poor battery performance?

[Skip]

I'm trying to understand if the performance I'm getting from my batteries is normal, or if something is wrong.
I turned my system on live about 18 months ago, the end of June 2021 and it has been running continuously since then. Fully off grid - no public power tie in. My house is a power miser. Propane cooking, hot water, clothes dryer and propane/wood heat. All lights LED. Refer and Freezer on timers so they only run during the day. Freezer in the garage where it's never above 40 in the winter.

Here's my setup:
6 Q panels outputting 2500 watts at 48 v DC
4 Kilovault AGM batteries - 2 pairs providing 360 amp hours at 24 v DC (max charge rate 14.1 or 14.2 - depending on which guide I consult - set to 14.1)
Conext inverter providing 220 v to service panel
5500 watt propane generator backup
Primus Air 30 wind turbine

Location: Central Montana West of the Rockies - prairie. Good sun and good wind (when they're available).

All wires and cables sized and torqued to manufacturer's specs.

What happened:
Going into my first fall as the days started getting shorter, I realized that I was going to need to start supplementing the solar with generator power I carefully configured the Conext per the Kilovault and Conext instructions as far as they took me, but the Conext was putting 29 volts into the batteries. This because I did not have the Conext-Kilovault integration guide and had the temperature correction variable set to factory, which was wrong. Until I got that corrected, I had several hours of overcharging over several days. (About two weeks and four tech support people later (altEstore and Schnieder Electric), someone finally sent me the integration guide.)

What's happening now:
Even on days when the batteries get a minimum of 8 hours of good solar charging with full sun, if I have no nighttime wind the batteries are unable to hold up to over 50% by morning. Typically, I'll go to bed with the batteries at around 60% to 65%. The overnight load is less than 3 amps - this consists of a few LED night lights whose amperage are almost immeasurable and a CPAP machine which is about 2 amps at 120 v AC. This doesn't seem right. I'm not expecting good performance during these short winter overcast days with only 1 to 2 hours of generator time in the evening, but with a full day of unobstructed sunshine on the panels, I feel like the batteries should be holding out overnight. 2 or 3 amps shouldn't put them in the red.

After a generator charging cycle of 2 hours, the batteries will immediately drop from 28.2 to around 26 in the time it takes me to get from the generator to the inverter. Then the voltage drops more slowly to around 25.2 (65%).

Yes, I know that the integration guide specifies 8 hour charge cycle with the generator, but that's not the only charging the batteries are receiving and running the generator for 8 hours a day is simply not feasible with fuel costs. Might as well hook up to public power.

Did the initial overcharging of the batteries by the conext damage them in some way?

I'm weighing the pros-cons of spending $2000 on a propane refrigerator vs. $2000 on four more batteries, but I'm not sure if doubling my battery bank will provide $2000 worth of improved performance in these adverse conditions, nor am I convinced now that taking off the refrigerator load altogether is going to make any difference in performance since nearly 100% of the refrigerator run time is direct through-put from the panels, even with moderate overcast.

The only times I feel pleased with the performance of my system are on bright sunny days and during periods of night time gale force winds (15 to 35 mph).

Experimenting with these batteries is a pretty expensive proposition, so any knowledge of reasonable performance expectations is greatly appreciated.

Thanks

 

[Bobert]

Are your batteries inside or outside. Any lead based battery has a significant decrease in performance in colder temperatures

 

[MisterSandals]

(max charge rate 14.1 or 14.2 - depending on which guide I consult - set to 14.1)

This seems odd. Amps?

Assuming 14.1A "rate"

360Ah is 50% usable so 180Ah
180Ah / 14.1A charging = 12.76 hours to recharge from empty

 

[Skip]

Reading some other threads, a light bulb just went on and generated a new related question: How much power is the inverter alone using overnight? The only critical device I need power for at night is my CPAP machine, which itself runs on 12 v DC. The wall plug is a transformer which converts 12v AC to 12v DC. So, if I use my 24v to 12v converter and run DC wiring to the bedroom, I can run the CPAP directly off the batteries and shut down the inverter at night. How much power will that save me over 8 hours?

Are your batteries inside or outside. Any lead based battery has a significant decrease in performance in colder temperatures

Batteries are inside an unheated garage. So temperature is usually around 40 degrees this time of year.

 

[Skip]

This seems odd. Amps?

Assuming 14.1A "rate"

360Ah is 50% usable so 180Ah
180Ah / 14.1A charging = 12.76 hours to recharge from empty

The 14.1 charge rate is voltage - or 28.2 as a series of two. My inverter system is 24 volt.

 

[MisterSandals]

How much power will that save me over 8 hours?

Maybe 30%. (15% each way: inverting to AC and converting back to DC)

You still have 24V to 12V losses but much less than either of the above (5-10%?).
This is a good solution!

The 14.1 charge rate is voltage

Voltage isn't a rate, unfortunate choice of words, and lack of units (V), in the docs. Good to hear you have not throttled your charger!

 

[Bobert]

Reading some other threads, a light bulb just went on and generated a new related question: How much power is the inverter alone using overnight? The only critical device I need power for at night is my CPAP machine, which itself runs on 12 v DC. The wall plug is a transformer which converts 12v AC to 12v DC. So, if I use my 24v to 12v converter and run DC wiring to the bedroom, I can run the CPAP directly off the batteries and shut down the inverter at night. How much power will that save me over 8 hours?

Batteries are inside an unheated garage. So temperature is usually around 40 degrees this time of year.

40 degrees is cold enough to have a decrease in the ability to accept charge especially if your charger does not compensate for temperature (you need higher voltage to properly charge cold lead batteries) age and damage exaggerates this. We use a 48v powered solar AIO inverter in our rv and can extend our power a lot by turning off the inverter at night. Our inverter uses 50 watts an hour idle some AIO units can clear 100 watts.

 

[Skip]

40 degrees is cold enough to have a decrease in the ability to accept charge especially if your charger does not compensate for temperature (you need higher voltage to properly charge cold lead batteries) age and damage exaggerates this. We use a 48v powered solar AIO inverter in our rv and can extend our power a lot by turning off the inverter at night. Our inverter uses 50 watts an hour idle some AIO units can clear 100 watts.

I found the data on Conext - the tare loss is 27 watts. If that is on the AC output, then the amperage over 8 hours is about 1 amp? (I'm not an electrical theoretician.) There is temperature compensation for both the Conext and the Classic 150. Both have battery temp sensors on the battery bank.

 

[MisterSandals]

the tare loss is 27 watts. If that is on the AC output, then the amperage over 8 hours is about 1 amp?

27W / 48VDC = .56A (the rate)
.56A x 8 hours = 4.48Ah (the amount, at 48V, your battery)

27W / 120VAC = .225A (the rate)
.225A x 8 hours = 1.8Ah (the amount, at 120VAC)

 

[Skip]

I've been doing more analysis on this and am convinced that the overcharging has damaged the batteries. When charging is removed, the batteries drop from 100% to 60% in less than 2 hours with a load of only 2 amps. Using an online battery life calculator and Peukert's Law number of 1.1, that level of discharge with 2 amp load should take about 100 hours!

Peukert Number Battery Life Calculator

Time to make a warranty claim.

 

[octal_ip]

How are you measuring your state of charge? Voltage alone isn't entirely reliable, particularly in extreme conditions.
Your batteries may be in better condition than you think. How do they perform under high loads (1000W or more)?

 

[MisterSandals]

I reread from the top and read the battery manual.

I was a little surprised that the equalisation voltage is 14.1V. AGM often specs on 15, close to 16 for equalisation.

After a generator charging cycle of 2 hours, the batteries will immediately drop from 28.2 to around 26 in the time it takes me to get from the generator to the inverter. Then the voltage drops more slowly to around 25.2 (65%).


65% Soc for 12 cells is (2.1V x 12 = 25.2V) as you say.

Wondering if batteries fully absorbed in 2 hours of generator charging. Do you know if the current was tailing off when you stopped charging? I do not know the characteristics of these batteries but it’s possible they are not fully charged.

The doc says:
>>
The charge current must taper down to a level between 1% and 2% of the total battery amp-hours while maintaining the absorption voltage.
>>

I dunno. Hope this helps. Those are nice batteries, I would think they would be VERY hard to kill.

 

[Skip]

I reread from the top and read the battery manual.

I was a little surprised that the equalisation voltage is 14.1V. AGM often specs on 15, close to 16 for equalisation.

After a generator charging cycle of 2 hours, the batteries will immediately drop from 28.2 to around 26 in the time it takes me to get from the generator to the inverter. Then the voltage drops more slowly to around 25.2 (65%).
View attachment 124302

65% Soc for 12 cells is (2.1V x 12 = 25.2V) as you say.

Wondering if batteries fully absorbed in 2 hours of generator charging. Do you know if the current was tailing off when you stopped charging? I do not know the characteristics of these batteries but it’s possible they are not fully charged.

The doc says:
>>
The charge current must taper down to a level between 1% and 2% of the total battery amp-hours while maintaining the absorption voltage.
>>

I dunno. Hope this helps. Those are nice batteries, I would think they would be VERY hard to kill.

Kilovault claims the following in their advertising:
-Super-Fast Charging - High charge rates allow the 2100 PLC to go from 50% up to 90% state of charge in under an hour.
-Partial State of Charge Applications - Pure lead + carbon = greater cycle life in both PSoC and non-PSoC off-grid operations. In PSoC/daily cycling applications, the batteries do not need to be fully charged every day, and they will still get 3000 cycles.
In all charging scenarios, longer days of sunshine, wind, generator charging of various durations from half hour to two hours, the behavior is similar: as soon as charging is taken away, the batteries immediately drop to 26 volts, regardless of load and then drop to 25 volts over two to three hours, then 24.6 (50%) or less by morning with a mere 5 amps of load.
After more research I'm convinced that the early over charging damaged the batteries while altEstore, Kilovault and Schneider Electric were looking for the right Conext charge settings for the Kilovault. I think I now have the data I need to submit a warranty claim to Kilovault.

How are you measuring your state of charge? Voltage alone isn't entirely reliable, particularly in extreme conditions.
Your batteries may be in better condition than you think. How do they perform under high loads (1000W or more)?

The batteries by themselves don't hold heavy loads at all. If there is no solar and no wind, and the batteries are at 70%, a two minute load of 2000 watts from the pump will send the batteries down to 40%, but once the load is removed, they will bounce back to something like 60 of 65%. Basically, I try very hard NOT to have the pump cycle when I don't have solar or strong wind. Microwave? Forget it. Coffee maker? Nope.

 

[octal_ip]

The batteries by themselves don't hold heavy loads at all. If there is no solar and no wind, and the batteries are at 70%, a two minute load of 2000 watts from the pump will send the batteries down to 40%, but once the load is removed, they will bounce back to something like 60 of 65%. Basically, I try very hard NOT to have the pump cycle when I don't have solar or strong wind. Microwave? Forget it. Coffee maker? Nope.

Ok, I only ask as internal resistance is one of the most important indicators of battery health. If they're not sustaining a heavy load like they used to, you're probably right in that they're reaching end of life. This will be important to mention in your claim with the vendor.

 

[Skip]

Still working this issue. Kilovault seems to be suggesting that the poor battery performance is entirely temperature related. I can't believe that having the batteries at 40 degrees below nominal temp of 77 should result in a 90 to 95 percent reduction in the ability to hold charge. I'm taking measures to get the batteries up in temp, but given power resources, I'm not sure I can regularly maintain much more than 60 deg. Even if I had them under the living room coffee table, they wouldn't normally be more than 65. Who keeps their house at 77 degrees?
So far, I've see no improvement in performance by raising the battery temperature to around 60 to 70 degrees.
Am I right in thinking that although lower temperature may by a minor contribution to poor performance, the real problem lies elsewhere?
Thanks

 

[jberger]

Temps have a very strong correlation to charging and discharging rates on Lead Acid Batteries. It will take hours for the center of the batteries to get to the room temperature, probably a day or more. So don't count out the temperature performance issues yet.
The manual shows a reduction in capacity between to between 80-85% of total around 40 degrees. So if you are limiting yourself to just 50% discharge, you only have 35% to play with assuming your batteries are fully charged when you start the evening.

Looking at the kilovolt manual, it's pretty through on the charging specifics, temperature impacts, etc.

https://kilovault.com/wp-content/uploads/2021/10/KiloVault-2100-PLC-Installation-and-User-Manual-Rev-1.05-a.pdf

How deep are you discharging the bank on a daily basis?
Just based on your install date and December 17 2022, you've got 565 cycles, thus far.
If you've haven't been charging to 100% every day, keeping them at 40 degrees and discharging below 50% you are probably just wearing them out early.

I would start by fully charging them and letting them equalize per the manual. Then let them settle and check voltage. I'll bet at least one of them will not be holding a full charge and will need to be charged more.
Do you have a separate charger you can use on a battery by battery basis?

If you want to spend money, I'd look into LFP batteries instead of AGM. They would be a lot more tolerant of partial charge, take the charge from the generator much faster, and handle your heavy loads without as much sag.

 

[Skip]

Thanks
I have the manual and have poured over it. It is pretty vague on temperature effects on charging/discharging. The only chart is Figure 7 in Section 4.2.2 the vertical axis is time and the horizontal axis is temp. This doesn't explain to me why the batteries instantly drop to 80% upon removal of active charging at between 60 and 70 degrees. Keep in mind that Kilovault, in their marketing statements, claims rapid charging with a full charge being attained in under an hour! They also claim that partial charging does not affect life of the battery.

As it stands now, I'm in a situation where I'm not getting enough energy to be able to keep the batteries warm without running the generator 24/7 with an electric space heater, which is not feasible due to fuel limitations. For batteries that are listed as having an operating range of -40deg F to 135deg F, to be at 40 or 50 degrees F and almost no capacity just doesn't seem right. I've used both the electric heater and a small propane heater for several days to get the core of the batteries up into a better range. Also, a 100 watt bulb running as much as it's able without killing the batteries, which are now in a small insulated enclosure. This has NOT helped their ability to hold charge at all.

Lessons learned: Sales staff won't tell you the full truth, or they just don't know. They don't understand climate implications for the buyer's location. Don't use expensive batteries for initial installation. There is no such thing as a free education. User's manuals only tell you, typically in technical mumbo-jumbo, what the devices will do under ideal circumstances, but they never teach you what to expect in real world applications. They should know that a fully off grid installation in a northern plains environment where winter temps routinely drop to minus double digits and maintaining survivable temps in the living area alone becomes a challenge, are probably not suitable for Lead Acid storage systems. I wouldn't think that putting lead acid batteries next to my wood stove in the living room a very safe solution. They expect me to keep the batteries to 77 degrees. I'm happy if I can keep my living room at 65 in the winter and that's the warmest part of the house. Taking more energy to make energy is a total system failure.
Unless Kilovault will acknowledge that these batteries are damaged (which I still believe happened when improper inverter settings caused several weeks over overcharge) and send me replacements, then I'm done with lead acid.

 

[Skip]

Thanks
I have the manual and have poured over it. It is pretty vague on temperature effects on charging/discharging. The only chart is Figure 7 in Section 4.2.2 the vertical axis is time and the horizontal axis is temp. This doesn't explain to me why the batteries instantly drop to 80% upon removal of active charging at between 60 and 70 degrees. Keep in mind that Kilovault, in their marketing statements, claims rapid charging with a full charge being attained in under an hour! They also claim that partial charging does not affect life of the battery.

As it stands now, I'm in a situation where I'm not getting enough energy to be able to keep the batteries warm without running the generator 24/7 with an electric space heater, which is not feasible due to fuel limitations. For batteries that are listed as having an operating range of -40deg F to 135deg F, to be at 40 or 50 degrees F and almost no capacity just doesn't seem right. I've used both the electric heater and a small propane heater for several days to get the core of the batteries up into a better range. Also, a 100 watt bulb running as much as it's able without killing the batteries, which are now in a small insulated enclosure. This has NOT helped their ability to hold charge at all.

Lessons learned: Sales staff won't tell you the full truth, or they just don't know. They don't understand climate implications for the buyer's location. Don't use expensive batteries for initial installation. There is no such thing as a free education. User's manuals only tell you, typically in technical mumbo-jumbo, what the devices will do under ideal circumstances, but they never teach you what to expect in real world applications. They should know that a fully off grid installation in a northern plains environment where winter temps routinely drop to minus double digits and maintaining survivable temps in the living area alone becomes a challenge, are probably not suitable for Lead Acid storage systems. I wouldn't think that putting lead acid batteries next to my wood stove in the living room a very safe solution. They expect me to keep the batteries to 77 degrees. I'm happy if I can keep my living room at 65 in the winter and that's the warmest part of the house. Taking more energy to make energy is a total system failure.
Unless Kilovault will acknowledge that these batteries are damaged (which I still believe happened when improper inverter settings caused several weeks over overcharge) and send me replacements, then I'm done with lead acid.

some more notes: last week I tore the battery bank apart and relocated it to the other side of the wall where I can insulate it better in an attempt to raise the temperature. At that time I checked the voltage of each separate battery. Within an hour of taking them off a five hour full sun solar charging session, they all read the exact same voltage of 12.9, which per Kilovault is 80%. This has been typical for quite some time. The moment charging is removed, they instantly drop to 80% SOC.
On a daily basis, the batteries go down to 50% every night. Sometimes to 45%. (24.4v to 24.6v) That's with a load under 1 amp - about 100 watts - and starting out at 65% (25.2v) when I go to bed. Really, the only measurable overnight load is a CPAP machine (medical device). Everything else is off. I can run the generator for hours in the evening, but after shutting it down, by the time I'm in bed, the batteries are already down to 65%.

The Kilovault manual advises strongly against using the equalization charge.

This behavior is not simply a winter short solar charge cycle issue - Even in summer the batteries will be down to 80% at sundown and close to 50% in the morning. It is just not such a crisis in the summer because the nights are so short and the sun is often up before I am so that one amp overnight load is on for under 8 hours.

I don't want to spend the money, but I realize now that I'll never get satisfaction from lead acid. Taking it out of retirement savings just means I have to die a year earlier than planned.
What gets me is that AltEstore designed the system for me knowing the geographic location. Don't use lead acid in cold climates!