Battery only charging at 13v - will it end up discharging?
Discussion
Erm... depends what the rest voltage is doesn't it?
Most cars with a healthy alternator will run with a dead battery (although it doesn't do the alternator any favours), although from experience large electrical loads can cause it to conk out, such as using the main beam 'flasher' with the headlights switched on.
Most cars with a healthy alternator will run with a dead battery (although it doesn't do the alternator any favours), although from experience large electrical loads can cause it to conk out, such as using the main beam 'flasher' with the headlights switched on.
Battery is on charge at the mo - reading 12.5 across the terminals.
Original alt as far as I know (20 years old) but regulator was replaced less than 2 years ago, the diodes are on that aren't they?
When running it is fine, but really struggled starting today, OK for first 2 shortsh journeys - on the third it wouldn't crank and I had to jump it.
Did a 220 mile journey yesterday without problems, but battery discharged this morning...
Suspect either duff alt or bad connection on it. Regulators are cheaper than alts though....
Original alt as far as I know (20 years old) but regulator was replaced less than 2 years ago, the diodes are on that aren't they?
When running it is fine, but really struggled starting today, OK for first 2 shortsh journeys - on the third it wouldn't crank and I had to jump it.
Did a 220 mile journey yesterday without problems, but battery discharged this morning...
Suspect either duff alt or bad connection on it. Regulators are cheaper than alts though....
In that case my next guess would be an internal short in the battery. Is it sealed? If not, can you check if all six cells fizz on charge and need a small top-up with distilled water? If one doesn't fizz and the terminal voltage after charging quickly drops to around 11V then it's new battery time.
driverrob said:
In that case my next guess would be an internal short in the battery. Is it sealed? If not, can you check if all six cells fizz on charge and need a small top-up with distilled water? If one doesn't fizz and the terminal voltage after charging quickly drops to around 11V then it's new battery time.
Sealed batteries are a con you'll probably find top up ports underneath some fancy sticker if its recent. Just been out for a poke around.
Alt earth seems OK (continuity)
Alt + seems OK (battery voltage present)
signal wire continuity OK as alt lamp comes on with ignition.
Started on the key (trickle charging for 2 hours), but voltage across battery while running now 11.4v (after charging
), and 12.2 after stopping engine.
If it's not charging then surely the alt light should be on?
Now beginning to suspect battery... Where's that receipt...?
Alt earth seems OK (continuity)
Alt + seems OK (battery voltage present)
signal wire continuity OK as alt lamp comes on with ignition.
Started on the key (trickle charging for 2 hours), but voltage across battery while running now 11.4v (after charging
), and 12.2 after stopping engine.If it's not charging then surely the alt light should be on?
Now beginning to suspect battery... Where's that receipt...?
I had a similar issue...very low charge rate. Turned out to be the alternator.
ETA - Mine didn't light up the charge light either. To be more specific, it was the regulator/rectifier within the alternator that had died...the brushes and windings were fine. Fitted a new rectifier/reg and it was fine.
ETA - Mine didn't light up the charge light either. To be more specific, it was the regulator/rectifier within the alternator that had died...the brushes and windings were fine. Fitted a new rectifier/reg and it was fine.
Edited by Dr.Doofenshmirtz on Tuesday 18th May 15:06
Hmmmm...
Question is, how do I test for either? Regulators are cheap but a PITA to fit on mine. How do you test a battery? (could put my tongue across the terminals I suppose
)
PS - lights / heated rear window don't seem to affect the idle speed of the engine - not sure what that means :-/
Question is, how do I test for either? Regulators are cheap but a PITA to fit on mine. How do you test a battery? (could put my tongue across the terminals I suppose
)PS - lights / heated rear window don't seem to affect the idle speed of the engine - not sure what that means :-/
Edited by NiceCupOfTea on Tuesday 18th May 15:39
The Wookie said:
NiceCupOfTea said:
It's sealed. It's a decent Varta battery and less than a year old...
But surely even if the battery was goosed the alternator would be putting out 14v-odd?
http://en.wikipedia.org/wiki/Ohm's_lawBut surely even if the battery was goosed the alternator would be putting out 14v-odd?
If the alternator is turning at a constant speed it should be putting out a constant voltage, n'est-ce pas? Would the battery beaing knackered have an effect on this?
My point is that the alternator may well be putting out 14v if you measure it at the connectors, but there's plenty of scope for voltage drop between there and the battery, including the battery itself.
My team nearly pulled the Alternator out of my brand new racing car at its first event because it failed to start (it'd been turning over slightly slowly in pre-season testing, but didn't seem to be a problem), showing about 11.5 volts rest and 12.5 volts running. It turned out to be a dead cell in the Varta battery.
I'd personally check the connections and try swapping the battery before I yanked the Alternator, particularly if the battery has been run flat at any point.
My team nearly pulled the Alternator out of my brand new racing car at its first event because it failed to start (it'd been turning over slightly slowly in pre-season testing, but didn't seem to be a problem), showing about 11.5 volts rest and 12.5 volts running. It turned out to be a dead cell in the Varta battery.
I'd personally check the connections and try swapping the battery before I yanked the Alternator, particularly if the battery has been run flat at any point.
Unless you've got a one-in-a-million fault, your alternator is goosed. The battery needs 14.2-14.5v across it at a fast tickover to maintain its charge. Anything less means a discharge.
As previously mentioned, the most likely cause is the diode board; depends on which alternator you have as to whether this can be replaced separately. I'd be tempted to get a service exchange unit which will also have had the brushes, bushes and bearings replaced.
As previously mentioned, the most likely cause is the diode board; depends on which alternator you have as to whether this can be replaced separately. I'd be tempted to get a service exchange unit which will also have had the brushes, bushes and bearings replaced.
Kay.
Not had a chance to get to the car but it's been on trickle charge for 48 hours.
It said it was still charging but after stopping and restarting the charger it thought it was charged.
Voltage across the battery was 12.8v when charger disconnected.
Started on the key, voltage when running across the battery 12.0v, across the alternator 12.1v - so clearly not charging, but no alt light on the dash.
After turning off the ignition, voltage across the battery 12.5v.
I agree that ordinarily that would spell out "dead alternator" (whether unit itself, brushes, diodes, whatever) - but the fact that there is no alt lamp lit makes me think it might be the battery.
But, if there was a dead cell would the battery charge to a full 12.8v?
Not had a chance to get to the car but it's been on trickle charge for 48 hours.
It said it was still charging but after stopping and restarting the charger it thought it was charged.
Voltage across the battery was 12.8v when charger disconnected.
Started on the key, voltage when running across the battery 12.0v, across the alternator 12.1v - so clearly not charging, but no alt light on the dash.
After turning off the ignition, voltage across the battery 12.5v.
I agree that ordinarily that would spell out "dead alternator" (whether unit itself, brushes, diodes, whatever) - but the fact that there is no alt lamp lit makes me think it might be the battery.
But, if there was a dead cell would the battery charge to a full 12.8v?
Batteries can play tricks, especially when freshly charged. The only reliable way to test the voltage of the battery itself is to leave it standing indoors (temp affects batteries) for about 8 hours after it's been charged and then check the voltage across the terminals. A fully charged battery in decent condition should give a voltage reading of 12.5v or more. Anything under that and it's on the way out; 12v or less and it's knackered.
Your problem sounds like alternator to me.
Your problem sounds like alternator to me.
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