Apologies if this has been done before, but if it has I'm unaware of it.

The HCH2 Civic has always had a problem with eating the battery packs.
A way of safely monitoring the voltage taps would be very nice to help identify weak sticks and the like.

Up to now we have had to use an HDS or special CAN device to request tap data via the OBDII port.
It's was not easy to get and IIRC? the data was only displayed to one decimal place or 0.1V

People have used multiple crude voltmeters, but that is not elegant or very safe.

So looking inside the HCH2 BCM we can see it has an isolated tap sensing HV section with it's own CPU and a simple opto isolator connecting it to the LV side.
Suspecting it was simple serial data stream being sent I grabbed some captures from the middle output pin of the opto!

Hey presto! Now we have an OBDIIC&C based device that can simply piggy back onto this safe LV side of the opto and gather the 5V logic voltage tap data.


It's basically 25 bytes 31250,9,O,1 format packets. Weird baud rate but that's what the shortest bit length 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.

So you can simply make a 5V serial reception device using your favourite cpu/PIC/Arduino etc
Power it from the LV side of the BCM and with three simple connections +5V or +12V, GND and 5V Logic serial input you can have a dash mounted safe voltage tap monitor.

 

As always... nice work Peter!

 

Cheers.

Another video here showing testing on a live pack.

 

Video showing the TAP monitor more sorted and plugged into an Insight G1 pack using a simple wiring adapter.
It would be trivial to make an HCH1 adapter as well but I don't have need for one at the moment.

You Tube

Need to tweak the software now to make the number of taps being monitored selectable.

I also recompiled the firmware for the cheap early PIC16F886 chip which I had loads of kicking around.
If you remember 15 years or so ago this was the first PIC I used in the OBDIIC&C gauge.
No point using a CAN enabled expensive 32mhz part for this simple job.

 

Interestingly the Nimh Insight G2, CR-Z, Jazz, 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 cannibalise 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!!

 

Nice!

 

Just finished the Nimh CR-Z/Insight G2 voltage tap monitor device. [img]data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7[/img]

This basically sniffs the serial data from the LV side of the Nimh MCM board and it is then displayed using one of my modified OBDIIC&C gadgets.

Now we can already get stick voltage data in a car from an HDS or from my earlier OBDIIC&C device.

This new method is basically a stepping stone towards future tuning where we can manipulate the voltages the MCM sees.

It's also useful for bench work where you can't use an HDS or my other in car device.

The Nimh battery in the video is a very well balanced (cycled) pack that has been in storage at least six months!

So we now have a plug in voltage tap gizmo for the G1 Insight, G2 Insight, CR-Z, Jazz and HCH2 Civic.