Tuning the Lithium cars for more IMA power.

Well I took another look at the HCH2 BCM pcb and it also has an isolated dumb HV section which measures the 11 battery tap voltages.
This is sent via 25 bytes of serial data 31250,9,O,1 via and opto to the battery monitoring chip. Blue zone.






So we could use exactly the same technique as in the inverter and intercept the data and modify/reduce it as we want.

So with the HCH2 BCM we have the external voltage divider option or the internal serial data interception or do both for maximum flexibility.



So I will make up another little board to send modified data and install it inside the BCM.

We might be able to do quite a few nefarious things with a voltage divider and/or serial interceptor.

Resistor Voltage Divider.

Fake perfectly balanced tap voltages.
Reduce battery pack voltage sensed with a pre-resistor.

Serial Data Interceptor.

Fake perfectly balanced tap voltages.
Reduce battery pack voltage sensed by a set %.
Extend the life and performance of an older OEM pack by reducing it's sensitivity to minor voltage variations.

We will have to be careful as it looks like some voltage data is also passing between the HV/LV sections elsewhere on the board.
It may just be a simple voltage present check or part of the HV leak detection we shall see. Red Zone.

So I modified yet another one of my OBDIIC&C devices to receive the internal BCM serial tap voltage data stream from the LV side of the isolation OPTO.



This could be the basis of a handy gadget for HCH2 owners with standard cars wanting to find out which sticks are bad etc.


It's basically 25 bytes 31250,9,O,1 format. Weird baud rate but that's what the shortest bits says.
We have a two byte rotating header $80,$52 or $C0,$52 and then 22 bytes of voltage data and a final checksum.

In this example packet below the header is $80,$52. The checksum is $43.
The two bytes that make up each tap voltage have the high byte and the bottom nibble of the low byte combined to form 12bits of data.

If we take (Voltage Tap 1) VHB0 the first part high byte $5E and low byte $05 low nibble $5 we get $5E5 = DEC 1509 = 15.09V
This is the voltage between VHB1 (negative) and VHB0 (positive)
VHB0 is the positive high end of the pack. VHB12 is the negative low end of the pack.

POS ------ VHB0 --- VHB1 ---- VHB2 --- VHB3 --- VHB4 --- VHB5 -- VHB6 & 7 -- VHB8 --- VHB9 --- VHB10 -- VHB11 - NEGATIVE VHB12
$80,$52,-- ($5E,$05),($5E,$0D),($5E,$06),($5E,$0E),($5E,$03),($5E,$0D),($5E,$05),($5E,$0D),($5E,$05),($5E,$0E),($5E,$06),$43

Note VHB6 and VHB7 are directly connected internally via the battery main switch when it is on.
So in effect they are the same connection but provide continuity for voltage sensing on the taps either side of the switch when it is off.

The operating sensing range of each voltage tap is about 0.5V to 20.15V
Resolution is to two decimal places with accuracy of about +/-10mv or so.

There is a full 25byte serial data packet sent every 15ms.
That is about a 66hz refresh rate if you wanted maximum speed for logging/processing the tap data etc.

In the video I also show the 11 x 10k 0.1% tolerance resistor matrix divider (BCM Fooler) for simulating perfectly balanced battery taps.



With a pre-resistor (inserted where the screw terminal jumper wire is) the voltage the BCM sees can be turned down to whatever we like...
i.e A 250V Battery can become 200V as far as the BCM is concerned.

Now to build and install the little serial fooling gadget into the BCM itself.

Interestingly the Nimh CR-Z MCM/BCM module has exactly the same sort of HV detection and opto isolated serial interface!
So you could power up a module like the one in the pic and read/display the voltages in the same way as I'm doing with the HCH2 BCM.



I don't have a spare voltage tap input socket so I would have to canabilise a dead MCM to get one and
hack off the bit in green to make an adapter. Not a lot of point in ruining a good MCM.

I might as well just reverse engineer the serial data in this module and add a 3.5mm jack socket so I can plug into it with the HCH2 gizmo!!
That's tomorrow mornings project then!!

Unless anyone has a dead/spare Nimh MCM and they want to send me the PCB out of it to support this research.