Senecat

I'm working on a subwoofer enclosure for a 15" sub for the Benz. My Maxima project/stereo car won't be finished for a bit and I need some bass. Nothing special, and I won't be making any other stereo modifications/additions, but I also wanted to beef up the electrical.

Grabbed a 320A alternator from DC Power Engineering Inc. to supply the electrons to a 4S1P LiFePo4 battery bank I'm going to put together. I'm waiting for two Group 49 battery cases to test fit everything before I decide where to put the battery. The stock location in the trunk appears to have been designed for a Group 49, so that should fit perfectly.

https://diycentralshop.com/product/diy49/

If I decide to stay under-hood with the Lithium, the stock location there also looks to have the space. Notice the factory-capped grommet on the firewall to the right of the stock battery, lucked out with that to run two leads of 1/0 power cable to the trunk for the amplifier/battery.

Nice OAP alternator pulley upgrade came with the new alternator vs the stock, solid alternator pulley. The OAP is + 1 groove, but that's not an issue.

The 4 cells you're looking at are each 3.2V, 280ah Lithium Iron Phosphate cells series-ed out to 12V.

At 5.3kg each cell, that's 3 times the amp-hour storage capacity (and Lithium power, at that) and about 15lbs lighter than the stock Lead Acid. Not to mention every other metric of Lithium blows Lead Acid out of the water.

Senecat

Just to emphasize the power I'm replacing the Lead Acid with, for those who are unaware; the amount of battery going into this car is insane. It is so because of several factors, but the most prominent being energy density.

To put it into perspective, this single 12V, 280ah Lithium battery is equivalent to SIX factory Group 49 Lead Acids. That's nuts! Energy storage and chemistry have come a long way.

https://www.epectec.com/batteries/cell-comparison.html

DFWdude

Am I the only one here wondering why?

KEY08

no you are not. Don’t Lithium batteries like to go boom on occasion?

S. Madman

Poorly made ones do. Lithium Iron Phosphate batteries are used on EV cars, so they should be safe.

Left Coast Geek

Lithium Ion batteries can explode if they go into heat runaway and are overcharged, or even if they have an internal cell failure while just sitting there. LiFePO4 are much more stable. LiIon are 3.6 V per cell and charged with 14.2 V per cell, while LiFePO4 are 3.2V nominal with a 3.6V charging, so a 4 cell '12V' battery is much closer to the sorts of voltages a 12V system expects than a 4 cell LiIon (Li-Ion is 4*4.2 = 16.8, far too high voltage for 12V electronics, while LiFePO4 is 4*3.6 = 14.4V)

Senecat

1. A three-fold increase in electrical capacity vs factory Lead Acid
2. A far, far safer and less toxic chemistry vs Lead Acid (many sub-points to this)
3. A 10x increase in life-cycle
4. Zero maintenance vs Lead Acid
5. A 10x increase in peak/burst current, suitable for high current applications (such as kW hungry stereo amplifiers)
6. A 30% weight reduction, translating to better mileage
7. Ability to resurrect a zero percent state of charge battery back to full SOC without harm to the cells
8. A 10x cost reduction per wH over the life of the battery
9. They look cool
10. etc. etc. etc.

Want me to keep going?

In my perspective, a better question would be why you wouldn't convert. But I understand that this is a relatively new technology and application for most.

pierrejoliat

I was kind of wondering how the new alternator and lithium batteries will interact with the "smart" charging system.

Left Coast Geek

does this new alternator /replace/ the Mercedes alternator, or did you somehow squeeze it into someplace around the engine?

did you REMOVE the stock lead acid battery so this LiFePO4 is doing double duty as the engine start battery?

does this new alternator have a lithium charger? basically constant voltage of 14.2-14.6V up to the max charging amperage, which is typically 1/5th C (so for a 400AH battery, 1/5th C would be 80 amps).

I hope you don't live where you get deep freezes, you can't charge a LiFePO4 thats below 0C/32F. the good batteries have BMS systems that will prevent charging at below freezing, but the cheap ones BMS might not do this.

Senecat

1. New alt replaces old alt
2. Yes, this LFP battery will replace the stock LA battery. No LA in the car.
3. Battery is charged via the alternator who's set point is 14.8V cold. My other DC Power 270A alt set point is 14.85V, and usually runs around 14.6V hot
4. Last question is complicated, but I live in Florida, so freezing isn't an issue. However, resting SOC for LFP is whatever it was last charged to. Another advantage of the chemistry, LFP does not statically discharge but a mere 0.01% per year, or something ridiculously low like that, meaning that the battery will not require a charge after sitting, much less need a high C rate bulk-phase charge or any active charger monitoring and executing a charge program. You are correct in that charging below certain temps is not advised.

No BMS is necessary. Once the (matched) cells are passively top-balanced, just throw them together and go. BMS's are overrated for certain, smaller applications, even some applications where larger banks of these cells are used for off-grid solar storage. Monitoring individual cell voltage once in a while (q6 months or so) is good practice.

As far as charging below 0°C; it can be done, and with some cell degradation, however, the charging rate the battery will see after startup and the time the battery heats to under-hood temps, in my opinion, would have negligible negative effects on the cells. Remember, the car runs on alternator after it's started, requiring little to no discharge current from the battery. Intelligent Power distribution Modules and other computers control all that.

As far as low-temp discharging, again, I believe negligible long-term negative effect on the cells. Sub-0°C discharging charts will show different characteristics even with the same chemistry, but with the alternator providing system power once the car is running, again, I think this application is largely exempt from many of the static test results found in manufacturer data.

Senecat

I have attached the Data Sheet for my cells if anyone is interested.

Senecat

As far as a "Lithium Charger", I'm not sure what you mean. An alternator IS a charger. It is simply a power supply. The battery cares not what produces the electrons. I use this el cheapo psu to charge several chemistries, including LFP, and this 120Ah Lithium Titanate bank for my other car. On constant voltage setting, the battery will only absorb whatever the voltage set point is. The psu will deliver current until that voltage is reached. The current absorbed by the battery slowly decreases to zero once the target voltage is reached. You can literally watch the current in the display drop to zero.

Left Coast Geek

well, presumably this battery gets partially discharged sometimes, certainly a chunk is taken when the engine is started, but a bigger load would be running your massive stereo with the car off for a length of time, and then when the car is started, that massive alternator is going to try and jam as much current into the battery as it can... If the battery is, say, 50% discharged, thats going to be the whole 300 amp output of the alternator

if you're never discharging the battery more than a tiny amount, why do you need such a high capacity battery ?

and I think no BMS on a 400AH LFP is suicidal. say your alternator regulator fails and starts dumping high voltage (its happens). you put high voltage with high current capacity into a LFP and you've just invented a car bomb. ditto if a cell fails and shorts, lowering the overall battery output voltage to 9.6 instead of 14.4, now your alternator outputs 300 amps into this, things go BOOM. The BMS shuts the battery pack down before this can happen.

I worked in and around engineering for 40+ years. Murphy was an optimist.

oldmots

I wasn't sure if your car is a sedan or coupe. The coupe does not have room for a group 49 (H8) battery under the hood, it will only fit an H7. I found this out the hard way a long time ago. Battery mags sometimes miss little things like this in fitment specs.

Left Coast Geek

Usually the h8's are used on diesels... are there no diesel 207(?) coupes? or did they relocate the battery to the trunk for those, like they did with the V8 w124 400E ?

rapidoxidation

The high amp alternator I can (sort of) understand if you're running high amp stuff or pulling a trailer. The battery pack seems like the answer to a question that nobody really ever asked. Weight advantage? Really? I've had bowel movements that weigh more than the difference between lead acid and lithium. On a 4000 pound car, 50 pounds isn't going to make a bit of difference. You'll do better by keeping your fuel tank only 1/4 full.
How much does your high zoot battery cost compared to a quality AGM? Twice? 3X? More?
I've never had to maintain the batteries in my cars... They're sealed.
Peak/burst current for your subwoofer might be a legit argument... but it's debatable. There's plenty of window rattlers out there running on lead acid.
Do you often drop the state of charge of ANY battery to zero, aside from a disposable alkaline?
Again, call me a naysayer but it seems like an answer to a question nobody asked.

Senecat

Tough crowd! I've tried starting like, 3 different upgrade threads for my car in the past on this forum and they either got **** on or got zero attention at all so I completely deleted and shut them down! Just not the forum for anything but "help me" threads I guess!

oldmots

The E550 sedans use an H8, they have more room. Found this out standing holding this very heavy battery wondering why it would not fit. The H7 isn't much lighter but it's about an inch shorter in length than the H8. Had to take the battery back and do research. Man, those things feel like a bucket of cement! I have a Jaguar XKR and it uses an H8, so I'm used to lugging them around.

oldmots

Don't get discouraged, this is a group discussion and all sides of the issue are getting looked at. You are trying something that most people have never considered, it's natural to be careful.
In that vein, I'm sure you are aware that LiFePO batteries will not charge below 32 degF. They will function down to 20 degF though. This can cause some issues in cold climates. They weigh about half as much as lead acid and last 10 times longer. They are costly, a group 24 60Ah LiFePO starting battery runs about $700. But if they last 11 times longer, so they save money in the long run.
Hang in there and I hope it works like you want. You seem to be set up for some heavy testing and research. I am too lazy to go through all that, so I am rooting for you.

S. Madman

I enjoy your posts, some people just don't like to experiment, and only follow what they know. Florida is pretty flexible weather wise in what we can try.

Don't let anyone deter you from trying different things.

BenzV12

I have just noticed this thread . I appreciate what you are doing and you must be gifted daring such things namely in a complex and modern car .
Kudos to you

ygmn

now what all is this costing you less the stereo?

If you did not have this insane stereo would you do this?

I cannot see a benefit for the normal "stock" car other then making my wallet lighter and voiding any warranty I have.

My guess is it will kill resale value later unless you find a buyer who wants all these electrical mods - rare my guess

Senecat

Thanks man. I'm going through with this anyway, so I'll keep the thread going so we can all see it through. If I cook the Benz, well, then we all learn, right?

Thanks guys. I do appreciate the input from all sides. I AM still learning myself. Pretty cool to have input from those with same car experience, opposition that inspires thought, +40yr engineers, et al. I'm no master at this by any means. Attempt at your own risk!

pierrejoliat

I would hope the questions and comments were meant to be helpful observations, I for one am amazed by the stuff people do to their cars, I wish you the best and enjoy following along, better clean up your kitchen before the wife gets home! LOL.