OT: New but interesting car battery issue

[trader_4]

This is just silly arguing over nothing. The issue was raised that the code reader being used for a couple mins could have drained enough energy from the battery so that it would not have enough energy left to start. I said whatever the code reader uses, it's a small hand held device with an LCD display and it doesn't use anything like the power used by the starter. I gave 1000 watts as a typical starter load. Use 90 amps if you like instead. Who cares? Either way, it's the same thing, the same point.

1000 watts, 90 amps, are both two orders of magnitude away from what the code reader uses. Capiche?

[RonNNN]

And all I did was point out that battery draw (starter draw) is measured in amps, not watts, in the real world. I'm sure the code reader had no direct bearing on whether the car started or not. The worst thing that might happen is a reset of timing and fuel control, not cranking power.

[clare]

Current draw is measured in amps but starter power is rated in watts. (which is amps times volts) Since under starter load the battery drops to roughly 10 volts, a 1000 watt starter draws roughly 100 amps.

[clare]

As a mechanic I sometimes determine what proper amp draw of a starter is based on it's power rating.

[clare]

The average automotive starter today draws less than 100 amps under normal cranking conditions. In extreme cold the draw may excede 150 amps. This is because the average starter today is a geared permanent magnet starter. A direct drive series wound starter of yesteryear could draw well in excess of 300 amps on a cold engine.

You need to remember the cranking voltage drops to well below 12 volts under cranking load. The actual voltage at the starter is much closewr to 10 volts than 12 - so the current is closer to 100 amps than 83 under full load.

Then again, starting a warm (but not overheated) engine can take significantly less than the full 1000 watts of power. It is not unheard of for an engine to start with the starter drawing less than

75 amps and the voltage dropping only slightly.. An overheated (tight) engine ot a very cold (stiff oil) engine will draw more.

[philo]

Irrelevant, the fact is that whatever little current the code reader draws it was sufficient to "flatten" the battery

[trader_4]

Here is an example spec, from a starter manufacturer, where the starters are spec'd in watts, HP, and amps:

Delco Remy 42MT Specifications TYPE

ENGINE SIZE

KW HP AMPS delco remy starter motor 42MT DIESEL

PETROL

42MT 12V 6.6 to 14.8 litres 7.76 KW 10.40 HP 1650 Amps

Or check out Denso:

Which comes up with this for a 2010 Honda CRV:

Notes: 1.6 kW Label: Reman Starter

I would think Denso and Delco are in the real world, they manufacture starters, don't they?

[trader_4]

Obviously you're jumping to conclusions that are unsupported. It's impossible that a small hand held code reader could draw enough power to "flatten" even a poor battery in just a couple of minutes. A battery that could start the same car fine 10 times the same day. It's almost certain that it's some other effect that's responsible, other than the small current drain from the code reader. Just because the car won't start after using the code reader to reset the codes doesn't mean that the current draw from the reader was responsible. How could a device that doesn't even get warm, draw enough power to drain down a battery in just a couple mins?

[trader_4]

ion of each piston. And when you go to start the engine, it knows which pis ton is ready for its power stroke. So it injects fuel into that cylinder an d then instantaneously commands

and?starts the engine.

tarter, and it?s going to incorporate that technology into its hybr id systems to hold down wear and tear and reduce the cost.

Now that is very interesting and could explain why it takes less energy to start it when the computer has not been reset. It's not starting it withou t a starter, but it could lessen the power needed.

[FromTheRafters]

[e-mail] expressed precisely :

You would need a battery with zero internal resistance to maintain 12 volts at the amperage drawn by a starter. If you want to get the value in Watts, you have to measure I and V and multiply them together. You'll find that the lower voltage from the battery means that even

*more* current than you thought is needed to get the required power. Just measuring amperage and multiplying by an assumed voltage gives the wrong answer.

[RonNNN]

Why not just address what I said.

Now, think of this. Does the starter draw *any* power when not in use, as compared to a hand held scanner turned on and taking readings while attached? Even at that, I doubt the scanner would draw more than 1/2 of 1 amp... likely much less.

I retired from automotive after over 45 years, and never measured starter draw or battery draw in terms of wattage. Battery capacity is measured in cranking amps and cold cranking amps, not wattage. Battery ability is usually measured by how many amps it can maintain being loaded down to

9.6 volts for 15 seconds. Rule of thumb is the battery needs to be able to maintain twice the cid of the engine in amps to be capable of satisfactorily starting the car.

[philo]

I could be wrong of course.

That said, if the battery has enough power to start the car once...it will of course immediately get charged again.

If you took the ignition wire off and could crank it several times then the battery of course should not have been drained by the code reader

[FromTheRafters]

RonNNN wrote on 10/13/2016 :

I think it's thirty seconds, and for CCA the voltage is 7.2 volts.

[Dean Hoffman]

Wouldn't jump starting it after using the code reader take the reader out of the loop? Bad connections do some really odd things. Cut rest due to aioe quotation limits.

[Ed Pawlowski]

That makes a lot of sense. If the code reader was taking the energy it would be very hot when you unplugged it.

[FromTheRafters]

trader_4 formulated on Thursday :

Wow, they even have a spec for adverse staring conditions. I wonder if it's measured in goats/minute.

[rbowman]

I've got a ScanGauge II plugged into the ODBII port permanently. It's been there for over 5 years on this car, and 4 on the previous one. Both cars only had the OEM battery.

[clare]

That WAS the rule of thumb. You won't go wrong using it today, but your battery will be significantly oversized.. Today's starters are significantly more "efficient" than the starters of yester-year.

The starters are rated in watts or kW. For instance some American market Toyotas used to get 1kW starters, while the Canadian standard was the 1.3kW "arctic" starter. A lot of diesel starters are upwards of 2.5kW

[Joe]

From:

When an engine stops, the computer that controls it knows the exact position of each piston. And when you go to start the engine, it knows which piston is ready for its power stroke. So it injects fuel into that cylinder and then instantaneously commands the spark plug to fire, which detonates the fuel, pushes down the piston and?starts the engine.

In other words, Ford has figured out a way to start an engine without a starter, and it?s going to incorporate that technology into its hybrid systems to hold down wear and tear and reduce the cost.

[DerbyDad03]

Good insulation, probably at least R-30. ;-)

(You are right - this thread is getting ridiculous. Par for the course.)