I did hear from Sean. They are working on an app and software revision. They have been through through 5 app revisions internally and still working on it. The software revision should address the cold weather charging issue I had posted earlier (V4+ would charge higher amps below 40F but not at low amps like float amps less than 1 amp.). Future batteries for cold climates will have a silicone heating element between cells but that will be later for the V4+ models. He states the heating element is not really needed but more of a "peace of mind" addition. Meanwhile, now that the weather is warming up, anyone having charging issues with the V4+?
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Longer term Ohmmu experiences?
- Thread starter Durzel
- Start date
Curious and ignorant question...why does only the Model 3 Ohmmu battery have these odd problems, but not the other Tesla model batteries they sell? Or do those also have issues? I considered this battery in the past, but it's an expensive price to pay to beta test something when the OEM battery isn't that expensive form Tesla. I'm aware that Tesla changed the way it manages the 12V, but I'm surprised if it only affects the Model 3 and not their other models.
Model 3/Y with the 12 volt system. X and S different charging system.
We're not entirely sure but most evidence argues that in late 2021 Tesla started monkeying around with what are called desulfation routines which involved brief pulses of charging of the battery after getting to its full float voltage. This can be tolerated by lead acid but not by a lithium ion battery. The internal battery Management system disconnects the battery to protect it and then the car treats the battery as dying and then does a suicide routine to discharge it
mstatkus
Member
Yeah 30A load shedding is violent if you don't catch it.
I don't think I could even bother putting my V4+ back in until a firmware update happens but at this point I'd bet I'm too cold in the winter to trust it charging reliably.
I've been using my old one to charge my back gate opener since there isn't much sun for solar and its 1000ft from the house.
I don't think I could even bother putting my V4+ back in until a firmware update happens but at this point I'd bet I'm too cold in the winter to trust it charging reliably.
I've been using my old one to charge my back gate opener since there isn't much sun for solar and its 1000ft from the house.
Dysan911
Member
Hey folks!. So I just posted to the M3 FB Group about how lately when I get in my car in the morning I typically have to wait for the main screen to boot up. Several people suggested checking my 12v battery. It didn't even occur to me that it might be an issue with my Ohmmu V4+ disconnecting through the night. . I have noticed on Teslafi each morning an unusually high count of Idles and Sleep attempts. (Perhaps suicide mode trying to kick in).
I was tempted to top off my 12v Lead Acid and put it back in but wanted to first ask this group if they've noticed anything lately. I just checked my Ohmmu BT App next to my car and everything appears to look normal. The battery level is at 100%. Voltage shows 14.02v. Amps in and out are at 0.0. I've got a cycle count of 37 now. All cells are pretty close and appear balanced. Delta 0.002.
I was tempted to top off my 12v Lead Acid and put it back in but wanted to first ask this group if they've noticed anything lately. I just checked my Ohmmu BT App next to my car and everything appears to look normal. The battery level is at 100%. Voltage shows 14.02v. Amps in and out are at 0.0. I've got a cycle count of 37 now. All cells are pretty close and appear balanced. Delta 0.002.
scottf200
Well-Known Member
Connect one of these and you can see a graph of it minute by minute.
QUICKLYNKS Auto Battery Monitor BM2 Bluetooth 4.0 12V Device Car Battery Tester
Specifications:
Input Voltage: 6V-20V
Average Current: 1.5mA
Operating Temperature -40 to 90℃
Bluetooth Range: 10 Meter
Product Dimensions: 5.5 x 3.5 x 1.6cm
Voltage Accuracy: (9-16V) ± 0.03V
Bluetooth Name: Battery Monitor
App Keyword: BM2
mstatkus
Member
Sean warned me a bit on the monitors. Using them in these LFP batteries is tricky. I have similar issues with my broke VATID power station and I find most these packs don’t list out their strings/banks
Try this:
Worked ok on the non-bluetooth Ohmmu.
scottf200
Well-Known Member
Curious as to why it'd be different than the lead/acid one.
Here is the Antigravity company website for that lithium one: Lithium Battery Tracker
Here is the Antigravity company website for that lead/acid one: Lead/Acid Battery Tracker
mstatkus
Member
Oh thats right have one sitting on the shelf when I had it in the car. I'll try it out on my gate to see if it can gauge capacity ok. Pretty sure the VATID BMS had something go wrong with it but all attempts I made to check the pack it self was a pain. I just plug the old v1 Ohmmu in about once every week or so to top it off and threw it in a fire proof box.
Doh, originally bought the lead acid one. Ok I'll pick this one up and give it a swing. The one I got asked way to many questions and the interface was meh.
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I love that Ohmmu acknowledges monitoring an LFP is "tricky" and Antigravity sells separate lead acid and a lithium battery monitors even though the only thing they have access to is voltage and the software could easily handle both curves.
But when it comes to Tesla actually fully using and charging a Lithium, it's annoying that they throw errors when you put a Lithium in place of a LA.
But when it comes to Tesla actually fully using and charging a Lithium, it's annoying that they throw errors when you put a Lithium in place of a LA.
I would say it is more of a matter of Tesla throwing errors when you put a crapily designed Lithium in place of a lead acid. (Really what do you expect the car to do when it tries to charge the LV battery to keep it healthy, and the battery suddenly disconnects and refuses the charge?)
They really needed to design their BMS to imitate the characteristics of the lead acid battery that Tesla uses, but that is very difficult to do. (As seen by the fact that they still haven't gotten it right.)
edit: While I think it is possible to fool the car in a short-term, I don't think it can be made to work long-term. The reason is that the car monitors SoC by how much it puts in and how much it draws out, and if it sees that it has to be in significantly more than it drew out, and to account for normal lead acid self-discharge, it will assume the battery is failing. (For example, if the lithium battery uses power to heat itself so that it can charge in cold weather, that would likely show as excessive self-discharge to the car.)
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This is not something any traditional BMS can solve.
Tesla charges to 14.8V at times, because this is OK for AGM batteries and can help restore them. As Ingineerix mentioned @9:55 :
3.6V times 4 is 14.4V. A proper LiFEPo4 BMS will shut off at 14.4V. The Ohmmu ones allow charging beyond 3.6V per cell because they have to in order to have any hope of working with the Tesla 12V charging system.
The only way to make a LiFePo4 look like a Lead Acid would be to do actual voltage conversion. Not just charge limits, but actual DC/DC so that the output looks like a LA. This is not a traditional BMS task. BMS's can just turn the output on and off, not do 1200W+ of voltage conversion. This would include charge and discharge curves. Because once you stop charging a LA, it drops to 12.6V pretty quickly. Meanwhile a LiFEPo4 will stay at higher voltages. While charging, the impedance at different voltages would be a clear indicator of what chemistry you have.
I've hooked a 40Ah LiFEPO4 battery to my Model 3, with NO BMS. It still detected the battery as failed within a day or two. Because flat out the curves for a LiFEPo4 don't look like Lead Acid, even if there is no BMS that shuts off at higher voltages.
LiFEPo4 worked in old school cars because they were just dumb chargers. They put 13.8-14.4V on the bus, and assumed any battery on that bus would happily be charged by that. Which very conveniently worked with the LiFEPo4 chemistry. But that doesn't mean that for a charger with any kind of smarts that it wasn't trivial to see this as a totally different chemistry.
This isn't why a Tesla can tell it's LiFEPo4. Lead Acid and LiFEPo4 self discharge rates are pretty equivalent (~5% per month). Plus, your Tesla ends up charging your battery a few times a day as the draw on it is non-trivial, meaning detecting self discharge would be hard. The Ohmmu does not have any self heaters, and people in Florida have issues with the Ohmmu when it's 90F out.
It's a simple as this:
If I put 14.4V on a LA AGM until it's fully charged and then I remove the charge current... The battery drops to ~13V.
If I put 14.4V on a LiFEPo4 until it's fully charged and then I remove the charge current... The battery drops to about 13.6V.
That right there would quite reasonably mess up a capacity algorithm that had been tuned for LA batteries.
Beyond that, 50% SoC for an AGM is ~12.0V. 50% SoC for LiFEPo4 is 13V, These are significant differences.
Yep, and even if they did that they would still run afoul of the energy monitoring, and the car would see it as having too-much self-discharge. (Unless you hooked an external power source to it to make up for the energy lost in conversion/heating/etc.)
Yep, the newer generation Teslas are just "too smart" for that, because Tesla has put a lot of work into the lead acid battery management system to try to make them last as long as possible. And what is good for the lead acid batteries isn't good for the LiFEPo4 batteries.
They don't now, but they have said that they are adding them to the next version.
scottf200
Well-Known Member
FYI, 7 day graph and typically upper charging limit on how the Ohmmu works in my 2017 Model X. (3.56v=14.27v/4)
Aside: Many OTAs ago it was like a constant 13.4v-ish charging line.
I realize the TM3/Y LA systems are apparently different but just for comparison.
They're very different, and my analysis applies to the Model 3/Y.
Ohmmu doesn't list any warnings against the Model X/S when you go to buy, but does for the 3/Y.
Pretty sure the S/X use a Flooded cell battery and the 3/Y use an AGM also.
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