[wd1]

 

[TechnicallyJeff]

I would like to clarify that my intention is not to pass judgment or cause any distress. Rather, I am here to share my expertise in professional discourse and present factual information that is often concealed by certain aftermarket solutions. It is important to address misconceptions, such as the notion that a partially developed design like Ohmmu can serve as a complete replacement for a lead-acid 12V battery.

Therefore, before becoming agitated or expressing uninformed opinions on the subject of discussion, I encourage you to be more transparent and ask questions about topics you may not be familiar with.

I have been the subject of criticism in my private chat by some members who have accused me of being stubborn or unwilling to accept their way of misleading information they have been filled in.

I'm glad you're here to help. I thought about messaging you privately to let you know I'm not trying to argue, but didn't know how that'd be taken.

I do wish Ohmmu was more open on the specs behind their batteries. I'll see if I can get some more info and maybe share some photos of more recent battery designs.

 

[EV- Technician]

View attachment 20721

What is your SOC at this voltage for Ohmmu battery?
My estimate is less than 20% SOC at this voltage.
But vehicles designed for lead-acid chemistry can't use 10V Ohmmu cut off anyway , and that would be in 1P4S setup that Ohmmu is using 2.500V per cell.

 

[wd1]

 

[EV- Technician]

View attachment 20723

This may be incorrect SOC ( but as LFP chemistry has pretty much flat curve between 95-19% SOC I will go with your picture).
Do you happen to have screen shot when Ohmmu is at 12.6V?

 

[wd1]

This may be incorrect SOC ( but as LFP chemistry has pretty much flat curve between 95-19% SOC I will go with your picture).
Do you happen to have screen shot when Ohmmu is at 12.6V?

I can.t remember it ever being that low. It usually varies between 13.0 and 14.0 depending if it is discharging or charging. I'll keep an eye on it and send you a screen shot if it gets that low.

 

[wd1]

This may be incorrect SOC ( but as LFP chemistry has pretty much flat curve between 95-19% SOC I will go with your picture).
Do you happen to have screen shot when Ohmmu is at 12.6V?

4 cells @ 3.2 -3.8 or so.

 

[dc30307]

Do you happen to have screen shot when Ohmmu is at 12.6V?

I can.t remember it ever being that low. It usually varies between 13.0 and 14.0...

I may be able to add a somewhat related data point. I'm using an LFP battery, but not as a replacement for the stock lead-acid battery. It's in tandem with an AGM battery. The AGM replaced the stock flooded battery, the LFP is wired in on the accessory side (50a trailer circuit). Therefore the car is still able to monitor the AGM's SOC and keep it charged as needed without a secondary BMS between it and the battery it's trying to maintain, while the LFP operates completely passively off the accessory side. The car sees the LFP as a load that sometimes "gives back". But since the LFP battery's natural voltage is slightly higher than a LA battery, the majority of the charge/discharge current is served by the LFP. The LFP will typically get charged to 100% when I charge my car, then during operation I see a slight drain on the LFP, as it tends to keep the system voltage above 13v. Interestingly, the car seems to carry the bulk of the accessory load, but the LFP seems to keep the voltage high enough that car doesn't try to charge the 12v battery (or more accurately, the car rarely charges the AGM because it's SOC is maintained by the LFP). At least not until the LFP gets fairly drained down. It usually takes 2-3 days of driving w/o charging the car for the LFP voltage get below ~12.9v, THEN the car will start doing its typical charging during deceleration,and the LFP will then bounce around in a lower in a lower state of charge until the next time I charge the car. I noticed this past winter the LFP SOC never dipped very low: it generally seemed to stay above 50%, while last summer I had seen it get as low as ~15% (then the car stepped in with its charging logic and it would then hover in the 25-35% range). I assume this seasonal difference is due to temperature compensation applied in the car's charging logic, since it's designed for a LA battery. On average, it's maintaining higher voltage in colder temps, and that's reflected by higher average LFP SOC in colder temps. But regardless, it still gets fully charged during L2 charging.

But to answer the question with that backstory out of the way, on the rare occasion that the system gets down in the 12.6v range, my LFP SOC could be as low as ~15%. But I think I've only seen that once. And of course at that voltage, there's still a decent amount of capacity left in the AGM, and the car is going to step in and start charging both of them up.

EDIT: Just went out and checked... it's been 2 days since I charged my car, LFP sitting @ 35% SOC @ 12.86v.

 

[EV- Technician]

4 cells @ 3.2 -3.8 or so.

Lfp chemistry operating voltages are 2.500V-3.650V in laboratory conditions testing. For extended SOH degradation it is usually set at 2.700V-3.550V. If you divide total voltage by 4, thus will give per cell voltage in 1P4S setup.
Nominall Lfp battery voltage are usually called as 3.200V ( because at this voltage thay have almost flat curve between 19-95% SOC)

 

[EV- Technician]

I may be able to add a somewhat related data point. I'm using an LFP battery, but not as a replacement for the stock lead-acid battery. It's in tandem with an AGM battery. The AGM replaced the stock flooded battery, the LFP is wired in on the accessory side (50a trailer circuit). Therefore the car is still able to monitor the AGM's SOC and keep it charged as needed without a secondary BMS between it and the battery it's trying to maintain, while the LFP operates completely passively off the accessory side. The car sees the LFP as a load that sometimes "gives back". But since the LFP battery's natural voltage is slightly higher than a LA battery, the majority of the charge/discharge current is served by the LFP. The LFP will typically get charged to 100% when I charge my car, then during operation I see a slight drain on the LFP, as it tends to keep the system voltage above 13v. Interestingly, the car seems to carry the bulk of the accessory load, but the LFP seems to keep the voltage high enough that car doesn't try to charge the 12v battery (or more accurately, the car rarely charges the AGM because it's SOC is maintained by the LFP). At least not until the LFP gets fairly drained down. It usually takes 2-3 days of driving w/o charging the car for the LFP voltage get below ~12.9v, THEN the car will start doing its typical charging during deceleration,and the LFP will then bounce around in a lower in a lower state of charge until the next time I charge the car. I noticed this past winter the LFP SOC never dipped very low: it generally seemed to stay above 50%, while last summer I had seen it get as low as ~15% (then the car stepped in with its charging logic and it would then hover in the 25-35% range). I assume this seasonal difference is due to temperature compensation applied in the car's charging logic, since it's designed for a LA battery. On average, it's maintaining higher voltage in colder temps, and that's reflected by higher average LFP SOC in colder temps. But regardless, it still gets fully charged during L2 charging.

But to answer the question with that backstory out of the way, on the rare occasion that the system gets down in the 12.6v range, my LFP SOC could be as low as ~15%. But I think I've only seen that once. And of course at that voltage, there's still a decent amount of capacity left in the AGM, and the car is going to step in and start charging both of them up.

I would suggest using DC-DC converter that is able to throttle current going to the LFP battery and set more tight calibration when is connected to AGM chemistry so it turns off discharging from Lfp if current is higher than what your wiring is between AGM and Lfp.
Being extra safe dosent hurt especially when you playing with LFP chemistry that can provide high current discharging.
This calibration values can be safely changed in BMS if you have admin access to this screen.

 

[dc30307]

I would suggest using DC-DC converter that is able to throttle current going to the LFP battery and set more tight calibration when is connected to AGM chemistry so it turns off discharging from Lfp if current is higher than what your wiring is between AGM and Lfp.

That hasn't appeared to be necessary. I put a 25a fuse on the lead to the LFP battery, the trailer circuit it's connected to is supposedly a 50a circuit. I don't think I've ever witnessed more than ~17a in/out of the LFP battery, and only for short periods. Since it and the AGM are in parallel, high loads/charges get split between them.

 

[EV- Technician]

That hasn't appeared to be necessary. I put a 25a fuse on the lead to the LFP battery, the trailer circuit it's connected to is supposedly a 50a circuit. I don't think I've ever witnessed more than ~17a in/out of the LFP battery, and only for short periods. Since it and the AGM are in parallel, high loads/charges get split between them.

Battery with lowest internall resistance will always take more current than one with more internall resistance.
Have you measured voltage drops across the wiring between AGM and LFP where is located?

 

[dc30307]

Have you measured voltage drops across the wiring between AGM and LFP where is located?

No, the LFP is in the back, at the trailer connector,so there's certainly going to be some resistance over that distance. I just know the current has never been high enough to blow a 25a fuse.

 

[tonester]

Look, in the end consumers can review the data offered by multiple sources, then make what they believe to be a well-informed/educated decision; me, I've chosen to not go with an Ohmmu mainly because there's no reason why I should need to be spending ~$479 today to replace a battery that's currently under warranty. You can purchase two reputable-brand AGM batteries or perhaps even three regular lead-acid batteries for the price of one Ohmmu--the only advantage here is that you'd probably spend less time and effort replacing an Ohmmu battery with another Ohmmu than you would having to deal with replacing your average lead-acid battery...LOL!

Personal opinion--for as much as they charge for their batteries you'd think Ohmmu could offer a longer warranty than 4 years which is only a year longer than that of your typical lead-acid battery.

 

[danbfree]

Look, in the end consumers can review the data offered by multiple sources, then make what they believe to be a well-informed/educated decision; me, I've chosen to not go with an Ohmmu mainly because there's no reason why I should need to be spending ~$479 today to replace a battery that's currently under warranty. You can purchase two reputable-brand AGM batteries or perhaps even three regular lead-acid batteries for the price of one Ohmmu--the only advantage here is that you'd probably spend less time and effort replacing an Ohmmu battery with another Ohmmu than you would having to deal with replacing your average lead-acid battery...LOL!

Personal opinion--for as much as they charge for their batteries you'd think Ohmmu could offer a longer warranty than 4 years which is only a year longer than that of your typical lead-acid battery.

To be fair, the warranty is not how long they will actually last, which is more like 10 years. You also get benefits like less strain on the ICCU that is prone to fail (so less warranty headaches), cleaner audio and less chance of being stuck with a dead battery you have to jump (another warranty hassle to avoid), these things all have value too.

Yes, absolutely, we shouldn't have to, but the point is they do use cheap batteries to meet a price point, and many of us find value in our mods based on previous experience, etc.

I also want to reiterate that I'm not here to argue either but the so called expert has been so far off on so many things here and so many people eating it up that I'm going to see myself out and go install my LFP battery that absolutely will be amazing knowing what I know and not just speculation.

But eriously, guessing only 20% SOC at 12.9v? To me that is straight up laughable and proof he doesn't know how much about LFP. But he will never be convinced without FAR more time then I have on my hands to dig up the thousands of examples of people using LFP as a 12v replacement flawlessly. I'm out!

 

[TechnicallyJeff]

Update - I talked to Ohmmu and got some info.

They just sent a new battery to Ingineerix. He should be doing a fresh analysis. Can't guarantee what he'll do or say though.

Regarding the low voltage leading to non-heating - they said the heating circuit is only active during charging and as a consequence it doesn’t matter how low the voltage or SOC are, as long as there is enough current going to
it (charging).

 

[dc30307]

You also get benefits like less strain on the ICCU

There is zero data to back that up. There have even been PCS failures in Teslas (their DC-DC converter, like our ICCU), that have been attributed to swapping to the Ohmmu. That doesn't mean the ICCU would have the same risk, but there's certainly no evidence switching to an LiFePO4 battery improves the ICCU reliability.

cleaner audio

Sorry, I don't care what you think you've heard, I call BS on this one.

less chance of being stuck with a dead battery you have to jump

This one is true.

I'm all for everyone doing what they want to their cars, but let's at least be reasonable and honest about the pros/cons.

 

[TechnicallyJeff]

There is zero data to back that up. There have even been PCS failures in Teslas (their DC-DC converter, like our ICCU), that have been attributed to swapping to the Ohmmu. That doesn't mean the ICCU would have the same risk, but there's certainly no evidence switching to an LiFePO4 battery improves the ICCU reliability.


Sorry, I don't care what you think you've heard, I call BS on this one.


This one is true.

I'm all for everyone doing what they want to their cars, but let's at least be reasonable and honest about the pros/cons.

Regarding the cleaner audio, LFP batteries do perform better for high output systems, but the EV6 is far from that lol.

 

[dc30307]

Regarding the cleaner audio, LFP batteries do perform better for high output systems, but the EV6 is far from that lol.

Due to the lower internal resistance, a lithium battery will generally have much higher current capability than an equivalent sized LA battery. That could make a difference on a competition level aftermarket system drawing 100s of amps, but as you say, we're FAR from that. No one is going to find any voltage sag due to audio dynamics in the stock system. Or even the stock system + a typical compact aftermarket sub like some of us have added. But it's also worth mentioning that the Ohmmu battery is not "equivalent sized" to the stock battery. The Ohmmu is reportedly somewhere around 40AH, while the stock is 60AH. That's not a problem from a capacity perspective, since you can use 100% of an LiFePO4's capacity, while a LA is best limited to 50% DoD, the point remains that for comparing current capability, it's not just lithium vs. LA since it's not apples-apples on size. The BMS can also have current limits. It would be interesting to load test one and see how they do.

 

[EV- Technician]

I believe that some individuals may have difficulty comprehending the technical aspects of 12V LFP chemistry and its incompatibility with the E-GMP platform.