General Versa Question

[Rockhound]

The other day I was driving the Versa and noticed something I hadn't previously experienced in this car (I don't get to drive it too often as it is my wife's car).

It's gotten quite cold around here (snowed a little yesterday) and we were using the heater liberally - and it got a little too hot in the car with the sun pouring in too - so I cracked the two back windows.

When we came to a stop at an intersection, I put the two windows up, and being the OCD individual that I am, I held up on the window switches a few more seconds to make sure they were *really* closed - and the engine's idle dropped about 150-200 RPMs. Similarly, turning on the rear window defroster also resulted in a momentary drop in RPMS (~100 or so this time).

I've experienced this before (in my old B13 Sentra) and I chalked it up to the car being old and having an old alternator/battery/so on and so forth. With the Versa, I'm a little surprised. I don't recall this happening in warmer weather, but I don't know for sure.

So is this just normal and to be expected due to the car's small engine also having a small charging system that is more susceptible to drain when various components are in use? I know small 4-cyl. cars suffer more of an RPM-shudder when the A/C kicks in over larger 6 and 8 cylinder cars, so I figured maybe this was analogous.

Anyone able to shed some light?

[gotak]

DC motors are basically just some coil of wires. As least electrically that's what they are. Wires don't have much resistances. When a motor's moving it generates what's call "back emf" which makes the motor looks like it has a certain resistance. This creates the voltage drop across the motor. When the motor's stalled there's no back emf and it looks more or less almost like a short circuit. This means a stalled motor puts a lot of load on the electrical system (if there's no design to prevent it from being a short circuit).

There's a bit more to it in the consideration in how the window motor and switching system is designed but overall it's not surprising that it causes a detectable load on the engine.

The drop in the RPM is simply due to the engine computer not compensating for the drop in idle RPM quick enough.

[Rockhound]

Thanks for the reply. I figured it was to be expected somewhat - and it makes sense, since the RPMs do quickly return to normal after stumbling a little.

Of course, all of this is only noticeable while idling, so unless you're in the habit of raising and lowering windows and turning accessories on and off at stop lights, this won't ever be a 'big' deal.

[BillyBeaneBall]

I've noticed this with my '97 Cavalier, '00 Sephia and now my Versa wen I turn on the rear defogger as well...I also just figured it was normal...good to know though