Car battery charger

petrol engine capacity.

It's just a vague handwave about the size of battery it can charge: 'cars up to 1.8L typically have batteries about XX Ah'. If you have a bigger car you'll want our Super Pro Plus Advanced Gold model (for extra $$$, because you're worth it). That model probably offers a higher charging current for faster charging of larger batteries.

Petrol or diesel doesn't matter because it's marketing that doesn't really make sense.

(If you were trying to charge a 9999 Ah battery it's possible the charger would overheat through prolonged use, but I expect charging a flat battery of any size is going to run it for a several hours and it must be designed to run at that temperature continuously)

Theo

Closer to bullshit. The battery charger will charge any battery of the right voltage and chemistry type but it may damage smaller ones.

I guess they do it so they can charge extra for the 2L and above one.

There is no clear upper limit to the maximum Ah capacity of battery that a 6A output charger can charge it will just take increasingly longer to do it as the Ah capacity of the battery increases!

However, if you connect a 1Ah battery or smaller to a 6A charger expect the magic smoke to come out together with a hot sulphuric acid spray.

I'd have thought higher compression ratio with diesel, would need bigger batteries, and therefore higher current to charge in a comparable time?

.....and glow plugs.

The size of the car engine.

They can't be referring

Yep, because that determines the size of the car battery.

Yep, diesel engines need more cranking capacity from the battery.

A charger capable of supplying 6A will only supply what is demanded surely?

That was my thought. As a general rule you can charge at 1C at 14.4V and the current will fall PDQ.

I suspect even 6C would be ok for a part charged Lead acid batter, for high C charging currents my main concern would be thermal runaway. The terminal voltage decreases with temperature, so current can increase over time.

just ignore the engine size bit ...bigger cars have bagger batteries

A 'smart' charger will have an initial constant current phase, which will normally be the rated output current. As the voltage rises and reaches a particular value, usually around 14.4 for lead-acid, the charger will switch to maintaining that voltage, and will progressively reduce the current in order to do that.

Finally, when the current has dropped below a particular value, it will set a target voltage of about 13.5 and further reduce current, which can be maintained long-term without (much) battery damage.

Many batteries, particularly leisure types, will have a maximum initial charge current marked on them. Use a charger rated at no more than this, preferably a little less. A swollen battery is almost always a sign that the charge current was too high.

I've been using these:

I have a 4 litre car but use any old charger fron 150ma trickle to a big transformer high current unit

Sounds like a very good reason not to use one I would have thought.

I have charged an 80Ah battery with a 1A charger. It simply took a long time.

totly

Why?

Such a charger is most efficient in putting Amp-hrs into a battery and won't apply an overly high voltage to the battery when fully charged to make it gas.

A truly smart charger will fallback to a float charge voltage. For that the tail current has to be known and matched to the battery.

Other smart chargers also apply a periodic equalisation voltage to stir the electrolyte through gassing. If used in a motive application and subject to movement, this isn't necessary, and also shouldn't be applied to a gel battery.

It depends what you are aiming for. If the objective is to be back in a position to maintain supply to whatever the UPS is protecting then when power becomes available you want to charge it back up again as fast at the prevailing temperature of the battery will permit.

It is only a problem if you connect a small battery to a large charger.

Many older lead acid battery chargers are as dumb as a rock. Mine certainly is it does nominal 6A or 3A into 6v or 12v accumulators! (yes it is old enough to refer to them that way)

Consists of little more than a transformer and a bridge rectifier.

Very smart modern chargers won't apply power to a battery that they think is already too far gone (which can also be annoying). Sometimes you can get a bit more life out of them by ignoring such failures and forcing charge in with a dumb as a rock charger. Only a good idea if it doesn't matter if the thing subsequently leaks.

I have seen UPS batteries swell up to the point where they would not come out of the equipment without deforming the metal frame. Although the record for a swollen battery came out of an iPad after it sprung the whole thing apart! I have a photo of that one somewhere!

It sounds as if you would need one for each car then check you are connecting the right one to the right battery instead of just connecting it up and going for a cup of tea.

But safe, doesn't matter which battery you connect to which charger, as long as you set the right voltage.

No it is the other way around you can safely use a smart charger on any car battery to top it up and be confident it will do no harm.

Where they can be a nuisance is if you want to charge a flat battery.