Battery Isolation

[anwat]

So, living in SoCal, have taken the necessary step of installing a GPS tracker in my vehicle. It's also nice to keep track of your route when out in the desert and you need to keep track of where you are on a satellite image. So the unit has a built in backup battery which will last a day or two, depending on how often it pings, since it's fairly common in the car thief arena to cut the battery cables when you take the vehicle. I purchased a little 2ah lead acid battery to allow the unit a few more days of operation. Problem is, when the main battery cable is cut, the little battery is going to try to power the entire electrical system unless I can put something on there to prevent the flow back into the system. I would think a diode would be the answer to this problem, but I'm just checking. Can I just add a diode in on the positive lead from the car to the new battery, or is something more sophisticated needed?

 

[Wes Harden]

For a low amperage charging situation yes a diode will work. I had to do this on some step vans at work. These vans have gas detector for check under ground utility vaults before crews entered. The detectors had a rechargeable back up battery, that was charged by the trucks alternator.

These trucks had so many electrical loads when parked,they would kill a yellow top Opitma in 30-45 mins, since the upfitter didn't seem to know what an electron was or how they flow, the Gas detector was drained at the same time. Making this vital safety device useless. I added a simple diode at the detectors battery, keeping the lights and fans from draining it at the job site. Only had to do it to 120 units Shh don't tell fleet engineering, modification is bad 4 letter word.

 

[anwat]

Yes, this tracker is a milliamp type of draw. Hid the little battery, connected everything up and it works perfectly. Thank you!
Out of curiosity, did you have to plug those trucks in when they were parked overnight? How did you keep from having to replace batteries every week? I've purchased a couple of police cars that were run-outs, and even after all the good stuff has been stripped out, I was able to salvage enough good quality wire for a few projects. It's amazing how much wiring is added to those vehicles by the upfitters.

 

[Wes Harden]

No the charging system was able to bring the aux battery back. The main battery was isolated from the aux load draw.
I did have some no engine power, miss fire, and stall complaints. Turns out the crews would start van and try to drive off, isolation solenoid would close and aux battery would bring system voltage down to 9-10 volts, truck would run poor or stall.
All that was needed was opperator training. I got them to start the trucks when they started packing up, by the time they were ready to leave system voltage stayed over 11v and engine ran fine. These were the spider poppet efi engines.