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Would there a more easy way?

It is a shame, but digging in the issue Roald run into, all could be solved by a mechanic easily, if he und erstand his tools:-(

It seems for this cases there is an option in Xentry to start the plugged in car to charge even with error messages.

Also there is a commando to send to the battery BMS to prevent the uncontrolled switching on in this case of empty 12V battery which should be activated when you disconnect the 12V Battery.


Opelord69's picture
the conclusion from all this:

The conclusion from all this: you shouldn't leave your car for a long time and without using it)  (just kidding)  I understand you perfectly I had the same issue with my 2018 nissan leaf. First of all, it was a second-hand car, so you can obviously already understand that its battery wasn't like "fresh". Well, I didn't drive the car for about a month and the problems started to appear. I wasn't able to start the car, so addressed an automotive garage. They said that the battery was changed once! Omg, and the seller didn't even tell me. Guys always check the VIN, to make sure the car is in great condition. Here is a VIN decoder. 

Best idea ever

Yes you are true.  :-) The bad issue for electric vehicles is a discharging over time in opposite of a piece of steel. But even there is corosion if you not protect it.
So use the OVMS as a protection device is a good idea.
Ok sometimes it would be good if the OVMS would act a little bit more stable, but i enjoy the options to follow the discharging of the battery and act on the right moment to rescue :-)

Roald Nakstad

Hi all.

Have now been driving my Smart EV for months since the 'near dead experience' without any issues or signs of battery degradations smiley. So I think the conclution is that cell voltages down to 2,5v for short period is no problem at all. 

But I did have another scary expirience. I removed the instrument cluster to change the speedo dials from miles to km/h. And during that night the instrument was out, the 12V battery totaly collapsed, and the HV battery was drained from 40% to below 10% surprise!!  So I beleive my 12V battery has been quite weak for a long time, but you newer know since it is always topped up by the HV battery. With the instrument cluster out I guess for some reason there is a higher 12V drain, and for my car resulting in total breackdown of an already weak 12V battery.

Luckely my HV battery did not go to low so by replacing the 12V battery, everything was back to normal and HV battery started charging right away.

So, my advice is to replase your 12V battery BEFORE it get to old/degraded. My experience was that just ower one night it suddenly colapsed, and almost totaly drained the HV battery. In conventional cars you simply won't crank the engine when battery is on its way out, but in an EV you do not get any prewarnings before it totaly dies and does not take any charge anymore resulting in a constant drain of the HV battery. 



Roald Nakstad


Lessons learned

Hi Roald,

great to hear your car is still running fine. In meantime i get much deeper in the overall 12V battery and HV battery topic. I even can fix all the BMS issues . I checked you old posts again.
Ok the 12V battery issues and the missing cluster together with the OVMS coul cause maybe a missing falling into sleep issue of the EV-CAN bus. By this the ECU drain addional current. You could monitor the 12V very nicely with the ovms app. so you see what happen the last 24 hours.

But i want come back to you about the status off your HV battery. Do you have a 22kW charger or a 3,7kW? Also do you charge often in very cold temperature conditions?
It seems you corner cells are very strong degraded.  This was also the root cause for the fast discharging during the big event in the April.
A lot of information were gave to you which all have a true but also wrong info inside.
We discuss about the 12V Battery and to connect or disconnect. By the very end most important is in this case just to hold the voltage level on the 12V side or totally switch of fast! Never let float the 12V battery  to discharged conditions.
This will cause the recharge via DC/DC Converter effect and empty the HV Battery till lowest cell 3,2V after the main contactor still get closed till 3,0V and try to recharge the 12V battery If needed.
If you discharge the lowest cell below 3,0V the contactors get open by the cell low failure  and you have an big issue. The P18051C failure is happen far later when the 12V die ongoing and the weak 12V supply  trigger some very bad effects inside the HV battery bms.

So maybe you could show us a latest BMSdiag report after extensive balancing and a charge from below 20% SoC to 100% SoC with most low charging current. By this the bms can calculate your real cell capacity in best way. But as mentiond it seems to me your battery have some very bad cells with very low capacity. How far you could drive actual till you need to recharge.

Maybe you could send me a PN in Going Electric Forum. Maybe you are a perfect candidate for predicitve maintenance of your HV battery :-)


Cheers JMK2020

HI all.

HI all.

I drive Smart Ed too. My car is from 2016 and always sleep in box. Do i need to change the 12V battery to prevent lockdown of the HV battery?

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