Electrical Engineering


Making a simple IMA bypass connector from an old pack relay board

Making a simple IMA bypass connector from an old pack relay board
simple IMA bypass connector
The IMA battery can be completely removed from the car, and the car will still function, if the DC/Dc converter can have the HV input it requires.
The typical way to do this is to remove the whole connector/relay board from the pack, and use it to make those connections.
If the fuse and connector from a used pack is available, a much safer and simpler IMA bypass can be construced.
You remove the DC/DC connector, the 30A fuse, and make up some wires with ring terminals, and make a short bypass connector with those components. It is important to keep everything well insulated, and prevent ant possible shorts, so here is how I made mine.
If you can leave the HV battery in the car, just pull the "A" connector of the BCM and turn off the HV battery switch
location of BCM A connector

Making an isolated hall effect current sensor with ring terminals

Making an isolated hall effect current sensor with ring terminals
simple isolated current sensor
Needed an isolated current sensor to sense the current in my cell level test fixture. Found a neat part made by alegro that has a compensated hall effect sensor with built in current shunt. Unlike a regular current shunt where the resistance of the shunt produces a voltage when current flows through it, this device has an integrated hall effect circuit built in. The device comes in many flavors, with unipolar or bipolar sensing up to +-150A. The best part is that the hall circuit is electrically isolated from the current path. The down side was that the device was designed to mount on a PC board, so attaching it to the big 1/4" studs that I required was dificult. I carefully straightened the heavy copper buss bar leads and sawed a slot in some heavy 1/4" ring terminals. The terminals were soldered to the straightened leads, and the fine hall effect wires were connected to three wires and strain relieved with some hot glue.
Works like a charm.

Measuring resistance of less than 1 ohm

Measuring resistance of less than 1 ohm
measuring less than 1 ohm accurately
Having some issues with the resistance of a db-25 cable, and need to compare the end to end resistance of several brands to find the lowest resistance.
Unfortunately when using most DVM's, the sub ohm accuracy and resolution is pretty poor.
Special sub ohm testers usually use a 4 connection meter. two leads apply a constant current, and two pick up the developed voltage.
I used my adjustable constant current lab supply, set to produce 1A CC.
This current through the sub ohm cable wires will develop 1V/ohm, so the cables actual resistance can be measured with 0.001ohm accuracy. The voltmeter will read 220mV for the 0.220 ohms.
Since the current is constant, and the current connections are separate from the measuring connections, the accuracy is very good.

Power semiconductors

Power semiconductors
Some huge power semiconductors
A beautiful assortment of power semiconductors.
How does 300A @ 1200V half bridge sound, yikes that is 360,000 Watts of power.

What actually goes wrong with the batteries????

What actually goes wrong with the batteries????
What is wrong with these things
Hybrid battery packs develop several problems as they age, which are aggravated based on temperature history, and length of time spent inactive.
Inactivity allows the cells to self discharge, and since all cells are going to do this to one degree or another, and the rate of self discharge can be quite different from one cell to another, a typical pack that is setting codes like the 1449,1447,1433, will have cells that have fallen way behind others , and the IMA control system which works to keep the cells in the 20% to 80%, has no mechanism to rebalance them.
All Nickle based batteries develop this self discharge because they can spend a lot of time sitting at a middle SOC, where Nickle dendrites (little whiskers of nickle) will grow and gradually provide a leakage path between the + and - plates, eventually leading to a shorted cell.

Storage and self discharge
Another thing that happens when a cell drops down in the SOC relative to the other cells is it develops an effectively reduced capacity that is recoverable called Memory effect.
memory effect
Memory effect capacity loss is reversible by fully cycling the cell from 100% to less than 1V/cell.

So the code setting pack has this unmatched set of cells with widely different SOC, and wide spectrum of effective AH capacities, which reduces the effective capacity of the pack as a unit to a value that sets the code.

When the car charges the pack to full, (80% SOC) it stops when it thinks the pack is full, with the assumption that all the cells are the same, where in fact some cells are still only partial charged.
The discharge limits are also skewed so the pack stops allowing assist long before the highest capacity cells are empty because one of the low capacity cells has dropped out.
When that happens the rest of the pack discharges through the empty cell effectively reverse charging the cell.
Cell reversal
The IMA safeties kick in causing the SOC guage to drop to the bottom, and aggressive charging begins to pull the reversed cell back from sure destruction.

The longer the pack is used like this, the worse the pack gets.
Another factor in this picture is heat.
Once a cell gets to 140F the internal pressure can get so high that it vents potassium hydroxide and the cell will permanently loose AH capacity. No amount of charging can bring back capacity lost due to venting.


The charger and discharger system will first fully charge all cells to 100% SOC, for the first time since the pack was installed. This can take a long time, as we have to limit the charge current so the cells that fill up first do not overheat.
When a cell is fully charged, all the charge energy becomes heat, which is why the cooling fan should always be used during charging.

Getting the whole pack to 100% will fix some packs, especially ones that have become unbalanced due to just sitting and self discharging, and have not developed any memory effect.
Hypermileing where you do not use the pack much can cause the pack to develop the same self discharge unbalance.

Most packs have both memory effects and real capacity loss, as well as differing degrees of self discharge, so the discharger aspect of the system becomes a great tool to extend capacity on the memory effected cells by cycling the pack between full and the detection of the dropout of the weakest cells in the pack, The idea being that the weakest capacity cells are the ones causing the problems, so since they will be the cells that get the deepest discharge, if the issue is memory effect those cells will recover capacity with each cycle, and the minimum voltage reached during the discharge should get lower and closer to the 1V/c level which would be 120V on a 120 cell Insight or first gen civic. A well balanced pack even if at low capacity will discharge uniformly so the discharge would stop at near 1V/cell.
In the real world that is seldom is seen, since all packs will have several of these issues happening at the same time, so there will be a point where the discharge will repeatedly stop at the same elevated voltage, like 138V. At this point the cell that is dropping out is likely one that has lost capacity due to venting or simply age, and to get that pack back in balance, we look at the other cells when that cel drops out to see if they are also ready to drop, or if the majority of them are still quite good.
At this point, if the car is still setting codes, we need to take the process from the car to the bench.
Using a procedure that we are still tweaking, we can use the charger/discharger, and datalogger to discharge the pack with the ends open so we have access to the ends of each stick, to make voltage measurements.
If the other cells are still well over 7V replacing the stick that dropped out with one of higher capacity, would then allow the cycles to continue to reduce memory effect and increase capacity of the rest of the pack.

The photos and graphs below were done with my cell level test fixture and Labview graphing program for my pc.
This is a graphical analysis of my Insights Subpacks after I got an IMA and Check engine light. The pack never did recalibrations, and it set the IMA code several days before setting the check engine code.
P1447 set the IMA, P1449 set the check engine. A system reset would not clear the codes. Each subpack was charged most of the way, topped off, then discharged while watching the temperature and voltage across each cell.
I looks to me like subpack 10 and 12 are the guys that set the code. I hope to be able to replace the cells that are bad, cycle and rebalance the rest and try the pack back in the car.
Please feel free to comment on the graphs with your opinions about what they show, my comments are very preliminary since I have only put them through a single cycle so far.
I charge @ 5-6A, and can do a high rate charge of 30A. The discharge is at 30A, and can be increased to ~70A.

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Inside the 100A semiconductor battery pack fuse

Inside the 100A semiconductor battery pack fuse
The insides of a high power fuse
The battery packs of all hybrid cars have a very special fuse to protect the circuits and the pack from short circuit and over current conditions.An Insight owner came over so that I could help him diagnose his IMA problem, and we found tht the main 100A fuse was blown. He had already replaced the inverter stage, which must have been the cause of the fuse failure.
Opening a high voltage high current DC circuit requires a special type of fuse. It is called a semiconductor fuse, but this name is misleading. There are no semiconductors in the fuse, the name describes it's ability to blow extremely quickly so any semiconductor devices it is powering will be protected, and this means rapidly quenching the hot arc that forms when a high power DC circuit is opened. The metal element is similar to a regular fuse, but the fuse is filled with an insulating glass like powder that rapidly melts and quenches the arc.I opened the blown fuse so we could see how it is constructed.

Put your exercize to good use?

Like most Americans I eat too much and do not get enough exercise. I also watch TV too much.
I modified an exercise bike to produce electricity. The electricity runs a tv, radio, lights, fans, to use the power that I am generating. Old car alternator, with a a small battery to get the field excited to start the generating. 250 Watts is a lot of work.
For a light workout pump during the show, and rest during the commercials, For a full workout watch a DVD movie and pump the whole time.
Put your exercize to good use?
Dont stop till the commertial

Some uses of laser pointers

We all should have a couple of laser pointers sitting in the "used to be cool toy box" There are many uses for those lasers other than the usual pointer application.
Detecting things:
I have used them for generating an electrical signal when detecting things. I needed a flow meter to detect the flow rate of the heat exchanger for my solar heating system. To buy a unit with high accuracy, and a readout, was in the several hundred dollar range. I found this cute German made home water meter for less than $100. It only had one pulse output for every gallon, which was not sufficiently accurate to measure the sub gallon per minute rates that were sometmes necessary. I mounted a laser pointer so that it shined through the notches on the rotating disk that was right on the flow turbine, so it turned hundreds of times to each gallon of flow, and gave multiple puldes per revolution. I mounted a photodetector in a blackened tube, and glued a lens on the front of the tube. The detector assembly was focused on the notches of the rotating disk. and was able to generate a pulse stream for each rotation. This pulse was buffered, amplified and converted to a digital pulse that was read by the controlling computer to regulate the speed of the pump to produce a constant flow rate.


Some uses of laser pointers
Detecting a rotating disk