Lithium 12v battery.

[Gauss Guzzler]

Of course you can't just drop a lithium battery into a system designed for lead acid but the Ohmmu is not a bare lithium battery - it's a complete system with a built in charger, balancer, and over-current protection circuity.

But the fundamental issue is that there is something about the way Tesla manages the battery that is causing these premature failures and it's not clear that switching to lithium would help in any way. If Teslas tend to overcharge/overheat the battery (very unlikely) the Ohmmu might be a cure since it will simply stop accepting power once it's full, no matter what the car tries to force into it. But in the likely event that the Tesla is excessively discharging or excessively cycling the battery then the Ohmmu will be subject to the same abuse and possibly the same fate.

Do we know if the 12V battery issue even applies to Model Y's or newer 3's? And if so, do we know that it's not caused or triggered by unapproved 12V access like jump starts or radar detectors that could be confusing the charge algorithm?

 

[roblab]

Just wondering if anyone has changed out there 12v battery to a lithium? Seems like I’m seeing a lot of dead vehicles in the middle of a trip due to a faulty 12v. I’ve had my MY for 2 months now. The only thing that worries me with this car is having the 12v die as I’m cruising down the road. Anyone else change it out just for the hell of it?

nope

 

[jcanoe]

I recall someone on TMC forum stating that Tesla has updated the 12V battery charging function ~4 times. The early production Tesla vehicles, i.e. Model S, Model X were overcharging the 12V battery. Not sure if this issue extended to the Model 3. The current output of the DC-to-DC converter seems to be ~13.5V. I have not observed the voltage over a long enough period of time to learn if it is a constant ~13.5V. At one time the output was ~14.3V at least part of the time.

 

[jcanoe]

I don't believe the Ohmmu 12V LFP battery has it's own charger (there is no place for a charger). I believe the Ohmmu battery is protected against over voltage/overcharging and is also protected from being fully discharged.

 

[Gauss Guzzler]

Yes the Ohmmu has a built-in charger, typically referred to as a "battery management system" in lithium-lingo. They put it all in a plastic box that looks like a familiar "battery" but actually inside that box are a bunch of cells wired to a circuit board with a microprocessor that manages all of the charging and discharging. Otherwise you wouldn't be able to just slap it willy-nilly into any old Buick and not have it explode into a spectacular fireball the first time you start the engine.

 

[NeverGoingBack]

I keep a small 12V lithium jump starter at home and for trips

I keep mine in the frunk …….. and a little 12v camera battery to open the frunk in a ziplock bag taped to the frunk-jump leads behind the front fender.

 

[mcsenerd]

I keep mine in the frunk …….. and a little 12v camera battery to open the frunk in a ziplock bag taped to the frunk-jump leads behind the front fender.

Where are located and when will be the next time you valuables stored in the frunk? LOL (Just kidding!)

 

[jcanoe]

Where are located and when will be the next time you valuables stored in the frunk? LOL (Just kidding!)

The hood latch mechanism will only release when you apply a 12V power source to the leads behind the tow hook cover if the Tesla vehicle's 12V battery is not functioning, i.e. when the Tesla's12V battery has failed.

 

[LoudMusic]

Yes the Ohmmu has a built-in charger, typically referred to as a "battery management system" in lithium-lingo. They put it all in a plastic box that looks like a familiar "battery" but actually inside that box are a bunch of cells wired to a circuit board with a microprocessor that manages all of the charging and discharging. Otherwise you wouldn't be able to just slap it willy-nilly into any old Buick and not have it explode into a spectacular fireball the first time you start the engine.

I don't believe it's fair to say that a BMS is a charger. A charger takes a power supply source and modifies volts and amps so that current can be accepted by the battery. The BMS monitors the battery, reports information, and disconnects it from the charger if "bad conditions" are met.

I have RELION batteries on my boat. They have an internal BMS. But I still have to have chargers to actually supply them with the correct volts in order to get them to accept charge. Nothing in the battery does that.

 

[sleepydoc]

I don't believe it's fair to say that a BMS is a charger. A charger takes a power supply source and modifies volts and amps so that current can be accepted by the battery. The BMS monitors the battery, reports information, and disconnects it from the charger if "bad conditions" are met.

I have RELION batteries on my boat. They have an internal BMS. But I still have to have chargers to actually supply them with the correct volts in order to get them to accept charge. Nothing in the battery does that.

Technically you’re right, but @Gauss Guzzler was exactly correct in his post. A charger is more than just a voltage source. The car has a charger that is (theoretically) designed for a lead acid battery. The ‘drop in’ Li battery has power management circuitry that allows it to use the car voltage without trashing the battery.

S/he is also spot on about there being something intrinsically wrong with Tesla’s 12v battery management. Our 11 year old Odyssey is still on its 2nd battery. Even a 2 year replacement cycle is incredibly short.

 

[NeverGoingBack]

Where are located and when will be the next time you valuables stored in the frunk? LOL (Just kidding!)

Yikes - good point - note to self: “no valuables in frunk”

Smile for the camera before opening

 

[ChrisMPK]

Most lead-acid batteries are very cheaply produced these days and often die after 2-3 years in any type of car. A good one will las 5-6 years but that is no longer the default. FWIW I replaced a 3yo 12v battery in my M3 with a lead battery from Autozone. Took maybe 5 minutes. There were warnings on the screen for a month before it failed.

 

[ucsdsig]

The 12v battery in my Model S had to be replaced twice over a three year period. Died without any advance warning leaving the car completely inoperable. Tesla roadside assistance sent a flatbed both times. Hoping the Model Y fares better.

 

[whisperingshad]

I would think main reason to change is weight... its almost 1/3 of the normal battery.....0000001 faster lol

 

[LoudMusic]

I would think main reason to change is weight... its almost 1/3 of the normal battery.....0000001 faster lol

Main reason to change is reliability. Lithium batteries can perform WAY more full cycles in their lifetime.

Also, they output much more consistent voltage through their charge range, so the attached consuming devices are less damaged by fluctuating voltage.

Side benefits they also provide are higher current charging and discharging, so they can charge faster and power more devices. Output from them is more consistent throughout power draw range making estimating remaining power easier, compared to other technologies where the faster you draw the less total wh you will be able to draw in total.

The two downsides to lithium phosphate batteries are cost and ... small potential sparky sparky boom boom (to quote Avatar). But the cost is just upfront cost - operational lifetime of the batteries almost always comes out way ahead of other chemistries. And other chemistries aren't fault free - many of them "off gas" which is highly dangerous as well.

 

[jcanoe]

Lithium batteries don't function well at cold temperatures and can't handle higher temperatures without damage. In the Tesla vehicle the 12V battery does not have to ever deliver high current. It just has to be able to deliver ~250W (20A @ 12.6V) for the first few seconds until the DC-to-DC converter takes over and also deliver ~25W (2A @ 12.6V) for long periods of time while the Tesla vehicle is parked. When the Tesla vehicle is powered on there is a DC-to-DC converter that is used to power all of the 12V systems including charging the 12V battery. The DC-to-DC converter is capable of delivering ~2kW (150A).

 

[jsight]

What 12v battery? The lithium battery would replace it. Then how do you regulate the voltage for the rest of the electrical system?

People who are saying this is a drop in have very obviously never converted anything from 12v lead acid to lithium.

And what is the point of a lithium battery when it is only charged to 12v?

People have made AA batteries with Lithium Ion. The charge controller and DC-DC converter are in a tiny little cell. Some of them charge via USB (@ 5 volts), and they provide 1.5 V output. The ohmmu folks had to do something similar here. They must have an onboard charge controller and probably a DC-DC converter on the output as well to make the voltages work as a drop in replacement.

The point is higher reliability, presumably. I'm not sure that it's worth it for this application, tbh. The ohmmu is expensive, probably in part because of the extra electronics that it requires.

 

[tangible1]

My understanding is they have a 3rd party battery designed for the car? Plus living in CA it never really gets too cold.

12V Lithium Battery for Tesla Model Y | ohmmu.com

Battery Terminals: SAE, Positive Top Back LeftDimensions: 185mm x 116mm x 198mm (L x W x H) / +20mm for postsWeight: 9 lbsWhat's Included: 12V LFP Battery, Warranty CardATTENTION: Please note that your vehicle may prematurely recommend 12V battery replacements when a LiFePO4 battery is installed...

www.ohmmu.com

Charging circuits for lithium batteries are different than for the SLA batteries used in Tesla currently.
That's a bigger deal than most people give credit to.
An SLA battery takes longer to charge and circuits don't go into 'float mode' quickly.
A lithium battery can be easily damaged if overcharged, so 'float mode' has to occur sooner.
So trying to put an expensive lithium 12V battery in a Tesla, which has a charging circuit designed for the SLA 12V battery, is asking for problems.

 

[avs007]

I know with ICE cars it was popular to replace the standard Lead Acid Battery with a drycell Optima battery... I'm surprised people haven't looked into using one of those for the 12v battery for a Tesla? I think charging wise, it is a drop in replacement for a lead acid battery. And potentially is more reliable than a traditional lead acid? Not sure if it's worth it honestly... I always keep a portable jump starter in all my cars anyways...

 

[jcanoe]

I know with ICE cars it was popular to replace the standard Lead Acid Battery with a drycell Optima battery... I'm surprised people haven't looked into using one of those for the 12v battery for a Tesla? I think charging wise, it is a drop in replacement for a lead acid battery. And potentially is more reliable than a traditional lead acid? Not sure if it's worth it honestly... I always keep a portable jump starter in all my cars anyways...

It could possibly work but several things would be needed. The Tesla vehicle's 12V system is not currently programmed for charging an absorbent glass mat (AGM) type 12V battery such as the Optima battery. AGM batteries have different charging requirements, a lower float voltage than a flooded lead-acid battery. If the float voltage is too high this would damage an AGM battery. The current 12V battery is specifically made for Tesla. It is a fairly compact deep cycle maintenance free lead-acid battery that is rated for 40Ah or 45Ah. This battery configuration is not readily available in this size other than from Tesla and the Ohmu lithium battery. While Optima does offer a deep cycle battery it would not fit in the space for the Tesla 12V battery.