On 28/03/2013 13:54, Dave Plowman (News) wrote:
In article ,
Andrew Gabriel wrote:
The thing is, the actual performance of the tiny Lidl one is actually
better than some conventional chargers costing a lot more - and taking up
several times the space. I have a Halfords one which says 11 amp on the
front - yet the Lidl one charges a battery faster.

The Aldi/Lidl one is a constant current charger with voltage monitoring
to control the charging process. You can select 0.8A or 3.8A charge rate
(selected as motorcycle or car battery). It will then charge at this
rate until the battery reaches fully charged voltage, and then steps
back to a very much lower maintenance charge rate.

Yup.

A conventional charger charges at the terminal voltage via a current
limiting resistor (or sometimes using the power supply impedance
instead of a resistor), so although it might supply 11A into a
completely flat battery, as the terminal voltage rises, the current
drops dramatically, possibly well below the 3.8A of the Aldi/Lidl
charger, which is why it will take longer to fully charge.
Some conventional chargers improve on this by charging towards
something over the terminal voltage which will charge faster, but
will also overcharge if you forget to stop the charging.

The Halford one claims to be 'electronic' and certainly does have
electronics, including the provision for charging SLA batteries. As well
as switching itself off after charging - and having reverse connection
protection. But seems as you say to reduce the charge rate considerably as
the battery charges. Which means it takes about 24 hours to charge a
battery so low it won't start a car. the Lidl one does it overnight. I did
stick an ammeter on it, and the most it showed was about 6 amps with a
very low battery. So I'd guess the marketing boys were out in force. ;-)


I have a couple of gripes with the Aldi/Lidl charger:
1) There's no way to configure it to automatically start charging
when mains is restored. If it had this feature, it would make a
very good basis for supporting mains failure battery supply.

It would be useful - but then that's not what it's sold as. It would
probably need to be made to a higher spec for this sort of use.

It is however sold as suitable to maintain a battery. The problem for me
is that if there is a momentary power drop out, everything in my house
that needs to restarts, except the charger. With cars out of use for
lengthy periods (kit car and my wife's car when she was ill), the
standing drain of security systems and the like then flatten the battery
totally in about three weeks. I have lost two batteries that way.

It is probably better this way than auto re-starting though, as you
don't know what conditions and dangers there might be if the charger
restarted when you might have deliberately had the power off for some
time and forgotten that the charger is still plugged in.

2) It claims to have a restoration charging mode for completely
flat batteries, but I've never got that to work - it ends up
thinking the flat 12V battery is a 6V battery, and almost
instantly thinks the battery is fully charged.

Not had the need to try it yet. I did have one battery so flat it wouldn't
even switch on - but jumping another across it for a few minutes then
allowed it to carry on charging after that was removed.

I have an old, non-smart charger for recovering "dead" batteries. It
recovered both the ones that I finally lost a couple of times, before
they finally gave up the ghost after yet another charger shut-off.

SteveW