Building a more accurate regen/assist guage

GICU812 · 12-01-2007, 02:13 PM

Ok, let's try it this way.

I am tired of the assist guage lying to me. For those of you who are still blissfuly unaware, full assist on the guage does not mean the electric assistance system is actually giving you 100 percent assist. Rarely, such as at low speeds and low gears, it actually will give its all, but mostly at higher speeds, while the gauge reads max, the true assist is much lower.

Can anyone provide insight into the signaling used with the current sensor, or a better signal to read off of? If nothing else, I would at least like to know what its really doing.

If I can get a reasonably accurate signal, I would even try to track SOC, with a numeric charge indicator.

Willie Williford · 12-01-2007, 02:36 PM

Here is a something that might help you in your research.

The IMA assist is mainly based on "load" on the engine.
Hook up a vacuum gauge in the system, drive around for a while and maybe you can see the what I mean.
Don't know the electrical happenings, maybe "Mike" can help you.

HTH

Willie

nemystic · 12-01-2007, 06:32 PM

There's a hall effect current sensor that provides an accurate voltage in proportion to the assist / regen current; IIRC; 2mV/Amp(?)
I tapped into this a few years ago, and used a small DVM that was velcro'd to the dashboard, to precisely monitor assist and regeneration current. (The stock indicator in the Insight is misleading, particularly for regen.)

After about a year, I removed the DVM and now observe assist / regen current with lower precision but similar accuracy, on an LED bar graph (which is part of a modification kit).

Information for the above referenced hall effect current sensor is in the Insight maintenance manual schematics (which I don't have). If you don't have them either, your best resource for electrical information is "Mike" as Willie has suggested.

b1shmu63 · 12-02-2007, 01:36 AM

One LED per horsepower might be nice.

Armin · 12-02-2007, 07:20 AM

I'm using a voltmeter like nemystic mentioned. Relatively easily installed if you have the service manual schematic, difficult and dangerous without. You also need some knowledge of electronics.

The sensor has three pins: +/-12V supply and output. I used an opamp to generate a virtual ground from the split supply. This is not vehicle ground! The output signal is as nemystic says a few mV/A. I calibrated my meter using a clamp-on probe for reference. With a potentiometer I adjusted the meter reading so it is directly in Amps.

nemystic · 12-02-2007, 12:56 PM

I was actually able to get an accurate voltage measurement (proportional to current) using the hall effect sensor output relative to MCM logic ground. However, the virtual ground, as Armin has implemented, is preferable, particularly if you scale the signal.
If you don't have access to a clamp-on current probe, you can scale the signal voltage output to 50% and then read amps (for assist / regen) on the millivolt scale of the DVM.
As a friendly reminder, always be careful working around high voltage, as it can be deadly.

I could be wrong about this, but I believe the signal from the hall effect sensor we've tapped into does not show the low level current that is from the IMA motor/generator to the high voltage battery pack which is at an average level to maintain charge of the 12V battery by way of DC/DC converter (during the daylight hours). That's a nearly constant, but necessary drain on the ICE power, and it probably has a small impact on fuel efficiency.
The additional current that's typically required to maintain charge on the 12V battery when the headlights are on is included in the HES signal.

I suppose it's just a matter of time before LED headlights will be available . I've found the now affordable 1 Watt LED lights to be more than adequate for bicycle commuting at night.
LED headlights should improve fuel efficiency in all cars, and it would be noticeable in the Insight.

I just read that a MIMA thread will soon be re-opened on this forum. I believe that's good news for Insight nation, and I hope that everyone abides by the forum rules so it won't become necessary to shut it down again.

Armin · 12-03-2007, 12:36 PM

Quote:

Originally Posted by nemystic

I believe the signal from the hall effect sensor we've tapped into does not show the low level current that is from the IMA motor/generator to the high voltage battery pack which is at an average level to maintain charge of the 12V battery by way of DC/DC converter (during the daylight hours).

There are two current sensors: one for motor current (between IMA motor/generator and PMU) and one for battery current (between battery and PMU). The difference between the two is the DC-DC converter current.

I tapped the battery current sensor, so I don't see the DC-DC converter current when the engine is running, but I do see it in idle-stop, when it's provided by the battery.

b1shmu63 · 12-03-2007, 08:21 PM

Yes Nemystic, one Mima post MAY be reopened. The matter has been under discussion for a while by the moderating team and Benjamin. Patience.....our moderators have busy shedules so the details/rules/cautions are taking time to discuss and work out.

Now back to our regularly sheduled topic, building an accurate gauge.

**IamIan** · 12-03-2007, 10:06 PM

if you wanted to build a counter to go with the real time reading as the SoC indicator is about as accurate as the assist and regen indicators.....

The efficiency of the Amps going in compared to the amps going out is around 80% for NiMH in general....

The simplest would be to include that scaling into your amp hour counter that counted in and out of the battery pack.... Maybe a calibrate every once in a while when you know the battery is at top or bottom...

Real world NiMH will actually vary in cycle efficiency depending on cell temperature, SoC , and rate of charge or discharge, and pressure, and of course internal materials ....

Since the Discharging of a NiMH battery is endothermic it will absorb some of the (I^2)R heat generated by the internal resistance and impedance of the cells.... Additionally the batteries in the pack do not get equal air flow... or equal air temperature of the air that flows over them... And the Thermal Mass of the Batteries will delay Thermal effects of charging and discharging.... so Thermal Temperature change can be useful... but will not really tell you accurately how the cycle efficiency is changing, or what energy is being lost to heat.

Voltage on NiMH tells you nothing other than top and bottom 10 to 20 % SoC..... so it won't be helpful.

We could use the Thermal Evaluation paper the government did on the Insight's battery pack and use their internal resistance numbers they got at various cell temperatures... combine that with the thermal temperature coefficient strips on each subpack to know the subpacks average ball park temperature ... combine that with a small computer chip that will adjust the (I^2)R losses as the current changes in and out of the pack... as the resistance changes in and out of the pack with temperature.... as a more accurate Amp hour counter.....

ultimate amp our counter would also include ambient temperature , air flow rate , atmospheric pressure , individual cell temperatures, memory to do comparisons for change in temperature and change in voltage of a change in time....

just thoughts.....

b1shmu63 · 12-04-2007, 03:23 AM

Congratulations Ian, I believe you have discovered who really killed the electric car!

I gather what you are explaining is that when a few cells get out of spec the computer gets surprised and throws a fit, otherwise known as a recal. Whereas, when everything is in spec it does a reasonably good job of estimating the remaining charge.

I hope that battery management for the new lithium cells doesn't require quite so much alchemy.