Window operation much better with new battery, especially LiFEPO4

[Wild Turkey]

A lot of us have noticed the slooooow window operation over time, and there is often improvement with Hugo / @whrdnsx pulley replacement of one of the nylon cable guides, as well as the SOS replacement teflon track slides. (@NSX2K5 makes one as well I believe.) Another problem is the small diameter wiring in the harness to the motor and I think people have commented on the voltage drop to the window regulator motor before. In general, under voltage is hard on electric motors, with higher current and more heat generation. Heavier loads (more friction in the mechanism as it gets gummed up over time) can exacerbate the required current and can lower the voltage even further.

I saw this voltage sensitivity as my windows operated much better when the car was running (Alternator supply >14V) vs. the battery (12-13 V), especially putting the windows up before shutting it off vs after. It was more apparent when starting a drive after the car had been sitting for a day and the battery voltage had come down a bit. Starting the car before putting the windows down resulted in much faster and smoother window operation, with my perception of less strain on the motor, because of the higher alternator voltage, (you can see looking at the battery gauge.) The battery also drops its voltage a bit under the load of the windows alone. I even thought I noticed an improvement when temporarily using an AGM lead acid battery, with it's slightly higher voltage, but I wonder if this was some sort of placebo effect.

However, when I got my AntiGravity LiFEPO4 battery, which runs around 15 V, there was no question. The windows operate much faster and more smoothly with the higher voltage. On top of this, they also run MUCH better on battery power alone, as the LiFEPO4 battery doesn't drop its voltage with draw. (The starter also spins much more enthusiastically when starting with the constant LiFEPO4 voltage.)

So, if you're considering a new battery, is it time to think about LiFEPO4, not just to save 30 lbs, but for better window operation?

Even if you're sticking with lead acid, should it be AGM?

 

[Old Guy]

This is interesting. First off, I agree that a higher voltage at the window regulator motor will speed up the motors.

That said, when the engine is running the vehicle system voltage is typically determined by the alternator voltage regulator in the long term. With lead acid batteries (AGM or conventional wet cell) the nominal for a 6 cell system (12 volts) is 12. 2 ish volts. The vehicle voltage running above the cell voltage is what keeps the battery charged. When running at idle, my NSX seems to run around 14.6 - 14.9 volts as measured at the jump start terminal. Unless you have fiddled with the regulator setting / control that is where you will end up in the long term.

Listed LiFePO4 cell voltages appear to be all over the place. If you have a battery with a charged cell voltage of 15.2 volts it will lift the vehicle voltage up to 15.2 volts and the alternator will do nothing in this condition. In a DC system current flow is always in the direction of high voltage to low voltage and if the set point on the alternator regulator is 14.7 volts and the vehicle system is running at 15.2 volts no charging takes place - current will not 'swim up-stream'. Unless you are putting the battery on a maintainer every night or have otherwise modified the regulator, at some point your vehicle electric system will return to a nominal voltage determined by the voltage regulator, not the battery.

 

[Wild Turkey]

Illuminating - this is the conundrum I've been struggling with - the voltage with the motor running should be dictated by the alternator/regulator, not the battery. I looked back to my thread when I was first contemplating installing the LiFEPO4 battery; I measured the alternator voltage at 14.8 V (Fluke meter, which agreed with the dash gauge) when running, within spec according to my SM, and my external charger only charged the battery to around 14.5 V as well.. AntiGravity's official accepted charging voltage is 14.4 (although their email correspondence stated that their BMS can handle up to 15 V, and it's been working fine so far). So I guess when my vehicle is running, the windows should be getting 14.8 V, regardless of the battery installed.

I'm considering that this is just some sort of a placebo effect, but the effect was so dramatic, I'm perplexed. The windows really do seem to work better with the LiFEPO4 battery than my previous Lead-acid. A bit better with the engine running, but dramatically better when the engine is off.

Just checked my battery after the car had been sitting 2 weeks - 13.2 V. I'll check it again after shut-off after a drive.