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Deeply discharged car battery - basic questions (no charger around).
Deeply discharged car battery - basic questions (no charger around).
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Old 29th November 2018, 09:11 AM   #41
avtech23 is offline avtech23  Australia
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Deeply discharged car battery - basic questions (no charger around).
There was an interesting piece on this in Popular Mechanics almost a decade ago:

Whatever Happened to the 42-Volt Car?
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Old 29th November 2018, 01:05 PM   #42
kevinahcc20 is offline kevinahcc20  United States
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There have been two major changes in mainstream automotive electrical systems in 125 years. Around 1920 the advent and spread of the self starter required a battery for starting and the early hand-crank started (where the term "crank the engine" originated) magneto based ignition system faded away replaced by a 6 volt lead acid battery and DC generator electrical system. This then supported the adoption of electric lighting, horns, radios and other electrical accessories.

By the mid-1950s the transition to higher compression engines was the primary driver to the adoption of the 12 volt system that remains today, as the cranking current demanded of 6 volt starter motors became excessive. In the 1960s the DC generator was replaced by an AC alternator with rectifying diodes allowing for much higher charging rates. Again as the system was upgraded it facilitated broader adoption of electric powered accessories like power windows, seat adjusters, and door locks.

This system with refinements has survived through the transformation of the motor vehicle, first driven in the early 1980s by emissions and safety (airbag controller) regulations, into a networked environment of many microprocessors. So the lesson of history is that a major change to automotive electrical system standards requires a prime driver to justify it. Wholesale adoption of hybrid drive systems would be the best candidate to prompt the adoption of a higher system voltage but so far that has been a niche application that has left conventional vehicle electrical architectures in place.

One factor that the current 12V lead acid battery has in its favor is that it is one of the most efficiently recycled commodities in existence. This dense and easily handled brick that is primarily lead by weight sees about 90% efficient reuse of spent batteries.
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Old 6th December 2018, 04:01 PM   #43
academia50 is offline academia50  Argentina
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Quote:
Originally Posted by kevinahcc20 View Post
................
In the 1960s the DC generator was replaced by an AC alternator with rectifying diodes allowing for much higher charging rates. Again as the system was upgraded it facilitated broader adoption of electric powered accessories like power windows, seat adjusters, and door locks.............

.

Just add something:

The dynamo did not load at low revolutions of the engine because obviously it was coupled to it and depended on those RPM, typically I remember that there was not enough current below the revolutions of idle (800 rpm) Then, the most important advance brought by the emergence of the altenator, is that it supplies load current even at low RPM. The rectification in the dynamo was made by the commutation between the coals and the delgas, when acting on the concatenated flow in each cycle or rotation, this process was successfully replaced by the diode bridge.
The other important advance long before the massive incorporation of the electronic ignition was the replacement of the electromechanical voltage regulator by the solid-state voltage regulator.
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Old 6th December 2018, 09:31 PM   #44
martin clark is offline martin clark  Europe
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The real advantage of the alternator in no small part due to the solid-state side of rectification and regulation was the fundamental change of operation -

1. the non-mech commutation allowed instead for the rotor to provide/control the magnetic field, and the stator to supply heavy output currents that do not need to pass through slip-rings/ a commutator (massive win); and so

2. as a result - simple regulation of a low current via slip rings to the rotor to provide the field magnetism. This current is still often at most only 4-5A, so lifespan was also massively improved.

A simply brilliant inversion, that also allows the control of rotor mag field (= generated output power) nearly-independent of input rpm. Hence - ramp the field current right up at low speed and you can draw a significant proportion of full-rated output current, often 70-ish% + even at engine idle. It made the 'generator' a near- constant-power device, rather than only the constant-voltage device a dynamo could be. That's the big step forward.

Interesting side diversion - this also means the drive torque to an alternator to deliver its rated power also drops off markedly as revs rise. Strange but true.

Last edited by martin clark; 6th December 2018 at 09:34 PM.
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Old 8th December 2018, 02:35 AM   #45
academia50 is offline academia50  Argentina
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Quote:
Originally Posted by martin clark View Post
The real advantage of the alternator in no small part due to the solid-state side of rectification and regulation was the fundamental change of operation -

1. the non-mech commutation allowed instead for the rotor to provide/control the magnetic field, and the stator to supply heavy output currents that do not need to pass through slip-rings/ a commutator (massive win); and so

2. as a result - simple regulation of a low current via slip rings to the rotor to provide the field magnetism. This current is still often at most only 4-5A, so lifespan was also massively improved.

A simply brilliant inversion, that also allows the control of rotor mag field (= generated output power) nearly-independent of input rpm. Hence - ramp the field current right up at low speed and you can draw a significant proportion of full-rated output current, often 70-ish% + even at engine idle. It made the 'generator' a near- constant-power device, rather than only the constant-voltage device a dynamo could be. That's the big step forward.

Interesting side diversion - this also means the drive torque to an alternator to deliver its rated power also drops off markedly as revs rise. Strange but true.


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Last edited by academia50; 8th December 2018 at 02:42 AM.
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Old 30th January 2019, 12:28 AM   #46
phase is offline phase  United States
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The advent of the gear reduction starter probably did more than a change in voltage alone.

I am surprised it took 13 posts before someone addressed the outgassing combustion risk with handling batteries!
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Old 20th March 2019, 02:38 PM   #47
davidsrsb is offline davidsrsb  Malaysia
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Originally Posted by Pano View Post
Wasn't that supposed to happen about 10 years ago? Cars were going to 42 volts. Can't remember why it didn't happen, will have to look it up.
Because everything has to migrate to 42V. Lights are no problem now as they are mostly LED with a switcher anyway. New motors everywhere and who makes a 42V stereo?
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Old 22nd March 2019, 06:56 PM   #48
russc is offline russc  England
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who makes a 42V stereo?
Ideal for insanely loud car audio surely?
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Old 22nd March 2019, 07:19 PM   #49
Mooly is offline Mooly  United Kingdom
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Deeply discharged car battery - basic questions (no charger around).
Its only in the last couple of weeks that I've discovered just how sophisticated the charging from the alternator is on my car, which is now 9yr old and still on the original battery.

I got curious after reading some background info and so decided to see for myself... cue cheapo DVM wired to a lighter plug.

Starting from cold sees around 14.5 volts. After a few hundred yards the voltage falls back to 12.6v (irrespective of loading) when accelerating or maintaining constant speed. Any deceleration sees this increase back to 14.5 volts. This is most probably some form of emissions control reducing the load on the alternator. There will also be a little added bonus effect from extra engine braking. At idle its back to 14.5 volts.

The above behaviour is not hard and fast, sometimes it can maintain 14.5 volts all the time, other times it will maintain this and then suddenly drop back to 12.6 volts for quite extended periods.

Cold weather seems to inhibit the above behaviour markedly.

The battery negative terminal has one of those monitoring do-dahs like this although its a Toyota and not a BMW as described here:

BMW Intelligent Battery Sensor (IBS) >> Bimmerscan

The original battery is specified as 'suitable for stop start' which the car has. I've read conventional old style batteries might only last a matter of months or even weeks and so always to use the correct type which I'm assuming is some AGM (absorbent glass mat) type or derivative.

Interesting though.
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Old 23rd March 2019, 02:02 PM   #50
phase is offline phase  United States
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Have you tried driving with the headlights on to see if that affects the voltage?

Assuming that you donít already drive with the lights on...
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