I have one "off the wall" idea after sleeping on it for a little bit.
1. Some gizmo that operates off of an SLA battery.
2. Charger that somehow knows the car is running. Alternator ripple is one turn-on method. Cigarette lighters are either always on or IGN only. Kinda wish they were selectable. Monitoring system needs to know when engine is running.
It's actually the opposite, we need to know when the engine is off and the key is out. At that time, more or less no current or very little current should be flowing. It should certainly be less than the amount that would drain a battery overnight.
It should be easy as any number of things change with key position.
3. The negative side of the battery cable can act as a current shunt. So, voltage measuring across this is surely possible.
(It may or may not find negative battery cable connection problems)
4.The +Bat to alternator terminal should take care of alternator type issues like diodes, winding breakdown and regulator.
(Measure voltage there too)
5. Maybe design some sort of power line disturbance monitor kind of software with a threshold which is a trigger.
6. I'd also monitor the dome circuit, It keeps track of car doors, trunk light possibly etc.
7. In other words 3, 4 and 6 are triggers. They wake the processor up.
Right, a wakeup / detection function is necessary.
8. One could then record the "power" and/or currents for those circuits and tally 2 and 4 into watt-hours or watt-minutes. This is some sort of threshold that the car goes in for analysis. Something like watt-mins accumulated with engine off.
Because the batteries are rated in Amp Hours, as one system, there is only so much time they can provide current at rated voltage...
9. If you want to be able to somehow find the problem, I might suggest a custom bed of nails that uses spring loaded pogo PCB test probes that would contact the test points of the fuses in one or more fuse blocks.
10. You would then multiplex the inputs and try to read differentially the voltage across the fuses. You would have already have told the computer the type and amperage of the fuses ahead of time, so hat voltages can be converted to approximate currents,
Re-iterating: Te dome, alternator to battery and bat neg to ground voltages measured across the respective cables becomes the microprocessor trigger to wake up.
it does the total watt-min and the watt-min on the alternator side of things.
Now it tries to measure the individual fuse drops using a bed of nails that's attached - kapton Tape?
This **broken link removed** is one such company that makes probes. A bed of nails can be made on a polycarbonate sheet.
What creates issues is multiple fuse boxes. At least two. One inside and one in the engine compartment.
The bed of nails creation could come from a photo, the turned into a drawing and then CNCed.
The problem can be explained simply and generalized from there.
Suppose we have a circuit with a switch and a bulb and a battery. On/Off, it works well. But the switch wears out and instead of OPENing the circuit, it has some resistance in the OFF position, and allows a very small current to pass through it.
The next day the battery is dead and the switch doesn't work.
In a vehicle there are some hundreds of circuits distributed across the car. When a hard short occurs, the fuse blows. And that provides diagnostic direction.
If a resistive short circuit occurs, it just slowly drains the battery. And these we diagnose by finding which fuse is providing power and going from there (while monitoring the net discharge rate in milliamps of the battery).
The type that is likely to bankrupt a car is one that occurs intermittently and leaves no evidence of where the fault occurred.
Starting from the battery we have 100 amp fuses, then 50 amp fuses, these feed power to fuse boxes around the car, in the dash, trunk, engine compartment, behind seats. From there power is fed directly to actuators and modules, and from modules to other actuators. There are 10-30 modules.
The engineers have different designs, so current flow often does not have a logical direction. I just dealt with a car that had one 20a fuse feeding 25 modules from the engine to the gas tank and within the dashboard and steering column, under the carpet. It had a bad splice. And several junctions where it joins six or eight circuits together.
That car had a lot of shunt-wiring that drove me nuts. A lot of circuits would have logical flow but have some kind of shunt going elsewhere that acted as a signal that the circuit activated.
So in a nut shell, I am wondering if there is a way to run a clock for example when the engine is off but current is passing through a circuit. I would apply this device to larger fuses first and then work down to Narrow the Field.
The whole body/chassis/engine is at ground potential so that means this device could be planted at a ground connection as long as there is enough voltage drop right there to indicate current flow. There are only a handful of groundsand a handful of large fuses, so a divide and conquer approach is how it could go.
Think of it like if you have ever seen the water meter for your house, they often have a numerical indication of consumption as well as a little black or red triangle. The triangle moves even if there is a tiny bit of wate flowing, like a broken sprinkler pipe in the ground.
it provides an indication of whether the system has a leak somewhere, or something is using water that shouldn't. It is only useful with all faucets closed, dishwasher and laundry machines off, etc. Much like my device would need to count mA so to speak with the engne off.
Regards.