Dave Plowman (News) wrote:
In article ,
Martin Brown wrote:
On 15/12/2020 10:22, Dave Plowman (News) wrote:
In article ,
Martin Brown wrote:
I charge my car battery old school with croc clips on the terminals.
Nice big fat spark jumps when I make contact. Initial current to a
flat battery about 8A falling to a steady 6A as the terminal voltage
rises.
Are you doing this with an old style charger switched on?

Yes. Its the simplest way to check it is still working. It can source 3A
or 6A at either 12v or 6v depending on its switch settings.
I've got several assorted chargers here. None spark when connected to
the battery. That's more what you get when jump starting from a
vehicle which has the engine running.

The initial state will be a 27v no load DC connected to 12v for a moment
and a lot of current flows. Enough to make a nice fat spark.

Personally, not too keen on sparks close to a battery or indeed under the
bonnet if they can be avoided.

That's why the last connection you make when dealing with devices
connected to battery, is making a ground connection to frame.
Then, the spark is (hopefully) far enough away from any hydrogen
to avert disaster.

You don't put the two crock clips right on the battery
as it sits in your car. The red (+) can go to the battery
terminal, the black (-) goes to the frame, and that's to
establish some distance from the battery. When you fit the
black one, that is the fitting that "sparks" - even an
unpowered charger, you can be charging up some capacitor
inside it, at the moment of connection. The "spark" can come
from positive current flow (out of the powered charger), or from
negative flow back into the (unpowered) charger, as you charge up
its flat capacitor.

When you charge a battery sitting on the ground, you can
always fit extension cables so you are a good distance
from it when connecting. The biggest risk is from the
old style batteries with screw caps and "breather holes"
in the caps.

*******

If getting a car charger, try to get one with temperature
compensation. Sometimes the adverts for the cheap ones
happen to mention it. Mine is missing that feature.

Paul