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diy solar

Battery charging confusion

Electrobob

New Member
Joined
Jul 25, 2021
Messages
30
Location
Arizona
I have two SOK 100 amp 12 volts wired in series and a Growatt 3000TL LVM being charged with 4 HQST 100 watt panels also wired in series. This little system is a portable hand truck solar generator.

I am having no issue with charging up either from pv or ac and then powering whatever I want until the batteries are depleted. The issue is the lack of information I get during the charging and discharging process which leaves me virtually in the dark regarding the status of my system. There is no accurate way of knowing SOC. It will show 4 bars until the very end when it shuts down empty, and during recharge it will show 4 bars again after maybe an hour in the sun, so this data cannot even be taken seriously and provides no information. Also, the Growatt will show my panels generating 250 watts, 10 amps at 65v during charging (this is data I did not think possible from 4 panels in series, each 100 watt, 20v, 5 amp, but that is a whole other thread). This is more power than a battery charger provides so I would like to believe the Growatt is metering this flow and not just allowing the power to be blasting into the batteries unsupervised, but if it doesn’t even know the SOC of the batteries how does it know when to quit? It causes me to doubt the true level of oversight this unit provides.

I live in AZ and have long stretches of strong sun every day. I let the 4 panels charge the system over 2 days, generating the kind of power I mentioned above for numerous hours each day. I have to believe the batteries were charged before the end of this. Possibly they were by the end of the first day, but how do I know? How do I know I am not damaging the batteries? Nothing ever shut down or turned off and the green charging light kept blinking the whole time, but with the kind of power I was getting I can’t believe they weren’t charged. Is it going to come down to the BMS in the batteries needing to save the day every time I recharge them? I spent a lot of money on the Growatt and it boggles me I cannot get even basic information.

Any advice or tips are surely appreciated! Thank you!
 

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Nice hand truck system.

Get yourself a shunt-based battery monitor. It will provide you with accurate state of charge because it keeps track of the current into and out of the battery rather than relying on voltage (which your Growatt probably does and it's likely calibrated for lead acid batteries. LFP has too flat a voltage curve to rely on this method).

Will recommends a high end (Victron) and a budget model on the sister site here:

My preferred budget monitor is the TF03K. You can find them on eBay and Amazon. Here's an example:
 
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