Tuesday, Feb 06, 2024 at 18:24
Hmm, your alternator is an expensive battery charger, $1500 for my Toyota unit so you sort of shot yourself in the foot there. Lead acid batteries aren't really suited for an automotive environment either and weren't designed for that purpose, they were the only option they had when cars came along so that's what they used and they originally died a quick death. They gradually improved the charging systems and batteries to increase battery life to a point that was considered exceptable and they haven't really changed much since then, cost versus benefit.
Today they could use smart alternators to better look after the battery but they don't again it just isn't worth it as the battery will probably die from vibration, heat and abuse rather than incorrect charging. As you pointed out the only reason we have smart alternators now is for fuel savings and anti pollution reasons. They could also use Lithium batteries but again cost versus benefit, Lithiums are widely used in racing cars for example for the weight saving and high energy density and therefore justify the cost.
The hybrid vehicle I'm buying has a Lithium battery for the hybrid unit, again weight saving and high energy density. It has a lead acid for the 12V system, the battery is charged by the Hybrid system DCDC and the battery is in the back of the car so heat not an issue, they could have easily used a Lithium instead and no doubt it would have a much longer life than the lead acid they have used but they didn't and that would have purely been for costs reasons.
Looking from an aux battery perspsective again it is cost versus benefit, how many with daul battery systems directly charge their AGM's or other directly off the alternator and don't use a DCDC charger? Most will use a DCDC as they investment cost in AGM's is high and they want to maximise battery life so again cost versus benefit. The DCDC they choose would have been done on cost versus benefit, some will go for expensive units with many charging options, others will opt for more basic units to save costs and wear the possible reduced battery life.
My Lithium is charged directly off the alternator without any issues. I could have put a DCDC in to charge it but see no benefit in doing so. The alternators output voltage is within the batteries design specs and the car never runs long enough for no float stage to be an issue. The Lithium has lasted longer than any lead acid battery I have had installed in the same position and longer than any cranker I have had in the car too. Heat and vibration is likely to kill it before incorrect charging will same for any battery installed in a car.
A BMS in a Lithium is there as an extra layer of protection to protect an expensive investment no mattery how it is charged. Alternator voltage regulators can and do go faulty, same for AC and DC chargers. If you build the battery yourself then can either include a BMS or not it is up to you. With a lead acid the cost versus benefit is just not there to warrant one.
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