12V battery pack

[Colouny]

hello all
I am trying to make myself a 12v battery pack for dual purpose.
1. automotive shop battery ( booster )
2. drift trike with car starter motor ( purely for fun )

1. Shop battery will be used as backup power source while programming ECU's, or mainly starting a cars or motorcycles with partially drained batteries.
2. Drift Trike - just for fun. it is almost done just need the battery. Is it made out of a leftover parts from cars :)

Anyway my thoughts on battery pack and I need some one to correct me if I am wrong !
I am planning to make a pack of 24 cells. 3 in series and total of 6 cells and BMS with balance for one section of 6 cells, so total will be 4 sections and each with separate BMS. If I will need more juice from the pack I will add more sections to the pack.

One thing I don't understand about the BMS modules and I would like someone to explain me these things, as I am not willing to spend a lot of money on the project I want to use the power supply (charger) the one I have at the shop. The charger is C-TEK rated at 25A. While charging a battery it gives constant 13.5V. So my general questions regarding BMS:

1. Can I use the charger I have at the shop as long as I am using BMS?
2. Does BMS control the CHARGE? I mean does it stop charging when the section is charged fully, Or I need to monitor this by my self?
3. As I understand MS also controls the max amp drained from the batteries. VTC6 is rated around 10A per cell, so from one section I should have around 50-60 amp. I am thinking that BMS rated at 50A constant and 150A peak should do the job, or I should go with 30A BMS? My considerations are mostly when starting a car it will draw lots of amps but for like 3-10 seconds and I am not willing to "overdain" the batteries.
The drift trike starter while drifting take around 30-50amp while drifting, so the battery pack I mentioned should handle this easily.

I am thinking of Sony VTC6 cells, at least I can source the locally for a reasonable price.

Thank you in advance for your thoughts and time. And excuse me if all what I wrote is a complete nonsense... I will learn everything eventually. :)

[max_volt]

If you search youtube I think they advise 4s for more compliant output voltages.

[AZguy]

For non-electric vehicle applications lithium iron phosphate is the chemistry widely used.

The voltages (~3.2V nominal, 3.65V max) is quite different than that of the typical batteries used in electric vehicles (~3.7V nominal, 4.2V max). With the higher voltage batteries a 3s configuration gives only 12.8V max which is not only incompatible with 12V vehicle electrical which charge at a nominal 14.4V but quite dangerous. In a 4s configuration the maximum voltage now is 16.8V which means they'll never get anywhere near fully charged and balancing is darn difficult.

With the lithium iron phosphate a 4s arrangement gives you ~12.8V nominal and 14.6V max which is compatible with non-electric vehicles. They still need BMS and over-voltage protection but the electrolyte in the lithium iron phosphate is non-flammable and so even in a catastrophic failure they don't catch on fire the way the others do - they can still release a tremendous of heat though.

Due to the lower voltage and less efficient chemistry these hold significantly less charge than the lithium manganese cobalt most here are using.

These are sold as complete batteries for various vehicle applications with complete BMS for 12 or 24V vehicle applications - they are expensive however...

[Colouny]

This battery pack is not going to be used i a car permanetly!!!!!!!!!! Is a simple backup battery thats lightweight enough to carry around. Currently i am using AGM 110AH and its like 25KG, its not an esay thing to carry around.

Lifepo4 are way too expensive, not going that route in any case.
4s config just has too much volts for my drift trike, this route is not going to happen.

As I said this all going to be a portable shop battery and battery for my drift trike and it is powered by a car starter.

According to my calculations this set up should cost me around 120 to 140€, and this is acceptable for me.

Anyway i still have the same questions that i mentionened the first post.

Thanks for replies.

[AZguy]

...
1. Can I use the charger I have at the shop as long as I am using BMS?

No

2. Does BMS control the CHARGE? I mean does it stop charging when the section is charged fully, Or I need to monitor this by my self?

No - the charger controls the charge, hence the reason the shop charger is incompatible

3. As I understand MS also controls the max amp drained from the batteries. VTC6 is rated around 10A per cell, so from one section I should have around 50-60 amp. I am thinking that BMS rated at 50A constant and 150A peak should do the job, or I should go with 30A BMS? My considerations are mostly when starting a car it will draw lots of amps but for like 3-10 seconds and I am not willing to "overdain" the batteries.

Don't underrate - if you need 150A, particularly for something longer than the milliseconds range - then go with 150+A components everywhere - this is not insignificant!

[Colouny]

AZguy, thanks, that really helped alot.

[AZguy]

FYI - when you had brought up the shop charger and the starting application that is why the lithium iron discussion seemed pertinent