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Alternator not charging battery....unless lights on...
Hi all
Just as the title says really.
Had to jump start the car to get it to the garage for an MOT. The mechanic I usually see said they'll check the battery (not even a year old) and alternator (squeals on some cold starts, planning to change aux belts soon).
Said that when the car is turned on, the alternator isn't charging the battery at all even if they rev the car. If they turn the lights on, it charges the battery
Had to jump start the car to get it to the garage for an MOT. The mechanic I usually see said they'll check the battery (not even a year old) and alternator (squeals on some cold starts, planning to change aux belts soon).
Said that when the car is turned on, the alternator isn't charging the battery at all even if they rev the car. If they turn the lights on, it charges the battery
Any insight would be appreciated.
Thank you
I'm near sure I've heard the alternator doesn't "activate" unless there's a load on it. Need to have something running, whether its lights or stereo or heater etc.
Yep - the alternators are supposedly "intelligent or smart" and as Charly says, only charge when it senses a load.
Sounds as if your battery was in need of a full charge anyway. In current climate/enviroment, a battery conditioner/trickle charger is a good solution.
As above. Probably the old Denso/mitsubushi (not-so) 'smart' alternators. Depends on model year on what's fitted; the ones where the charge control is all housed and managed solely by the alternator are the ones that give the trouble (Other car makes use the Engine ECU or body ECU to regulate the alternator output; the non-ECU controlled 'smart' charge setup on Japanese cars of the mid 2000's was crude at best and always gave issues on low mileage cars).
I never bothered to research a long term solution other than a good intelligent trickle charger (Accumate, Ctek or a proper solar charge controller). But I bet there are aftermarket regulators/brush boxes out there now that don't have the 'smart' control (usually a £20 part ).
Of course goes without saying belt and braces check should be made before making assumptions;
Battey state of charge see table below; If below 50% after resting for 30mins (doors closed everything off, or battery disconnected It is FLAT. And will IRREPARABLY SUFFER LOSS OF CAPACITY if left like that due to sulphation. Even if it still starts the car the battery is being damaged by leaving it like this. Generally speaking to maximise battery life, avoid letting it drop below 75% (unless it's a deep cycle battery designed for deep discharge).
The alternator WILL NOT fully charge the battery. An occasional 'long run' is not enough. It will only bulk charge to about 80%.
Battety condition; Age. How often/long if been left below 60% charge will dictate its life/capacity. Fully charge and make sure that after standing for 24hys it's still above 12.6v (disconnected). If it's dropping to 12.5v or less, it has a duff cell (or it's very very cold). Garage battery testers are not always accurate but they give a general idea of condition. Either way it a fully charged battery should never drop below 9volts when cranking the engine.
Parasitic losses; It's always worthwhile getting an ammeter and checking what drain there is on the battery (everything closed, locked and left for 30mins). Ideally it should be below 100 milliamps. If it's above 150mA then that will flatten a typical battery in two weeks. Above 200mA you have a problem that you need to investigate.
Everything you need to know about caring for lead acid batteries:
Wow, lots of brilliant information there! I posted this and then remembered that about the alternator but (rather embarrassingly) I couldn't figure out how to delete a thread via mobile site.
I've been reading a fair bit on here about how Scoobynet isn't as great as it once was. Nice to know there are still some really helpful people on here
As above. Probably the old Denso/mitsubushi (not-so) 'smart' alternators. Depends on model year on what's fitted; the ones where the charge control is all housed and managed solely by the alternator are the ones that give the trouble (Other car makes use the Engine ECU or body ECU to regulate the alternator output; the non-ECU controlled 'smart' charge setup on Japanese cars of the mid 2000's was crude at best and always gave issues on low mileage cars).
I never bothered to research a long term solution other than a good intelligent trickle charger (Accumate, Ctek or a proper solar charge controller). But I bet there are aftermarket regulators/brush boxes out there now that don't have the 'smart' control (usually a £20 part ).
Of course goes without saying belt and braces check should be made before making assumptions;
Battey state of charge see table below; If below 50% after resting for 30mins (doors closed everything off, or battery disconnected It is FLAT. And will IRREPARABLY SUFFER LOSS OF CAPACITY if left like that due to sulphation. Even if it still starts the car the battery is being damaged by leaving it like this. Generally speaking to maximise battery life, avoid letting it drop below 75% (unless it's a deep cycle battery designed for deep discharge).
The alternator WILL NOT fully charge the battery. An occasional 'long run' is not enough. It will only bulk charge to about 80%.
Battety condition; Age. How often/long if been left below 60% charge will dictate its life/capacity. Fully charge and make sure that after standing for 24hys it's still above 12.6v (disconnected). If it's dropping to 12.5v or less, it has a duff cell (or it's very very cold). Garage battery testers are not always accurate but they give a general idea of condition. Either way it a fully charged battery should never drop below 9volts when cranking the engine.
Parasitic losses; It's always worthwhile getting an ammeter and checking what drain there is on the battery (everything closed, locked and left for 30mins). Ideally it should be below 100 milliamps. If it's above 150mA then that will flatten a typical battery in two weeks. Above 200mA you have a problem that you need to investigate.
Everything you need to know about caring for lead acid batteries:
This makes for a very interesting read, I'll be replacing the belt soon as there is a cold start squeal. It can last for some time, and I've notuced the sound comes from the alternator pulley. If that doesn't cure it, I'll be sourcing a second hand alternator.
Could be belt tension is wrong (overtight can make noise as well as too loose). Pulleys not aligning is another...crank pulleys can fail on models that have the rubber damper which perishes allowing the pulley to become misaligned, slip and/or wobble (also worth checking crank pulley bolt hasn't come loose).
Alternator bearing easy enough to check by removing the belt and giving it a turn by hand to check for smoothness.
I'm glad you mentioned the crank pulley. I thought that it looked a bit wobbly when I looked under the bonnet a few days ago. I gave the theottle cable a quick pull and once it settled to idle again, the pulley looked fine. Odd. If it is loose, how much am I looking at to get it replaced?
08 January 2021, 09:31 PM
Alternator not charging battery....unless lights on...
