hey, ever since i got the avic installed, i've always kept the vehicle dynamics page up. the voltage has always fluctuated between 13.8-14.2v. yesterday and today though, i havent seen voltage above 13.6v. it has been a little warmer than normal lately, but other than that, everything else has remained the same.

is this something i should be concerned about?

 

Is your car driving any different?

Also didn't u say you got a new power inverter for the ps2?

 

if it is warmer, doesn't heat have an effect on conductivity of electricity? slowing down he current and reducing the amount of volts you read?

 

Definitely. That's what I was thinking. But I wouldn't worry, this shouldn't cause you any problems at all.

 

Takes a while to fully charge the battery - like hours - if you keep starting and running around with the battery being drained the alternator can not fully charge it back up and you will eventually kill it by having it under charged for a long time. When you park it over night get a smart battery charger multi stage with float and let it charge up the battery. Don't use the cheep ones because they will end up cooking your battery and drying out the electrolyte with too much voltage. Also check the temperature of the alternator after driving and see if it is getting too hot and also check the battery to make sure it is not getting too hot. Good voltage regulation is temperature compensated and will charge to a lower voltage as the temperature increases or gets below freezing.

 

Yes. heat effects conductivity but it's the other way around. Should be more current flow when it's warmer. That's why starting your vehicle in colder temps. is much harder.

As far as the voltage drop concern, one possible cause could be the operation of the A/C compressor magnetic clutch creating an extra load on the alternator output as well as a load on the engine. 13.6volts with the engine running is nothing I would be concerned about.

 

There is no electric clutch in the A/C pump it uses variable vane compression internal to the pump and requires very little power to operate it. You have something loading down the battery - where are you measuring the voltage ? If inside the car then you are getting a voltage drop in the wiring going to the instrument panel. You need to measure the voltage right at the battery terminals lead posts with an accurate meter! Higher temps makes the battery chemistry work better - doesn't have anything to do with wires conducting better at different temps - that effect is almost not measurable.

 

Where did you get your resources from my friend? Either someone told you wrong or you're thinking of another vehicle with that sophisticated type of A/C system. tC's would definitely have a higher sticker price if it was equiped with a variable vane A/C compressor. Last time I checked under the hood of a tC I visually can see 2 wires going into the compressor near the pulley. Wait, I can also see a clutch plate on the outer side pulley. And when I turn my a/c on, it clicks as a sign of a functional magnetic clutch engagement.

Still not convinced?
Try accessing your fuse and relay panal in the engine bay near the battery. Take the cover out and look on the back side of that cover. There is info that identifies fuses and relay locations. On the top left corner of the cover you will see a relay icon that says MG/C. Pull out that A/C relay and see if your A/C system will engage. I doubt it will.

 

No, I'd have to disagree with that because resistivity increases with temperature. If you increase the resistance in a circuit while keeping the source emf the same, the current has no choice but to go down.

I think that starting the engine in cold weather has more to do with the nature of an ICE rather than the actual electrical component of it all. For example, if you use a block heater, you can start up the engine easier, even though for the most part its just heating up the actual engine block and not all the wiring in the bay.

Heat is basically the enemy of cicuitry. Just ask any of us computer nerds

 

I do agree on "high resistance plus heat in the circuit reduces current flow". But that's got to have some execessive temperature to effect a 12V power source. Computers operate at much lower power sources which I can see very little heat will effect its operation. Anyway, I made my statement with the battery state or condition in mind. A cold battery effects voltage or current pressure. I know my previous statement wasn't clear.

 

Sorry but I have the xB and I was thinking of the power steering pump - the A/C pump is burried in the xB and really hard to see but I am pretty sure it also is variable vane as are most imports these days and even so the clutch pulley take less than 5 amps.

 

correct... that is why RTDs (resistence temperature detectors) work and are used to measure temperatures (mostly commonly used in insanely high temp. environments where any regular thermometer would fail)

they are based on the principle of heat increasing resistance.. and by measuring that resistance.. having previous documented data.. it will correlate to a specific temperature.

(now i just pulled out my geeky former job related card out just for the hell of it)

now we can get into other crap like thermal runaway.... which btw does come into play in our vehicles when you buy a crappy aftermarket headlight bulbs with a poor connection.... but that's another story...

anyway.. unless there are some other issues you are experiencing, i wouldn't worry too much.

 

If the battery does not get up to 14 volts it will be under charged and have a shorter life - check the color of the eye on top to check the state of charge - it should be blue.

 

I believe our cars have that RTD built into the MAP sensors for measuring intake air temperature. The engine ECU monitors the resistance value from the MAP sensor to determine intake temperatures.

Anyway, I can't see why a 70 to 80 degree atmospheric temperature would have an effect on the internals of a 12V circuit. I mean that's an outside heat source and that isn't very hot. Now heat generated internally in a circuit from resistance I can see it will effect the current flow. (Unwanted resistance probably caused by corrosion in the circuit.) If current flow was effected by an outside heat source, it would have to be dramatically hot. It may seem ironic that I just said this considering that I mentioned how the MAP sensor works, but really, that's the designed operation of the MAP sensor. It's meant to have, in its circuit, a resistor detector exposed to the atmosphere. A regular circuit without it wouldn't be designed for that.

In fact, using your heater during the winter time would generate excessive outside heat behind the radio because of the vents above the radio. The guy who originally posted this thread said that he had higher voltage readings when it was colder outside leading to the use of his heater. But he's from Florida so I don't really know how often he uses his heater.

 

Not sure about the tC but the xB has a Mass Air Flow sensor not a MAP Manifold Absolute Pressure sensor and the Mass Air Flow sensor uses an electrically heated wire to sense how cool it gets as air flows over it compensated by the air temp sensor before it for the wind chill factor and yes the wire changes resistance as a function of temp. This should not affect the voltage regulator charging the battery - check for loose connections - poor grounds on painted surfaces with light wire to a steel frame and fuse panel voltage under the dash for voltage drop when under load.

If you are pulling more than 80-90 amps total (1100 watts) from the electrical system then the alternator will not be able to keep up with the load and you will run the battery down.