "PV to Con." and to the right of that is "Con to Battery." Bottom right is "12v from batt" handwritten in black marker, and bottom left is a breaker box labeled "generator" with a 20A line going to the inverter and another 20A breaker going to the house...

Anyway that would seem normal enough except that when the generator is on, the light on the charge controller flashes to indicate charging, and the other anomaly is that no power seems to come from the panels unless the generator is running... which makes me think that the line in to the box labeled "pv array to con" may be the ONLY line in and includes the generator as well... I don't see any other obvious "line in" to the entire setup here, and the fact that the charge controller indicates when the generator is on means that there must be a line in from the generator somewhere...

Anyway I know that the entire thing needs a major overhaul, but I have to leave my family here alone for a few months for a major business trip before I can do that and just need a quick "patch job" for now.

I could just replace the ten 6v batteries wired in series to make a 12v system but, I would really prefer to use something that doesn't require regular maintenance in case my wife doesn't add water and the batteries get fried again while I'm away.

I guess I'm just wondering if I can use AGM instead of FLA with the current charge controller... I know it's *supposed* to prevent overcharging, but every "modem day" charge controller I've seen has different settings for different types of batteries so I'm nervous about changing the battery type, even to another type of lead acid battery, and was thinking that an additional "HVDC" would be wise, just as there's an additional LVDC that kicks in before the one on the charge controller when the voltage drops on the battery bank...

Maybe the additional High Voltage Disconnect on the line into the battery bank is unnecessary though. Would it be safe to just switch from FLA to AGM and leave everything else as it is?

 

[Solarcabin Channel]

It occurred to me that I should probably post pics of the current setup so my question (maybe) doesn't sound quite as retarded.

The pic showing the entire setup has the charge controller on the top left (a 60A PWM), and in the top right there's a thick line running into a box labeled "PV to Con." and to the right of that is "Con to Battery." Bottom right is "12v from batt" handwritten in black marker, and bottom left is a breaker box labeled "generator" with a 20A line going to the inverter and another 20A breaker going to the house...

Anyway that would seem normal enough except that when the generator is on, the light on the charge controller flashes to indicate charging, and the other anomaly is that no power seems to come from the panels unless the generator is running... which makes me think that the line in to the box labeled "pv array to con" may be the ONLY line in and includes the generator as well... I don't see any other obvious "line in" to the entire setup here, and the fact that the charge controller indicates when the generator is on means that there must be a line in from the generator somewhere...

Anyway I know that the entire thing needs a major overhaul, but I have to leave my family here alone for a few months for a major business trip before I can do that and just need a quick "patch job" for now.

I could just replace the ten 6v batteries wired in series to make a 12v system but, I would really prefer to use something that doesn't require regular maintenance in case my wife doesn't add water and the batteries get fried again while I'm away.

I guess I'm just wondering if I can use AGM instead of FLA with the current charge controller... I know it's *supposed* to prevent overcharging, but every "modem day" charge controller I've seen has different settings for different types of batteries so I'm nervous about changing the battery type, even to another type of lead acid battery, and was thinking that an additional "HVDC" would be wise, just as there's an additional LVDC that kicks in before the one on the charge controller when the voltage drops on the battery bank...

Maybe the additional High Voltage Disconnect on the line into the battery bank is unnecessary though. Would it be safe to just switch from FLA to AGM and leave everything else as it is?

Not seeing any pics.

You may need to edit your post and click on the pic after you upload to add it.

In general, yes you can replace flooded with AGM with that controller for now and get a newer controller for AGM and LI later.

 

[Hedges]

Measure what voltage is reached. Compare that to allowed AGM charge voltage. They are less forgiving than FLA; you can't replace lost water.

If you put a lot of money into batteries, consider getting charge control that supports their desired settings.

 

[OTG 4 LIFE]

Failure to fully charge is said to be the primary way lead-acid batteries get killed.
Charge controller should limit voltage so not over-charged.

Need to check on balance between cells or batteries occasionally. Or at least resting voltage, if several cells are combined in one battery. If FLA, check specific gravity. In the event some cells get to lower SoC, other cells will be over-charged. The low cells will proceed to die. Separately charging (if accessible) or equalization, can be used to get all cells to similar SoC.

What is between the generator and the batteries? Inverter/charger? Stand-alone battery charger? What kind?

Hedges, thank you so much for the response! I was posting the pics and description of the current setup while you were posting your response apparently, hopefully that helped some.

I hear you on the importance of all the cells being balanced and I used to check that and they were all equal. But then I was away for a few months and my wife didn't add water, I think at least some cells ran completely dry bcuz I checked the voltage and some are significantly different from others now. In short, my current battery bank is no longer functioning adequately. I ran the generator all day a few days ago and the charge controller never indicated that it was at a full charge like it would have before she let the batteries run dry.

I just need a quick fix, and ideally one that would not require adding water so I don't have to worry about her forgetting again (I'll be gone for several months most likely).

Do you think I could just replace the FLA with AGM and have it work for at least 6 months (long enough for me to get back and get everything planned out and buy the new equipment for the complete overhaul that is obviously needed for the long term?

Thank you SO MUCH for your help! I know this is an unusual situation and it's a bit much for me at my current level. I could probably figure it out but the need to be gone yesterday for the business trip has me seeking help from those with more experience...

 

[OTG 4 LIFE]

Attempting to re-post pics one at a time... this is the charge controller

 

[OTG 4 LIFE]

Thank you Solarcabin Channel for your response as well, just saw that I had two replies while making the original attempt at pics....

Here's the entire setup (inside the kitchen pantry, the nearest spot in the house to the battery bank box outside

 

[OTG 4 LIFE]

Left and right sides of charge controller (I realized I had to shrink the file sizes to post em, the originals were too big)

 

[Hedges]

AGM should be great, assuming
1) Max charge voltage is not too high, and any automatic equalizing cycles are disabled
2) Low voltage cutoff prevents over-discharge.

AGM has shorter calendar life and higher cost than FLA. For both types, wide range of quality/cycle life and price available.

FLA can be enhanced with catalytic recombining caps or automatic waterers, or manual manifold, just push a plunger occasionally.

I don't have that much experience with their care and feeding. I paid $5000 3 years ago (would be $6000 today) for a 20 kWh gross, 14 kWh usable SunXtender bank. Hope to get 10+ years, mostly float occasionally cycling. Others here have run forklift or Rolls Surette FLA for 20 years, shallow cycling for the most part, I think.

LiFePO4 can be better, but requires a number of considerations so you have to take time to do it right.

 

[Hedges]

Schneider PWM SCC should be fine for lead-acid if voltage setting is suitable.
I'd have qualms about using that for lithium, but them I'm cautious with "smart" things that can disconnect, or worse.

In the future, an MPPT charge controller should give better regulation. Some can fail shorted and over-voltage everything, while others have an isolated design preventing that issue. Lithium BMS can't withstand excessive voltage coming from SCC.

 

[OTG 4 LIFE]

Measure what voltage is reached. Compare that to allowed AGM charge voltage. They are less forgiving than FLA; you can't replace lost water.

If you put a lot of money into batteries, consider getting charge control that supports their desired settings.

That sounds like the way to go. I definitely need to replace the charge controller but was hoping to put that off until I get back.

I knew that AGM batteries were "less forgiving," that was my main reason for the post. I think your advice to check & compare the voltages is a good way to make sure I don't buy expensive AGM batteries only for them to get fried while I'm away, heh... I just don't trust this older charge controller and don't really have time to replace it rn (I'm already having to do lots of explaining to my business partners for every day that I'm still here)

I currently have ten 6v Trojan FLA batteries rated at 225Ah for 20hrs and 185Ah for 5hrs.

I'm not *terribly* concerned about the calendar life of AGM vs FLA since I'm using them as a "patch job" and really just need them to work while I'm away. I have a pallet of LiFePo batteries (SOG if memory serves, I hope they're decent, I saw a good deal and grabbed it without researching them as much as I would have if I'd had time to without someone else possibly buying them out from under me), and plan to upgrade charge controller and switch to the LiFePo and add panels, and put another system on the workshop and lots of projects when I have time, heh... just need to make sure the wife & kids have power while I'm away making the $ to pay for it all, heh

 

[OTG 4 LIFE]

Schneider PWM SCC should be fine for lead-acid if voltage setting is suitable.
I'd have qualms about using that for lithium, but them I'm cautious with "smart" things that can disconnect, or worse.

In the future, an MPPT charge controller should give better regulation. Some can fail shorted and over-voltage everything, while others have an isolated design preventing that issue. Lithium BMS can't withstand excessive voltage coming from SCC.

Thank you SO MUCH for the confirmation! I have heard the water boiling in the FLA batteries when the generator was left on for longer than it should have been and I'm guessing that's not normal, so I was concerned about just blindly switching to AGM not knowing how everything was set up by the previous owner (for all I know he was charging the batteries with 12v which, I don't know if that's okay with them being wired in series in pairs to make a 12v system... but I guess whatever it is, it's been working for many years now until my wife let the water go dry so, it's probably okay and that voltage check will give me peace of mind about spending all that $ to replace the FLA with AGM when I plan on replacing the AGM with LiFePo as soon as time permits. And definitely getting an MPPT controller with settings for specific battery types once I get back!

I appreciate you confirming that the charge controller I have should be compatible with AGM (assuming input voltage is within AGM tolerances), that was a big concern for me.

I am so grateful for everyone's help, this forum is awesome!

 

[pollenface]

So, is there a simple way to install a "HVDC" (High Voltage Disconnect) for the battery bank to prevent overcharging from the generator if it gets left on while I'm away?

I figure replacing the FLA with SLA batteries will take care of her forgetting to add water while I'm gone. But I've read that SLA batteries are vulnerable to overcharging, and I need a quick and easy way to make sure that doesn't happen while I'm away over the winter.

As long as the charger attached to the generator goes into "float" there shouldn't be an issue.

lead acid batteries need more volts when charging during winter, going from flooded to AGM I would set temp compensation to -4mv/c/cell

 

[MichaelK]

Trying to scrape details out of your posts, what I'm seeing is that you have 5 parallel strings of 6V golf-cart batteries, and two panels in the roof of unknown wattage. Is that correct?

This is more or less the reason why your system is dying, and just replacing the batteries is just going to mean you start killing a second set.

With 10 batteries, you have 5 parallel strings of 225Ah each at 12V. That amounts to a total of 1125Ah of battery capacity. No two panels of any size whatsoever could properly charge a battery bank that large.

Both Trojan and Rolls recommend 1/8th of C as the proper charge rate for their golf-cart batteries. So, for a 1125Ah battery bank, that works out to be 1125Ah/8 = 140A. That is really, really high. There is no single charge controller on the market that can handle amperages that high. Even at only 1/10th of C, that's still 112A.

I can't find any information with a quick surf about your controller, but it looks like Schneider's older 40A PWM controller. That means you are limited to selecting solar panels in the 18-20V range, wired in parallel to charge your battery. To get an honest 40A, assuming you can get about 85% of nameplate out of your panels, that works out to be (40A X 12.5Vcharging)/0.85 = 588W.

How big are the panels on the roof right now? Are they 100W? If yes, you could immediately upgrade the system with four additional panels, all wired in parallel. ~600W will likely give you the 40A your controller can handle.

I can't say whether or not your batteries are salvageable, chronic undercharging is typically how lead-acid dies, and that appears to be exactly what has happened. Still, 40A is not even 1/20th of C, so I'm not going to expect any miracles.

In the long-term, after you come back from your trip, gut the entire system and start over from scratch. Go with larger L-16 or larger batteries and reduce the number of parallel string to just one or two. At 48V, a string of eight 6V L-16 batteries will have more stored energy than your five parallel strings at 12V. 18.2kWh vs 13.5kWh. At that point we can figure out how to salvage the smaller panels you have now. Most likely, the six panels could be wired into one parallel string at ~108V, and pair those with larger residential grid-tie style panels. Maybe three wired in series to get ~108V.

Of course though, high-voltage strings of panels will NOT work with the old controller you have now. But, getting a modern MPPT controller in the 60A range will allow you to upgrade to around 2800-3000W of panels, which your new batteries will be very appreciative of.