diy solar

diy solar

Quick discharged lifepo4 battery bank

Vlad_AU

New Member
Joined
Nov 12, 2020
Messages
2
Hi everyone,
Need some help with my battery bank. It's just about 5 months old, and at the moment is start dropping voltage very quickly.
I'm have 330w solar panels, 60a MrPow charging controller, 280ah 4s eve prismatic cells, and 80a BMS.
So solar charger is showing full changed battery, but soon like I'm trying to use any electronic devices (light for example) voltage drops from 13.6v to 12v in 10-15 minutes time....
If trying to start some more powerful devices (120w water heater for example) BMS shut down the battery.

I'm believe it's just something wrong with connection or just 1 cells need to be replacing.
But I'm not electrician so if someone can recognise a problem, I'm be very appreciated for help.
Thank you.
 
Get yourself a cheap Digital MultiMeter & set it to Volts DC. Measure the voltage across each of the cells & report back
 
with lifepo4 you need a coulombmeter to count amps and give you an accurate SOC. I had the same thing happen to me where I thought my battery was fully charge because it read over 13.3 volts after charging all day. But little by little if not fully charge everyday, eventually it gets so low that as soon as you put a large load, it shuts off.
One more thing, the voltage reading on a solar controller LCD is always wrong from what the battery terminals read. I used 2 mppt controllers and they both read at least a .5 volt higher then the battery. Always check the voltage at the battery terminals, lifepo4 is only fully charge if it reaches 14.6 volts at the terminals, anything less is just trickle charging the battery.
From your description, it sounds to me the battery is good, it just discharged too much from chronic undercharging. If the the battery is at 10 percent and you only use solar to charge, it might take up to 2 weeks to fully charge with a 330 watt panel.
If you do have voltage drop from controller to the battery you will probably not get max amps out of your controller. Some controllers, you can calibrate the voltage on the lcd screen to the battery terminals. On my ecoworthy 20a mppt(no calibration), I had to raise the bulk setting to 15.5 volts, to get 14.6 volts and 12 amps charging on my 4s lifepo4, anything less then 15.5 volts and the battery would be charging at 6 amps.
 
Hi, thank you for quick reply. Will try checking charge rate first. Also what parameters I'm need for MrPow mppt controller?
 
If you charge an LFP pack to 3.5Vpc (confirmed with hand held meter), then the pack is essentially fully charged. From there you can put a load on the pack, and check if there is a big voltage drop somewhere.

If you aren't getting to at least 3.45Vpc before your solar controller drops to float, then you have some other issue going on.
 
I have a makeskyblue 60a mppt that looks similar to the mrpow 60a mppt, I was reading through the mrpow manual and its different then my controller, it doesnt have a feature to calibrate the battery voltage.
For the bulk/absorbtion, I would go with 14.6 volts and check how many amps your panel is putting out (my 240 watt panel puts out 9 amps in winter) , so you should be getting more amps at least 12 amps with the sun out. If your only getting less then 8 amps then you probably have voltage drop from controller to the battery. Measure what the lcd screen voltage is and then measure battery terminals.
With voltage drop the controller will think the battery is at 14.6 volts when its actually at 14 volts and will switch to float too soon reducing amps. To compensate you would have to raise bulk/absorbtion accordingly, if you have .5 drop, you need to raise to 15.1 volts. When lcd reaches 15.1 volts measure battery terminals to see if its 14.6 volts.
The higher the bulk setting the more amps your battery will receive. In your situation with such a large lifepo4 battery, you want maximum amps going into your battery every day.
On my 220ah lifepo4 with a 240watt solar panel, the battery has been at 60ah for the past 3 weeks because of cloudy conditions. I cut my power usage to try and speedup the charging but at a max of 9 amps charging its slow going.
I have the chargery bms8, so I don't worry about the battery getting overcharged, it sounds warning alarms and disconnects the solar panel if any of the cells ever gets close to the limits.

this is your controller?
1 mrpow mpt.jpg
 
Back
Top