A Look at Vehicle Electrical Loads

Piratetip

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This is another informative post to follow up on some of my others.

Short story:
I am testing another style datalogger for work, so I thought I would use the Supra as a quick platform to learn something on.
This is only about 20 minutes of testing total, so very very limited compared to what I would typically do for work.
Still lots of interesting things learned though.

Couple things to note:
- I was only measuring Amperage IN and OUT of the battery, and voltage sense at the battery. (As well as Temperature, but that is not shown here. Assume 25°C battery temp due to current weather.)
- Sampling rate was set to 10mS or 100Hz
- 20 minutes of logging results in ~120MB of data. :D
- The battery I am using is not stock - its a DIN sized AGM H4/LN1 battery - Ratings C20-60Ah CCA-540

On to the data: (Click the photos to enlarge, you are going to want to view on a large monitor)
This first graph is showing Amperage on the top and Voltage on the bottom, an overview of most of the log.
@5:28 this is the first of 2 engine cranks - Max Voltage drop 8.48V, Max Amperage 447A - Peak Wattage of 3,790
5:28-5:45 is the vehicle idling (Alternator active) charging the battery and supplying the vehicle load
5:45:30 is the 2nd engine crank after idling, shutting down and restarting - Max Vdrop - 9.00V, Max Amperage 487A - Peak Wattage of 4,383
At this ambient temperature the alternator sustains a constant ~14.2V charging voltage level.
The battery I am estimating is sitting ~85% SoC before testing begins.
After the first engine start the battery is accepting a peak of 55A charging as the alternator field is excited.


Next graph:
This is showing in detail the 1st engine crank. (zooming in on just the crank)
Gives a good look at how much amperage the stock starter motor is using to crank our engines. (And the resulting kW as calculated from the instantaneous Battery V.)
So this was the 1st crank and cold start - so the starting duration was longer @ 1.92 seconds.
There was an 8.8A vehicle load prior to engine starting & Voltage of 11.93V. (Key on load, vehicle ECU's ON, some lights, fuel pump running ect..)
Each of the peaks during starting is an engine compression stroke, so about 7-8 compression strokes before engine is running on its own.
As mentioned before - Max Voltage drop 8.48V, Max Amperage 447A - Peak Starter Motor Wattage of 3.8kW
@ 7.15s in the log the amperage crosses the 0 axis and goes positive, this is the alternator field being excited and thus generating power.
The voltage starts ~13.5V and ramps up to ~14.2V and stays there.
One thing I do find interesting is how low of peak amperage the starter motor is drawing.
Most new cars I test will peak around 600-700A, so its somewhat interesting to see this.
Most people would think older vehicles demand higher power levels, but this is showing the opposite.
This is due of course to a number of factors, kW rating of starter, compression ratio of engine, starter speed, gearing ect...


Next graph:
This is showing that same 1st engine crank.
But this graph is showing Amp Hours or Ampere Hour (Ah). (A calculation of the Integral of each instantaneous amperage sample)
If you have ever calculated area under a curve, its similar. (My x-axis sections have a width of 10mS)
Simple way to think about this:
- The C20 battery rating is 60Ah
- The entire 1.9 second cranking event used ~0.045Ah from the battery.
- So 1 cranking event used ~0.075% of the capacity of the battery.
These numbers are pretty much right in line with what I usually see with testing.


Next graph:
This is showing again an Ah graph.
This is only the idling section of the log, so only battery charging.
The Battery was able to accept 3.18Ah over 16 minutes.
Or another way - It was able to charge 5.3% of its total capacity in 16 minutes.
On average the battery was accepting ~10A during idling.


Next graph:
This is showing a zoomed in section of the charging/idling. (Amperage and Voltage)
I thought it was interesting because you can actually see the voltage ripple and corresponding amperage fluctuations at this high sampling rate.
Amperage coming from the alternator into he battery is fluctuating between 14A and 5A.
Voltage is fluctuating between 14.26V and 14.20V.
Peak to peak I am measuring 30 milliseconds @ idle RPM.
So really is quite a dirty regulation going on here. (Alternator is a 3 phase generator using a diode bridge to convert it to DC the vehicle can use)
I would bet the older style alternator diode bridge is to blame here, as well as other components in the charging system.
Newer vehicles do not exhibit this level of fluctuations.
Of course higher engine RPM's would help bring down the time between peak to peaks and clean it up slightly.



Ok more to come, I have some other graphs to show once I get some time to sit down again and type out the explanations.
Stay tuned!
 
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suprarx7nut

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Now we're talking. This is the stuff I want to see. Very cool. That's an amazingly small amount of battery usage to crank! I always wondered how many Amps were really used to crank.

If you have a data visualization request, let me know. I have a license for Spotfire and use it for work. Really great tool for making pretty graphs with enormous data sets. I work with ~3-4GB text files so I know it's capable at least up to that much data.

Anxious to see what else you share! Nerd session at its finest, haha!
 

Piratetip

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Now we're talking. This is the stuff I want to see. Very cool. That's an amazingly small amount of battery usage to crank! I always wondered how many Amps were really used to crank.
Yep this is pretty typical power usage for a cranking event.
Amperage usage is determined primarily by the starter motor ratings, and will be very consistent regardless of a hot crank or cold crank.
The peak of course is always the highest amperage, but for a very short period.
Once the starter starts spinning amperage drops significantly and is usually ~200-300A to sustain the engine spinning.
The resulting voltage drop is determined by a number of different factors, but can dip quite low especially as battery temperatures drop.

If you have a data visualization request, let me know. I have a license for Spotfire and use it for work. Really great tool for making pretty graphs with enormous data sets. I work with ~3-4GB text files so I know it's capable at least up to that much data.
Yeah the software I use here is able to also process these large data sets with little effort.
I will look into Spotfire to see what its like.

Anxious to see what else you share! Nerd session at its finest, haha!
I figured you would like this.
My hope is that everyone is able to take some learnings from this short log I performed.
I love digging into data from a high speed logger, there is usually a behavior there I would not have predicted.

Just a fun little side project.
 
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Piratetip

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Next Dataset.
This is showing the 2nd engine crank in the log. (Hot start)
This is much more in line with what I typically see for engine cranking duration on new vehicles.
Most new cars will have a cranking event between 600-800mS duration.
There was an 8.9A vehicle load prior to engine starting & Voltage of 12.5V. (Key on load, vehicle ECU's ON, some lights, fuel pump running ect..)
So as before the load was the same prior, but the Voltage was much higher, this is due to the time spent charging the battery. (Surface charge)
Again it is showing the compression strokes, so this time about 5 compression strokes before engine is running on its own.
Max Voltage drop 9.00V, Max Amperage 487A - Peak Starter Motor Wattage of 4.4kW
@ 28.25s in the log the amperage crosses the 0 axis and goes positive, this is the alternator field being excited and thus generating power.
The voltage starts ~13.1V and ramps up to ~14.2V and stays there.

**Important to note: The peak kW here is actually higher than the cold start, seems backwards right?

It actually makes sense when you look at the whole picture.
-kW is a calculation of momentary Amperage and Voltage multiplied.
-Starter motors peak at nearly the same amperage regardless of ambient temperature and vehicle temperature. (I have tested this from 50°C to -30°C and have data to back it up)
-So at a lower temperature the battery chemical reaction takes place at a slower rate than when warm, this results in a deeper voltage drop when colder. (At the same amperage draw) There is a lot to explain behind this, but I will not go into those details here.
-This equates to actually lower peak starter motor kW loads when colder. (remember this is a calculation of amperage and voltage multiplied)
-What you DO end up seeing different between very cold (-30°C) and warm (25°C) engine cranks is the actual duration of the crank.
-The 1st crank at cold temperatures vs. warm will generally end up cranking for a slightly longer duration. (Time)
-Again a number of factors are at play here, cold start enrichment, cold fluids, fuel vaporization temperature, ect...


Next Dataset.
This continues where I left off on the previous point.
-Time cranking duration -
This is the same 2nd crank, but showing Ah usage.
- The entire 0.77 second cranking event used ~0.032Ah from the battery.
- So this cranking event used ~0.053% of the capacity of the battery.
Again as mentioned before these numbers are pretty much right in line with what I usually see with testing.
To summarize: the 1st crank event was a duration of 1.92 seconds vs 2nd of 0.77 seconds and 0.045Ah vs. 0.032Ah.
So much shorter cranking duration is required to start the engine when warm.


Next Dataset.
This is just a graph showing what it looks like after the engine starts and the alternator is active.
The voltage ramp up to 14.2V and the resulting amperage acceptance of this battery at this temperature and SoC level.
You can see the amperage acceptance quickly falls off on the battery.
The surface charge removed from cranking is quickly and easily put back into the battery when the alternator is activated.
Beyond this point the battery charge acceptance level is determined primarily by charging voltage level, battery temperature, battery technology and SoC level. (Very high level explanation, there is a lot more happening here on the battery side)


Next Dataset.
This is a graph showing just prior to engine start.
After turning the key to the ON position, I am manually switching the fuel pump ON.
So as the data shows, the key ON position is drawing ~4.5A.
Once the fuel pump is turned on the electric motor is initially drawing peak load (very similar to the starter motor)
Peak load on the fuel pump is 14.4A - BASELINE of 4.5A = 9.9A
For reference this is using the typical Walbro 225lph fuel pump.
Steady state amperage draw is 4.31A while providing pressure and flow to the fuel rail.

The drop in amperage I can also account for between 53.75 seconds and 54.15 seconds: This is due to the crappy Aeromotive fuel pressure regulator bleeding off fuel rail pressure when at rest. ( It could also be a check valve issue with the Walbro pump)
The drop in amperage is due to the fuel pump just re-filling the system with liquid fuel (It is only flowing volume of liquid to fill the void not actually yet providing any pressure to the system.)
After that happens the fuel pump then starts providing pressure to the fuel rail at the fuel pressure regulator setpoint (38psi).
This is where the amperage level increases again slightly and then levels off at 8.8A.



The very last graph I made was just more of a curiosity for me.
This is showing how much amperage and for what duration the vehicle lock draws.
So this would be the amperage draw of both drivers and passenger door lock solenoids.
As shown I tested this twice.
Both cases the duration of the load was exactly 0.264 seconds.
The amperage draw was 13.03A - 1.8A = 11.23 Amps
So both lock solenoids were drawing 11.23 Amps simultaneously for 264 milliseconds.


That's pretty much all I tested for!

I hope this was informative and someone learned something they didn't know before.
:D
 
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