2 Millisecond short

[MadMax03]

So a little update. Got the battery case and put it together. It's not finished, have yet to drill holes, mount terminals, etc., but you get the idea.

So thanks to you guys I realized the error in my ways. I should re-wire the cells in 4S3P, so that I only require one BMS, and thanks also to those that mentioned that there are high-amp BMS's. I have found this one:

https://www.amazon.com/gp/product/B08VHYV4S6/ref=ox_sc_act_title_1?smid=A22QWF3YLLYB17&th=1

So, now that we have BMS protection, am I correct in my integration into the car? I think I need to wire the B+ cable from the alternator to the BMS, and have the main vehicle power in the middle of those two, then wire the Positive out ot the BMS to the battery. This is in case the BMS shuts off charging to the battery, the car still runs on alternator. Does this sound correct? See diagram I drew (nevermind the balance lead placement, just there as a visual).

Edit: Starter cable to be wired directly to battery + terminal

 

[MadMax03]

I guess I just need the manual for that BMS and figure out how it works.

So if one cell runs into the 4's, for example, the BMS cuts charging to the battery and the car dies?
What if the Benz doesn't like running on only alternator? CAN it run on only alternator?
Is the BMS always on? What is it's standby power consumption?
Are the two BMS positive pads always live (parallel) unless it senses a condition to cut charging?

 

[MadMax03]

If the car current consumption is 100A, and my subwoofer amplifier spikes to 250A, will the BMS cut charging?
If the spike is transient, will the BMS restore charging as soon as it senses a return to acceptable current draw?

I had a good, simple idea and you guys had to go and make it all complicated! GEEZ!

 

[MadMax03]

If the current draw from the subwoofer amplifier occurs in series, such as in the frequency of a kick drum in a song, would the overcurrents be constantly tripping the BMS cutoff?

The dilemmas caused by adding a BMS seem to be introducing more problems than solutions. Guys run Lithium all day every day without one and don't have problems. I'm just not seeing the benefit. I don't understand this well enough.

 

[DerpsyDoodler]

I'm going to comment on a couple of your posts at once. So here goes.

First, 3P4S is what you need for 1 BMS. The notation 3p4s means 3 cells in parallel wired in series with another 3 cells in parallel 4 times OR 4 sets of 3 paralleled cells wired in series.

4s3p means 4 cells wired in series, then connected in parallel to another 4 cells wired in series 3 times. The BMS would need 15 or so sense leads for this. a 4s BMS only comes with 5 sense leads.

Hopefully you clearly under stand how this works now

3p4s = -PPPsPPPsPPPsPPP+

+++++++++++++++
4s3p = SSSSpSSSSpSSSS
-----------------------

Next, usually BMSs only conduct on the negative side of the circuit. Meaning BMS B- line connects to battery negative, and BMS C- line connects to load or charger negative. Only the negative side of the circuit flows through the BMS. There are some exceptions, and Daly BMSs may be one. That said, definitely refer to the instructions for your BMS and make sure you fully understand how to do it before you do it.

Finally, I can't tell you anything about running LifePo4 as a starter battery in a car (there are different lithium chemistries, you need to understand this), and I can't tell you what lithium chemistry is being primarily used by the audio crowd. I can tell you some pitfalls about the starter battery part, though:

1. If the starter draws more than BMS rated amps, you won't be able to start your car without the BMS protection tripping.

2. LifePo4 has very low internal resistance and will quickly and wholly try to suck up any amount of energy thrown at it. If it's connected to an alternator that doesn't have a built-in regulator, and the battery is at or at some point drops to a low state of charge, Lifepo4 can and will burn up the alternator. When LifePo4 is connected to an alternator, it is usually done so through a DC to DC charger that will regulate the current that the battery can draw.


So, with all of that said, make sure you understand the specific Lithium chemistry that is typically used in your application (car audio).

Lithium Iron Phosphate
AKA LifePo4/LFP is what we're using and what I just described. I can't tell you much of anything about the next 2 chemistries

Lithium Polymer
extremely dangerous and fire prone

Lithium Titanate
Higher charge and discharge rates than LFP, more resilient to temperature confitions.


Note that the ones mentioned above are just a few of the many different Lithium chemistries. They are all known as "Lithium" or "Lithium Ion" batteries, but they all are used in different applications.

Good luck. Please be careful. These batteries are dangerous.

 

[DerpsyDoodler]

One more note: If I were going to use LifePo4 in your application, I would not replace the starter battery with it. I would add it to the vehicle with a DC-DC charger, and then wire my amp(s) directly to it.

That said, seeking car audio advice on a solar forum may not yield the best results, and do take in mind that any advice you get here is probably going to be safety-oriented.

 

[DerpsyDoodler]

LifePo4 is temperature sensitive. The heat in a car (when its sitting parked in the sun) will degrade and/or destroy your battery if you let it charge/discharge when you first start the car up. You would need to give it time for the cells to normalize to a working temperature.

TBH, based on what little I know, I don't see how your chosen application is practically viable. Would love to hear others' comments on the matter.

 

[740GLE]

I love when people set out on a journey of knowledge without knowing it.

Good luck madmax, you’ll get there eventually and learn a ton in the process!

 

[wholybee]

If the current draw from the subwoofer amplifier occurs in series, such as in the frequency of a kick drum in a song, would the overcurrents be constantly tripping the BMS cutoff?

The dilemmas caused by adding a BMS seem to be introducing more problems than solutions. Guys run Lithium all day every day without one and don't have problems. I'm just not seeing the benefit. I don't understand this well enough.

Probably not. I'm not sure about the Daly, but other programmable BMSs will let you set the overcurrent trip time. It could be as high as a couple seconds. So an instantaneous peak should not trip it.

There are other Lithium Chemistries that are better suited for starting applications, and that do not need a BMS. Maybe that is what the people you are referring to use? I believe it's LTO, but I'm not sure. Very few people can use LFP batteries without a BMS and be successful with it.

Connecting as you suggest, with the starter directly to the battery, would work if it were possible. Because the BMS is connected to the negative terminal, you somehow need to connect the negative from the starter directly to the battery. On most engines the starter is grounded to the engine block, so if you connect that bypassing the BMS, you effectively bypass the BMS entirely for everything, not just the starter.

The common solution here (on this forum) is to use a separate starter battery and then a Lithium for other electronics. I'm not a car audio guy, but I think they also sometimes use super capacitors in their installations. A super capacitor can start a car, and will handle all the high current peaks from an audio system. I have no experience with them though.

 

[MadMax03]

This has been an interesting thread. I've learned that this forum is mostly speculation by folks who have a lot more time than experience on their hands.

I have already been running this exact battery in the E Class, under my hood, for two years, with no BMS, no balancer, and no problems.

I also run 120ah LTO in my Maxima stereo car, in the back seat compartment, for two years, with no balancer, no BMS, and no problems.

The battery I'm building in this thread is just another LFP going into the S class.

 

[justgary]

I also run 120ah LTO in my Maxima stereo car, in the back seat compartment, for two years, with no balancer, no BMS, and no problems.

LTO is a completely different beast than LFP. I suppose you can get away with no BMS if you plan to keep the charge well inside the knees on both ends of the cycle, but if you develop a poor connection you will never know that a cell is outside of your parameters. This is the job of a BMS.

 

[justgary]

So if one cell runs into the 4's, for example, the BMS cuts charging to the battery and the car dies?
What if the Benz doesn't like running on only alternator? CAN it run on only alternator?

The car alternator will not appreciate having the battery disconnect suddenly. It will likely damage the diode plate or the rectifier. In that case, the car will probably quit on the spot.

 

[justgary]

I don't understand this well enough.

I've learned that this forum is mostly speculation by folks who have a lot more time than experience on their hands

Or perhaps you met people with a respect for the money they put into their systems, and they want them to last as long as possible. I have not read any speculation here except from those trying to figure out exactly what you have and what you want to do with it.

What others are doing or what is in your other car is not important. You are getting really good advice here, but you confuse people with talk of LTO and other cars. Please remind me what your other LFP battery does in the Mercedes and why you need another one?

 

[740GLE]

Sounds like two different cars, so he’s looking for two different set ups.

As for why the need to spend 10x for an LiFepo battery vs a normal FLA.

There are lightweight lithium ion batteries designed for FLA replacement so my guess is he needs the capacity for running accessories (audio equipment?) or like everyone he just likes tinkering around.

 

[DerpsyDoodler]

The car alternator will not appreciate having the battery disconnect suddenly. It will likely damage the diode plate or the rectifier. In that case, the car will probably quit on the spot.

I was going to mention that, but it got lost among all the other thoughts. Anyway, I think this guy just came to troll or perhaps thumb his nose at people he foolishly judges as fools. I suggest he go look at the "fire" sub.

And regardless of whether or not he gets away with it in his competition vehicle (which he may or may not drive rarely and/or mostly only to competitions), #1) I would not trust the safety of my home to blind chance, #2) even if fire weren't a concern, $100 is a drop in the bucket for easy insight and maintenance assist of your batteries. It's like monitoring for mission-critical IT systems. Do you want to glance at an app to know everything is OK, or do you want to have to log into every system every morning to ensure everything is as it should be? And if the latter, lets be honest, how long before you say, "its been fine" and just wait for users to tell you when there's a problem? By then maybe its too late and you've lost important data (or in the case of batteries, your car or your home).

If he's "investing" in competition car audio events, he must have money to burn, no pun intended (unless he has sponsors). There's only so many first place winners.

 

[740GLE]

As for the alternator charging a battery, prob all depends on how depleted the battery gets, if he draws the cells down to 10v sure, but if it’s constantly at 13.7 it will probably be fine. Modern alternators and charging profiles of cars are smart enough to not dump 100s of amps into the battery. Heck my VW charging system changes if it’s an FLA or AGM.

As for starting the motor and drain on the battery, I cant imagine starting the car 2-3 times would drop the voltage very much, the flat voltage curve LiFePo is in his favor. Again, as long as the charge/voltage is maintained by routinely driving the car and avoiding freezing conditions.

Sounds like the OP has had success running similar set up, so something works.

Would I want to invest in lithium when my $140 FLA battery dies? Hard no.

 

[A.Justice]

This has been an interesting thread. I've learned that this forum is mostly speculation by folks who have a lot more time than experience on their hands.

The people in this thread easily have over $100,000 of combined solar equipment installed. Most of us have done most of the work ourselves. There's a handful of EEs / professional solar / battery workers on the forum that won't hesitate to correct BS. There's one guy here who literally writes the product manuals for battery manufacturers. Some of us are relying on our battery systems to power our homes in places that would otherwise be hard to survive. I sleep with a battery backup system just a few feet from my head with my wife and kids, and I trust it totally, unsupervised, under maximum use.

I think you severely underestimate the depth of knowledge and experience on this forum.

But we're definitely allowed to disagree, and I do understand that the importance of safety in your "audio" vehicle is very different than what I would require at my home. ? I still think safety precautions like a BMS, and fuses are still a no-brainer though.

 

[Sojourner1]

Be damned with knowledge must have thumper sound.

 

[Partimewages]

This has been an interesting thread. I've learned that this forum is mostly speculation by folks who have a lot more time than experience on their hands.

I have already been running this exact battery in the E Class, under my hood, for two years, with no BMS, no balancer, and no problems.

I also run 120ah LTO in my Maxima stereo car, in the back seat compartment, for two years, with no balancer, no BMS, and no problems.

The battery I'm building in this thread is just another LFP going into the S class.

Again if you already had knowledge why did you come here for help? It only takes one fire to destroy everything!

 

[Odjono]

Lto batteries buy every test I've seen are safer than lead acid ever hear someone you know tell a story of a hydrogen explosion can be like a bomb. A carpenter I knew said they were jumping a dozer and boom!! He said it was miracle no one was hurt and lto I'd say is the safest currently in use but not technology in development.