On Tue, 09 May 2017 09:53:30 +0100, Harry Bloomfield
wrote:

on 09/05/2017, Brian Gaff supposed :
The lighter is not going to sink the sort of current you need to charge it
really, and yes you could current limit this by a simple circuit (Look in
many of them old Bibani Books!)

It may not charge at full speed, but charge it would.

I'm sure little modules exist for this nowadays.

No need, the resistance of the wiring and the small voltage difference
between vehicle battery and car battery will provide an effective limit
to the charge current.

I would no want a battery on charge in the passenger compartment.


*Years ago*, Dad bought a portable battery system that consisted of 2
x 6V lead acid batteries in a fibreglass carry case that strapped into
the boot of the car and took power from the car 12V system when the
engine was running.

There was some form of electronic controller you fitted inside the
boot that would charge each battery independently and then when you
wanted 12V in say a tent, you unplugged it, lifted it out and flicked
a big rocker switch from 'Charge' to '12V'.

If you needed a charge you just put it back in the car when you were
out and about, or using a 12V mains charger of course.

Before campsites offered mains hookups, most places would allow you to
charge such things in their garage / store for a few pence. Not sure
'the rules' would allow them to do such these days?

Cheers, T i m