Battery voltage dropping when connected to solar charge controller

[sultan]

I have two 12 volts lithium batteries (Redondo)

Being charged by 1000 watt solar array via a 60 amp mppt solar charge controller (powmr)

For some reason yesterday the whole system shut down

I checked the battery voltage at the positive and negative terminals of the lithium battery and I get a total of 20 volts in series

But when I connected to the solar charge controller suddenly the same battery terminals on the lithium batteries show me two to three volts?

I can't seem to figure out why it would be 20 volts when not connected to the solar charge controller and suddenly two to three volts when connected to the mppt

In between volts certainly will not turn the sword charge controller on so I'm stuck,

Same thing happened if I connected to the inverter suddenly the voltage will drop from 20 volts down to 2volts

I'm stuck, any idea??

 

[Don B. Cilly]

At 20V the batteries are dead. 0% charge. So any load, even as small as a controller, would bring the voltage to close to zero.
Do you have any other way to recharge them?
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[sultan]

That makes sense

I do have a 12-volt charger I could use to charge One battery

Not sure what the minimum voltage the powmr requires before turning on

The lithium batteries I have inbuilt BMS
Any idea of how I can prevent this from happening again?

 

[mikefitz]

My guess is BMS shutdown. Need to charge. Connect each battery to a power source at over12.5 volts.

What discharged the battery so low?

A battery monitor or even a voltmeter will give you some idea of SOC

Mike

 

[sultan]

I'm using it to irrigate a field

Pump draws 8 -10 amps ,110v

Don't know why the BMS would shut down,

However I was undercharging the batteries to about 75% capacity 27v because the solar charge controller would cause voltage spikes in excess of 33v when I had it set to 29v causing the inverter to reset because of it's 30 volt cut off.

Go to avoid the a voltage Spike are lowered the charge goal


Are there any inverters that prevent this type of voltage spike

 

[Don B. Cilly]

the solar charge controller would cause voltage spikes in excess of 33v

It should not do that. Try using it as a paperweight instead ;·)

29V is rather overcharging, 27.0 slightly undercharging. Try 27.5-27.7.
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[sultan]

I figured the problem was the mppt

Not sure exactly why it exceeds the rated voltage but it only lasts one to two seconds

Someone recommended using zener diodes to prevent it from happening which is beyond my DIY abilities at this time.

Are there any reputable mppt controllers you would recommend

The one I bought was a $100 Chinese product

 

[cs1234]

I figured the problem was the mppt

Not sure exactly why it exceeds the rated voltage but it only lasts one to two seconds

Someone recommended using zener diodes to prevent it from happening which is beyond my DIY abilities at this time.

Are there any reputable mppt controllers you would recommend

The one I bought was a $100 Chinese product

It sounds like the type of voltage spikes a charge controller might do if it were trying to desulfate or otherwise condition a lead acid battery.

I have a supposedly high quality NOCO battery charger, the Genius 10, that does this on the lithium setting when it shouldn't.. kicks up the voltage on a 12v lifepo4 battery as high as 17-19 volts and causes the BMS to drop out. I also have a little 1 amp NOCO Genius and it doesn't do that on it's lithium setting. I discovered this problem with the Genius 10 right outside my 30 day return period on Amazon and haven't felt like dealing with it, I just charge lead acids with it now.

Maybe your charge controller is doing something stupid like that, try looking around in it's charge settings for any type of battery conditioning or desulfating and disable those or drop the settings down to some reasonable voltage for lifepo4.

 

[sultan]

Best theory I've heard sofar as to y the spike maybe happening, unfortunately no such setting on the powmr

 

[cs1234]

Best theory I've heard sofar as to y the spike maybe happening, unfortunately no such setting on the powmr

What is the exact model you have? Maybe we can look through the manual and see if we see anything in there that might be what we are after?

 

[sultan]

https://www.google.com/url?sa=t&source=web&rct=j&url=https://powmr.com/index.php%3Fdispatch%3Dattachments.getfile%26attachment_id%3D27&ved=2ahUKEwikytfsoKL5AhWgbDABHTfpDqsQFnoECBsQAQ&usg=AOvVaw0FJRoxqI9XWy_XPSAUkcvT

 

[Don B. Cilly]

Not sure exactly why it exceeds the rated voltage but it only lasts one to two seconds

Honestly, my best guess would be it's defective. It probably stopped charging altogether, didn't it?

Someone recommended using zener diodes to prevent it from happening which is beyond my DIY abilities at this time.

Dodgy, would also need a transistor/heatsink to drive the current, not worth it.

Are there any reputable mppt controllers you would recommend
The one I bought was a $100 Chinese product

I've been using a <$100 Chinese one for more than a year, and so far am quite happy with it.
Epever Tracer3210AN (30A). Was €70 when I bought it, now €90.
It's fully programmable if you also get the USB cable or the WiFi box.
-

 

[mikefitz]

Although there may be issues with the MPPT controller, there may be BMS shutdown at high charge volts .
With many low cost batteries cell Imbalance will cause BMS shutdown at lower charge volts than expected. Having two batteries in series can make matters worse unless they are similar in performance.
Ideally the 12v batteries should be charged in parallel at 12v before connecting in series.

When BMS shutdown occurs under charge, its possible the MPPT controller creates a voltage spike. This perhaps what you are seeing.

1000 watts of solar in, with 8 to 10 amps at 110 volts out, doesn't leave much/any power to charge the battery.

Mike

 

[cs1234]

Ideally the 12v batteries should be charged in parallel at 12v before connecting in series.

I agree with this, try charging each 12v battery by itself first until they are reporting the appropriate 12v battery voltage by manufacturer specs. They should end up nearly identical, if not, one of them is shot.

 

[HRTKD]

Putting LiFePO4 batteries with a BMS in series is likely to lead to balance problems between the two batteries. For example, Battery A reaches a 100% state of charge before battery B does so battery A stops the charge which in turn prevents battery B from getting any further charge. Extrapolate this cycle out a hundred times and you get battery B with a much lower state of charge than battery A.

If you need 24 volts, build or buy a 24 volt battery, don't put two 12 volt batteries in series.

 

[sultan]

If I am understanding correct, the facti have it in series may be contributing to the problem

if i connect them in parallell, would i need to buy a new inverter?

I run the irrigiation pump for about 4 hours a day, approximaly 3.5KWH, but he capacity of both batteries is 5kwh,

are there any good 12v pure sine wave inverters thatare 3000w peak? I find that most these inverters run at 50% of their rating, i need about 1000 to 1200 watts?


I need a 60a mppt sot he 30a wouldnt work, and also i htink the max solar watt on those 30a is 400W

 

[sultan]

one other problem i would run into ifi connected them in parallel 12v

would be the maxsolar wattage would be exceeded

currenty i have 1200w solar array, dropping the battery to 12v i hink allows a max 720watts on the scc

 

[cs1234]

@sultan
They might just not be individually balanced any more for a variety of reasons from being in series. Charge them each individually using a 12v lifepo4 charger and then you can put them back into series and try again. Plenty of people use lifepo4 batteries in series without significant issues, but they have to be FULLY charged first before putting them in series.

 

[HRTKD]

I would get the batteries charged well before making any changes. Then monitor each battery over a few days to see if they deviate in voltage/state of charge.

Switching to 12 volt is a bit like throwing out the baby with the bath water. Your probably appears to be the battery, not the solar charge controller or inverter.