Mito
Posts: 25
Joined: Sun Apr 09, 2017 11:55 pm

Re: BMW i3 auxiliary battery sizes

Thu May 18, 2017 2:04 pm

Bawareca wrote:
jadnashuanh wrote:Apples and oranges....

Wasnt it obvious?
My whole point for this discussion, and my decision to go with a larger battery, is that if there is the slightest consumption over the normal sleep mode (0.05-0.15A) the 12v battery will go flat and it will probably be dead too. It happens, and will happen with the modern BMWs.
My car has no warranty and i have no desire to buy $170+ battery multiple times and deal with dead car recovery with my wife inside. Or rely on a tow truck driver to jump-start it :o To each it's own, I just share my modification and the logic behind it.


I agree after having to rescue my Mrs when the battery failed.
The 20ah battery is underspec'd and of questionable quality
A 40ah battery is cheaper and less likely to fail
All 3 of my cars have had failed batteries its an epidemic and a weak point on the car so you can learn from history or be doomed to repeat it, your choice...

alohart
Posts: 842
Joined: Sat Nov 01, 2014 7:36 pm
Location: Honolulu, HI, US and Uppsala, SE

Re: BMW i3 auxiliary battery sizes

Fri May 19, 2017 12:42 am

Mito wrote:The 20ah battery is underspec'd and of questionable quality

Of questionable quality, maybe. Maybe that explains your repeated 12 V battery failure.

Underspec'd, almost certainly not. Since driving with a voltmeter in the center auxiliary power port, I've noticed that the DC-DC charger is almost always charging the 12 V battery, not only when driving, in effect adding the capacity of the Li-ion battery pack to the 12 V system. But unlike in an ICE vehicle, there's no slow starter motor to indicate that the 12 V battery is failing, so i3's 12 V battery can fail without warning.
Aloha,
Art

Honolulu, HI, US: 2014 BMW i3 Arravani Grey, Giga World, Tech + Driving Assist, Parking Assist, DC Fast Charging, JuiceBox EVSE
Uppsala, SE: CONDITIONALLY SOLD: 2000 Honda Insight hybrid

alohart
Posts: 842
Joined: Sat Nov 01, 2014 7:36 pm
Location: Honolulu, HI, US and Uppsala, SE

Re: BMW i3 auxiliary battery sizes

Fri May 19, 2017 2:14 am

alohart wrote:
Mito wrote:The 20ah battery is underspec'd and of questionable quality

Of questionable quality, maybe. Maybe that explains your repeated 12 V battery failures.

Underspec'd, almost certainly not. Since driving with a voltmeter in the center auxiliary power port, I've noticed that the DC-DC charger is almost always charging the 12 V battery, not only when driving, in effect adding the capacity of the Li-ion battery pack to the 12 V system. But unlike in an ICE vehicle, there's no slow starter motor to indicate that the 12 V battery is failing, so i3's 12 V battery can fail without warning.
Aloha,
Art

Honolulu, HI, US: 2014 BMW i3 Arravani Grey, Giga World, Tech + Driving Assist, Parking Assist, DC Fast Charging, JuiceBox EVSE
Uppsala, SE: CONDITIONALLY SOLD: 2000 Honda Insight hybrid

Bawareca
Posts: 28
Joined: Wed Apr 12, 2017 6:40 pm

Re: BMW i3 auxiliary battery sizes

Mon May 22, 2017 8:17 am

alohart wrote:
Mito wrote:The 20ah battery is underspec'd and of questionable quality

Of questionable quality, maybe. Maybe that explains your repeated 12 V battery failure.

Underspec'd, almost certainly not. Since driving with a voltmeter in the center auxiliary power port, I've noticed that the DC-DC charger is almost always charging the 12 V battery, not only when driving, in effect adding the capacity of the Li-ion battery pack to the 12 V system. But unlike in an ICE vehicle, there's no slow starter motor to indicate that the 12 V battery is failing, so i3's 12 V battery can fail without warning.

The 12v battery is good enough when everything is working Ok. It is not enough when for some reason there is no power coming from the HV battery, and this is also when the 12v battery dies. Not under normal circumstances, but when it is exposed to a deep discharge.

Mito
Posts: 25
Joined: Sun Apr 09, 2017 11:55 pm

Re: BMW i3 auxiliary battery sizes

Tue May 23, 2017 12:05 am

Having a battery that works ok during " normal circumstances " is all well and good but the test of a well designed system is how it copes with circumstances outside normal parameters and as we can all see the batteries regularly fail when this is the case hence this is why the small battery system is not fit for purpose.
The battery is so small that any degradation of its performance easily pushes it below its level to adequately perform that would not have happened on a larger battery. This is coupled to the fact that the car needs the small battery to run its systems and when it fails the car breaks down completely unlike a combustion car which you could possibly bump start for instance.

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