The Almost Ultimate 12 Volt Battery Backup System

[FrankM1]

Here is a 12 Volt Battery Backup System that I added to my Mach E to prevent being stranded. It uses a standard jump starter system that is modified for direct connection to it’s Sealed Lead Acid Battery through a breaker. It is a straight forward design using a Standard Key Ignition Switch that selects the Frunk Jump connection (Start Position) or the Main Vehicle Battery (Accessory Position) for a jump start. Breakers are used in the battery line. There is no modification to the vehicle’s electrical system (no wires cut). It is all additive. There are holes drilled in the Frunk storage basket for 6-to-8-gauge Battery cables to pass through. There are connectors on both sides in case the basket has to be removed. A hole is drilled in the Charge Port to allow for the key switch to be installed. This was the best place for water protection. If you are only interested in a way to jump open the Frunk, a single pole key switch will be much smaller and easier to install. Then, you can jump the battery in the usual way. The jump starter has a test mode to show the current charge of its battery. It charges by plugging into an AC Outlet. In the event its battery fails, you still have the option of using an external Frunk Jump connection by opening the waterproof box and connecting to the vehicle’s Jump Terminals.

The system works. It opens the Frunk and will start the vehicle with a dead battery (simulated by disconnecting the Ground terminal of the Vehicle’s Battery). The Battery Jump was turned off after starting and the vehicle continued to run with the charge power from the HV battery system. This was discussed in a prior thread. These tests were done at “idle”. No tests were done to see how far it would go under those conditions. The Battery jump could be left connected but charging conditions are unknown at this point. Also, you would have to use a bent key in order to close the charge door or get a switch that will allow the key to be removed in any position. I’m still searching for one like that. The Mach E does not need a lot of power to start. My preliminary measurements were less than 30 Amps that quickly settled down to less than 4 Amps with the Radio on and AC running.

Note: If you want to do this, you should have some knowledge of basic electrical systems. You do this at your own risk.

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[NY_Cade69]

Very interesting...

 

[Homestead]

So if the car door won't open or you can't remote start the car then you turn the key and try again or do you have a way to monitor the 12V ?

 

[FrankM1]

The first step would be to open the Frunk as a precaution. The reason is that you don't know the cause of the battery condition. There could be short in the line. If you went to the jump battery mode first and a short existed, this would trip the breaker and negate the possibility of being able to jump open the Frunk. I used a self-resetting breaker in the Jump Starter Unit. You would have to wait for it to reset.
Using a meter for measuring the battery: Many could still indicate 12 volts in an unloaded condition but applying a load would cause the voltage and current capability to sag and fail to start the vehicle. The Ford App is better at warning you of a possible failure due to its monitoring capabilities.

 

[rhfritz]

Your backup system is fascinating. Did you take any pictures of the space behind the charge port, presuming you had to remove it for your keyswitch install?

The idea that comes to mind comes from what others have done to drill holes in the Frunk storage basket to add extension battery lugs or otherwise access the battery with jumper cables without removing the basket. But if there's space for a key swtich and wire lug connections behind the charge port, how hard would it be to put a 2 connection key-selectable box there? My idea is to have one set of wires running from the front bumper emergency connector and another from the battery itself going to a key-selectable box. Then, you'd key select which 12v connection you wanted and use jumper-cable compatible lugs at the charge plate to either measure existing voltage and/or with an external 12v backup pack to jump the Funk open or the battery itself from the charge plate. This is consequential because you can presumably access the driver's door / charge port no matter how you've parked, but access to the front of the car may be inconvenient depending on how you parked your now-dead car.

 

[SnoMike]

FrankM1, could you make a simple wiring diagram of what you did? I could better understand it then.

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