Odd behavior today

[Eli]

Ah crap, dp.

[retepsnikrep]

Originally Posted by JohnVirginia

It will be interesting to learn in the future whether the full capability of the higher mAh batteries can be utilized without either firmware changes or BCM foolers like in the lithium application. Is this already known? Was the 10ah limit from the lithium system testing determining the exact “energy” above the stock battery level was really being used or simply the car monitoring system did not work once the available energy went past 10ah?

When I first did my Lithum conversion we did not know anything about the limits of the BCM. I found when a 40ah capacity system was fitted that the stock BCM would allow approx 10ah to be discharged from 75% (pos recal) down to 0%. In practise that meant the ima worked normally until it got down to 3 bars ~28% when it would hang and then continue to allow limited assist for quite a few more AH. However during this period it would be trying to charge unless it was overidden by ima control. Eventually the soc would fall down to zero and it would try to force charge even harder and assist would be stopped.

That's why I made the BCM interceptor which faked the soc at 75% to stop the car reacting to a lower soc by reducing available assist and trying to regen all the time. It also allowed unlimited capacity to be drawn the BCM limitations no longer mattered.

We can't change the oem BCM operation only fake it's inputs or intercept it's outputs sadly. However we could possibly build a substitute device designed to replace it. But that requires quite a bit more research work.

[JohnVirginia]

Originally Posted by eq1

I don't really know, but I pulled this off wikipedia, about ohm's law:

"For a wide variety of materials and conditions, V and I are directly proportional to each other...In other cases, such as a diode or battery, V and I are not directly proportional, or in other words the I–V curve is not a straight line through the origin, and Ohm's law does not hold. In this case, resistance and conductance are less useful concepts, and more difficult to define...."

Shucks. Just when I thought I had figured out the world was flat, someone comes along and tells me it is round.

In all seriousness, this helps me. Thanks.

[JohnVirginia]

On a slightly different tack, is battery internal resistance constant or at least linear versus battery voltage (at the same temperature). I would guess that IR changes with temperature. Any links known that have plots of typical IR versus various parameters?

What about the idea of substituting a low resistance/high current capable shunt in for a battery stick (or two battery sticks) as a fix for a high IR (bad cell(s)) situation? Fool that battery tap to make appear to the BCM/MCM/whatever that all is well at all times. Fool the total battery voltage reading (if there is one) to the BCM to be whatever it needs to be to operate the system at a reduced voltage. Removing one stick would reduce the battery voltage by 6 X 1.2V = 7.2V to 144V-7.2V=136.8V or 129.6V if two sticks. If these voltages are input to the MDM can it still convert the DC to three phase AC suitable to running the assist motor? Stupid idea?

[Eli]

Originally Posted by JohnVirginia

On a slightly different tack, is battery internal resistance constant or at least linear versus battery voltage (at the same temperature). I would guess that IR changes with temperature. Any links known that have plots of typical IR versus various parameters?

Battery IR is not constant and changes dramatically with both temperature and SoC.

Here's a pic from a NREL study that shows the batteries IR under charge and discharge at various SoC.

What about the idea of substituting a low resistance/high current capable shunt in for a battery stick (or two battery sticks) as a fix for a high IR (bad cell(s)) situation? Fool that battery tap to make appear to the BCM/MCM/whatever that all is well at all times. Fool the total battery voltage reading (if there is one) to the BCM to be whatever it needs to be to operate the system at a reduced voltage. Removing one stick would reduce the battery voltage by 6 X 1.2V = 7.2V to 144V-7.2V=136.8V or 129.6V if two sticks. If these voltages are input to the MDM can it still convert the DC to three phase AC suitable to running the assist motor? Stupid idea?

The voltage is high enough for the DC-DC to still work, but I don't think it would work overall. The Insight has many checks and balances. It wouldn't throw codes as long as the voltages match, so that might not be necessary. But you're crippling an already crippled pack.. Don't think there would be many benefits.

The minimum voltage under 6.5kW of assist seems to be 140V.