Lower the output of the alternator?

nate0031 · Feb 8, 2015

Lug_Nut said:
Oh. To drop the voltage to the 2.1 per cell that everyone else gets I need to partially discharge the battery? Got it!

I've been investigating the charger I have (Schumacher 8/2). When charging it puts out about 14.55* volts (I just measured it). When it switches to the maintain mode it puts out about 13.54* and adjusts the amperage from 0 to a maximum of 2 to maintain the 'float' charge. I can't believe this results in an "overcharge" situation that super saturates the battery and results in an artificially high, and temporary, voltage above the reading when full (not partially discharged as advised by the quote above).
F.W.I.W.: the Jetta's alternator puts out 14.34* volts when the engine is running (measured that just now as well). Compare this to the 14.55 of the charger and I really doubt that I'm "overcharging" and reading a temporary charge state.

I also don't buy the 'surface charge' theory as contributing to the reading I reported. The low current (8 amps max) of the charger I use means the charge rate is slow enough that the full volume of the plates are charged, not just the electrolyte contact surface area, when the charge is 'done'.
The volt meter isn't reading the apparent voltage charge of the plate surface which then drops as the interior of the plate charges up to equilibrium and lowers the surface voltage as a result.

* The meter is one that I never had questions about until now. I simply trusted it to be accurate enough and never had it checked for accuracy.
So I have it connected to a regulated DC power supply putting out a claimed 12 VDC and read 12.13. Maybe the meter is inaccurate by 10%. Maybe every meter I've ever had has exaggerated the DC voltage by about the same error.
Maybe the regulated power supply is really putting out something just over 12 volts...

A man with a watch knows what time it is.
A man with two watches isn't sure.

Here's my brand new battery, charged on the same charger as you. It was charged when I first bought it, started a car once, and then put back on the charger. It has been in float mode ever since. I removed the charge leads for a moment and took this shot. It's about 60°F out today. Surprisingly, falls right where it should. Reading taken both on a Fluke and a cheapy Wal-Mart meter. The Fluke reads 14.64 with the charger in charge mode. Funny, still ~2.1 volts per cell. I guess everyone's not making this up just to screw with you after all, lol.

The charger:

macoombi · Feb 9, 2015

Awesome. Thanks for posting.

Powder Hound · Feb 11, 2015

Wankel7 said:
...
I wonder if it would extend the life of the battery?

That depends on when the voltage is reduced to 12.6 in relation to the charge state of the battery. If insufficient time at charging voltage is experienced by the battery, you will have chronic undercharge, leading to early death of the battery.

Cheers,

PH

Lug_Nut · Feb 11, 2015

[486] said:
My response is "but soy doesn't mean biodiesel in latin, it means a little bean plant"

That's OK. Descartes wasn't a native latin speaker either. He originally (1637) wrote: "je pense, donc je suis" and didn't publish the latin version "ego cogito, ergo sum" until 1644.
The spanish "soy" translates approximately to "I am" as in "Yo no soy marinaro. Soy capitane, soy capitane. Bamba, bamba" or "Soy un perdidor. I'm a loser, baby, so why don't you kill me?"
It's that "I am" soy that is not quite a match to the latin I am "sum", and it's similar three letters long length, that prompted me to 'misquote'.

Just a Walt Kelley's Pogo possum misquoted "We have met the enemy, and he is us." the misquote is more appropriate in a specific circumstance.

I can't explain why everyone of you (except shakescreek) are wrong.

I can accept that I'm not wrong and move on.

Oh, it's a week later and still above 13 volts.

Ol'Rattler · Feb 12, 2015

macoombi said:
Residual charge. It's simple chemistry.

Here's some more reading (from http://www.batteryfaq.org/):
4.3. Remove Surface Charge

Surface charge (or "counter voltage") is the uneven mixture of sulfuric acid and water along the surface of the plates as a result of charging or discharging as the electrolyte has an opportunity to diffuse in the pores of the plates. It will make a weak battery appear good or a good battery appear bad. Larger wet lead-acid batteries (especially over 100 amp hours) could also have electrolyte stratification where the concentration of acid is greater at the bottom of the cell than near the surface. The Open Circuit Voltage (OCV) will read higher than they actually are. Stratification can be eliminated by an equalizing charge, stirring or gently shaking the battery to mix the electrolyte.

A surface charge can be eliminated by one of the following methods after recharging a lead-acid battery:

Allow the car or deep cycle battery to sit (or rest) without discharge or charge for between two and eight hours at room temperature, if possible, to allow for the surface charge to dissipate. (Recommended method.)

For car batteries, turn the headlights on high beam for five minutes and then wait ten minutes.

For car batteries, apply a load with a battery load tester at one-half the battery's CCA rating for 15 seconds and then wait ten minutes.

For car batteries, disable the ignition, turn the engine over for 15 seconds with the starter motor, and wait ten minutes.

For deep cycle batteries, apply a load that is 33% of the amp-hour capacity for five minutes and then wait at least ten minutes.

See this section here for more info on open circuit voltage:
http://jgdarden.com/batteryfaq/carfaq4.htm#ocv_soc

There's a good chart there but it doesn't cut and paste well here.

Best explanation I have heard about "surface charge".

Many years ago when I was learning how to maintain our Army wheeled vehicles, we were taught that to properly checking a vehicle for charging you could do a quick check by leaving the lights on for about 10 minutes to remove the battery surface charge, hook up your VOM, and watch for the voltage to rise when the vehicle started.

They never really explained surface charge, except that on a normally charging system a fully charged battery will show a couple of volts higher than nominal right after you turn off the engine due to surface charge.

nate0031 · Feb 12, 2015

Lug_Nut said:
I can't explain why everyone of you (except shakescreek) are wrong.
I can accept that I'm not wrong and move on.

Oh, it's a week later and still above 13 volts.

I'm thinking you're either joking or 'trolling' at this point, lol. Well, hoping at least. If not, you have a pretty penny to be made, since you'll be correcting my textbooks, professors, and the scientific community at large. However, I think it foolhardy to declare everyone else wrong and yourself correct based on a handful of extremely unscientific readings.

That said, I don't doubt your firsthand readings. I do doubt the conclusion it led you to, that lead acid batteries have an open circuit voltage of 2.2 volts per cell. Your readings are anomalous, which indicate there is another factor at play. They do not indicate that the fundamentals of this battery chemistry have changed.

For kicks, I tested all the 12 volt batteries I have. One was at 12.23, two at 12.28, two at 12.39, one at 12.61, and the last at 12.63. One of those was AGM, the others were flooded cell. These were taken at 31°F. The three lowest were the ones used just hours before for our daily commutes. The middle of the pack 12.39's have been setting in cars parked outside, unused and unstarted for about a month. No charging. The two highest are both under a year old, one being the one I previously pictured. None are close to 13 volts. Not the brand new ones, not the 8 year old ones, not the one on the same charger as you, not the deep cycles, and not the ones getting a steady 14+ volts from their alternators.

If your conclusions were correct, they'd be correct for all batteries using the same chemistry, not just the ones you touch.

macoombi · Feb 15, 2015

I want to know what kind of battery Lugnut has. I need one of those. It might make starting my ALH easier in the extreme cold we've been having lately.

Maybe his battery has an extra cell. They do sell those. Check out Turbostart batteries. They make 16v batteries for racing applications. Thinking about one of those for a booster battery myself.

Houpty GT · Feb 19, 2015

nate0031 said:
Hit the nail on the head. Alternators are in the neighborhood of 75% efficient, so you'd need to save around 1000 watts to reduce the mechanical load by 1 HP.

This is wrong. You only need to cut 560 watts of power to reduce engine load by 1 horsepower. It is 25% of the 1 hp that is loss going into the alternator.

nate0031 · Feb 19, 2015

Houpty GT said:
This is wrong. You only need to cut 560 watts of power to reduce engine load by 1 horsepower. It is 25% of the 1 hp that is loss going into the alternator.

Thank you. You are correct. I was thinking completely backwards. Updated.

SkeeterMark · Mar 3, 2015

http://www.batterystuff.com/kb/freq...ies-faq/12-volt-battery-reading-13-volts.html

"All Lead acid batterieshttp://www.batterystuff.com/batteries/(Gel, AGM, Flooded, Drycell, etc) are made up of a series of 2.2 volt cells that are bridged together in series to reach their final desired voltage. For instance, a 6 volt battery will have 3 cells (3 x2.2= 6.6 volts), a 12 volt battery will have 6 cells (6 x2.2=13.2 volts) and so on.That 2.2 volts is the fully charged, straight off the charger number. The actual resting voltage, or the voltage a battery will settle at 12-24 hours after being removed from the charger, is closer to 2.1 volts per cell, or about 6.4 volts for a 6v battery, and 12.7 volts for a 12v battery. These numbers assume 100% healthy cells, and may vary a bit lower for older batteries."

nate0031 · Mar 3, 2015

SkeeterMark said:
That 2.2 volts is the fully charged, straight off the charger number. The actual resting voltage, or the voltage a battery will settle at 12-24 hours after being removed from the charger, is closer to 2.1 volts per cell, or about 6.4 volts for a 6v battery, and 12.7 volts for a 12v battery.

AKA, surface charge. The 2.2 is a transient cell voltage which is an artifact of the charging process.

Westro · Mar 9, 2015

Put on my Electrical Engineering hat of 22 years here:

The 2.2 is a transient cell voltage

Transient = changing. 2.2V/cell is not what a dynamicly changing cell will see. Incorrect.

AKA, surface charge.

All of the available electrons are "surface charge". Electrons are only dislodged at the Lead/Acid barrior. IE we refer to this as a real issue with high speed serial channels (fast changing transient voltage swings). We even pay attention to copper 'roughness' in PWB fabrication process.

artifact of the charging process.

The higher cell voltage is the "artifact of the charging process". You need to overcome the cell voltage to get electrons to "move" into the battery and convert the 2H20 into 2H2SO4 (acid) to complete the chemical reaction.

As you load the cell the voltage will drop with increased current, reduce the current load and the cell return closer to the NOMINAL 2.1V/cell. Ability to give up electrons and convert the acid to water is what we refer to as a higher Amp/Hour battery. Cold Cranking Amps (temperature rated) and such.

Remember batteries have internal resistance, lower internal resistance makes it easier for the battery to give up its electrons (higher transient current). The internal resistance will also bring that battery down to its NOMINAL cell voltage after some time which is determined by the battery's internal resistance.

I think you guys are down in the mud on this. Back to the original posters idea. I wouldn't suggest this, I am going through this on my wife's 2013 Honda CRV. The "econ" button on the dash does this exact thing. It limits the duty charge cyle to help fuel economy. What it means is when my wife has the seat heaters going full bore in Minnesota winter and she shuts the car off in -25F temps and goes into Walmart the car wouldn't start. Thus no more Econ button in winter and I have thus installed a larger capacity lead acid battery so that there is a larger reserve.

nate0031 · Mar 9, 2015

Westro said:
Put on my Electrical Engineering hat of 22 years here:
Transient = changing. 2.2V/cell is not what a dynamicly changing cell will see. Incorrect.

The higher cell voltage is the "artifact of the charging process". You need to overcome the cell voltage to get electrons to "move" into the battery and convert the 2H20 into 2H2SO4 (acid) to complete the chemical reaction.

The internal resistance will also bring that battery down to its NOMINAL (2.1V/cell) voltage after some time which is determined by the battery's internal resistance.

I think you guys are down in the mud on this.

The relevant definition of transient = "lasting only for a short time; impermanent," which is precisely what I was trying to convey; that the 2.2 volts per cell is an impermanent state of charge.

It appears we are in agreement, that a car battery will eventually return to it's nominal cell voltage of 2.1 volts after being removed from a charger. That was the idea to be communicated. I agree that we really dove down the rabbit hole on this, lol.

Seems a really poor design to actually allow the battery to discharge while driving. Were you able to measure the alternator output when running in econ mode?

Houpty GT · Mar 9, 2015

Can a savings be had running the 90 amp or 70 amp alternator instead of the stock 120 amp? It surely must be better than regulating the output.

nate0031 · Mar 9, 2015

I don't think it'd do you any good. As mentioned earlier, the mechanical load imposed by the alternator on the engine is directly proportional to the electrical load on the alternator. For example, ceteris paribus, a 70 amp alternator producing 20 amps to run an accessory will present the same mechanical load as the 120 amp alternator producing 20 amps to run that same accessory.

Westro · Mar 10, 2015

Can a savings be had running the 90 amp or 70 amp alternator instead of the stock 120 amp

In theory yes, a small alternator will have less parasitic (bearing) and windage losses. I really can't believe that they are much savings though.

One of my ALH's the AC compressor went bad, I ordered the compressor but while I waited I drove it to work with no accessory belt. No AC, No charging and NO power steering. I would charge the battery at night and I could get back and forth to work. Gained about 4-5 MPG over that short time. I think you would gain more by going to an Electric power steering pump than what you could save by downsizing the alternator.

I think there are gains to be had if you moved to an electric water pump, electric brake booster and electric PS booster. AC and Alternator most likely will always have to be driven off of the IC engine.

macoombi · Mar 10, 2015

Speaking of that, I seem to remember reading about a hybrid car that uses an electric air conditioning compressor so that the AC still cools the car when stopped.

Now making an alternator that isn't driven off the engine, that'll be a bit trickier.

[486] · Mar 10, 2015

macoombi said:
Now making an alternator that isn't driven off the engine, that'll be a bit trickier.

them thar NASCAR dun it

they drives it off the driveshaft!

compu_85 · Mar 10, 2015

Many / most hybrid cars have electric AC compressors.

-J

nate0031 · Mar 11, 2015

Westro said:
I think there are gains to be had if you moved to an electric water pump, electric brake booster and electric PS booster. AC and Alternator most likely will always have to be driven off of the IC engine.

I agree on the brake booster and power steering, as you can eliminate the pumping losses associated with constantly running a vacuum and hydraulic pump. You can go electric on both and eliminate the vacuum and hydraulic components entirely (well, some electric brake boosters use an electric motor to pressurize a hydraulic accumulator).

The water pump I'm more skeptical on. You can't eliminate the water circuit, so you end up using a ~70% efficient alternator to drive a 80-90% efficient motor to pump the same volume of water. Far less efficient than driving the pump directly off a cog belt. The only way to recoup that would be different (previously unavailable) strategies, such as shutting the pump off when not needed, etc, and I doubt you'd recover all the extra energy that was lost, let alone see a net drop in the energy required to drive the pump. If I had to guess, you'd be much better served by a variable, belt driven pump. That would allow you to vary the pump output based on demand and not incur the losses of an electric pump.

evoblade · Mar 13, 2015

Lug_Nut said:
A volt meter is about as useful as a tire gauge that displays how many tires are on the car.

LOL. I'm gonna use this phrase someday.

evoblade · Mar 13, 2015

nate0031 said:
I agree on the brake booster and power steering, as you can eliminate the pumping losses associated with constantly running a vacuum and hydraulic pump. You can go electric on both and eliminate the vacuum and hydraulic components entirely (well, some electric brake boosters use an electric motor to pressurize a hydraulic accumulator).
The water pump I'm more skeptical on. You can't eliminate the water circuit, so you end up using a ~70% efficient alternator to drive a 80-90% efficient motor to pump the same volume of water. Far less efficient than driving the pump directly off a cog belt. The only way to recoup that would be different (previously unavailable) strategies, such as shutting the pump off when not needed, etc, and I doubt you'd recover all the extra energy that was lost, let alone see a net drop in the energy required to drive the pump. If I had to guess, you'd be much better served by a variable, belt driven pump. That would allow you to vary the pump output based on demand and not incur the losses of an electric pump.

Electric pump may bring in losses, but there are also mechanical losses from driving the pulley, bearings, etc (all the components of mechanical drive). I'm not saying they are equal or greater to losses from electric motor, but they are not 0. Plus you could vary the speed of the pump to save energy when not needed as much. Like once you are fully warmed up, crank the thermostat wide open and slow down the pump to maintain coolant temp right at the correct band. Plus you could design much more efficient water pump impeller and casing if you didn't have to design a pump that would work at any RPM the driver wanted to do. Having a pump that works at 500 rpm idle to 7000+ RPM (well 800-4500 for TDIs) means there are going to be some serious compromises.

nate0031 · Mar 13, 2015

evoblade said:
Electric pump may bring in losses, but there are also mechanical losses from driving the pulley, bearings, etc (all the components of mechanical drive). I'm not saying they are equal or greater to losses from electric motor, but they are not 0. Plus you could vary the speed of the pump to save energy when not needed as much. Like once you are fully warmed up, crank the thermostat wide open and slow down the pump to maintain coolant temp right at the correct band. Plus you could design much more efficient water pump impeller and casing if you didn't have to design a pump that would work at any RPM the driver wanted to do. Having a pump that works at 500 rpm idle to 7000+ RPM (well 800-4500 for TDIs) means there are going to be some serious compromises.

I agree that you could likely design it to me more efficient since you have gained so much flexibility. I know the belt drive isn't without losses, but you incur those losses with electric drive as well, on top of the energy conversion losses. On a retrofit where you remove the mechanical pump, you likely need to add an idler pulley in it's place, so bearing losses are still incurred to some minute level. I just think it'd need to be a very well engineered solution to give appreciable gains in efficiency. I have a feeling that simply removing the mechanical pump on an engine and replacing it with an electric pump you found online, would make you less efficient and less reliable.

The EA288 engines received allot of attention on the coolant system though. They have a micro circuit that uses an electric pump if the engine is not warmed up. The main pump is still belt driven, but it can be unloaded by covering the impeller with a shroud.

Houpty GT · Mar 13, 2015

Westro said:
In theory yes, a small alternator will have less parasitic (bearing) and windage losses. I really can't believe that they are much savings though.

One of my ALH's the AC compressor went bad, I ordered the compressor but while I waited I drove it to work with no accessory belt. No AC, No charging and NO power steering. I would charge the battery at night and I could get back and forth to work. Gained about 4-5 MPG over that short time. I think you would gain more by going to an Electric power steering pump than what you could save by downsizing the alternator.

I think there are gains to be had if you moved to an electric water pump, electric brake booster and electric PS booster. AC and Alternator most likely will always have to be driven off of the IC engine.

My car showed a surprisingly high increase of 4 MPG when I removed the power steering pump. That leaves about 1 MPG for an alternator delete.

[486] · Mar 13, 2015

Houpty GT said:
My car showed a surprisingly high increase of 4 MPG when I removed the power steering pump.

What? That's nuts.

Might have to find a belt that'll flop on there to try this out.

macoombi · Mar 13, 2015

I got about 54 mpg (US) last summer with no serpentine belt. I don' t think that I've even got over 50 before that with a working serpentine belt (alt pulley failure actually). So I'll buy that 4 mpg increase.

I did some research a while ago and found a belt length that would work to delete the AC compressor and another for the AC & P/S. I'd have to dig that up. That would be cool for long road trips in the spring and fall.

josh8loop · Mar 17, 2015

macoombi said:
I got about 54 mpg (US) last summer with no serpentine belt. I don' t think that I've even got over 50 before that with a working serpentine belt (alt pulley failure actually). So I'll buy that 4 mpg increase.

I did some research a while ago and found a belt length that would work to delete the AC compressor and another for the AC & P/S. I'd have to dig that up. That would be cool for long road trips in the spring and fall.

I would be interested in the belt measurements for sure.

macoombi · Mar 19, 2015

Not sure where I put that info. I did find a power steering by-pass thread though:
http://forums.tdiclub.com/showthread.php?t=420670

Lower the output of the alternator?

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