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matt1309 avatar image
matt1309 asked

Understanding smart shunt

Hi,

I'm trying to decipher what this scenario means for my battery health/true capacity (battery is DIY LiFePO4 48v 304AH battery)

Sytem has been running for awhile and note none of this is done is perfect conditions just normal house powering usages so may be due to normal percentage movements but seems too repeatable for that.

Victron states 100% then I fully discharge to 0% (confirmed 0 based on voltage) then i recharge however now the battery is full at 93% (ie fully absorbed). AFter a certain time it jumps to 100% i assumed the smart shunt it syncing itself.

I'm trying to understand what that means in terms of my battery. If it was the other way around and the battery BMS disconnected the battery at say 7% per victron then I would assume that my battery is 7% under 304ah due to degradation etc.

However it goes down to 0% smoothly ie no jumping which makes me assume smart shunt is not applying any corrections close to 0%. However at almost full it does.

So 100% -> 0% then back to fully charged and i end up at 93%. Does that mean my battery is greater than 304ah and I've been lucky with the cells I've purchased? It's almost as though i can discharge more than i can charge. Or am i simply missing the correction closer to 0% and infact it is just a case that my battery is 7% less than 304ah.


Thanks,

Matt

SmartShunt
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3 Answers
derrick thomas avatar image
derrick thomas answered ·

What is your charging efficiency setting? Sounds like it may be set too low.

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matt1309 avatar image matt1309 commented ·
Think you've spotted in one!

I've upped the setting. I'll see what happens at next recharge cycle.

Thank you!!

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klim8skeptic avatar image
klim8skeptic answered ·

You forgot to mention your battery charging regime.

BMV Youtube tutorial. Guide to set up your BMV..

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matt1309 avatar image
matt1309 answered ·

Thanks for reply.

By charging regime do you mean settings such absorption/float voltages/times or how I charge as in current and for what length of time?

If the former, absorption fixed 55.2v for 4hours (excessive I know however prepping for winter, in summer set to just 1 hours) and current is near enough 0 by end of that period. Float 54V.

If the latter: I've not tested this in "lab" conditions so charging rate has varied depending on sun which I understand will impact the SoC however it was consistently circ 93% in various scenarios regardless of whether it was charged fast or slow or if temperature was high or low, which was the part that was odd to me.

Made think it wasn't a variable as noted in the video and more just my capacity I've set in smart shunt being set wrong ie the battery true size is not what it's rated as. Was hoping to understand what capping out at 93% likely meant rather than forking out on battery charger to calculate true capacity of cells exactly.

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