Battery current during engine start

[Salvo]

I was a bit curious how much current is pulled during my 5-cylinder diesel start. It's more than I thought.



Just before the 8 sec mark the ignition is turned on. The glow plugs pull over 100A.

After 12 sec the engine is cranked. Current spikes to over 700A. It takes about 1 sec to start. After ignition, glow plug current settles to about 90A.

At 16.5 sec the alternator kicks in. Battery current ramps (negative) to about 20A. The battery is now charging. Negative current is charging current.

[Salvo]

Some do fail at that mileage. I doubt it's more than 5%. As always, those that fail are vocal about it. Many tow, I just keep a motorcycle on the back.

For $3k you can get a rebuilt one. Not the end of the world.

I change the fluid every 40k. We'll see how it goes.

[NinerBikes]

Salvo wrote:
This is not a van. I get 16 - 17 mpg, usually driving at 62 mph.

Any truth to the rumor that the transmissions on those MB based chassis fail at 100 to 120 k miles and need a complete R&R?

[Salvo]

This is not a van. I get 16 - 17 mpg, usually driving at 62 mph.

[NinerBikes]

LScamper wrote:
" I'd guess that the ripple there is more due to the starter motor hitting up against a compression stroke on the engine. That would also explain why each successive peak is a little less severe, as the engine gains momentum."

X2.

The first peak do to starter turning engine from dead stop. Like locked rotor current.

Amount of energy to overcome all that inertia, heavy diesel pistons, crank and flywheel is massive.

Once turning and getting up to speed on 2, 3rd, 4th and perhaps 5 piston compression stroke, a full 720 degrees, so all crank angle sensors have been measured by Hall effect sensors on the flywheel, the common rail injection system then fires fuel to light things off. But it has to get ignition timing bearings first from all 5 cylinders, before doing so.

What kind of MPG's do you see in your Sprinter Van? Speed traveled on interstate?

[Salvo]

You guys got it right. The dynamic loading of the starter motor, created by piston compression is causing the current gyrations.

I think most if not all new cars have the ignition switch turn on a relay which in turn activates the starter solenoid. A lot less current goes through the ignition switch. On my new Miata, there's no key for ignition. Just a push button switch. The "key" is left in my pocket. The car doesn't use a key.

On a side note, automotive relays don't use a despiking diode any more. A resistor in parallel with the coil is now used. It allows the contacts to switch faster.

[LScamper]

" I'd guess that the ripple there is more due to the starter motor hitting up against a compression stroke on the engine. That would also explain why each successive peak is a little less severe, as the engine gains momentum."

X2.

The first peak do to starter turning engine from dead stop. Like locked rotor current.

[DrewE]

SCVJeff wrote:

Salvo wrote:
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.

That ripple out at 200A was what I was presuming was the back EMF of the starter coil collapsing

:h Why would the solenoid field collapse while the starter is apparently still turning? I'd guess that the ripple there is more due to the starter motor hitting up against a compression stroke on the engine. That would also explain why each successive peak is a little less severe, as the engine gains momentum. The waveform does look like ringing, though, I admit.

I suspect we don't actually see the solenoid ripple because of a couple of possibilities things: there may well be a snubber rectifier to shunt it away, and even if not presumably the opening of the starter keyswitch (or equivalent) disconnects it from the circuit being measured. In the latter case, without a snubber, I would not be surprised if there is some arcing in the switch.

[SCVJeff]

Salvo wrote:
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.

That ripple out at 200A was what I was presuming was the back EMF of the starter coil collapsing

[NinerBikes]

Salvo wrote:
I see no signs of an inductive kickback. Here's a plot of the battery voltage during the cranking sequence. Data logging connections are at the battery. I would need some gummy arms to snake through the engine compartment to get to the starter. I'm fairly confident any inductive flyback would be evident at the battery.



Around 1.4 sec there's a little dip in voltage. That could be the solenoid getting energized. Shortly thereafter, the starter motor pulls battery voltage down to 9.4V. A little after 2.2 sec the solenoid releases. This is where the inductive voltage spike would occur. There isn't any evidence of one.

Voltage is measured every 1.5 ms.

Yeah, the Arduino data logger is amazing. All for about $20. The clamp-on current probe is a bit more pricey at $75. There's a few brave souls here that are getting into Arduino.

I don't have enough geek in me, but I did buy a EVSE charging station from e-motorwerks to recharge my elecric car, and it does indeed have an Arduino Open Source data logger in it.

E-motorwerks EVSE electric car charging boxes with Arduino loggers.

[Salvo]

I see no signs of an inductive kickback. Here's a plot of the battery voltage during the cranking sequence. Data logging connections are at the battery. I would need some gummy arms to snake through the engine compartment to get to the starter. I'm fairly confident any inductive flyback would be evident at the battery.



Around 1.4 sec there's a little dip in voltage. That could be the solenoid getting energized. Shortly thereafter, the starter motor pulls battery voltage down to 9.4V. A little after 2.2 sec the solenoid releases. This is where the inductive voltage spike would occur. There isn't any evidence of one.

Voltage is measured every 1.5 ms.

Yeah, the Arduino data logger is amazing. All for about $20. The clamp-on current probe is a bit more pricey at $75. There's a few brave souls here that are getting into Arduino.

[MEXICOWANDERER]

"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.

[Salvo]

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.

[MEXICOWANDERER]

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.

[Salvo]

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.