Charging 12V mini-pack from car battery

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I need to run a 12V low-power electronic device from a small
rechargeable battery pack.

Could such a pack be recharged or maintained at full charge by leaving
it plugged into a car's 'cigar lighter' socket more or less
continuously, whether or not the engine is running?

If not, what additional components would be required to avoid run-down,
overheating, exhaustion etc?

Alternatively, is there a cheap commercial device for trickle-charging
a little 12V pack from a big 12V DC source?

What type of batteries would be most suitable?

Lionel

 

[Rich Grise]

I need to run a 12V low-power electronic device from a small
rechargeable battery pack.

Could such a pack be recharged or maintained at full charge by leaving
it plugged into a car's 'cigar lighter' socket more or less
continuously, whether or not the engine is running?

If not, what additional components would be required to avoid run-down,
overheating, exhaustion etc?

Alternatively, is there a cheap commercial device for trickle-charging
a little 12V pack from a big 12V DC source?

What type of batteries would be most suitable?

To plug into a car system with no other circuitry, use a 12V gel cell
(sealed lead-acid). They'll happily coexist with your car system. I think
you can even get 2V gelcells in approx. D size - just a sec...
http://www.google.com/search?q=sealed+lead-acid+batteries
Yeah, but it isn't worth the bother, if you have room for one of the boxy
ones.

Good Luck!
Rich

 

[Lion_Elk]

Thanks - I'll chase this up.

Lionel

 

[colin]

I need to run a 12V low-power electronic device from a small
rechargeable battery pack.

Could such a pack be recharged or maintained at full charge by leaving
it plugged into a car's 'cigar lighter' socket more or less
continuously, whether or not the engine is running?

If not, what additional components would be required to avoid run-down,
overheating, exhaustion etc?

Alternatively, is there a cheap commercial device for trickle-charging
a little 12V pack from a big 12V DC source?

What type of batteries would be most suitable?

A typical 12 pack wont charge unless the engine is running, unless you boost
the voltage with a dc-dc converter.
alternativly if you can get away with spliting the pack into 2 x 6 volt ones
...
you realy need something to limit the current for a smal pack and it depends
what type it is how big etc, eg resistor, current controled regulator, at
the very least a fuse !

I tend to use AA size NimH @ 2AH as theyr quite versatile and easy to get.
depends how much capacity you need, and how much you want to pay.

Colin =^.^=

 

[Lion_Elk]

Colin - thanks.

There'd be no problem limiting the charge period to when engine is
running - if I add a diode to prevent discharge could that dispense
with the DC-DC convertor?

I reckon the AAs you suggest would suit my purpose - what rating fuse
and/or regulator would I need?

Lionel

 

[Luhan]

I need to run a 12V low-power electronic device from a small
rechargeable battery pack.

Could such a pack be recharged or maintained at full charge by leaving
it plugged into a car's 'cigar lighter' socket more or less
continuously, whether or not the engine is running?

Hi,

I would use a small 12 volt gel-cell. Connect it to your cars
accessory line via a shotkey diode. This will charge the gel-cell to
nearly full charge when the car is running.

Luhan Monat (luhanxmonat-at-yahoo^dot^com)
http://members.cox.net/berniekm/
"Reality: what a concept!"

 

[ehsjr]

Colin - thanks.

There'd be no problem limiting the charge period to when engine is
running - if I add a diode to prevent discharge could that dispense
with the DC-DC convertor?

I reckon the AAs you suggest would suit my purpose - what rating fuse
and/or regulator would I need?

Lionel

If you add a diode to prevent discharge, you'll drop
voltage across the diode and the Batt won't charge
fully.

car +12 -->|---+-------Device Gnd
|
Batt
|
Gnd

Just take the +12 from a wire that is +12 only when
the ignition switch is on.

This all presumes that the battery you are
using is the same technology as vehicle battery.

Ed