12V Battery Backup powe rsupply for GPS Tracker

Thread Starter

omega1974

Joined Dec 3, 2012
3
Hi All,
I'm new to the Forum as its quite a few years since I built electronic projects.
I have a small project I'm working on at home and I would be grateful for some assistance.
I'm fitting a 12v Tracking device to a horse box trailer, and I need to include a long life back up battery for the Tracking unit. The tracking device itself runs off 12v and it does not have an internal battery. My plan is to enclose the tracker and a 12v 1.2AH Lead Acid Rechargeable battery in a Waterproof poly-box. I will then connect the circuit to the trailers rear lights (12v). Therefore when the vehicles lights are on, it will recharge the battery and power the Tracker unit also. When the lights are switched off, the Lead Acid battery does the work. The Tracking device will switch to "sleep" mode when it scenes movement has stopped. In "Sleep" mode it consumes only 2mA. When in Track mode it consumes 150mA.
I must also ensure that the backup battery does not try to power the trailers electrical system also.
I'm sure this type of circuit is very common, but its years since I buit circuits and I'm a little out of date.

All help appreciated.

Barry
 

#12

Joined Nov 30, 2010
18,223
I say use a better diode and add a fuse. Automotive electricity is awfully spikey.
Maybe a 3 amp diode rated at 200 volts instead of a 1 amp diode rated at 50 volts.
 

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Thread Starter

omega1974

Joined Dec 3, 2012
3
Thanks guys...
Is it that simple?
I thought a Lead Acid battery would need a regulated charge current?
Also, if the vehicle was a 24V system, are there any 24/12v regulator components available?

Thanks again.
Barry
 

#12

Joined Nov 30, 2010
18,223
There is already a regulator in the charging system for your cars' battery. With this rig, the Aux battery gets a few tenths less voltage applied to it, so voltage regulation is not a concern. The internal resistance of a battery that small might be enough to limit the current to less than 3 amps. If it isn't, that's what the fuse is for. Blow a fuse? Ask about a current limiting resistor.

As for a 24 volt system charging a 12 volt battery, that is when you'd need a voltage regulator. Us nerd types don't even think about buying a retail priced 24V to 12V regulator, we just make one.
 
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