how long idling to charge the battery?

Plus, if I understood the OP properly, and the battery has been left in a state of discharge for some time, buy a new battery as well. Lead Acid's do not like being left at a low charge state and some damage will (should) have occurred.

Regards

Mike

The battery needs recharging properly with a charger, disconnected from the car. Depending on its size and level of charge it could need 12hrs +. You wont do it with the alternator.

With a sub 2litre petrol car and a self ~8A regulating charger and an 80% discharged battery in good order you'd need about 8hrs to properly recharge it.

As an extreme the 200aH batterys on some of the plant here need at last

Tim..

Diesel engines have a much higher compression ratio and use a larger starter motor. Usually around about a 2-2.5kw starter motor. A 2litre petrol car would have around a 1.7kw starter (or thereabouts). You're talking around

The initial surge to get the engine spinning over is high and whereas most petrol engines will start fairly easily at even 50% of normal cranking speed (assuming sufficient power left over for ignition / fuel pump etc) with a weak battery, a diesel wont. To generate the heat the motor has to spin over as fast as possible. Even more so when cold.

Again the diesel engined plant I work with easily draws over 1000amps initially when cold- we're talking 24v systems and upto 19litres mind!

Tim..

Also sprach " Tim \(Remove NOSPAM." :-

Most cars don't give two hoots whether the battery's connected or not - and neither do the chargers. It's only these new fangled modern things which protest - and I suspect a lot of that isn't actually the case, just excessive caution.

Absolutely. Saying in the instructions to disconnect it prevents any claims for possible damage to the car's electronics - however unlikely this is.

Not forgetting a diesel also has to run the glow plugs for a few seconds before trying to crank, and that put a big hit on the battery before you even start cranking....

Of course if you do this to a sealed cell system you can easily overcharge it and cause it to blow. You don't want to be exceeding the maximim permissible current that a battery can take on charge.

Apart from the fact that most modern ones cut out when they over heat their max current is limited at idle, it'll be fine

Connect the -6A one back to front :-). & don't leave it connected, it tends to over 15V when the batterys charged.

On our old landrover it peaked at 800A, total under currentxseconds used on my old audi:-( was 600AmpSeconds to start, recharged at about 8A on a part discharged battery at idle, about 25A on a heavily discharged battery.

WEll you may need a really large expensive ( £20 i think my mate payed) panel and they may not work too well in the winter but they work well enough to keep my mates bike battery charged enough over the discharge of his alarm and whatever other drain he's got going on. Ref the car windscreen cutting out most of the uv light, really couldnt comment on how much it'd cut out ( in fact i'll give it a go on my meter tommorow ) as i have no idea tbh. So far as a cheap battery charger goes, i was only suggesting an alternative that didnt have any thought/remembering involved.

Also sprach "Chris" :-

I had a go with a panel and a multimeter a few years ago. The output current dropped by about a half when I put the car glass between it and the sun. Not tinted windows, either!

Although it can extend your battery life a bit, handy for airport car parks.

Quite so, and some leave the glow plugs energised *after* the light has extinguished for upto 3 minutes *after* engine start.

Typical figure is 10-12amps per plug- easily 50amps.

Tim. .

Yep. I think the recommended float charge voltage for sealed batteries is 2.3V per cell, 13.8V for a 12V battery - A bit lower than for car batteries.

They can still vent even at that rate though sometimes. A company I once worked for used to use SLA batteries in sealed enclosures way back when everyone, including the battery manufacturer, used to think that was OK as long as you kept to the charging spec. Made a right mess of some very sturdy stainless steel enclosures, they did :o). The battery manufacturer couldn't really argue - we were even using their own branded chargers! After that, they started printing dire warnings about charging in sealed boxes on all their batteries...

Cheers,

Colin.

I recall hearing a super F gel-cel cell letting go when some idiot charged it with 13.8V (yes a single cell on a 6 cell charger). The mess was quite spectacular, including tacky sticky sulphuric acid gel stuck all over the tech who was charging it. Fortunatly he was wearing his goggles otherwise it would have been very nasty indeed. His beard was wrecked though which upset him a little.

It sounded like a shotgun going off and I was five rooms down behind a shut class-A fire door.

This might come in handy, stolen from topbuzz.co.uk:

What is a car battery?

The car battery is a storage device, which stores energy. This supplies a current at a particular voltage (DC) to the conductive parts of the circuit. The standard car battery in today's vehicles are rated at 12 volts. Each battery has six cells which are 2.1 volts each. A car battery is considered fully charged at 12.6 volts. When a battery drops voltage, even by a small amount, it makes a big difference.

For instance, when a battery drops from 12.6 to 12.0 volts, its power drops from 100% to 25%! At 12.4 volts, a car battery is only 75% charged. At 12.2 volts, it's 50% charged. A car battery is considered charged at 12.4 volts or higher. It is considered discharged when it's at 12.39 volts or less. The current is heavily dependent on the type of battery and the resistance of the 'load'.

Alternator Charging:

Usually when a car is jump started, it is driven long enough to fully recharge the battery. The length of time to fully recharge the battery depends on the amount of discharge, the amount of surplus current that is diverted to the battery, how long the engine is run, engine speed, and ambient temperature. That is, an alternator is sized by the car manufacturer to carry the maximum accessory load and to maintain a battery and NOT to recharge a dead battery.

For example, if 300 amps were consumed for two seconds to start a car from a fully charged battery, it will take an 80 amp charging system approximately nine seconds to replace the power used. If 25 amps are available to recharge the battery, it will take 12 minutes and 30 seconds at one amp. With a dead 120 minute RC battery, it would take approximately 45 minutes at 80 amps, 2.4 hours at 25 amps, or 60 hours at one amp to obtain a 90% State-of-Charge.

If you have added lights, audio amplifiers, two-way radios or other high powered accessories to your vehicle and engage in stop-and-go driving, the alternator might not produce enough current to keep your battery fully charged. You might need to increase the capacity of the charging system. Ideally the combined load of all the accessories should be less than 75-80% of the charging system's maximum output, so that at least 20-25% is available to recharge the battery.

Really useful site, BTW.

--Nick.

When I was at school, it was 2.2 volts a cell.

Also sprach "Dave Plowman (News)" :-

Didn't Callahan devalue it in 1967?