2 Amp draw from battery when fully charged - where is it going?

[RedJellyBean]

Per the OBDIIC&C, when my SOC reaches 80-81 percent it stops charging and starts doing a slow forced discharge at about 2 amps, sometimes as low as 1 amp, sometimes a little over 3 amps if I have a lot of accessories running. Where is this draw going? The drain goes away once the SOC reaches 76 percent. Is it charging the 12v battery, or is it wasting the charge somehow? Most of the time I need to conserve that charge because I have a SOC window of 80 to 65 for assist before I throw a P1449. I switch the Calpod switch "on" sometimes and the draw goes away.

[Rush]

Interesting - 80-81%... my OBDII, even after a grid charge never showed more than 70% with a normal battery pack, the same with the BBB pack I have in now. The BCM will background charge up to 70% only. If I regen after it is at 70%, I can get up a little, but it never goes near 80%. I don't have a Calpod.

I should get my ass moving on the MINI BCM Interceptor...

[Mario]

I'm pretty sure the car uses a small amount of assist sometimes, even without showing it on the cluster. Can somebody else confirm this?

[retepsnikrep]

The car uses the IMA motor to smooth out the engine, that does not show anywhere ASFAIK.

Re the battery discharging.

What happens is that the car is bleeding off the excess SOC from the battery instead of using the IMA generator to provide 12V aux power. So If you have the OBDIIC&C you notice the battery is discharging and perhaps a small increase in IC performance as the IMA generator is unloaded.

Normally when battery soc is < ~75/80% the IMA motor provides the generated power needed to run the car 12V side, which is a small but significant load on the engine. Clearly when the soc is over >~75/80% it takes that power instead from the battery to bring it down to within it's optimal soc band and this eases the load on the engine during the period it is discharging.

People who grid charge with the BCM powered and get upto 100% will certainly notice this first thing as the car bleeds off charge and the load on the engine from the IMA is very light. That is perhaps one advantage of grid charging with a good battery with the BCM powered.

Differences in the cars ecm/mcm/bcm software versions will also likely lead to different values for and exact timing of these events.

[Eli]

Like Peter says, it's being used to run the DC-DC.

Interesting that the Calpod switch turns it off? Only sometimes?

We clearly need to analyze the car's signals more. I would really like to delete this "feature". It's highly annoying! Even with MIMA, you can't disable this. With MIMA set to override the systems(you have to command assist/regen), it's even more annoying because it happens any time the DC-DC would normally be drawing current from the battery side of the circuit, like while you're accelerating heavily(so would be using assist) or decelerating(so would be getting regen). The effect of this is to slowly draw your battery down even though you may have MIMA overriding to save from using it.

Rush - If you have old computers, the positive recal point is 75.0% and maximim SoC is ~82%. If you have new computers, the positive recal point is 81.0%, and that is maximum SoC.

[retepsnikrep]

If you fit a BCM interceptor we could program it so that it nevers reports higher than 75% soc to the MCM.

So operates normally from 0-75% but above 75% say after an overnight grid charge with the BCM powered and a reading of 100% it only sends 75% to the MCM. That might stop the MCM bleeding that extra soc off as it thinks the battery is only at 75%

One possible issue would be that regen would still be available and with the battery full at 100% that might cause heating. Just an idea.

[RedJellyBean]

Thanks for the feedback. The calpod switch disables charging and amp draw in all conditions except extremely low soc.

[diamondlarry]

Originally Posted by RedJellyBean

Thanks for the feedback. The calpod switch disables charging and amp draw in all conditions except extremely low soc.

Not necessarily. On a recent trip to Columbus, OH I had an odd .3-.4 amp charge showing on the OBDII C&C (but of course, not on the dash gauge) and the SOC was at 76% and it continued all the way until around 80% or so and my calpod switch would not stop it.

[Eli]

Originally Posted by diamondlarry

Not necessarily. On a recent trip to Columbus, OH I had an odd .3-.4 amp charge showing on the OBDII C&C (but of course, not on the dash gauge) and the SOC was at 76% and it continued all the way until around 80% or so and my calpod switch would not stop it.

Trickle charge top off.

I've seen this many times before, and I suspected it happened even before the advanced instrumentation came to be. The car's systems are much smarter and more complex than we can even comprehend at this point, I think. The systems aren't just black and white. They have routines that change based on who knows what. That's one of the reasons the computer's behavior is so hard to nail down. As soon as you think you have it figured out, it does something like that and throws you off.

If only the car's trickle charge actually did something to balance the cells. It's better than nothing, but without getting to 100% SoC, it doesn't do much in that regard. It's just a nice gentle charge, something I'm sure the cells appreciate now and again.

[RedJellyBean]

Originally Posted by diamondlarry

Not necessarily. On a recent trip to Columbus, OH I had an odd .3-.4 amp charge showing on the OBDII C&C (but of course, not on the dash gauge) and the SOC was at 76% and it continued all the way until around 80% or so and my calpod switch would not stop it.

After it charged to 80% at trickle rates, did it proceed to try to discharge again at 1.5-2 amps until it got back to 76%? If you switched the calpod off, that is. Our crazy car!