Car Starter Battery with AMP20M1HD-A

[hmh]

Hi Guys,
im coming from Germany and have red a Lot of topics Here, but didnt find any good solution for my Project:

Im bought some A123 AMP20M1HD-A Cells for a really good Price at eBay. My plan is top build a 40ah Starter Battery (4s2p) for my Audi A3. The Point where my "mind ist blowing", ist the Thing with the BMS.

Read a Lot, that some Guys don't use one, some only Initial Balance the Cells with a RC Charger (i have one) and Install a passive/ active balancer. Im confused... Die Somebody have experience with this Cells Put together as a Car Starter Battery? Espacally using a BMS or No BMS?

I read a Lot, that there are issues with the alternator (heating until dead, because of Low Resistance when Cells are reaching 3,65 V). Can i prevent this with installing a passive load Module?

Sorry for my Bad english, i Hope everything is understanable!

Thanks in Forward and best Regards
Moritz

 

[hmh]

Thought of balancing all Cells (Toolkitrc ms8) and then installing this for every Pack:

https://shop.lipopower.de/Balancer-15A-fuer-4-Zellen-LiFePo4-LiNANOZ-Lastmodul-mit-LED

(Loadmodule at 3,58V with max 2,1A Bleedcurrent)

Some more safety necessary?

Regards

 

[scianiac]

So I've thought about this a bit and have some experience building such a battery and seeing commercial units that lack BMS fail and I think I have the best solution. You install a BMS as normal with a reasonable current rating, enough to run everything except the starter and then you connect the starter solenoid directly to the battery. This way the BMS manages charging, balancing and will prevent the battery from being killed if you leave your lights on but also allows full current available for starting. You could of course still kill the battery with the starter but you'll probably never get there as it will be pretty obvious it's dead or actually depending on how things are wired that would also be impossible as you won't be able to fire the starter solenoid since the BMS will have cut power to the rest of the car.

 

[Hillhater]

A BMS is not a charger.
You should also install in the car a proper Lithium capable DC/DC charger to provide the correct charge profile ,voltage , and current to protect the battery.
It will also protect your alternator
Search dcdc charger for more info and suggestions.

 

[dominik h]

Last year I bought a used 40Ah A123 Lifepo4 Battery from a Porsche Taycan, BMS is included in the battery.
I would not recommend using lithium batteries without BMS in a daily driver.

I use a 6S 60Ah LI-NMC as mobile charge power for my RC lipos, there I have no BMS inside, but the RC-chargers stop charging when the battery drops below 20V (3,3V/cell) and the battery is only charged with an RC-charger which does the balancing.

 

[hmh]

Hi all,
First thanks for your great anderes!

Installing an extra cable for the Starter would bei an Option, but very tough Work because Battery ist in the Back and think that the Problem with the alternator (geht's hot because of Low Resistance of the Cells) ist Not solved with this!?

The Info with the DC/DC charger is good, but in my Case a Bit overdone. Get this Cells really cheap, so won't Invest so much, when there ist a cheaper solution.

I know this Porsche Starter Packs, Looks Like there are also build in the 20 ah Cells. Perhaps you have a Photo from the BMS? This Kind/type of BMS would be the perfekt solution for my Project

Thanks for your ideas!

Regards Moritz

 

[hmh]

Looking at the Porsche lifepo Battery, let me guess that there is a CAN based regulation of the voltage/Current and no classical BMS ... But Perhaps you have some Pictures of IT!?

 

[dominik h]

Sorry , I did not open the batterie.
I have a 140A generator in the car and nothing that needs a lot of current, about 100A left for battery charging. After a 20 minutes drive the battery is fully charged and the voltage is at 14,4V..
I testet the capacity before the Installation and 8 months later, it was exactly the same. With lead accid bateries I loose between 20-25% ecery year.

The battery has an undervoltage and overvoltage protection which completly turns of the batteries output voltage.

 

[hmh]

Ah ok, my fault.

What about this BMS:

https://www.lithiumbatterypcb.com/product/4s-or-3s-12v-lifepo4-battery-pcb-for-14-4v-or-14-6v-lifepo4-battery-of-back-up-power-bms-and-power-inverter-battery-protection-circuit-2-2-6/

Did you See any Problems? I think the biggest Problem could bei, that the BMS disconnect the Battery when end voltage of every cell ist reached. Don't See any other way this Board (Like Bleeder Resistors) realize this...

 

[dominik h]

I tested my battery with an RC-Charger.
The battery shuts off at 14,7V and at 10,4V.
In my car the generator stays at max 14,4V and does not get higher.
The biggest problem I see with lifepo battery is charging at low temperatures.
For me this is no problem, I use this car only during the warmer period.

 

[hmh]

Regarding Low Temperatures i See No issue with the a123 Cells, in the Datasheet the operative Temperatures are marked with -30°C Till +50°C

The Last Winters in Germany we're very mild and located in the Trunk, there should be no Temperatures under -10C i guess

I will try the BMS posted above, If anybody has some comments in this one feel free to comment!

Thanks for your Input so far

 

[scianiac]

Is that the safe discharging temperature range or charging range? Generally LFP cells should not be charged below freezing but can be discharged fine at lower temperatures. Many BMSs have temperature probes that will limit charging at low temperatures, the issue is of course be does your trunk get warm enough in normal operation to start charging the battery, something I also considered but I figured the engine bay would get warm enough, especially given my generous winter grill block and I have an attached garage that generally is above freezing anyway.

 

[Hillhater]

I am amazed that you are content to rely on the BMS to regulate the charge of that lithium pack. !
Any other application a charger with CC/CV specific profile would be deemed essential.
But,..your car, your battery, your risk

 

[hmh]

Not really shure If this also for Charge, i wrote an e-mail to a Shop who sells These Kind of Cells to bei Sure. Otherwise i have to add some Kind of Temperaturen Monitoring and Heat element.

The Last Post regarding the Charge of the Battery let me overthink the BMS version at all! I've read a Lot in Forums and YouTube comments try to Figuren Out whats the efficient way to get a save Charge/ no damage to the alternator:

Some people just Install the Battery without BMS, Just with a bleed circuit which Switch top load Resistors at a voltage of 3,58V each cell and are fine since years! The internal Resistor of my planed Battery should be around 1,4 mohm, so in range to the original agm Battery. Isnt the way Car start bms + passive load modules @3,58V also save Like a dcdc charger? The Last think i want top acchieve with my lfp Battery is a damage to the alternator, so i am very thankful for you comments!

 

[hmh]

Perhaps another Option:

A LTC3780 DC Buck Boost Converter in series with the Alternator and the BMS in Series should solve the Problem with the possible high Charge Current!? With this Module the Charge Current would be Limited to 8A ..

 

[dominik h]

Why should the battery damage the alternator?
You have 4m wires to the battery, this will limit the charging current to.
If you install a low residtance AGM battery, no one cares about the alternator.

 

[hmh]

Not the Battery itself, but the Resistance going to Zero when reaching their full load ajd overheating the Alternator because of the high amount of Charge current?! Or is IT because lifepo takes Generally more Charge Current and can burn down the windings?

 

[dominik h]

In a modern car the alternator delievers its rated current and not more, or what happens when you turn on all the fancy things in a good equipped car.
Front and rear window heating, ventilation on full speed, electric heating system, this all together easily exceeds the rated current from an alternator. Alternators must be CC/CV power supplies.

 

[hmh]

Mhhh OK, this modern alternator should be also in my 2005 Audi... So you don't See any need for an DC DC charger or Step down Module that Limited the Maximum loading Current? I think at least there should be an overvoltage control (that would be included in the BMS)

Edit: See this Video https://www.youtube.com/watch?v=jgoIocPgOug where my concerns come from... But Like they Said one Help could bei to Install a Current Limiter or load Module (?)

Regards

 

[dominik h]

They charge a 300Ah lithium battery 50% SOC with short wire lenght. They say nothing about the time it took to burn the alternator.

How long does your alternator need to run until your 40Ah battery is full? How much voltage drop do you have on the way to your battery at 100A charge current?
Do you leave your car with an empty battery running at idle for 15minutes or more?

Under normal conditions, ( battery at SOC 50%) it takes only a few minutes until your 40Ah battery reaches 13,8V and you will see the current decreases rapidly.
If you fear of burning your alternator then just measure what happens in your car.

 

[eee291]

In a modern car the alternator delievers its rated current and not more, or what happens when you turn on all the fancy things in a good equipped car.
Front and rear window heating, ventilation on full speed, electric heating system, this all together easily exceeds the rated current from an alternator. Alternators must be CC/CV power supplies.

I measured my current draw out of curiosity once and i remember that will all devices on it didn't draw more than 70A. I also managed to get an alternator to release some smoke by starting charging a 3S Li-ion battery in under a minute at idle.

You can probably get away with it if you only charge those few Ah that are used for starting, but you only need to leave the lights on once to ruin your day.

 

[hmh]

They charge a 300Ah lithium battery 50% SOC with short wire lenght. They say nothing about the time it took to burn the alternator.

How long does your alternator need to run until your 40Ah battery is full? How much voltage drop do you have on the way to your battery at 100A charge current?
Do you leave your car with an empty battery running at idle for 15minutes or more?

Under normal conditions, ( battery at SOC 50%) it takes only a few minutes until your 40Ah battery reaches 13,8V and you will see the current decreases rapidly.
If you fear of burning your alternator then just measure what happens in your car.

Good comments! I will measure next week when i get the new (preliminary) agm Battery

 

[hmh]

In a modern car the alternator delievers its rated current and not more, or what happens when you turn on all the fancy things in a good equipped car.
Front and rear window heating, ventilation on full speed, electric heating system, this all together easily exceeds the rated current from an alternator. Alternators must be CC/CV power supplies.

I measured my current draw out of curiosity once and i remember that will all devices on it didn't draw more than 70A. I also managed to get an alternator to release some smoke by starting charging a 3S Li-ion battery in under a minute at idle.

You can probably get away with it if you only charge those few Ah that are used for starting, but you only need to leave the lights on once to ruin your day.

How many Amps were requested from the Lipos?

Couldnt this be prevented with the Bulk Module posted a few topics before? Top load the lifepo Battery with around 7 A th while time should be enough i guess

 

[ZeroEm]

What about charging the battery to fast. This is an interesting thread. Wanting to replace my SLA in my Nissan Leaf with a Lifepo4. have waited to figure out the down side of this.

 

[amberwolf]

Not the Battery itself, but the Resistance going to Zero when reaching their full load ajd overheating the Alternator because of the high amount of Charge current?!

Well, resistance is never zero. If you mean "full charge" then effective resistance goes up at that point, because charge current would drop as battery voltage rises vs charge source voltage, simply because the voltage difference is smaller.

Charge current would be highest at the lowest state of charge, because the voltage difference between the charge source and the battery would be greatest.