Is there a way to show the discharge rate of the HV battery on the SGII? I tried the discharge max but it seems to have no relation to the HV battery.

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Mark Smith
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The max charge/discharge absolutely depend on the HV battery, but they are not what you are looking for. The HV battery current is PID 4915, but it is scaled 2's complement, so I haven't yet figured out how to get it to display correct numbers for both charge (negative) and discharge (positive) using the simple xgauge math.
If you take HV battery X HV current, you get what the instrument cluster displays as watts in test mode.

The TXD,RXF,RXD are the same whether you want it to display charge or discharge. The difference is in the MTH section.

TXD: 0745224915
RXF: 046285490615
RXD: 3010

For correct discharge,
MTH: 027108000000
Charging will display a large positive number that is offset by 1999.9.
e.g., 20A of charge would display as 1979.

For correct charge:
MTH: 02710800B1E1

You could program both these, but could only get one to display at a time.

The HV current from the TCM is PID 496E and is similar except scaling is different.

TXD: 07E122496E
RXF: 04628549066E
RXD: 3010

For correct discharge,
MTH: 027102000000
Charging will display a large positive number that is offset by about 1446.
e.g., 20A of charge would display as 1426.

For correct charge:
MTH: 02710200C781

This is from my memory, so if there are mistakes I will edit the post............

Carl, mine behaves as you describe, and I am getting good at subtracting charge current from 1444 mentally.

I am gong to visit a math professor friend of mine who is also an EE over Xmas. We'll discuss these issues.

Also, I have been watching the Max Ch/Dch current statistics.
While they do vary based on Battery SOC and temperature, it seems to me the FEH battery does not adhear to them.

I think the Max Ch/Dch value is what the generator only is allowed to contribute, and is NOT a HV battery constraint.

So if my MAX charge is at 45A for example... cruising, the generator will never contribute more than 45A. However, if I brake hard, the traction motor will contribute up to 70A at this time.

Just my observations this week.
-John

I don't agree. When MxC goes to zero in my FEH, NO regen occurs. An FS in L will just produce an RPM run-up when MxC is zero or very low. Hard braking will use the friction brakes only. I have never seen an exception to this since I've had the xgauges, almost 4 months now. Zero MxC happens in my FEH only briefly, but frequently.

Odd that your professor friend is only an EE over Christmas. I am one year round.

Funny!

I'm sure you understand I only visit him over Christmas!

When do you see zero for MxC?
I have only seen that once or twice, but I don't have any hills where I'm at in Minnesota, so I hardly ever exceed 53-54% SOC these days.

When cold ( 15-25'F ) my MxC is mid-twenties and slowly climbs as the battery warms up. MxD is usually 20 higher ( do we assume amps? ).

So when cold ( 25'F ) MxC = 25.0 and MxD = 45.0.
When cool ( 45'F ) MxC = 35.0 and MxD = 55.0.
When mild ( 65'F ) MxC = 45.0 and MxD = 65.0.

I have never seen MxC over 45.0.
I don't think I've seen MxD over 69.0.

Maybe the scale and/or offset is not correct.
When the pack is 65'F and I slam the brake, I get 70A ( a ~1375 reading on the SG for current ) and I think 1445 = zero.

-John

Has anyone figured out what in the world is going on with these current numbers? It seems like either there is a bug in the SG II, we are using incorrect scaling factors, or something on that order, because these numbers don't make sense to be the result of a binary math error. Unless we should only be looking at 15 bits or 12 bits? If so, that might explain all of the problems.

I assume you are referring to the traction battery current xgauge not giving correct readings for both charge and discharge. This is due to the PID being a scaled 2's complement format. In the case of PID 4915, the scaling is .030518 (1000/32768). So, 20A of discharge would have a PID value of 656 (290h) and 20A of charge would have a value of -656, which is FD70h in 2's complement form. So if we take the negative value and scale it with the MTH, we get (FD70h*0271h/800h+0)/10 and get in decimal 1979.9. No bugs in the SG, just the limitation of the simple math. The SG assumes any numer 8000h or higher to be a negative value and displays it as such in the xgauges.

Reading fewer bits and then adding them back flips the sign and gives wrong values for discharge current. I have tried various other things without success so far. I mentioned this to Ron at Linear Logic in August of 2007 when I was beta testing the xgauges, but he has not had time to look into it due to other pressing concerns.

See my post over on the other site:
http://www.cleanmpg.com/forums/showt...?t=5747&page=6

It isn't a limitation of the math on the Scangauge, it is an error in the 2's complement math. Now that I know the error, I have communicated this to Ron so maybe he can fix it. Also, the error factor is really 1999 not 1995.

You are absolutely correct regarding the number of bits however, it is definitely 16 bits. I just couldn't see why it turned into 1995 (or 1999) but after playing with it for a couple of hours I finally found the problem.