Battery voltage drop

[Camp Host]

New battery: 12v Lifepo4 230ah - solar charge to 14.6v - resting voltage 13.8v until sun goes down... however at night the voltage drops to 12.8. Is this normal?
My system: 4x100w panels, Epever 4210an controller, MT-50.
My charging parameters are:

 

[12VoltInstalls]

at night the voltage drops to 12.8. Is this normal

Maybe- some of the cheap LiFePo batteries do not contain cells that ‘hold’ at what we might expect to be normal for LiFePo (14.2V-14.6VDC) if ‘we’ bought ‘good’ batteries.

With my cheaper batteries 13-13.4V is normal (measured). While I never capacity tested them, napkin math suggests that, roughly, they put out their labeled amp hours. For the price I was willing to pay I got what I paid for with satisfactory performance.

My system: 4x100w panels, Epever 4210an controller

The voltage you see with the sun out and charging is not reflective of either the rested battery voltage, nor the present disconnected battery voltage. Since the 4210 must present a voltage greater than the static battery voltage at any time to provide current to actually charge the batteries, the voltage shown is ‘weighted’ up as voltage displayed or measured might be thought of as an average of the present static battery voltage and the voltage of the SCC (it is not literally an average, I am providing a visual analogy).

Other factors ignored, you need ~200W of panels for every 100Ah of battery (at 12V nominal) to successfully charge the battery bank. You are skating just below that, and assuming you are using some of the solar power over the day you may not be fully charging the battery daily. It also can take an exceedingly long time of 14.6V charging for the LiFePo to achieve full charge or ‘saturation’ when charging. With LiFePo4 that is not harmful (ignoring internal cell balance issues btw).

I hope this information is helpful.

*if you have a means to capacity test your battery, perhaps you should if you think the battery ain’t quite right. If it makes the labeled amp hours, then you are just experiencing the effects of buying batteries that you didn’t need to sell one of the children to pay for it- metaphorically speaking. If it doesn’t put out- warranty claim

 

[mikefitz]

solar charge to 14.6v - resting voltage 13.8v until sun goes down

... however at night the voltage drops to 12.8. Is this normal?

I don't think you have a battery issue.
The charge volts are perhaps too high, causing the battery to enter protection mode. The 13.8 volts you are seeing before the sun goes, is from the charger , not the battery.
Monitor the charge current, if it drops to zero under charge, its the BMS entering protection.

Suggest lowering the charge volts, boost and equalise, to lower values, try 14.0 volts.
Float is too high for lithium, set to 13.4 or 13.5 volts. ( this is the resting voltage of a 'full' battery)

The 12.8 volts you are seeing, is not true cell volts due to the charge fets being off. Try connecting a load of a few amps , you should see the true battery voltage.

What battery do you have, is it possible to view BMS status via an app?

Mike

 

[Mattb4]

You have a fairly high voltage of 14.6. It may be causing a high runner cell to trip the BMS and thus you are not getting a good charge. You might consider dropping it down some. New batteries cells are prone to not be in balance.

 

[Camp Host]

Maybe- some of the cheap LiFePo batteries do not contain cells that ‘hold’ at what we might expect to be normal for LiFePo (14.2V-14.6VDC) if ‘we’ bought ‘good’ batteries.

With my cheaper batteries 13-13.4V is normal (measured). While I never capacity tested them, napkin math suggests that, roughly, they put out their labeled amp hours. For the price I was willing to pay I got what I paid for with satisfactory performance.

The voltage you see with the sun out and charging is not reflective of either the rested battery voltage, nor the present disconnected battery voltage. Since the 4210 must present a voltage greater than the static battery voltage at any time to provide current to actually charge the batteries, the voltage shown is ‘weighted’ up as voltage displayed or measured might be thought of as an average of the present static battery voltage and the voltage of the SCC (it is not literally an average, I am providing a visual analogy).

Other factors ignored, you need ~200W of panels for every 100Ah of battery (at 12V nominal) to successfully charge the battery bank. You are skating just below that, and assuming you are using some of the solar power over the day you may not be fully charging the battery daily. It also can take an exceedingly long time of 14.6V charging for the LiFePo to achieve full charge or ‘saturation’ when charging. With LiFePo4 that is not harmful (ignoring internal cell balance issues btw).

I hope this information is helpful.

*if you have a means to capacity test your battery, perhaps you should if you think the battery ain’t quite right. If it makes the labeled amp hours, then you are just experiencing the effects of buying batteries that you didn’t need to sell one of the children to pay for it- metaphorically speaking. If it doesn’t put out- warranty claim

Let me start by saying thank you for taking the time to help me with this, I really do appreciate it. Going from SLA to LiFePo4 is a whole new ball game for me. This new battery is: LiTime 12V 230Ah Plus Low-Temp Protection Deep Cycle LiFePO4 Battery, Built-in 200A BMS... I realize that it takes time so "solar" charge to 14.6, and their manual even suggests 800w to be able to charge in a day. That said we have had some cloudy days so wasn't expecting much. So when the charger arrives I want to charge it up to the 14.6 and start at that point.
I did alot of searching for the "right" values to enter, but in the end I contacted LiTime support and this is what the sent me.
Thank you for your patience. I am an old dog trying to learn a new trick

 

[Camp Host]

You have a fairly high voltage of 14.6. It may be causing a high runner cell to trip the BMS and thus you are not getting a good charge. You might consider dropping it down some. New batteries cells are prone to not be in balance.

Thanks, that's what I am hearing.

 

[Camp Host]

I don't think you have a battery issue.
The charge volts are perhaps too high, causing the battery to enter protection mode. The 13.8 volts you are seeing before the sun goes, is from the charger , not the battery.
Monitor the charge current, if it drops to zero under charge, its the BMS entering protection.

Suggest lowering the charge volts, boost and equalise, to lower values, try 14.0 volts.
Float is too high for lithium, set to 13.4 or 13.5 volts. ( this is the resting voltage of a 'full' battery)

The 12.8 volts you are seeing, is not true cell volts due to the charge fets being off. Try connecting a load of a few amps , you should see the true battery voltage.

What battery do you have, is it possible to view BMS status via an app?

Mike

The battery is: LiTime 12V 230Ah Plus Low-Temp Protection Deep Cycle LiFePO4 Battery, Built-in 200A BMS

 

[RV8R]

The battery is: LiTime 12V 230Ah Plus Low-Temp Protection Deep Cycle LiFePO4 Battery, Built-in 200A BMS

LiTime 12V 230Ah Plus Deep Cycle Lithium Battery

LiTime lifepo4 lithium deep cycle battery 12v 230ah Low-Temp Protection perfect for RV, trolling motor and home energy back up. 12v 230ah deep cycle lithium battery.

ca.litime.com

Always good to have the exact model & specs & manual ,,, or anything else dcumented from the Battery Manufacturer . Says a paper manual comes with it ,,, do you have a link to a pdf manual you can post here ?

Welcome to the forum @Camp Host !!

 

[Camp Host]

LiTime 12V 230Ah Plus Deep Cycle Lithium Battery

LiTime lifepo4 lithium deep cycle battery 12v 230ah Low-Temp Protection perfect for RV, trolling motor and home energy back up. 12v 230ah deep cycle lithium battery.

ca.litime.com

Yes a paper manual came with it, but no pdf that I could find. I looked at the SPECS... a few were helpful, most above my comprehension. I did make the changes that Mikefitz and Matb4 suggested, and it seems to be working much better. I will need to give it more time. Thanks for you reply.

View attachment 205103



Always good to have the exact model & specs & manual ,,, or anything else dcumented from the Battery Manufacturer . Says a paper manual comes with it ,,, do you have a link to a pdf manual you can post here ?

Welcome to the forum @Camp Host !!

 

[mikefitz]

I want to charge it up to the 14.6

Because the BMS has protection settings that disable charging you will find 14.6 volts is too high. The battery enters protection and will show incorrect volts at its terminals.
Almost all 'off the shelf' batteries will have unbalanced cells leading to issues where the charge volts are too high.
A lithium battery with a low charge current compared to capacity, will be almost full by the time the battery volts exceed 13.8 volts. It's not necessary to charge to 14.6, in fact its probable the battery won't reach that value. When under charge and in protection, the voltage you see is that provided by the charger, don't confuse charger votage with battery volts.
14.0 volts or slightly higher, 14.2 volts is more than adequate to charge your battery. Using higher voltages will have no advantage and are possible stressful.

 

[sunshine_eggo]

12.8V-ish is a very suspicious voltage for LFP especially when it doesn't make sense the battery should be at 12.8V.

It often indicates:

1) battery has engaged charge protection due to a single cell over-volt due to cell imbalance.
2) BMS has entered a standby/low power mode.

Either of the above can be confirmed by drawing a small load for a few minutes - the voltage will "jump" up to an actual 13.X volts.

FWIW, if you're patient, LFP batteries can attain very near 100% SoC (99.7% in my case) at a measly 13.6V if you're in no hurry:

LFP full charge @ 3.4V/cell

Thought I'd try a little something on a cheap 12V I've been testing... Charge to 20A @ 13.6V (3.4V/cell), 2A tail current. When testing at cell level and dealing with testers that don't have separate sense leads, lead resistance plays a big role, and I would typically observe cells get charged...

diysolarforum.com

 

[Camp Host]

Because the BMS has protection settings that disable charging you will find 14.6 volts is too high. The battery enters protection and will show incorrect volts at its terminals.
Almost all 'off the shelf' batteries will have unbalanced cells leading to issues where the charge volts are too high.
A lithium battery with a low charge current compared to capacity, will be almost full by the time the battery volts exceed 13.8 volts. It's not necessary to charge to 14.6, in fact its probable the battery won't reach that value. When under charge and in protection, the voltage you see is that provided by the charger, don't confuse charger votage with battery volts.
14.0 volts or slightly higher, 14.2 volts is more than adequate to charge your battery. Using higher voltages will have no advantage and are possible stressful.

Thank you for this explaination this definately helps my understanding of what is going on.
That said, I have made the following changes based on the forum's advise:
Charge Limit = 14.0v
Equalize Charging = 14.0v
Boost Charging = 14.0v
Float Charge = 13.5v
Even though we have another cloudy day here, it has been holding at 13.5v, so I think I am getting it dialed in.
One more question, I have a 20ah lifepo4 charger... is there any benefit for me to charge this battery any more, or was it a waste to buy it in the first place? TIA

 

[Camp Host]

Because the BMS has protection settings that disable charging you will find 14.6 volts is too high. The battery enters protection and will show incorrect volts at its terminals.
Almost all 'off the shelf' batteries will have unbalanced cells leading to issues where the charge volts are too high.
A lithium battery with a low charge current compared to capacity, will be almost full by the time the battery volts exceed 13.8 volts. It's not necessary to charge to 14.6, in fact its probable the battery won't reach that value. When under charge and in protection, the voltage you see is that provided by the charger, don't confuse charger votage with battery volts.
14.0 volts or slightly higher, 14.2 volts is more than adequate to charge your battery. Using higher voltages will have no advantage and are possible stressful.

Thank you for this explaination this definately helps my understanding of what is going on.
That said, I have made the following changes based on the forum's advise:
Charge Limit = 14.0v
Equalize Charging = 14.0v
Boost Charging = 14.0v
Float Charge = 13.5v
Even though we have another cloudy day here, it has been holding at 13.5v, so I think I am getting it dialed in.
One more question, I have a 20ah lifepo4 charger... is there any benefit for me to charge this battery any more, or was it a waste to buy it in the first place? TIA

 

[Camp Host]

Maybe- some of the cheap LiFePo batteries do not contain cells that ‘hold’ at what we might expect to be normal for LiFePo (14.2V-14.6VDC) if ‘we’ bought ‘good’ batteries.

With my cheaper batteries 13-13.4V is normal (measured). While I never capacity tested them, napkin math suggests that, roughly, they put out their labeled amp hours. For the price I was willing to pay I got what I paid for with satisfactory performance.

The voltage you see with the sun out and charging is not reflective of either the rested battery voltage, nor the present disconnected battery voltage. Since the 4210 must present a voltage greater than the static battery voltage at any time to provide current to actually charge the batteries, the voltage shown is ‘weighted’ up as voltage displayed or measured might be thought of as an average of the present static battery voltage and the voltage of the SCC (it is not literally an average, I am providing a visual analogy).

Other factors ignored, you need ~200W of panels for every 100Ah of battery (at 12V nominal) to successfully charge the battery bank. You are skating just below that, and assuming you are using some of the solar power over the day you may not be fully charging the battery daily. It also can take an exceedingly long time of 14.6V charging for the LiFePo to achieve full charge or ‘saturation’ when charging. With LiFePo4 that is not harmful (ignoring internal cell balance issues btw).

I hope this information is helpful.

*if you have a means to capacity test your battery, perhaps you should if you think the battery ain’t quite right. If it makes the labeled amp hours, then you are just experiencing the effects of buying batteries that you didn’t need to sell one of the children to pay for it- metaphorically speaking. If it doesn’t put out- warranty claim

Realizing now that 400w of solar is barely enough to charge this battery, would it be foolish to entertain the idea of purchasing an additional 230ah battery so as to increas my "days of autonomy" ?

 

[12VoltInstalls]

would it be foolish to entertain the idea of purchasing an additional 230ah battery so as to increas my "days of autonomy"

It is not foolish. LiFePo4 doesn’t care that much about being fully charged daily like lead does. Just know that usage greater than the solar input is going to eventually run out in low-sun circumstances that last for days. But there’s no real harm in it imho

However a) I’d plan for more panels down the road, and b) decide if more battery Wh compared to actual Wh of use is actually a benefit.

 

[RV8R]

Realizing now that 400w of solar is barely enough to charge this battery, would it be foolish to entertain the idea of purchasing an additional 230ah battery so as to increas my "days of autonomy" ?

As @12VoltInstalls posted, not foolish at all !!

Caveat; These electrical systems we cobble together & the design decisions we make factor in as a “System of The Whole” rather than stand alone.

To properly analyze biggest bang for the buck the entire system has to be analyzed aling with your weather & how you use your system.

I am not familiar with your solar charger;

https://www.epever.com/wp-content/uploads/2021/05/Tracer-AN-Manual-EN-V2.6.pdf

But on 12v batteries you are limited to 520W ,,, You can double that with 24v.


Electrical design is performed from the “Loads” back to the battery & charging systems. I see many DIYers buy a battery 1st & design a system around that ,,, “bass akwards”.

Further if you are attempting to charge by Solar there is one factor you need For Sure - The Sun Sometimes the best Solar equipment you can but is a fuel generator for crappy weather periods

There are some advantages to “Equipment Choices” ,,, I picked out a Victron 100 | 50 which records our Cabin power usage / generation. We run our Cabin April to Nov primarily on Solar ,,, 600W array & 250Ahr AGMs;





If those record graphs are not self explanatory let me know & I will explain them. The 80Wh use days are when we are not occupying the cabin.

Another factor we practice is conservation. Our system is 12vdc only ,,, no inverter standby drain. Years ago I purchased a Victron Multi 12 | 3000 | 120 for a van & never used it. Someday I will install it into the system & for the most part it will remain off.

 

[Camp Host]

Thank you both for your advice, learning (trying to learn) about solar is really facinating to me.
My need for solar is very small. Living in a MH with frequent power outages that can last for days, my primary concern has been our fridge.
Not really an option to add more panels, so will have to make do with what I have.

 

[mikefitz]

that 400w of solar is barely enough to charge this battery

It will charge the battery, the issue is what power is needed for the loads on the battery. Since the system is for back up power, having a second battery seems a valid concept. On a good solar day the yield, with 400 watts of panels, will be around 1500 watts. The 230 Ah battery holds around 3000 watts. Medium sized fridge needs, at a guess, 1000 watts per day.

 

[RV8R]

Thank you both for your advice, learning (trying to learn) about solar is really facinating to me.
My need for solar is very small. Living in a MH with frequent power outages that can last for days, my primary concern has been our fridge.
Not really an option to add more panels, so will have to make do with what I have.

Primary Concern The Fridge

Ultra-Quiet 2200i™

powerequipment.honda.ca

If you can’t rely upon The Sun ,,, here ya go

 

[Camp Host]

Primary Concern The Fridge

View attachment 205805

Ultra-Quiet 2200i™

powerequipment.honda.ca

If you can’t rely upon The Sun ,,, here ya go

Yep, got one!

 

[sunshine_eggo]

Thank you both for your advice, learning (trying to learn) about solar is really facinating to me.
My need for solar is very small. Living in a MH with frequent power outages that can last for days, my primary concern has been our fridge.
Not really an option to add more panels, so will have to make do with what I have.

Is this a fridge that can run on propane or a "compressor" fridge like is in a home?

If propane, you need to run it on propane. A 7.6cu-ft propane fridge run on AC will use about 5kWh - about 5-6X the electrical energy needed by a residential fridge of the same volume.

If it's a compressor fridge, they use about 1.5kWh/day for a ~18 cu-ft fridge.

 

[Camp Host]

Is this a fridge that can run on propane or a "compressor" fridge like is in a home?

If propane, you need to run it on propane. A 7.6cu-ft propane fridge run on AC will use about 5kWh - about 5-6X the electrical energy needed by a residential fridge of the same volume.

If it's a compressor fridge, they use about 1.5kWh/day for a ~18 cu-ft fridge.

No, it's electric...

 

[12VoltInstalls]

But on 12v batteries you are limited to 520W ,,, You can double that with 24v.

He is not limited to 520W just to expand that thought fully.
The SCC max at saturated capacity is 520W for a single unit of that controller.
I personally would want those panels on a 40A SCC

Living in a MH with frequent power outages that can last for days, my primary concern has been our fridge.

FWIW I have ~5kWh of LiFePo4 currently being charged by 630W of panels on a “60” amp standalone SCC and 1260W of panels on the 80A output of an MPP Solar 1012LV-MK (inverter turned off). I can run 1.5 to 3 days of poor sun running a 12V RV furnace, lights, water pump, 120V 8cf top-freezer fridge, cell booster, phone & laptop charger, etc.
I still get some charge in snowstorms and cloudy days with vertically mounted panels (no snow accumulation) here in Vermont.

The last ~60 days required about 90mins of running the generator but I only was using 1260W of panels up until a week ago. (I’m offgrid but I play musical panels and stuff sometimes)

So that is how you can imagine ‘protecting’ your fridge.

Not really an option to add more panels, so will have to make do with what I have.

There’s always options

300W panels can be mounted to the side of the RV to gain capacity. Just park with that side S-facing.
300W panels are roughly 40” wide by 74” or so tall. So just about the largest panel that conveniently mounts on an RV. Bonus is the price of that size is pretty low/watt.

 

[Camp Host]

This may sound crazy, but I purchased a 20a charger for my 4x100w, 230ah system, but now I am not sure when it would be useful... any ideas? Or should I just send it back.

 

[sunshine_eggo]

20A * 14.5V = 290W, so you'll never get more than 290W out of the 400W array; however, you'll produce 290W for as long as a 400W array will produce 290W.

I would get at least a 30-40A controller

Consider the Victron 100/30... it's a workhorse.