Charge or jump start?
Discussion
kambites said:
If that's the case, they have a really crappy charging implementation. Surely the whole point of having an alternator over a dynamo is that engine speed has no bearing on electrical output?
I wonder if not charging the battery at idle is another one of these adft things they do to fool the emissions tests? NEDC spends quite a lot of time idling and I bet they don't check that the battery is in the same state of charge at the start and end of the test.
Alternator output currents can be higher (and much greater at idle than a dynamo) but an alternator is not the best current source to charge a battery.I wonder if not charging the battery at idle is another one of these adft things they do to fool the emissions tests? NEDC spends quite a lot of time idling and I bet they don't check that the battery is in the same state of charge at the start and end of the test.
Many cars now have active alternator management where the alternator only generates power when the demand is there or under favourable conditions (e.g. overrun / braking as "recuperation").
E65Ross said:
Another vote for a ctek. I have the MXS5.0 charger and it's bloody great. Also been recovering from an op which meant my licence has been revoked for 12 months, I've had friends drive it periodically but the charger has stayed on pretty much every time the car isn't in use and the car has started faultlessly every time.
I've just bought one of these for my bike over winter. They seem to get a very good review. My dad recommended them to me, he used one to recover his R129's battery after it went flat due to some dodgy electrics in the roof mechanism. After being as flat as a fart, the reconditioning function of the CTEK brought it back from the dead, and he's used the CTEK habitually ever since. I'd be wary of just idling the car for a while though, definitely start it and drive it (hard!) if you can. I recently started a Vivaro at work with a battery pack after someone left the interior lights on and flattened the battery. I gave it a right Italian tune up for about five minutes, then switched it off. It was flat when I came back half an hour later, but the battery seems to have been saved by re-starting it and driving it hard for a while. Mind you, the drain on the battery in that vehicle is far larger than the manufacturer intended, I guess, because of all the extra electrical systems onboard.
Actually the alternator is the best to recharge a battery compared to a dynamo. If you have a volt meter just check the battery with everything off and the engine not running that could be around 10 - 12 volts depending on charge. Start the engine and straightaway you will see the voltage jump to 13.5 - 14.2 volts - a little electrical knowledge you will appreciate that as the alternator voltage is higher than the battery voltage you will cause a current to flow into the battery - this will cause chemical reactions to occur which effectively charge the battery.
Dynamos are speed dependent - they generate a voltage that depends on the speed of the engine so would be geared to be producing a good charging voltage at running speed at an idle the voltage may well have been too low to charge the battery.
With an alternator this is generally a three phase generator - the voltage stays pretty much the same through the rev range its the frequency of the output that changes. And as its rectified it is put out as dc to the battery.
Electronics in modern cars will pick up on the battery condition and increase the engine speed to ensure that the battery gets charged. It wont take much increase to better charge the battery though so you wouldnt hear it so much compared to a car equipped with a dynamo.
Dynamos are speed dependent - they generate a voltage that depends on the speed of the engine so would be geared to be producing a good charging voltage at running speed at an idle the voltage may well have been too low to charge the battery.
With an alternator this is generally a three phase generator - the voltage stays pretty much the same through the rev range its the frequency of the output that changes. And as its rectified it is put out as dc to the battery.
Electronics in modern cars will pick up on the battery condition and increase the engine speed to ensure that the battery gets charged. It wont take much increase to better charge the battery though so you wouldnt hear it so much compared to a car equipped with a dynamo.
The alternator can maintain the battery in a good charge state if the battery is not excessively depleted (as in the case with a jump-start being required) otherwise a battery charger is required.
This is because a lead-acid battery goes through four different charge stages (refer to earlier post http://batteryuniversity.com/learn/article/chargin... which alternators are not intended to support.
E.G.
https://www.optimabatteries.com/en-us/experience/p...
http://carbibles.blogspot.co.uk/2013/02/your-alter...
This is because a lead-acid battery goes through four different charge stages (refer to earlier post http://batteryuniversity.com/learn/article/chargin... which alternators are not intended to support.
E.G.
https://www.optimabatteries.com/en-us/experience/p...
http://carbibles.blogspot.co.uk/2013/02/your-alter...
Flip Martian said:
CTEK arrived and plugged in. Put it on the full recondition setting and it started on stage 3 (bulk charging) within a minute. Nice and easy, thank God (for a technical numpty like me). Thanks once again! 
It'll probably take something like 24-36 hours to complete the conditioning cycle (from what I've seen it's not a fixed time, it depends on how the battery behaves). Re jump start and alternators - this usually works. However there are certain circumstances (I hear) where some alternators don't start charging until the engine is revved to about 2k rpm. At this point the coils are energised (I'm told) and the thing will continue charging until it's turned off. Under normal driving nobody notices because you get to 2k rpm as you change into second gear for the first time, but I have heard tales of cars being started and left to idle without them charging at all. VW used to be afflicted wsith this, don't know if they still are.
100SRV said:
The alternator can maintain the battery in a good charge state if the battery is not excessively depleted (as in the case with a jump-start being required) otherwise a battery charger is required.
This is because a lead-acid battery goes through four different charge stages (refer to earlier post http://batteryuniversity.com/learn/article/chargin... which alternators are not intended to support.
E.G.
https://www.optimabatteries.com/en-us/experience/p...
http://carbibles.blogspot.co.uk/2013/02/your-alter...
That Carbibles blogspot post is utter sThis is because a lead-acid battery goes through four different charge stages (refer to earlier post http://batteryuniversity.com/learn/article/chargin... which alternators are not intended to support.
E.G.
https://www.optimabatteries.com/en-us/experience/p...
http://carbibles.blogspot.co.uk/2013/02/your-alter...
t, the guy has no idea what he's talking about: Blogspot clueless twit said:
"In a properly functioning car, the 12V electrical system is mostly reliant on the battery itself. The alternator provides a 'topping off' charge to help maintain the battery, but can't really be relied on to charge it."
Even a moments thought suggests this must be bks. His comment about 2 - 3 year lifespan for a battery is also complete bks, it is not even slightly uncommon for a 10 year old car to have the original battery now. This might have been true for Leyland st stuffed with subpar Lucas bits and "cheapest bidder" batteries from the factory, but I'm not sure even that is the case.Flip Martian said:
CTEK arrived and plugged in. Put it on the full recondition setting and it started on stage 3 (bulk charging) within a minute. Nice and easy, thank God (for a technical numpty like me). Thanks once again!
Remember it's a trickle charger leave it plugged in for 24 hours. 
kambites said:
If that's the case, they have a really crappy charging implementation. Surely the whole point of having an alternator over a dynamo is that engine speed has no bearing on electrical output?
The whole point of an alternator is that they provide increased output at lower speeds, they last longer and they are more efficient, but they can't perform miracles. At typical idle speeds they will not provide anything like their maximum rated output current.Mr2Mike said:
The whole point of an alternator is that they provide increased output at lower speeds, they last longer and they are more efficient, but they can't perform miracles. At typical idle speeds they will not provide anything like their maximum rated output current.
So you are telling me if I get my vault meter out and check at idle it will be less volts than if I Rev it? battered said:
Re jump start and alternators - this usually works. However there are certain circumstances (I hear) where some alternators don't start charging until the engine is revved to about 2k rpm. At this point the coils are energised (I'm told) and the thing will continue charging until it's turned off. Under normal driving nobody notices because you get to 2k rpm as you change into second gear for the first time, but I have heard tales of cars being started and left to idle without them charging at all. VW used to be afflicted wsith this, don't know if they still are.
It's very simple...The charge light tells you if there's more electrickery coming out of the alternator than there is in the battery.
If that theory was correct, the light would stay on whilst the car was idling, until you hit 2k rpm. It doesn't.
TooMany2cvs said:
It's very simple...
The charge light tells you if there's more electrickery coming out of the alternator than there is in the battery.
If that theory was correct, the light would stay on whilst the car was idling, until you hit 2k rpm. It doesn't.
Apparently when this was the case with VWs (some years ago, admittedly) the alternator telltale light didn't let on to this. I don't remember the details (didn't own a VW), and I'd be surprised if it still applies, but that was the received wisdom at the time.The charge light tells you if there's more electrickery coming out of the alternator than there is in the battery.
If that theory was correct, the light would stay on whilst the car was idling, until you hit 2k rpm. It doesn't.
Pesty said:
So you are telling me if I get my vault meter out and check at idle it will be less volts than if I Rev it?
Yes it will almost certainly be lower at idle, particularly with a discharged battery. There is a very good reason that ECUs have to monitor battery voltage to correct coil dwell and injector opening times etc.shake n bake said:
A battery charger will give it a thorough charge, if you do jump it, leaving it to just idle does close to nothing. Driving it's ok though.
Driving it is ok.... Unless the battery is actually completely gubbed and you head out without your leads, and get caught in the rain and have to turn the lights, blower and wipers on at once and end up coming to a halt on a single track road blocking traffic on a slight uphill. Then it's not so ok!
2004 Mk 2.5 on the original battery.
Mr2Mike said:
kambites said:
If that's the case, they have a really crappy charging implementation. Surely the whole point of having an alternator over a dynamo is that engine speed has no bearing on electrical output?
The whole point of an alternator is that they provide increased output at lower speeds, they last longer and they are more efficient, but they can't perform miracles. At typical idle speeds they will not provide anything like their maximum rated output current.In fact the ECU in my car does raise the idle speed to meet alternator demand because if I jump start it when it's got a completely flat battery, it idles at about 2500rpm for a while (which is rather noisy).
kambites said:
In fact the ECU in my car does raise the idle speed to meet alternator demand because if I jump start it when it's got a completely flat battery, it idles at about 2500rpm for a while (which is rather noisy).
Is that not the standard ECU idle learning program once flat?Extra alternator load will often raise the revs of an engine a little, but not that far. After all, even a 200A alternator (well beyond what's fitted to normal cars, especially an Elise) would only need 4hp to power it.
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