Car lead acid charger

[Steve2381]

Hi all
I am fitting a mini DVR in my car for security. I want to run it off its own 12v lead acid battery, so that when parked, it doesnt drain the main car battery.
Does anyone have a good lead acid battery charger circuit that will run off the 12v cig lighter outlet in the boot of my car?
I always have trouble designing battery chargers.
Thanks
Steve

 

[davelectronic]

Battery charger

Hi Steve2381.
There are some charger circuits in the transistors book on this site, you can replace the wall adapter for cigarette lighter socket in the car.
Click the interactive link and scroll down looking on the left of the screen, the transistors circuit book is available as a download, i have a copy.
Dave.
PS, You will need to open the book link, then either save it, or print out a copy of the circuits, there some way down 3/4 or so.

http://talkingelectronics.com/

 

[Resqueline]

You'll need a switchmode booster charging circuit, aka flyback or step-up converter, to efficiently & quickly recharge that battery.
A full recharge of a SLA battery can nevertheless take 3 hours.

 

[Steve2381]

Thanks for all your help guys, I am working on the system now

 

[davenn]

Hi all
I am fitting a mini DVR in my car for security. I want to run it off its own 12v lead acid battery, so that when parked, it doesnt drain the main car battery.
Does anyone have a good lead acid battery charger circuit that will run off the 12v cig lighter outlet in the boot of my car?
I always have trouble designing battery chargers.
Thanks
Steve

charger circuit that will run off the 12v cig lighter outlet in the boot of my car?

and what is supplying power to that cigarette lighter outlet ??

Dave

 

[Steve2381]

Hi Dave

Not sure, its not going to be much! I believe its fused at 15A, but the socket certainly could not provide that.
If I have to, I can always run a new supply to the boot from the battery

 

[davenn]

you didnt really answer the question

WHERE is the power coming from that is going to the cigarette lighter output

Dave

 

[Resqueline]

I must admit I'm not quite sure what you're getting at Dave. Are you concerned about the logistics around draining and recharging of the two batteries (ignition circuit etc.)?

 

[(*steve*)]

I presume Dave wants to know that the socket in the boot (do people really smoke in the boot?) is powered from the battery only when the ignition is on (for example) otherwise how would a charger running from it know when to charge the auxiliary battery?

 

[davenn]

I presume Dave wants to know that the socket in the boot (do people really smoke in the boot?) is powered from the battery only when the ignition is on (for example) otherwise how would a charger running from it know when to charge the auxiliary battery?

yes I'm sorta assuming he is running that socket off the main car battery ?? and using the main battery to charge the secondary battery whilst the car is running....
but he hasnt clarified that... hence my question "where is that socket being powered from ?"

If so, then he doesnt need a charger cct, the batteries are going to be basically paralled with some switching to stop main battery drain when car isnt running.
ie. the car's existing system is going to charge the AUX battery !!

A lot of us ham radio operators do the twin battery thing with switching.

Dave

 

[Resqueline]

Yes, given that he's capable of rewiring the circuit with a heavy gauge straight from the car battery (via fuse & relay) he could get away without a booster charger.
But then there's also the question exactly what charging voltage his alternator is set up with. There's a considerable difference between 13.5 & 14.4 Volts.
My suggestion was based on using the existing wiring, which is long & thin, giving too much voltage drop for efficient charging (without using a booster charger).
A booster charger would not care what voltage is in the far end of the car wiring, always giving 14.4V out to the aux battery.