sdobbie
Posts: 18
Joined: Sun May 31, 2015 4:09 am

12v system reaching 15.4v

Thu Apr 11, 2019 4:56 am

I am trying to find a point in the car where I can take upwards of 40 amps from the 12v system. I removed the back cover in the boot which covers the motor and attached my lipo battery charger to the 12v points which are on top of the motor inverter. The more current my battery charger took from the car, the higher the voltage went until the car was supplying 15.4v into the charger and the 12v battery in the car was reading 15v. It was also a warm day.
Is there any way to run high powered 12v devices from the car? The 12v points are capable of supplying 2000 watts, I read this in a datasheet from BMW.

I would add images but this forum lacks the basic feature of uploading attachments so I have put a link instead.


https://1drv.ms/u/s!AkcSioC2FIVAijjkylS_RnnJT1Rg
Electric for ever more.

jadnashuanh
Posts: 4430
Joined: Thu May 22, 2014 2:07 pm
Location: Nashua, NH USA

Re: 12v system reaching 15.4v

Thu Apr 11, 2019 8:04 am

As I understand it, BMW specifically says not to try to charge the 12vdc battery unless you follow a very specific procedure. It may be that you toasted some controller.

Keep in mind that the 12vdc battery in the car is quite small, and to provide that amount of current, you'd have to have the DC-DC converter working. I do not know how big that is, but given the relatively small battery and mostly LED lights on the car, it probably isn't a lot. This is not like a ICE that needs a fairly large battery to turn the engine over in the cold...the battery in the i3 only needs to power the computers...then, the high voltage battery can provide the current to run everything else.
Jim DeBruycker
2011 535i x-drive GT, 2014 i3 BEV

sdobbie
Posts: 18
Joined: Sun May 31, 2015 4:09 am

Re: 12v system reaching 15.4v

Thu Apr 11, 2019 8:28 am

jadnashuanh wrote:As I understand it, BMW specifically says not to try to charge the 12vdc battery unless you follow a very specific procedure. It may be that you toasted some controller.

Keep in mind that the 12vdc battery in the car is quite small, and to provide that amount of current, you'd have to have the DC-DC converter working. I do not know how big that is, but given the relatively small battery and mostly LED lights on the car, it probably isn't a lot. This is not like a ICE that needs a fairly large battery to turn the engine over in the cold...the battery in the i3 only needs to power the computers...then, the high voltage battery can provide the current to run everything else.
I am not charging the 12v battery, I am trying to use the output from the DC converter to power my electric bike charger.
Electric for ever more.

sdobbie
Posts: 18
Joined: Sun May 31, 2015 4:09 am

Re: 12v system reaching 15.4v

Fri Apr 12, 2019 1:12 am

Can anyone else offer any help on this? I have heard of people running power inverters from the car without issue but they never said how they did it.
Electric for ever more.

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