Dead 12v battery, jump starting

Sparky63

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When your 12 volt battery dies, I hope it is at the dealership and they replace it. Unfortunately, it may happen at 2:00 a.m. Sunday, in the airport parking lot with 24 degree temperature and blowing snow. You, your spouse and children will be locked out. There is no key. You will need a 12v battery to connect to the 2 wires located behind the front bumper access port. (This is where the non-existent recovery hook would connect). Connecting 12v to these wires opens the “frunk”, allowing you access to connect jumpers to the car’s 12v battery. Once jumped, you will be able to open the doors and start the car.

How long will it take to get that 12v jump?

The diagram proposes to install an additional 12v AGM battery to provide self jump start capability. It also provides a power source for dash cams. If used for dash cams, a low voltage cut-off should be used to preserve capacity for jump starting.

In normal use, an accessory power source ( fuse 15, 15A if not used) provides 12v to power the dash cam and charges the auxiliary battery. The diode prevents power flowing from the aux. battery to the car 12v battery.

Switch 1 (S1) is extended to the front bumper access port. When S1 is closed, the relay is closed and both 12v batteries are connected. This accomplishes a jump start. Hop in and start your car!
I have not installed these components. I do not know if it will work as intended. Your comments and suggestions are encouraged.

Ford Mustang Mach-E Dead 12v battery, jump starting 12vJum
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louibluey

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Hyundai put a spare jump battery into some versions of Ioniq (not the BEV). On entering the cabin with the physical key (see youtube video below), push a button lower left dash (probably a lot like your proposed solution). It certainly would be a nice upgrade to have a spare battery charged along with the LVB which could be called up in reserve.

But, here I doubt it is worth the effort. Most MME 12V problems get fixed quickly by Ford (such as that initial problem early last year). There does seem to be another crop of them recently, not clear if the warnings (e.g. FordPass 12V service) are bogus, related to a major OTA update hanging (one theory), or some other reason. I suspect this one too will be fixed by Ford in short order.

For those really super worried about a flat LVB, such as in the scenario you described, there are two easy options, keep 8 AA batteries (@CHeil402) in the bumper (maybe Lithium AA for winter) (Frunk Bumper Release 9V battery does not work, 12V works), or add a hidden pull string (Indiana Jones and the Emergency Frunk Release) to open frunk and keep a jump pack (like a NOCO GB-40 or equiv.) in the frunk. In any event, add those (@dtbaker61) caps (How to - add 'access ports' for LVB connection points) for easy access to the + and ground jump points.

Or, just hail a passing motorist with jump cables.

 
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Motomax

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Dual battery setups are very common, you could get a setup that will keep both charged but it’s a bit overkill.
If I was really concerned I would just keep some AA or maybe a small 12v (I wonder is an A23 has enough juice) in the bumper and store a capacitor jump starter in the frunk. The NOCO jump packs are nice but they lose capacity within a couple years of being fully charged. Although, you don’t need much to jump an EV so it will probably still work once it’s deteriorated.
 

louibluey

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Dual battery setups are very common, you could get a setup that will keep both charged but it’s a bit overkill.
If I was really concerned I would just keep some AA or maybe a small 12v (I wonder is an A23 has enough juice) in the bumper and store a capacitor jump starter in the frunk. The NOCO jump packs are nice but they lose capacity within a couple years of being fully charged. Although, you don’t need much to jump an EV so it will probably still work once it’s deteriorated.
Interesting, your post had me looking at dual battery products. It is similar, and could be the same with the extra relay in OPs post, but I think most of those are trying to run accessories on the second battery. So, it's similar, charge the second battery when you can, but different (in the common application), where most are running other loads on the second battery so as not to drain the starter primary LVB.

This video is really good at explaining the dual battery concept and why the conventional voltage sensing isolator relays are not working well with modern systems that lower the alternator voltage for fuel efficiency (@BMT1071 was talking about this in another recent thread). Plus look at the mega 12V setups later in the video, wild stuff, especially at about 10:48.
 
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macchiaz-o

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Hyundai put a spare jump battery into some versions of Ioniq (not the BEV). On entering the cabin with the physical key (see youtube video below), push a button lower left dash (probably a lot like your proposed solution). It certainly would be a nice upgrade to have a spare battery charged along with the LVB which could be called up in reserve.
I looked into this a bit in 2017 when I was considering the Ioniq. The Ioniq Hybrid for North America has no lead acid battery. Instead, they partition off a small (probably ~14V?) portion of the lithium ion pack, with the remainder of the pack being high voltage.

Pressing the button by the driver's knee causes a DC-DC contactor to close for 10 seconds or so to allow the low voltage battery to be replenished enough to start the vehicle.

AFAIK, they don't do this on the plugin hybrid or the full electric. I'm not sure why, but there must be some good technical reason?

So back to the Mach-E... Other than the possible technical issue(s) that I'm ignorant about, and the lack of easy way to get into the driver's seat, it would be nice to have the same button to enable the DC-DC converter for low/dead 12V emergencies. :)
 

louibluey

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I looked into this a bit in 2017 when I was considering the Ioniq. The Ioniq Hybrid for North America has no lead acid battery. Instead, they partition off a small (probably ~14V?) portion of the lithium ion pack, with the remainder of the pack being high voltage.

Pressing the button by the driver's knee causes a DC-DC contactor to close for 10 seconds or so to allow the low voltage battery to be replenished enough to start the vehicle.

AFAIK, they don't do this on the plugin hybrid or the full electric. I'm not sure why, but there must be some good technical reason?

So back to the Mach-E... Other than the possible technical issue(s) that I'm ignorant about, and the lack of easy way to get into the driver's seat, it would be nice to have the same button to enable the DC-DC converter for low/dead 12V emergencies. :)
Yes, that is an interesting approach, fire up the DC/DC converter. Still a bit of chicken and egg though, with a flat LVB, that would take a small aux LVB or a partition of the HV battery like you say to get the DC/DC converter started, which itself, requires 12V to fire up. Also, the HV power relay, the HV contactor, cannot close without 12V.

Alternatively, manufacturers could consider some technique to power on a DC/DC converter without needing a live 12V bus. However, there are safety aspects too (not saying there is not a solution, but I think HV safety is the main problem) in that killing the 12V bus (often cutting a wire) is an important part of the rescue response to guarantee no HV present in the orange HV wires. So, no DC/DC converter ops without 12V for safety reasons.

Just a thought, there could be an extra partition or LVB section inside of the HV battery enclosure, so no external HV wiring required. Then there could be an aux 12V output connector on the HV battery enclosure itself. Then use that aux 12V to jump the MME LVB (no HV involved). (If Ford uses this, I want a discount on a MME GTPE Ford ;) ). hmm, maybe I just went full circle, that also sounds like the Ioniq 12V partition you described.

As an aside, another difference between the dual battery systems above and the OPs proposal is that presumably for BEV recovery/startup the second back up battery is relatively small, say 10 - 20 ah compare to the regular 35 ah LVB, which is already on the small side. Most of the dual battery folks are looking for the same ah or larger to power aux equipment.

I tried out an Ioniq electric for a year when they were giving them away, $99/mo lease, no early termination penalty with pay off. It was a nice little car, very efficient, 5 mi / kWhr was possible. I think the 2019 had a 28 kWhr battery and in summer could do about 120 miles. It was kind of like a little "glider" of BEVs. The 2019 BEV did not have the LVB boost button, not sure why. With 120 reduced to 90-100 miles winter, it was only useful as a second car, at that time, a Honda Clarity PHEV for trips.
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