Power window speed depending on engine revs?
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Joined: May 2023
Posts: 61
Likes: 8
From: The Netherlands, Europe
Power window speed depending on engine revs?
Hi, on my 1982 CFI it seems that my power window speed has a relation with engine revs.
On idle (approx. 550-600 rpm) my windows are noticeable opening and closing slower than when the engine revs over say 1200 revs.
That may seems logical as the generator rotates faster but i assume this would be rectified somewhere to a constant voltage.
I don't know a lot about electrical stuff but is this normal or not? Bad rectifyer or voltage regulator? bad battery, too small battery?
Both doors are to be completely gutted next winter as i want to replace, relube, adjust any moving part inside the doors. Power window rollers and mechanism seems to be in original 41 year old condition and doesn't show any signs of receiving maintenance ever. Tracks, track rollers, locks, all one gunky mess, so i can imagine my windows are suffering from some resistance in the tracks.
Thanks in advance!
On idle (approx. 550-600 rpm) my windows are noticeable opening and closing slower than when the engine revs over say 1200 revs.
That may seems logical as the generator rotates faster but i assume this would be rectified somewhere to a constant voltage.
I don't know a lot about electrical stuff but is this normal or not? Bad rectifyer or voltage regulator? bad battery, too small battery?
Both doors are to be completely gutted next winter as i want to replace, relube, adjust any moving part inside the doors. Power window rollers and mechanism seems to be in original 41 year old condition and doesn't show any signs of receiving maintenance ever. Tracks, track rollers, locks, all one gunky mess, so i can imagine my windows are suffering from some resistance in the tracks.
Thanks in advance!
Last edited by Renevette1982; Jul 11, 2023 at 03:57 AM.
Racer
Joined: Jan 2017
Posts: 271
Likes: 120
From: Rock Hill South Carolina
I think you’ve answered your own question. The mechanical drag in the tracks and guides will cause the motor to slow and draw more power. At idle, your alternator isn’t putting out its full amperage capability so everything runs slowly.
When the RPMs go up, so does alternator output. Extra juice = more power available to overcome the resistance of the gunk in the tracks.
Clean everything up, replace worn components and everything should work like new.
When the RPMs go up, so does alternator output. Extra juice = more power available to overcome the resistance of the gunk in the tracks.
Clean everything up, replace worn components and everything should work like new.
Burning Brakes
Joined: Dec 2005
Posts: 1,153
Likes: 341
For starters, "Rectifiers" aka "diodes" convert AC to DC by only letting current flow ONE DIRECTION through them.
An alternator naturally produces 3-phase AC. 3 sets of windings, three sinusoidal waveforms. Three (or more) diodes convert it to DC.
Maybe go watch some Youtubes about alternators, diode bridges???
The latest, best alternators use transistors instead of diodes to rectify AC to DC. More efficient!
Diodes convert AC produced by the alternator to DC used to power accessories and to recharge the SLI battery. (Starting, lights, Ignition)
A voltage REGULATOR limits the voltage the alternator puts out. On a 1983 the regulator is probably built into the alternator, not a separate
little box on the fender or firewall. BUT --- the alternator has to be spinning fast enough for the regulator to do much. It mostly just limits the output
of the alternator at higher rpms so it doesn't overcharge the battery, boil off the electrolyte, and burn out bulbs.
At idle the alternator is BARELY keeping up with electrical demand on MOST cars, sounds like yours ISN'T. Your battery may be slowly discharging AT idle.
Measure the voltage at the battery while idling and post it here. Try it with and without the air conditioning on. Then measure it again with someone holding the rpms to 2500.
The voltage at the battery, engine running, should be 13.5 or better. Engine off, 12.6 or better. Less indicates a problem. But it may not be a "bad" alternator,
it may simply be dirty connections, burned contacts, too-thin wires, poor grounds....
The DC motors in your power windows run faster the higher the voltage. It's that simple.
A qualified auto electrician can tell you what's going on. You could have a tired alternator. You could have dirty, burned (from arc'ing) contacts in the window switch. Is it both windows or just one. That's a clue!
The window tracks, etc. could simply be so gummed up with dirt and old grease.. the motor's doing the best it can given the size of wire that was used. Individual copper strands INSIDE the wire powering the window motor(s) could be broken where they flex at the door hinge. All of these can contribute unwanted VOLTAGE DROPS that cause a slow window motor. Window motor itself may be worn, tired.
Again, just one window or both? Typically if it's a switch or a wire problem, it's driver's door since it gets used a lot more.
Voltage Drop testing, which I go into here, is how you determine WHICH of these "usual suspects" is the guilty party. Or several!
Feel free to go to Youtube and watch a half dozen videos on voltage drop testing! The simplest, most powerful auto electric diagnostic technique there is!
Take your battery out, down to a battery store, and ask them to load test it. Test should be free. If it's borderline, REPLACE IT.
All about batteries and charging. Swimming pool analogy
Simplest improvement you can make is simply to remove and clean the (-) ground strap from your battery to the frame. Wire brush, shiny metal to shiny metal, dab of anti-seize.
I cannot tell you how many cars I've seen that were "undercharging" because the main ground connection was oxidized / dirty / loose resulting in the alternator having to work harder than it needed to. Alternator was putting out 13.5 but the voltage drop through the bad ground meant the battery was only seeing 13.2 or so. Or less! See:
Bad ground on a C3. Bolted on paint/undercoat.
On my 1968 the "charging wire" from the alternator to the battery was WAAY too small. Intentionally, that's how Chevy wired up the ammeter, but it resulted in the battery NEVER getting a full charge. The ammeter worked by "detecting/measuring" the voltage drop in that "too thin" charging wire/ fusible link. ARGH! (So I could either have a functioning ammeter OR a well charged battery! I chose #2!
Clean your battery terminals. EVEN IF THEY LOOK CLEAN. Take them off, use a battery terminal brush to make both post and terminal shiny. Re-assemble then spray 'em with the red battery terminal protectant available at the parts store.
Clean yer ground strap, engine to frame. EVEN IF IT LOOKS CLEAN. Unbolt, wire brush both ends and what it bolts to till shiny. Use a dab of anti-seize to prevent future corrosion. After re-assembly, a blast of black spray paint.
All of the actions I've recommended will reduce unwanted voltage drops, getting higher voltage to your window motors.
After you do all these things see if your headlights aren't noticeably brighter, and your power windows faster!
Just going crazy inside the door with a can of spray white lithium grease made the windows in my 1968 a lot faster!!!
Do all these things and report back. I can't make an auto electrician out of you but we can rule some things out. Others you may just choose to live with.
On my Honda CRV beater I simply gun the motor a little when I get home and roll the windows up, LOL.
An alternator naturally produces 3-phase AC. 3 sets of windings, three sinusoidal waveforms. Three (or more) diodes convert it to DC.
Maybe go watch some Youtubes about alternators, diode bridges???
The latest, best alternators use transistors instead of diodes to rectify AC to DC. More efficient!
Diodes convert AC produced by the alternator to DC used to power accessories and to recharge the SLI battery. (Starting, lights, Ignition)
A voltage REGULATOR limits the voltage the alternator puts out. On a 1983 the regulator is probably built into the alternator, not a separate
little box on the fender or firewall. BUT --- the alternator has to be spinning fast enough for the regulator to do much. It mostly just limits the output
of the alternator at higher rpms so it doesn't overcharge the battery, boil off the electrolyte, and burn out bulbs.
At idle the alternator is BARELY keeping up with electrical demand on MOST cars, sounds like yours ISN'T. Your battery may be slowly discharging AT idle.
Measure the voltage at the battery while idling and post it here. Try it with and without the air conditioning on. Then measure it again with someone holding the rpms to 2500.
The voltage at the battery, engine running, should be 13.5 or better. Engine off, 12.6 or better. Less indicates a problem. But it may not be a "bad" alternator,
it may simply be dirty connections, burned contacts, too-thin wires, poor grounds....
The DC motors in your power windows run faster the higher the voltage. It's that simple.
A qualified auto electrician can tell you what's going on. You could have a tired alternator. You could have dirty, burned (from arc'ing) contacts in the window switch. Is it both windows or just one. That's a clue!
The window tracks, etc. could simply be so gummed up with dirt and old grease.. the motor's doing the best it can given the size of wire that was used. Individual copper strands INSIDE the wire powering the window motor(s) could be broken where they flex at the door hinge. All of these can contribute unwanted VOLTAGE DROPS that cause a slow window motor. Window motor itself may be worn, tired.
Again, just one window or both? Typically if it's a switch or a wire problem, it's driver's door since it gets used a lot more.
Voltage Drop testing, which I go into here, is how you determine WHICH of these "usual suspects" is the guilty party. Or several!
Feel free to go to Youtube and watch a half dozen videos on voltage drop testing! The simplest, most powerful auto electric diagnostic technique there is!
Take your battery out, down to a battery store, and ask them to load test it. Test should be free. If it's borderline, REPLACE IT.
All about batteries and charging. Swimming pool analogy
Simplest improvement you can make is simply to remove and clean the (-) ground strap from your battery to the frame. Wire brush, shiny metal to shiny metal, dab of anti-seize.
I cannot tell you how many cars I've seen that were "undercharging" because the main ground connection was oxidized / dirty / loose resulting in the alternator having to work harder than it needed to. Alternator was putting out 13.5 but the voltage drop through the bad ground meant the battery was only seeing 13.2 or so. Or less! See:
Bad ground on a C3. Bolted on paint/undercoat.
On my 1968 the "charging wire" from the alternator to the battery was WAAY too small. Intentionally, that's how Chevy wired up the ammeter, but it resulted in the battery NEVER getting a full charge. The ammeter worked by "detecting/measuring" the voltage drop in that "too thin" charging wire/ fusible link. ARGH! (So I could either have a functioning ammeter OR a well charged battery! I chose #2!
Clean your battery terminals. EVEN IF THEY LOOK CLEAN. Take them off, use a battery terminal brush to make both post and terminal shiny. Re-assemble then spray 'em with the red battery terminal protectant available at the parts store.
Clean yer ground strap, engine to frame. EVEN IF IT LOOKS CLEAN. Unbolt, wire brush both ends and what it bolts to till shiny. Use a dab of anti-seize to prevent future corrosion. After re-assembly, a blast of black spray paint.
All of the actions I've recommended will reduce unwanted voltage drops, getting higher voltage to your window motors.
After you do all these things see if your headlights aren't noticeably brighter, and your power windows faster!
Just going crazy inside the door with a can of spray white lithium grease made the windows in my 1968 a lot faster!!!
Do all these things and report back. I can't make an auto electrician out of you but we can rule some things out. Others you may just choose to live with.
On my Honda CRV beater I simply gun the motor a little when I get home and roll the windows up, LOL.
Last edited by wadenelson; Jul 13, 2023 at 03:31 PM.
1967 Pedal Car Champion
Joined: Mar 2020
Posts: 9,027
Likes: 4,174
From: US-PNW
Wow, what a write-up -- good on you for taking the time to be so thorough.
To the OP, at night, when just the bare system with no other unusual demands (A/C, aux. fog/driving lights, WindowRattler stereo) do you notice the headlights getting brighter & dimmer with rev levels? That really shouldn't happen. As recommended above, clean all of the alternator contacts & terminals with a small brass brush, clean the grounds, plus all the other good advice. I'm assuming the idle speed is fine in that it's not actively trying to die on you...
To the OP, at night, when just the bare system with no other unusual demands (A/C, aux. fog/driving lights, WindowRattler stereo) do you notice the headlights getting brighter & dimmer with rev levels? That really shouldn't happen. As recommended above, clean all of the alternator contacts & terminals with a small brass brush, clean the grounds, plus all the other good advice. I'm assuming the idle speed is fine in that it's not actively trying to die on you...
