question

sebcbien avatar image
sebcbien asked

Help, my SmartLithium doesn't allow me to discharge, says voltage is too low.

Help,

Altrought the voltage of all my cells is higher than 2,8V my SmartLithium 100A doesn't allow me to discharge, says voltage is too low.

I've been to 2.79V, the internal bms then stopped discharging.

Now the voltage is back to 2.96V -> 3.18V after charging a little and I still cant start using the battery... the battery says "discharge deactivated"

I want to start my webasto to heat up my caravan and have some light, but all is turned off !

Please HELP !

See screenshots below, status and parameters.

Lithium BatteryBMSSmart Battery Sense
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8 Answers
wkirby avatar image
wkirby answered ·

First you need to charge that battery. It is empty and the cells are not balanced.
Also the temperature is quite low, so maybe you will not be able to charge it quickly.

Sure all the cells are above 2.8V, but that is not really good enough, you have more problems that just this. That battery really needs to be fully charged so that the cells can be balanced.

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sebcbien avatar image
sebcbien answered ·

ok, thanks for your answer, I know that I have to recharge it and balance it, that's what , I'm doing now... but in case of "emergency" this is not acceptable that the battery doesn't respect the threshold values that are set... that's the reason I wrote this.

The battery became in that state because it seems like it self-discharged, as on my BMV-712, the battery should still be at 56% ... the state I left it 3 months ago, well balanced, for "hibernating" as I was not using it...

For the temperature... the battery is at 11° but the inside temp sensor has a BIG offset of 6.5°... already mentioned here: https://community.victronenergy.com/questions/2142/temperature-offset-of-the-sensor-inside-a-smart-li.html

This is not acceptable that a battery at 1000€ has such random behavior...

So if the battery discharged at 2.9v per cell and the outside temps is 9°C ... I cannot use it although it is still in the recommended range...

WOW, what if in a real emergency ???

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scubasail avatar image
scubasail answered ·

I feel for you, Sebastien.

As I'm developing batt electronics myself, this is always a touchy area: do you want to allow the user to override the safety mechanism that was defined by the BMS manufacturer?

We have a user override in our system but we might take it away again, as there is a chance that people turn the override on and forget about it. If something bad happens 6 months later (say the batt went into thermal runaway and caught fire, burning down your caravan or cottage with your whole family in it) and this was caused by this override, do you think you would remember that you changed it? Would you confess to the police/insurance/her mother that you disabled the safety fuses in the software?

Just think about it for one minute!

You're asking "what if this was an emergency"? Well, mate, this already is an emergency as far as the BMS is concerned and the system is protecting you and your family. Aren't there enough horror stories about "Lithium batts" catching fire? Most of them are exaggerated, but some disasters, like a plane crash, are real.

Let me guess your family wasn't on that plane?

In other words, you need a different backup system in order to get the generator running to charge up your main system. Maybe solar?


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sebcbien avatar image
sebcbien answered ·

Thanks for your answer scubasail....

but but but :-)

They give the possibility to allow discharge only LOWER than 2.8V I didn't try but when I hit "minus" it shows 2.79v... so even more insecure ... I cannot set the limit to 3V for example...

So well ... why at 2.9V, "0.1V" safer than the limit of 2.8V (their "up" limit) the battery doesn't respect the limit and allow discharging ?

That's a big bug for me, or a bad design, or ...

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That's something for the Victron guys to address..
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boekel avatar image
boekel answered ·

A LiFePO4 in resting condition below 3 volts per cell is -really- empty, even if you could turn it on you'd have very little energy left (like 2%), and you would damage the cells.


If one of the cells gets below 2,5 volts, it get's permanently damaged (Li-ion is more forgiving).

As to why it has slowly drained: there must be some small current somewhere.

I can't help you with the other questions (temperature), but trust me on the capacity. I'll include a discharge curve of a LiFePO4 cell (remember these values are under load)


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graham avatar image
graham answered ·

sebcbien You say they were left for 3 months, what was connected to the?

The BMV?

The BMS?

anything else that could draw current?

Did you turn the battery Isolators off?

Does the Battery Isolator totally Isolate the batteries from everything?


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Only the BMV and BMS where connected.

The BMS was switched "off" no charge/discharge allowed

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sebcbien But is the BMV connected directly to the battery or where is it connected to ?

I suspect it was connected direct to the batteries and therefore would be live and operating for the whole of the shut down period and that is where the small current is that has drained the batteries. Which BMV do you have?

Which BMS are you using?

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Paul B avatar image
Paul B answered ·

dont go on SOC so much VOLTAGE is the real reading, so read up on SOC, it needs to be checked against voltage every now and again, so in reality you may not have left it in a medium charge state as you thought,

I dont know how you system is setup but 100% SOC is only real when the voltage is 14.1 or there abouts.

if you have never got the batteries to 14.1 then the SOC would never have been reset to 100% level

Set alarm up in your BMV for low voltage at 2.95v then you will have some reserve capacity for emergencies


SOC is basically a flow meter and depending on how its setup it may not be accuarte as it may have never been calibrated correctly.

Ie has the Phuket setting been set to lithium ie NOT 1.25 but 1.05

has the efficency been set correctly ie NOT 0.85 but 0.95

Battery Charge setting should be 14.1

The BMV comes standard setup for lead acid batteries.

HAVE you changed the settings

also under relay on the BMV DISABLE SOC setting currently 50% this is for lead acid lithium the setting should be ZERO


If the above have not been set then your SOC will be way out

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kiko avatar image
kiko answered ·

Hi,

I am also not totally clear on this topic. The VE.Bus BMS manual only talks about disconnecting the charge side on high voltage and high temperature, not on low temperature.

Could you please post the link to the blog article, thank you!

I can confirm, that my Smart Lithiums have a low temperature setting:


As shown in the Victron van setup (https://community.victronenergy.com/articles/15035/victron-vw-van-electrics-install-schematic-drawing.html, https://community.victronenergy.com/storage/attachments/2676-ds-victron-van-automotive-full.pdf), I used the relais of the BMV 712 to disconnect the charge side using the BatteryProtect in combination with the BMS:

This would be unnecessary, if the comments above are correct.


I also set the low temperature of the MPPT to stop charging, before the BMV disconnects it:

I learnt, that the MPPT does not like beeing disconnected on the battery side when the panels are still producing energy.


This leaves me with the uncertainty, if the MultiPlus will stop charging at low temperatures, as it is not connectect through a BP but directly and the BMV does also not control it.


Regards



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I just tried it using the maximum minimum charging temperature of 20°C in the Smart Lithium settings. The MultiPlus stops charging, even though the LED shows bulk. But there are no amps flowing through the shunt. The BP also closes using the charge disconnect of the BMV.

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