Cold related voltage drop?

[dark92xj]

This just started with the cold snap here in Co. Maybe its just a coincidence but i thought I would ask to see if its just temp related or not. I have a 2000 xj. When im stopped at idle the voltage will be about 14v on the gauge. If i use my power windows, defrost, wipers etc. while I am stopped the battery gauge will drop to between 12-13v. If i use my accessories while the vehicle is moving (above idle) the voltage still drops but never below 12v. I had the battery tested and the parts store said it was fine just in its last 1/4 of life. My thought is a bad alternator but im not sure. Can anyone give me an idea of what to do next?

 

[Digger87xj]

dont rely on the dash gauge....think of it as a rough estimate

 

[dark92xj]

It was fine and read proper up until a few days ago. Cold causing gauge to be off? The lights dim and heater blower motor drag when the voltage drop occurs.

 

[Digger87xj]

The lights dim and heater blower motor drag when the voltage drop occurs.

this tells you something is using a lot of power... like rear defroster.. also, when the front windshield defrost is on it will cycle the A/C, and the electric fan.

As long as it's still above 12v when everything is running, no worries.

 

[Digger87xj]

Also, an old battery will consume more amperage after a cold start, especially if it is marginal.

 

[dark92xj]

I put in a known good battery and it still did the same thing...thinking alternator for sure.

 

[Digger87xj]

Probably wouldn't hurt, if it's original. Time to upgrade if you have a winch or plans for one in the future.

 

[DigJeepsBrah]

Not to thread jack but on the topic of batteries...

My XJ's battery gauge has maxed out a few times in the last couple of months. I always pull over, check under the hood for anything obvious. Turn it back on and it's just fine. It has no other symptoms when the gauge is maxed out. Kinda strange.

 

[dark92xj]

No plans for one but wouldnt mind a better alternator...does anyone make one more than 117 amp?

 

[dark92xj]

When i tested my voltage with a meter today about 4 mins after start up it read 14.9-15.1v. I also watched it as i put a load on the system with the wipers defrost brights etc. Dropped to 11.8v. Im just confused weather its the battery or alternator. The alternator is original so i might just replace it anyways.

 

[old_man]

What you are seeing is normal. Battery voltage drops with temperature due to the reduced chemical reactions. Starting at low temps draws a large amount of energy from the battery, dropping the voltage. During the recharge which may take 30 minutes in cold temps, the battery will load down the alternator. After the battery warms up and gets to full charge the voltage will rise.

Even in the summer, if you turn on the headlights (a fairly large drain) you will see a voltage drop. A blower motor also takes quite a few amps.

Don't waste your money on an alternator without having it tested, and even then, many places that test batteries have a vested interest in saying it is crap so they can sell you a new one.

 

[O-Gauge Steamer]

^^ What Old_Man said. It is a completely normal happening. The PCM restricts the charge voltage during cold weather. This is what the battery temperature sensor is for. At first blush, it make no sense at all but... It is how it works.

I friend of mine works in the Toledo Plant for Chrysler (care to guess what they build there?) and I asked him about it back in 2000 when I purchased my first XJ. It did not seem right. Completely at odds to what I was used to seeing. He claimed that Chrysler had found that reducing the charge voltage during the cold promotes battery life by not overcharging the battery.

All I know is, that it seems to work just fine.

 

[dark92xj]

I guess we will see when it starts to warm up. Thanks all for the good knowledge!