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Tesla Batteries Overvoltage Charge


I have recently upgraded an existing solar system by adding a second MPPT Bluesolar 150/70 Tr. The original system was composed of 2 Multiplus-II and a single Bluesolar 150/70 Tr all connected to a Cerbo GX. The battery was composed of the 2 cells from Tesla.

Upon connecting the new MPPT we measured the voltages at the battery side and it was 57V but what I wasn't aware of at that time, was that these batteries could only be charged up to about 49V so I didn't find it strange to have that voltage. As the new MPPT was also connected to the Cerbo GX I wrongly assumed that the voltage from both MPPTs was being controlled by it and thus no further configuration was needed to the system.

Unfortunately the system was left like this for 2 days before we finally realizing the mistake. Upon disconnecting the battery and measuring its voltage it was at a safe level of 49V.

My question is if has this killed the batteries or do they have an internal BMS that effectively disconnects them from the 57V source causing no harm to the cells inside?

Please let me know your thoughts.

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jjbond avatar image jjbond commented ·

Remember, you asked (Please let me know your thoughts).

Posts like yours make it hard for all of us who use Tesla modules responsibly based on experience and respect for the dragon we're taming to be taken seriously (or be viewed as responsible users) and them to be treated as a viable option (which they are, when deployed with awareness as to the outcomes if you don't).

Posts like yours are also the reason that companies like Victron and others are hesitant to support the modules use for fear of litigation and other reputational risk (thankfully Victron did change some restart voltage settings for us in inverter firmware so that's appreciated, it's why I'm loyal to them). You can't blame them for being nervous when we have people like you running around acting irresponsibly and risking not only your own life and property, the fire fighters that have to come into your burning ash pile to rescue you and your family, and finally the the reputation of all of us. People like you are the reason that Will Prowse (DIY Solar) took down all his Tesla module for off-grid use videos. Some of us do it the right way, we pay over $3,000 for the BMS alone (EVTV BMS) before we buy modules, some like you who take the cheap/easy way out, instead assume we're all here to help you after the fact. You own this, you reap what you sow.

I see you posted just before X'mas day..... Merry X'mas because you definitely got a present this year, next year you may not be so lucky. Please do us all a favor, rip everything out, get back on the grid where you belong before you kill yourself and increase all our fire insurance rates (not that you'd be covered if it was your fault). If you're not going to invest in a proper BMS and some time researching how serious these are, then please take that $3,000, go to Costco and stock up on fire extinguishers, donate to your local volunteer fire dept. and go increase your families life insurance, you're going to need it.... not 'if' but 'when'.

After reading this, before you se-comb to that urge to hit reply and flame me, grab some popcorn and watch a good movie, the key phrase to listen for in the below video is "we can't put it out", this was only 2 modules.

PS: It's called "tough love", appreciate it. When you play stupid games, you win stupid prizes. Ruining the battery is the least of your problems, if that's all that happened and your house isn't a smoking pile of ash, you should be thanking the lord above.

It's called "The Grid", Get On It!!!!


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Jason - UK avatar image Jason - UK jjbond commented ·
@jjbond My thoughts the same. The 18650 cells are the cells you really don't want to get wrong. Connecting up a power source to any battery with no idea its design limitations is dangerous. @pedroply as said above, make the batteries safe and do your research.

On my tesla battery ESS arrangement, I even have a smoke alarm and heat alarm above mine interlocked into the Multiplus so should something ever go wrong, it stops the charger / inverter.

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2 Answers
snoobler avatar image
snoobler answered ·

Assuming two 6S Tesla battery modules in series for ~48V?

Terrifying things in your post:

  1. "what I wasn't aware of at that time, was that these batteries could only be charged up to about 49V"
  2. "do they have an internal BMS"

These kinds of questions are usually from people who catch their batteries on fire or severely damage them.

You should know this information.

6S Tesla modules do not have a BMS unless one is installed.

All chargers must be individually configured to charge the battery properly.

All load must be individually configured to not discharge the battery excessively.

The GX can be programmed to control certain devices, but that doesn't negate the above two requirements.

Certain BMS can be configured to interface with and control the GX and attached devices.

Recommend you stop using your system until you have educated yourself, confirm that a BMS is present (or you install one), and attain real time cell level voltage information either by direct measure or through a BMS interface.

Given that you didn't experience a catastrophic fire, I can only surmise that the supplier of your battery modules had the sense to install a BMS. If that's the case, they are not damaged. If there is no BMS, and the battery truly experienced 57V, you're extremely lucky it didn't catch fire, and you likely caused severe damage to the battery.

Most Tesla modules in second life applications are made from NCA Lithium cells. They are hands down the most dangerous.

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oxy avatar image
oxy answered ·

To add more, you also cannot charge these batteries in cold temperatures - as others said, you really have to know them.

I recommend you (or anyone tackling the Tesla batteries for that matter) to find the Jack Rickard (EVTV) channel. He has passed away since, but had the most in depth research done on their use for off-grid storage. Amazing stuff.

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