Why do we have a 12V battery?

[guinn]

I appreciate the responses. Some of them seem valid to me, so not so much. (My degree is in Electrical Engineering, Rice University, '71. Yes, that's a long time ago!) Someone mentioned that this may just be cheapest and easiest solution for Ford, but that puts the onus on us to replace the 12V battery every few years which is both expensive and a PITA in some cases! Again, thanks to all of you.

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[Mach-Lee]

I appreciate the responses. Some of them seem valid to me, so not so much. (My degree is in Electrical Engineering, Rice University, '71. Yes, that's a long time ago!) Someone mentioned that this may just be cheapest and easiest solution for Ford, but that puts the onus on us to replace the 12V battery every few years which is both expensive and a PITA in some cases! Again, thanks to all of you.

There is not a single EV that I know of that does not have a low voltage battery (LVB). You can't get around it for safety and startup reasons. You can start a DC/DC converter as soon as the car wakes up to cover electrical loads, but there will always be that initial startup period that requires low volt battery power to switch on high voltage and boot the DC/DC module. The DC/DC also cannot be continuously powered because the battery needs rest periods where there is zero load in order to sense cell capacities and perform cell balancing accurately. In summary, the inclusion of a LVB in EVs is an industry-wide practice that is necessary to meet high voltage safety requirements, not a cheapest/easiest solution for Ford.

The industry is moving towards smaller lithium LVBs. They have some advantages, but also some disadvantages compared to lead acid batteries (such as being more susceptible to extreme cold). Lithium batteries still need periodic replacement every 5-10 years, and cost more to replace.

Below is Tesla's 16V lithium LVB, you can see it's significantly smaller than our battery (6.9 Ah/99 Wh). There is not much room for error with power management, if the high voltage shuts down you only have minutes until everything goes dead.

 

[Kamuelaflyer]

Why do North America households operate mostly on 120 volts when much of the world is 230 volts?

Thomas A Edidon.

Mr Edisons signature invention, the incandescent light bulb ran best at 100 v. So he designed the first utility to run between 110 and 120 which then would in turn sell more lightbulbs.Then everything else was designed around that voltage.

Europe started electrification later and had different priorities. They listened to Tesla (No, the real guy) and Westinghouse who realized that higher voltages are more efficient to distribute. Plus higher voltage means lower current. Lower current means less heat loss in wires.

By the time the USA realized it had climbed aboard the wriong ship, it was too late. So we invented a good compromise: split phase. So Mr Edison’s lightbulbs illuminated the states on 110v, while washing machines and other such stuff got 240v.

Because, why use a superior system when you can invent another one to wallpaper over the issues caused by your earlier system. For an encore, the USA also did this with the metric system.

This is an issue for early adopters. Ask any company that pioneered corporate computing and signed on with Univac.

Besides, Edison was a notorious grifter and world class ah.

 

[guinn]

There is not a single EV that I know of that does not have a low voltage battery (LVB). You can't get around it for safety and startup reasons. You can start a DC/DC converter as soon as the car wakes up to cover electrical loads, but there will always be that initial startup period that requires low volt battery power to switch on high voltage and boot the DC/DC module. The DC/DC also cannot be continuously powered because the battery needs rest periods where there is zero load in order to sense cell capacities and perform cell balancing accurately. In summary, the inclusion of a LVB in EVs is an industry-wide practice that is necessary to meet high voltage safety requirements, not a cheapest/easiest solution for Ford.

The industry is moving towards smaller lithium LVBs. They have some advantages, but also some disadvantages compared to lead acid batteries (such as being more susceptible to extreme cold). Lithium batteries still need periodic replacement every 5-10 years, and cost more to replace.

Below is Tesla's 16V lithium LVB, you can see it's significantly smaller than our battery (6.9 Ah/99 Wh). There is not much room for error with power management, if the high voltage shuts down you only have minutes until everything goes dead.

So, I will make a prediction. With 10 years, many EVs will not have a low voltage battery. If I had to guess, I would guess that the Chinese will figure out a good way to do this and the American manufacturers will play catch up. Watch this space!!

 

[Shayne]

I've been wondering why the MachE has a 12-volt battery.

You’re looking at how a 400v system might work, which is fine of course. That, however, is not what the op asked; they wanted to know why its the way it is. I tried to answer that question in a relatively simple manner. Could BEV manufacturers eliminate a 12/24 v battery? Probably, but its not particularly simple or cheap, and would likely cost more. And despite Ford’s losses on BEVs, they’re not a not for profit organization.

Not looking at any voltage and Ford's 365V and the 400V's will not be around forever now most are transitioning to 800V. It is becoming a computer on wheels with that whole AI thing that is just happening but has really been going on for years. You know Y2K was the fall of the machines now we have the rise of the machine that will happen tomorrow .

If you can feed 120V AC into a PC power supply that provides 12V DC to the MB and components on a desktop computer it is obviously possible to make that power supply convert 800V DC to 12V DC for one on wheels. In fact this ford has one just bad logic. PC's have always had a small non-rechargeable battery that last for years so why are the 12V rechargeables being sucked dry and killed for the computers on wheels? Use the power supply. OP had a good question and I wonder when and by who we will see it happen? Will need a battery but a lead acid is not optimum for longevity to just booting a PC and that is not what it is currently doing for many. A rechargeable could last for decades just like the big packs. I still install a pc speaker on all my boards. Image pushing the button on the car and hearing beep before all boots up clean! No 12V battery required.

Solid state minimal fire risk should change the equation/regulations.

 

[E90alex]

So, I will make a prediction. With 10 years, many EVs will not have a low voltage battery. If I had to guess, I would guess that the Chinese will figure out a good way to do this and the American manufacturers will play catch up. Watch this space!!

It’s impossible to be able to isolate the HVB without some sort of separate LV power source, so no. Automakers may move on from lead acid for the LVB like Tesla has, but you will always need some sort of LVB.

 

[SonicBlue]

It’s impossible to be able to isolate the HVB without some sort of separate LV power source, so no. Automakers may move on from lead acid for the LVB like Tesla has, but you will always need some sort of LVB.

I doubt it’s technically impossible. I would guess a physical means of connecting and disconnecting the HVB could be designed. Whether that’s a good idea or not…

 

[guinn]

It’s impossible to be able to isolate the HVB without some sort of separate LV power source, so no. Automakers may move on from lead acid for the LVB like Tesla has, but you will always need some sort of LVB.

They aren't totally isolated now. The HVB charges the LVB even if the car isn't "on".

 

[Mach1E]

So, I will make a prediction. With 10 years, many EVs will not have a low voltage battery. If I had to guess, I would guess that the Chinese will figure out a good way to do this and the American manufacturers will play catch up. Watch this space!!

I’ll take that bet and bet that in 10 years most (if not all) will still use 12v.

Why?

Money.

It’s cheaper and easier to use existing components.

No 12v would also not really “solve” anything. It’s a simple solution to a simple problem. No need to complicate things.

2nd reason (and maybe a larger one than money) is safety.

12v creates redundancy. If you HVB fails, you don’t get trapped in the car. Same thing after an accident etc.

 

[Kamuelaflyer]

They aren't totally isolated now. The HVB charges the LVB even if the car isn't "on".

Via the DC-DC converter and only under certain conditions when the car is off. The rest of the time while off, the 12v pretty much has nothing to do.

 

[guinn]

I’ll take that bet and bet that in 10 years most (if not all) will still use 12v.

Why?

Money.

It’s cheaper and easier to use existing components.

No 12v would also not really “solve” anything. It’s a simple solution to a simple problem. No need to complicate things.

2nd reason (and maybe a larger one than money) is safety.

12v creates redundancy. If you HVB fails, you don’t get trapped in the car. Same thing after an accident etc.

If you are right, come see me in 10 years and I'll buy you a steak dinner!!

 

[Peugfan]

I endorse Mach1E’s opinion here and I also point out it’s always good to have a surge buffer in the systems. Electrons can travel pretty fast.

 

[Jerrytball]

The “chicken vs egg” scenario is the key.

Even battery storage backup power systems normally have a small “cold start” battery.

This is so interesting. I was just asking my wife because we were watching a commercial on TV her and my daughter do not like chicken but they like eggs and I’m like if you ate chicken honey you know how easy it would be for me to cook? It would open up so many more options.

 

[E90alex]

They aren't totally isolated now. The HVB charges the LVB even if the car isn't "on".

HVB charges the LVB only when the HVB is connected. When the HVB is not in use, it is disconnected and isolated from the rest of the cars electronics. The 12V system is what controls this isolation. The HV battery can be connected and disconnected as needed via the 12V powered contactors.

Without a separate LV system and battery there would be no way to connect and disconnect the HVB from the rest of the electrical system.

 

[Shayne]

Via the DC-DC converter and only under certain conditions when the car is off. The rest of the time while off, the 12v pretty much has nothing to do.

It sits here for a long time on a 12V installed 12/17/21 (4.25 years ago). Ones that refresh the app too often may have 12V problems. My apps are off when not using the car as the ford app sucks too much phone battery here. The car will come on 2 to 3 times a day plugged to L2 to condition itself when below -20C so it does come on.

If you are right, come see me in 10 years and I'll buy you a steak dinner!!

Some manufactures taking the workload off the 12V and onto the pack is something we may see in the next 10 years. One would hope software and hardware will evolve.

HVB charges the LVB only when the HVB is connected. When the HVB is not in use, it is disconnected and isolated from the rest of the cars electronics. The 12V system is what controls this isolation. The HV battery can be connected and disconnected as needed via the 12V powered contactors.

Without a separate LV system and battery there would be no way to connect and disconnect the HVB from the rest of the electrical system.

All it needs to do is close the contacts and its job could be over. That fires up the power supply that takes over. You do not need a 12V lead acid rechargeable with CCA's to close the contacts. With some 12V lasting only 3 years it indicates that the 12V has a much higher workload than putting 12V across contacts.

Solid states packs should lower the regulations on isolation if the fire hazard is minimal to nil. Maybe start wi-fi connecting all to components and get rid of all that wiring that would isolate and should be cheaper. Ford is working on that

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