Tesla module charging voltage higher than cut off limits

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jstone asked May 13, '21

Tesla module charging voltage higher than cut off limits

Setup as follows..

1x tesla module

9x 330w mono perc panels

100/50 victron smart mppt

Smart shunt

Bmv 712

CCGX

24v 5kVA multiplus.

I have been living off this system for two years now and have recently upgraded my array with 9 new panels.

We are just coming into winter in New Zealand and I haven't had this problem over summer.

The charging voltage is reading about .3 max higher than what I have it set to, to go into float and absorb mode. For example, I have it set to go into absorb at 24.3v for 6 hours and float at 23.35.. trouble is even with these settings it is charging up to around 24.6! It sets the alarms off and my relays. I have always had my absorption and float settings at around 24.4 and 24.5 respectively.. but I have had to lower my voltages due to risk of over charging my tesla module. Any ideas?

So far I have thought it might be a temperature issue, but I have read that temp compensation does not apply with lithium?

Or 2, my array is to big for my battery? I do notice that we charge A LOT more efficiently on a cold sunny day compared to summer.

I have just purchased the temp sensor for the BMV 712, but if my MPPT is already reading ambient temp in the same room as my battery, this won't solve anything. It never gets below freezing where I am in New Zealand, lucky to get a low of 5 degrees Celsius in the middle of winter.. and we haven't had many cold days this year so far, so I'm confused when thinking it might be a temperature issue other than the better performance of the panels...

battery charging

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Answer 1 · 2021-05-13T13:07:33Z

JohnC answered · May 13, 2021 at 01:07 PM

Hi @Jstone

It's possible you may have temp compensation enabled in the mppt. If you've started with a Li preset it won't be, but if you just modified the pb default then it might have. If so, just make the temp comp value zero.

One thing that worries me with your 9x panels is that you likely have them in 3x series strings (3S3P). If all in parallel you'd be over the max Isc. It's possible that when cold a 3S3P might exceed the 100 Voc limit, and this will destroy the mppt. Run the panel specs through this.. https://mppt.victronenergy.com/#

Don't fudge the temp figures as it's important. 5degC isn't a practical NZ figure for a min, flying pigs don't count.. :)

If you can't get the calculator to recommend a 100/ mppt, then you've overdone it. (Fiddle with the number of parallel strings to see if it will find any 100/).

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