Alternators, TALK TO ME!
Discussion
I often put my ‘for best’ car on charge during the week, which got me to wondering about alternators. Is the rate they charge the battery constant, or does it increase with engine revs and how does their performance compare to a charger plugged into the mains. Also, how long would you have to drive your car for it to fully charge a battery that say only just managed to turn the engine over, roughly? Cheers!
Alternators are designed to keep a good condition full battery topped up. Asking an alternator to fully charge a dead battery significantly increases the load on the alternator and reduces its lifespan accordingly.
In terms of answering your question of how long, it depends on the amp:hour rating of the alt. and the capacity of the battery.
In terms of answering your question of how long, it depends on the amp:hour rating of the alt. and the capacity of the battery.
wolfracesonic said:
I often put my ‘for best’ car on charge during the week, which got me to wondering about alternators. Is the rate they charge the battery constant, or does it increase with engine revs and how does their performance compare to a charger plugged into the mains. Also, how long would you have to drive your car for it to fully charge a battery that say only just managed to turn the engine over, roughly? Cheers!
Alternators only put a small current into the battery - typically around 5-6 Amps. If it's a typical car battery of about 50 Ah capacity and starting at 50% charged then it would need about 30 Amp-hours put into it which could take 6+ hours of continuous driving. Read this to understand how to properly charge a battery and why just driving around for 30-60 minutes wont charge a battery that is low:
https://batteryuniversity.com/learn/article/chargi...
I have many batteries both in cars and in the garage and I keep them all topped up and make sure they never get low.
Shoving a 30amp charger on a dead battery (under 10.5) does it no good whatsoever.
https://batteryuniversity.com/learn/article/chargi...
I have many batteries both in cars and in the garage and I keep them all topped up and make sure they never get low.
Shoving a 30amp charger on a dead battery (under 10.5) does it no good whatsoever.
Difficult one this
Batteries that have been slowly drained to flat will take much longer to charge than batteries that have been quickly drained to flat
Alternators will happily work away giving their maximum output which then reduces over time as the battery charges up for several hours and will eventually charge a flat battery to a fully charged state
There's a catch though
Batteries don't like loads of amps being fired at them for long periods as the heat generated can damage their plates
This tells us that trickle chargers are good for flat batteries
The above is for standard lead acid type batteries
OP mentions flat and not dead flat, dead flat is a different ball game
Batteries that have been slowly drained to flat will take much longer to charge than batteries that have been quickly drained to flat
Alternators will happily work away giving their maximum output which then reduces over time as the battery charges up for several hours and will eventually charge a flat battery to a fully charged state
There's a catch though
Batteries don't like loads of amps being fired at them for long periods as the heat generated can damage their plates
This tells us that trickle chargers are good for flat batteries
The above is for standard lead acid type batteries
OP mentions flat and not dead flat, dead flat is a different ball game
Edited by Penelope Stopit on Sunday 23 February 12:41
paintman said:
Mmmmm best edit my above post as it's for standard lead acid batteries, didn't consider other battery typesGassing Station | Engines & Drivetrain | Top of Page | What's New | My Stuff