Battery current during engine start

"Ain't inrush a ----- ?"

You've got a nice program!

I remember from 50 years ago, an alkylation plant compressor motor that inrushed 22,000+ amperes at 1,600 volts direct current. PG&E was notified, and only one attempt (not all were successful) was allowed every three hours. I believe Shell purchased the small brick PG&E generation plant (60mw)from PG&E. They certainly had enough No 6 fuel oil for it.

Dedicated Data Logging back then cost tens of thousands of dollars. If I was still in the business I certainly would employ Arduino data acquisition. The Tektronix is a 4-channel storage scope albeit it with a CRT display.

For the heck of it here's the starting current from my new toy: '16 Miata.



Charging current slowly increases to about 30A after 8 sec.

When the field / armature / solenoid / electromagnetics collapse it puts on a real show on an oscilloscope screen. Measure both the starter motor connection, then on the battery supply voltage of the solenoid connection. Watch for peak inverse voltage as well. A stout avalanche rectifier will greatly mute the battery side hysterics. I've cooked a number of Motorola MR2535 rectifiers doing this on the starter motor side of the solenoid.

A gear-reduction type starter motor significantly reduces peak current cranking amperage) values.

The surface charge is long gone. The glow plugs are pulling 100A for about 5 sec before the starter is engaged. As seen from this plot, battery voltage starts below 12V and drops below 10V from the 700A spike.



This is a plot of the current in the starter cable and chassis battery voltage. The data rate is limited due to the speed of the A/D multiplexer (switching between voltage and current measurements).

Data is taken on a Sprinter (Mercedes 5-cylinder) diesel with 80k miles.

tatest wrote:
That 700 is a spike fed by surface charge on the battery plates. Internal resistance in most lead-acid starting batteries limits deliverable current to 400 amps or less. NiMH could deliver more.

That chart looks... Very reasonable.

Guess there's a reason many diesel trucks have 2 starting batteries in parallel.

Salvo wrote:
I'm using a current clamp (Hantek CC-650). The Hantek has an analog output which is connected to a 16-bit A/D. The A/D connects to an Arduino datalogger. Data is recorded at 1.5 ms rate.

What is EMF?

The field collapsing on the starter solenoid. Or.. That which knocks you on your pattutie if you have a hand on the coil.

We were trying to measure starting current on a QD7500 without removing fuel lines. We looked at two and there is a 100A difference between them but we think it's just bad sampling.

That 700 is a spike fed by surface charge on the battery plates. Internal resistance in most lead-acid starting batteries limits deliverable current to 400 amps or less. NiMH could deliver more.

Good stuff, any idea what the compression ratio is on that 5 banger? Miles on the odometer, and how well it's now broken in, or not?

Sweet graph, Thanks.

I've looked at my digital ammeter when cranking a gas engine,and see it go as high as 140 amps cold and 75 amps hot.

Do not know how much it would spike too if the refresh rate of the ammeter was higher