You are forgetting the internal resistance of the battery. The fact is that the most charge a car will give a flat battery is around 30A, it it drops off very rapidly. The high alternator output is to support accessories.
Bill
A quick look at a few battery specs suggests that a charge rate above
50A can damage a lead acid battery if maintained for more than a few minutes.Bill
I am the one with the degree in that subject, I am not forgetting it. You simply have no idea of its value.
The fact is
Like I said the battery has sufficiently low internal resistance to be able to deliver 700A to a starter motor, it can sure handle 50A with only a half a volt or so increase in charge voltage.
I see you just make that statement with no link to back it up.
The charging rate must be deliberately limited to avoid damage to the battery. The acceptable charge rate is much higher when fairly flat than when nearly fully charged. Probably improved electronics is why we can have much higher output alternators nowadays without risking battery damage. The old system of just regulating the voltage could not reliably avoid overcharging unless the maximum charge rate was artificially limited.
BINGO.
Imagine what happens when you jump start - seen the size of the spark?
Long term charge rates are obviously low, but just after a hard cold start the battery will soak up a lot of amps very quickly.
Because if it doesn't and its doing stop-start, the battery will be flat PDQ .
Yes. Any modern car battery charger will work. All there is to choose is cheapos versus high MTTF ones, £12 versus £40+.
I might fix the old one.
NT
What, your a Bachelor of Batteries?
I fit ammeters in all my vehicles, ever the tractor. Even after a bump start because of a flat battery the charge settles to below 30A within seconds.
As a matter of fact, I initially fitted 60A meters in the motorhome but soon changed them for 30A ones. (Later I re-did the control panel and fitted digital ones.)
I've just done a search for vehicle and marine ammeters. The vast majority are 30-0-30. A few are 60-0-60. According to you they should all be 150-0-150.
Yes but the alternator keeps the charge to a sensible level, to prolong battery life. Extremely rapid charging is bad for lead-acid cells. That's why milk floats are on charge all all the time they are in the depot. It's why disability scooters are charged at 8A or 4A depending on the battery, which can be inconvenient in summer if the user wants to go shopping in the day and out for a meal in the evening.
There's no doubt you can push 100A into a big lead-acid battery if the supply is of high enough voltage, but do it routinely and the battery won't last as long as it should.
The other factor concerns the alternator voltage. Once a flat battery has received a bit of charge, its terminal voltage rises to the point where to maintain a 100A (say) charge the alternator voltage would have to be so high as to over-run filament bulbs and other equipment.
So if you spent three years getting that Bachelor of Batteries degree it looks like you wasted your time, because you know nowt.
Bill
Look it up yourself then.
Bill
Quite agree with the charging rate limitation. If one observes the meter on a battery charger, the starting currents through the charger would be around 4 amps in the worst case, coming down slowly to 0.5 amps in about 12/16 hours; if this is any guidance the alternator charging load would be about the same, not of the order multiples of ten amps!!
But only for a short time.
Depends on the state of charge of the battery.
The metal enclosure is riveted together so I can't open it up. Anyway IMLE the failure mode for devices based on a transformer is nearly always shorting or burning out of the windings which can't be fixed.
Aren't such heavy duty alternators there for heated windscreens, bum warmers, memory seats etc?
The Natural Philosopher was thinking very hard :
That is a rather odd statement. Some alternators output a maximum fixed voltage, more modern ones vary the voltage slightly depending on demand. Because a battery can deliver 700amps does not mean they are capable of accepting 700amps as a charge current. The 700amps is for a very short period of time.
The point of having such a large potential current output available, is nothing to do with putting that current into the battery - it is there to cope with the massive current demand of lights, cabin fans, cooling fans, screen heaters and etc.. My cooling fan at maximum demands
50amps.I tell you again - you need a much larger voltage difference between the battery and the charging supply, to get an effective, high current rapid charge into a battery. Such a high voltage would burn lamps out and electronics.
williamwright was thinking very hard :
Correct! I have taken the trouble to actually measure it and have seen
20 to maybe 30amps delivered by a 130amp alternator, into a near flat battery. That level of charge current rapidly declines as the flat battery gains in voltage.
The BatteryUniversity explains some of this.
Manufacturers recommend a charge C-rate of 0.3C, but lead acid can be charged at a higher rate up to 80% state-of-charge (SoC) without creating oxygen and water depletion.
Oxygen is only generated when the battery is overcharged.
The 3-stage CCCV charger prevents this from happening by limiting the charge voltage to 2.40V/cell (14.40V with 6 cells) and then lowering to a float charge about 2.30V/cell (13.8V with 6 cells) at full-charge. These are voltages below the gassing stage.
Test show that a healthy lead acid battery can be charged at up to 1.5C as long as the current is moderated towards a full charge when the battery reaches about 2.3V/cell (14.0V with 6 cells). Charge acceptance is highest when SoC is low and diminishes as the battery fills.
Battery state-of-health and temperature also play an important role when fast-charging. Make certain that the battery does not "boil" or heat up during charge. Put an eye on the battery when charging above the manufacturers recommended C-rate. "
A manufacturer suggestion of a C/10 rate, is likely so that charging can be "without supervision". And at least the smart chargers use CCCV, and there's little chance of trouble, even if you bought a 10A smart charger. (That's because if you watch it, if you're just topping up the battery, the average current pumped in is less than the rating. Just as the dumb chargers had pretty poor current flows near the end. This means they're all approximately equivalent, even if the approximation is a pretty strange one. When I stuck the ammeter on the smart charger charging experiment, I was expecting to see the "name plate rating" value being used. It became apparently pretty quickly, that I was in CV mode at the time, and the current drops with time in that mode.)
"What cars do" is another matter, and varies with generation. I don't see a problem with a bit of extra current flow if the battery is completely flat.
The advantage of the smart charger, is not having to worry whether the behavior of a dumb charger, might be shortening battery life. I think most of the time, when I was using the dumb charger, the battery was already knackered and I did most of my little experiments with "bad materials". On the current car, it was the alternator that was doing a poor job, and probably cost me more than one battery. When asked whether I wanted a new one or a rebuilt alternator, for a change I decided to go with a new one. If they can't rebuild them right, I no longer want the rebuilt ones.
And it turns out my smart charger is *not* temperature compensated, as the chilly day I ran my test, it was charging to the values appropriate for 25C air temperature, which is not correct. This means, if you charge outdoors, the charger is not using the correct objectives. You could be overcharging or undercharging, by a small amount. I did find a smart charger used for commercial services, which has a plugin temperature sensor on it (that doesn't mean they use it of course, it could be a hood ornament).
Also on the topic of smart chargers, I noticed a big difference between the Chinese manufacturer user manual and what the seller was claiming. The Chinese manufacturer correctly indicated it was for "inside charging" (thus covering the temperature issue). There was no mention of automotive applications at all in the manual. The seller was the party "extending" the feature set to cover cars.
Paul
I have battery chargers that will dump full permitted current into a battery until it is =99% full.
heated seats?
I hope the bum warmer in my car seats is not thinking of running at
1800W. That'd be like sitting on an electric fire.HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.