2 Millisecond short

[MadMax03]

Any BMS that uses a relay or contactor.

Doesn't work like that with an alternator in a car application. The ECU must sense battery state. My vehicles are Mercedes W221 S Class and W212 E Class. My competition stereo car with the 120ah LTO bank is a 5th gen Maxima.

Why did you wire the cells like that?
You've got three 12v packs in parallel.
I'd rewire that to put 3 cells in parallel. Then 4 of those in series.

I thought about that, wasn't sure what the benefit would be? I series out to get my voltage then parallel out to get my capacity. Other than monitoring cells, which I'm not (I will check them manually, or throw an Arduino wifi monitor that I built on them), I am not aware of any benefits.

Also, 320 amp alternator! That's a hell of a thing

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[MadMax03]

It's actually kind of normal for guys into Mobile Ham Radio systems and guys with big car stereo amps.
Most of these guys have 1Kw or more of Amplifiers bolted in the back.

Yep, I have a total of 14kW in amplifiers powering my stereo car. Many guys are running two, three, and more 300a alternators to power their systems. But those are really big systems.

 

[Sojourner1]

After reading the thread with replies and corrective criticism and OP "knows" what he's doing because the audio crowd all do it.... other than I guess the 1st step of proper top balancing.

Besides it's only 2 cells right now over 4 volts and the rest in the 3v range. Atleast the pack is under 14.6v. ????

 

[MadMax03]

My Maxima stereo car is run stolely off the LTO battery which is located in the rear passenger compartment. There is no under-hood battery. I want to convert both Mercedes to Lithium as well. The battery in question is a proof of concept battery that I am installing into the E Class to see how it plays with the Mercedes computers and electrical system, which are far more advanced and complex than the Maxima.

 

[MadMax03]

After reading the thread with replies and corrective criticism and OP "knows" what he's doing because the audio crowd all do it.... other than I guess the 1st step of proper top balancing.

Besides it's only 2 cells right now over 4 volts and the rest in the 3v range. Atleast the pack is under 14.6v. ????

Not top balancing was a brain fart, AND it also taught me something. I charged each LTO cell THEN top balanced them for my stereo car. The lesson learned here is; If I had charged each cell, then top balanced, how would I have known that two of the cells that charged higher would have behaved that way? I consider this a learning experience. I have extra 40ah cells. I may replace the two that charged higher. I am dumping voltage from those two cells into other lower cells passively balancing rather than discharging them with a load. I'm working on it now. They've sat overnight. Once those two are balanced, I'll charge all cells individually to 3.60 then passively balance them and top them off like I did with the LTO bank.

 

[MadMax03]

I admit I don't know a whole lot about this stuff. What I do know is thanks to Will. I have been a fan of his since long before he moved to Vegas and was living in a van. I have bought product from and used his affiliate links to help support him for a long time, maybe 5 years or so. He's the nicest guy in the world and has helped me learn more than I ever would have on my own so I do my best to give back by using his links, purchasing his stuff through his site, etc.

I wouldn't have attempted any of this on my own without the stuff I've learned from Will. The majority of car audio guys buy the retail market batteries. With the knowledge I've gained from Will's channel, site and literature, I've been able to save on, and even expand on the grossly overpriced retail market car stereo electrical stuff. There are car stereo companies selling 40ah 12V batteries to the car stereo crowd for $1000 each. That's just highway robbery in my opinion when I can buy four raw 280's and make a 12V battery myself with seven times more capacity for around $600.

 

[MadMax03]

I also live in Florida, so thermals are a non-issue, even under the hood.

 

[Sojourner1]

You are talking about LFP original from the first pic shown early in the thread and not LTO chemistry which you're showing now.
LFP 2.5-3.65vpc compared to 1.6-2.8vpc is quite the difference.

Why not just use larger ah prismatic cells with less connections than small ah capacity cells with more connections and headaches?

 

[MadMax03]

You are talking about LFP original from the first pic shown early in the thread and not LTO chemistry which you're showing now.
LFP 2.5-3.65vpc compared to 1.6-2.8vpc is quite the difference.

Why not just use larger ah prismatic cells with less connections than small ah capacity cells with more connections and headaches?

I was just making a reference to my charging and balancing procedure with the LTO cells. I did that project a couple years ago. The reason for the 40ah cells is that they will fit into a Group 49 case which is the same case as the Factory Mercedes LA battery I am replacing it with.

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[DerpsyDoodler]

Not top balancing was a brain fart, AND it also taught me something. I charged each LTO cell THEN top balanced them for my stereo car. The lesson learned here is; If I had charged each cell, then top balanced, how would I have known that two of the cells that charged higher would have behaved that way? I consider this a learning experience. I have extra 40ah cells. I may replace the two that charged higher. I am dumping voltage from those two cells into other lower cells passively balancing rather than discharging them with a load. I'm working on it now. They've sat overnight. Once those two are balanced, I'll charge all cells individually to 3.60 then passively balance them and top them off like I did with the LTO bank.

You need to put the negative charger lead on the opposite end of the negative bus bar if you want to properly share the current between those paralleled batteries.

 

[MadMax03]

You need to put the negative charger lead on the opposite end of the negative bus bar if you want to properly share the current between those paralleled batteries.

Thank you! That is brilliant!

 

[Sojourner1]

That's what I thought just making sure.

Back to the original thread.... as you might know or realize after you properly top balance the cells that "should" put them in a more equal capacity range, why a couple started to run.

I'm guessing here because I'm not into the audio competition or hobby that it more demanding in charge/ discharge higher 'C' rate for shorter periods of time. Whereas most of use here are using a lower slower 'C' rate seeing our packs are larger or demands are less "sort of" and possibly being offset with solar during the day.
I suppose using your configured battery without a bms isn't that big of a deal, best case scenario you bloat the cells and done, worst case you get to become a youtube star as it possibly goes up in flames. At least you'll have music to listen to for a short bit by the fire.

Most of us that use and live with lfp take as much precautionary steps to the chemistry as not to burn our homes down or worse lose life.

 

[DerpsyDoodler]

Most of us that use and live with lfp take as much precautionary steps to the chemistry as not to burn our homes down or worse lose life.

Yeah, even if you can get away with it in theory, in practice it doesn't always work that way. Much better off just putting a BMS on the pack and calling it done.

 

[MadMax03]

Most of us that use and live with lfp take as much precautionary steps to the chemistry as not to burn our homes down or worse lose life.

Understood. A fire is the last thing I want. That's why I'm even less concerned with my LTO battery being a flamethrower than the LFP batteries. Both chemistries are very safe if not abused.

Thanks for the tip on top balancing. I still wonder if I had done that first, if the two cells that ran would still do the same thing?

 

[Kornbread]

" ... are car stereo companies selling 40ah 12V batteries to the car stereo crowd for $1000 each. That's just highway robbery in my opinion when I can buy four raw 280's and make a 12V battery myself with seven times more capacity for around $600. ... "

Not sure what kind or size of battery you need, but cheap 12v ready to play Lifepo4 batteries like Ampere Time, or Chins, can be had for around $300 on occasional sale.

 

[Hedges]

Yep, I have a total of 14kW in amplifiers powering my stereo car.

Is that at 12V?
Do they really deliver 14kW, or is that just sum of labels printed on boxes?
Would like to see a photo of the wiring. And an IR picture after it's been putting out full power for a while.

It's not that difficult to design something which delivers 1 MW. For 1 us. Sustained power handling is another story.

I also live in Florida, so thermals are a non-issue, even under the hood.

"Thermal" has two ends to the spectrum.

You need to put the negative charger lead on the opposite end of the negative bus bar if you want to properly share the current between those paralleled batteries.

Given large cross section of aluminum angle, and much higher resistance contact where the LTO batteries make pressure contact by weight, I have little concern about driving opposite ends vs. same.


Once top-balanced, if the cells have similar capacity, aren't charged to as high a voltage as they were top-balanced to, and aren't discharged fully, the battery may run a while without any cells going over/under voltage.

If you connect a BMS to monitor cell voltages, without having current sense or FET/contactor in series, it won't interfere with your excess amperage operation. It won't protect the batteries. But it could trip an alarm telling you to shut off and prevent damage. If you have a switch (remote enable wire) to amplifiers, BMS could feed that for low-battery shutdown. Can't readily shut down alternator (and don't want to disconnect alternator from battery with engine running; some people consider keeping lead-acid connected for that protection.) What you could do is wire BMS to engine run/kill signal. These two (amplifier remote, engine kill) would accomplish similar to BMS controlling an external relay.

 

[Supervstech]

Understood. A fire is the last thing I want. That's why I'm even less concerned with my LTO battery being a flamethrower than the LFP batteries. Both chemistries are very safe if not abused.

Thanks for the tip on top balancing. I still wonder if I had done that first, if the two cells that ran would still do the same thing?

At the moment, we don’t know you have two that run, we only know two got more of the charge than most.

If not top balanced, two may have been much closer to full than the rest.

Each cell is a 40Ah tank. And if some tanks are at 35Ah and the rest are at 15Ah the voltage will still show 3.2V… so, when the full tanks reach 100% at 3.65V and the rest are still at 3.2ish, the charger’s 14V keeps pushing watts in, and it has to go somewhere… destroying the cells with the full tank.

 

[MadMax03]

At the moment, we don’t know you have two that run, we only know two got more of the charge than most.

If not top balanced, two may have been much closer to full than the rest.

Each cell is a 40Ah tank. And if some tanks are at 35Ah and the rest are at 15Ah the voltage will still show 3.2V… so, when the full tanks reach 100% at 3.65V and the rest are still at 3.2ish, the charger’s 14V keeps pushing watts in, and it has to go somewhere… destroying the cells with the full tank.

All cells were passively, parallel balanced and all cells rested at 3.272v before I assembled the battery and threw the charger on it. My logic is that if they were all balanced at whatever voltage, they would all take a close enough charge to my power supply voltage set point. But I guess this was obviously flawed thinking. Is it due to tiny differences in internal resistance that would cause what happened with the two cells that ran?

 

[Supervstech]

All cells were passively, parallel balanced and all cells rested at 3.272v before I assembled the battery and threw the charger on it. My logic is that if they were all balanced at whatever voltage, they would all take a close enough charge to my power supply voltage set point. But I guess this was obviously flawed thinking. Is it due to tiny differences in internal resistance that would cause what happened with the two cells that ran?

This was faulty logic…

 

[Supervstech]

No.
It was the fact that below 3.4v a cell can hold huge differences in Ah.

Only way to know how full a cell is, is to fill it, or empty it.

IR differences will play a part in Voltage drift over the course of the pack life though, that’s where a balancer or BMS with charge balancing comes in.