12v LiFePo4 main battery

[Uaciuganadu]

Hello,

I see many of you buy expensive, low power battery packs for parking mode.

Did anyone consider replacing the normal acid or AGM battery with a LiFePo4 of 100ah?

What are the cons of this? Lets have a discussion.

Thanks

 

[Julian1415]

Well it's not that simple. You'll need to replace it with a LiFePo4 battery specifically designed for this kind of replacement.
Reasons are:

• Needs to be able to charge in a broad range of temperatures (some of us can have -20 C in winter and +34 C in summer)
• Most of not so old cars have a BMS configured to work with AGM batteries. If you switch to LiFePo4 you might need to do additional changes to the car's BMS
• Internal resistance needs to be close to the internal resistance of AGM (if much lower you might cook the alternator; if much higher it will not charge fast enough)

I know two companies offering these type of batteries:
Liteblox (DE) and Antigravitybatteries

You basically need a specific LiFePo4 chemistry, maybe some supercapacitors and a good BMS inside the battery.

 

[EdSM]

Yah you basically need a battery-to-battery charger that has an amperage input limit on it so you don't burn your alternator. I used a 60A one on a Sprinter van from sterling and it costs about 400USD. At minimum you will need an isolator. The cheapest one with less power would be around 50USD. On top of that you need to make sure your lifepo battery has a BMS included to take care of the temperature and power charge limitations. Most batteries come with a BMS but the biggest issue is the placement of this battery . You cannot replace your chassis battery with it because it won't work in low temperatures so you have to accommodate both. In a big Sprinter van that is easier to tackle but im not sure about a Sedan or even an SUV. The battery needs huge power cables (that carry 20-60A) fuses, the dc-dc charger and so on.

 

[Uaciuganadu]

Lets just say my alternator is a DC to DC converter, and that the battery module has a BMS with cold cut out protection and heating.

Any other cons that we can find in this scenario?

The car is a EV. It used the 12v for basic electronics and connectors.

 

[EdSM]

If the car is an EV why would you need an extra battery? The car sits on a mound of battery cells which have more power storage capacity than what you can reasonably carry inside your car

 

[Uaciuganadu]

If the car is an EV why would you need an extra battery? The car sits on a mound of battery cells which have more power storage capacity than what you can reasonably carry inside your car

Because that's not how EVs work, the DC to DC charger will only function during the ”power on” state of the car.

It dose however have a recharge during ”sleep” feature, but it will only check for low battery once or twice a day and if it finds its too low will start a few hours long re-charging session.

A dual new gen dashcam in parking mode, will drain the normal acid battery to its 50% useful charge, in under an hour.

So the question remains: Do we find any other cons that will prevent this setup?

 

[EdSM]

Im afraid you missed the question. Let me reformulate for you: why you would need an extra battery in your car whose capacity is insignificant compared to your EV's power bank? The DC to DC charger for your extra battery would be useful if your extra battery was justified. Nevertheless, i don't think I can help you.

 

[Uaciuganadu]

Im afraid you missed the question. Let me reformulate for you: why you would need an extra battery in your car whose capacity is insignificant compared to your EV's power bank? The DC to DC charger for your extra battery would be useful if your extra battery was justified. Nevertheless, i don't think I can help you.

I still do not think you understand fully how a EV works. The EV lithium battery has hundreds of volts, its not a 12v battery. The DC to DC converts it to 12v and charges the 12v bat in certain situations.

On a 24/7 parking mode setup, the converter would need to run non stop on a acid battery, to keep it in the 50% useful charge between 13v and 12.6v. This is 1, impossible to set up during sleep mode and 2, highly inefficient because of the conversion from high voltage to low voltage .

 

[EdSM]

I still do not think you understand fully how a EV works. The EV lithium battery has hundreds of volts, its not a 12v battery. The DC to DC converts it to 12v and charges the 12v bat in certain situations.

On a 24/7 parking mode setup, the converter would need to run non stop on a acid battery, to keep it in the 50% useful charge between 13v and 12.6v. This is 1, impossible to set up during sleep mode and 2, highly inefficient because of the conversion from high voltage to low voltage .

Man... you came here for help and you keep repeating what you think about what I know and ... you know nothing about me .

A DC-to-DC converter that would take a high input voltage and transform it down to 12V makes little sense for an EV since EVs have 12V plugs for compatibility reasons as most car accessories run on 12v. And they don't even need a converter to give you 12V if you understand what their battery is made of.

You complain that the DC to DC converter would have to reduce voltage from what your EV has in its power bank to 12 V and lose power in the process when most dash cams work of 5V and therefore you have to convert down to 5V no matter if you have a 12V battery or higher voltage. Look at the hardware kits form Viofo and other major brands to see their its electrical specs. I trust you can do that.

Given your complaints I wonder if you know your EV or have an EV at all. But that does not matter anymore. You're welcome to help yourself whatever your problem might be.

 

[Uaciuganadu]

Ok, now I know for sure you have no idea how an EV uses and recharges its 12v battery.

Anyway, thank you for trying to help.

If there is someone else here, that actually has an EV, or actually knows the basics of how they recharge the 12v using the onboard DC to DC converter, I would love to continue the conversation about any cons that an acid to LiFePo4 swap may have.

Thank you

 

[SPL15]

For ICE vehicles, the issue of cold weather is the primary concern w/ LiFePO4 batteries as a replacement for the lead acid.

Lithium starting batteries would actually be an ideal use case for ICE vehicles if it weren’t for the temp sensitivity issue. Lithium batteries prefer to not be sitting at 100% full charge state, automotive electrical systems NEVER keep the starting battery at 100% full charge state unless you charge every night, or drive for hours everyday.

The practical reality with swapping to lithium iron primary batteries from a lead acid type in most modern vehicles, the issue of charge control comes about. My car’s 240 amp alternator is connected to the engine management computer, where output voltage can reach 15.5 Vdc depending on ambient temp & charge state of the battery, as well as some other factors. There’s also two 105 AH AGM batteries in my car from the factory, with a DC-DC converter / power management controller for the auxiliary battery, as well as to put the batteries in series for the electric power steering.

Installing another DC-DC converter isn’t a viable solution for a starting battery in my case, nor is it feasible for the auxiliary battery. Programming the ECU to modify alternator charge characteristics is WAY outside of most people’s ability, hacking the firmware for the auxiliary battery’s controller & re-coding it to modify charge behavior is also not realistic, and to top it off, it costs less to buy a $350 BC8 than it costs to buy a reputable, appropriately sized & quality LiFEPO4 battery that could take the place of one of the AGM batteries in my car. Then there’s still the issue of temperature sensitivity in the winter that puts the idea of swapping to lithium to bed.

If I had a simpler charging / electrical system, I’d gladly install a large auxiliary Li Iron battery w/ charge controller to power all of my gear when camping / overlanding out in the deep woods.