Are you pro- or anti-start-stop?

[Isaac Zachary]

Originally Posted by JSH

I'm pro stop - start tech done right. That is with a 48V hybrid or conventional hybrid. With those types of systems the engine starts seamlessly when your foot comes off the brake and moves to the accelerator. I've also driven vehicles with 12V stop / start systems. They work but feel clunky and in my opinion gave stop / start a bad reputation. Plenty of people with 12V systems just turn them off.

Doesn't Mazda put 48V super capacitors in it's cars nowadays that charge up quickly from the alternator when you slow down (which it converts from 48V down to 12V)? It seems like a system like that would work great for a start-stop system in a non-hybrid, plus the fact that the alternator doesn't start charging while you're driving until it has too.

[JSH]

Originally Posted by Isaac Zachary

Doesn't Mazda put 48V super capacitors in it's cars nowadays that charge up quickly from the alternator when you slow down (which it converts from 48V down to 12V)? It seems like a system like that would work great for a start-stop system in a non-hybrid, plus the fact that the alternator doesn't start charging while you're driving until it has too.

I've not aware of any company using super capacitors in a production car. 48V systems have a motor/generator that replaces the alternator. That charges a 48V Li-Ion battery when the vehicle is slowing through regenerative braking and pulls power from the battery under acceleration. The motor can also be used as a regular generator on long flat sections without regen.

The 12V battery is charged from the 48V battery with a DC/DC converter.

[Isaac Zachary]

Originally Posted by JSH

I've not aware of any company using super capacitors in a production car. 48V systems have a motor/generator that replaces the alternator. That charges a 48V Li-Ion battery when the vehicle is slowing through regenerative braking and pulls power from the battery under acceleration. The motor can also be used as a regular generator on long flat sections without regen.

The 12V battery is charged from the 48V battery with a DC/DC converter.

Here it is...
Mazda i-Eloop
It's available on some Mazda cars, or at least was.

So basically the same idea, except ultra capacitors instead of lithium ion.

I almost decided to get a LiFePO4 12V battery for my Avalon seeing how no parts store sells a 12V battery for the Avalon (really) and the OEM battery is over $300. However, the problem with lithium anything is it needs protection from the cold. So I ended up getting another OEM battery this Saturday for $326 at the dealership that's 60 miles away from here. (Ouch!) But ultra capacitors would seem like a suitable alternative for cold places. Either that or a heating system of some kind for lithium. I hate paying $300 for a lead acid battery.

[JSH]

Originally Posted by Isaac Zachary

Here it is...
Mazda i-Eloop
It's available on some Mazda cars, or at least was.

So basically the same idea, except ultra capacitors instead of lithium ion.

I almost decided to get a LiFePO4 12V battery for my Avalon seeing how no parts store sells a 12V battery for the Avalon (really) and the OEM battery is over $300. However, the problem with lithium anything is it needs protection from the cold. So I ended up getting another OEM battery this Saturday for $326 at the dealership that's 60 miles away from here. (Ouch!) But ultra capacitors would seem like a suitable alternative for cold places. Either that or a heating system of some kind for lithium. I hate paying $300 for a lead acid battery.

Interesting - I don't remember seeing that. Odd that they decided to spend more for capacitors than just using Li-Ion batteries. I'd be curious to see the logic on that.

I tried a LiFePO4 battery once for my Piaggio MP3. It had good good voltage when it arrived do I installed it in the bike without charging. It started the bike once, then left me stranded at my destination. The voltage dropped to something like 4 volts. I returned it to Amazon (and I'm sure they sent it to someone else) Being Amazon it is likely that it was someone else's failed return or a counterfeit battery but the experience soured me on LiFePO4 batteries.

[cRiPpLe_rOoStEr]

A good thing about supercapacitors is their chemical stability, yet they're more suited to a quicker charge and discharge cycle instead of accumulating energy for a longer period.

[redpoint5]

Yeah, I heard supercaps were used in Mazda's too. Excellent for not worrying about thermal regulation, and much better wear and efficiency characteristics. Only 2 drawbacks are extremely small energy density (by volume), and linear voltage increase/decrease during charge/discharge.

[Isaac Zachary]

Most people brake and slow down in just a few seconds. No lithium ion battery can charge from, say 25% to 75% in that amount of time. So a lithium ion battery has to be made bigger, which adds to weight and cost, and the extra size doesn't really help with anything other than extending the life of the battery unless you go engine braking down a long hill.

Also batteries tend to charge up as fast as or slower than they can discharge. With a system that quickly charges up and slowly discharges it would be nice to have something like a super capacitor that can charge as fast as need be and still be sized to whatever capacity makes sense for stoping from 80mpg to 0.

[Piotrsko]

Lithium can discharge and recharge at similar rates if you can keep it cool such that the volatile solvents dont change into gas. Not worth the effort however since cooling at this level would be massive

[cRiPpLe_rOoStEr]

Originally Posted by redpoint5

Only 2 drawbacks are extremely small energy density (by volume), and linear voltage increase/decrease during charge/discharge.

As it's not meant to be used in a full-hybrid, the supercapacitors are already quite cost-effective. On a sidenote, now that much is said about graphene and how it would revolutionize the batteries, maybe it would be also interesting to take a look at carbon-based capacitors.

[redpoint5]

Originally Posted by cRiPpLe_rOoStEr

As it's not meant to be used in a full-hybrid, the supercapacitors are already quite cost-effective. On a sidenote, now that much is said about graphene and how it would revolutionize the batteries, maybe it would be also interesting to take a look at carbon-based capacitors.

That's what allows current generation supercapacitors. They're already using it to achieve hundreds or thousands of farads; something that wasn't possible not long ago.

I thought that's why Tesla acquired Maxwell, but apparently not.