Are you pro- or anti-start-stop?

[Isaac Zachary]

Originally Posted by 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

You'd also be losing quite a bit of energy to heat and then even more energy to cooling. Supercapacitors are pretty expensive, but I'm still tempted to try to make a more efficient charging system for some of the cars in the family.

[JSH]

Originally Posted by 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.

Capacitors are good for that usage but the problem is that only allows for start / stop function. It doesn't have enough energy storage to provide a boost for acceleration or run HVAC while the vehicle is stopped. Customers hate that type of system and often turn them off. (Nothing like sitting at a light on a nice hot and muggy Alabama day and having the HVAC blow hot air at you.)


(The EPA requires a stop / start system provide 1 minute of heat on a 30F day. There is no requirement to provide A/C with engine off.)

[redpoint5]

Originally Posted by JSH

Capacitors are good for that usage but the problem is that only allows for start / stop function. It doesn't have enough energy storage to provide a boost for acceleration or run HVAC while the vehicle is stopped. Customers hate that type of system and often turn them off. (Nothing like sitting at a light on a nice hot and muggy Alabama day and having the HVAC blow hot air at you.)


(The EPA requires a stop / start system provide 1 minute of heat on a 30F day. There is no requirement to provide A/C with engine off.)

If the industry standardized on 48v, it would probably make a mild hybrid stop/start system fairly trivial. Keeping the Ah the same and boosting the voltage would provide 4x the energy available; allowing acceleration assistance and running accessories while the engine is off.

Vehicle wiring gauge could be downsized too saving cost. Finally, since it would still be considered "low voltage", it would still be safe for the typical person to be around.

[Isaac Zachary]

Originally Posted by JSH

Capacitors are good for that usage but the problem is that only allows for start / stop function. It doesn't have enough energy storage to provide a boost for acceleration or run HVAC while the vehicle is stopped. Customers hate that type of system and often turn them off. (Nothing like sitting at a light on a nice hot and muggy Alabama day and having the HVAC blow hot air at you.)


(The EPA requires a stop / start system provide 1 minute of heat on a 30F day. There is no requirement to provide A/C with engine off.)

Very true. Pros and cons.

Running the HVAC with the engine off means you'd need an auxiliary electric motor. Adding boost acceleration means you'd need another auxiliary electric motor. Sounds like you're pretty much at a full hybrid by that point. All you'd need is to have two motor/generators for the drive system, one for starting and charging and the other for acceleration and deceleration, and then you'd have a full hybrid capable of turning off the engine even during deceleration or low power acceleration.

A start-stop system that only has a high recharge rate via the "alternator" into a capacitor around 50V during deceleration would be simpler and cheaper. But yes, it wouldn't give you those advantages you mentioned.

It also can have an effect on the second hand market. A used 15 year old Prius, for an example, is the kind of car only dedicated afficionados can appreciate. For anyone else, finding out that they now need a $2,000 OEM battery once it goes bad they usually instead get a $600 one that lasts them a year or two if that, or go through the whack-a-mole stage. The complexity, cost and lack of longevity leads to frustration.

The same may be true of lithium ion higher voltage batteries for start stop systems or full hybrids. At some point they're going to die. The smaller they are the higher their charge and discharge rates and the lower their longevity may be. Not that super capacitors can't die either. But on the surface it seems they should outlast their lithium cousins in such a case. I guess we have to wait to see what small lithium ion packs will do. I would avoid Nissans at all cost on this one with their history of lithium ion in cars.

What I want to know is how to convert my 12V battery to LiFePO4 and get it to work without breaking the bank and without killing the battery. Seriously I do. But the complexity of thermal and battery management is holding me back.

[Piwoslaw]

You can have start-stop with HVAC fan on a single 12V battery.

My Peugeot 308 with e-HDi start-stop engine has only 1 battery. It is a normal 12V, 70Ah, 700A battery, dimensions same as for regular car battery. And the ventilation fan still works when the engine turns off. It will turn the engine back on after a while (30-60sec), either to circulate the coolant (heating) or run the compressor (A/C).

The only requirement is that the battery needs to be AGM technology for the Start-Stop feature to work consistantly. When I bought the car it had a lead acid battery, and the start-stop activated only 1-2 times, at the end of a very long road trip, otherwise the engine would stay on. When I invested in an AGM (roughly twice the price of comparable lead acid), suddenly the feature started working. Though now, when the battery is 3 years old, it hardly works during winter, even though I trickle charge once or twice per week.

So, it's doable, but with limitations. I'm sure it puts a large strain on the battery, tho, shortening it's useable life.

I have kept the old battery as a spare, which I've contemplated connecting parallel, but not sure about the consequences of connecting lead acid to AGM?

[MetroMPG]

Even the lowly Mirage in Europe & Japan has auto stop/start (single 12v battery). Not sure if it activates with HVAC running.

[Mifunego]

The start/stop in my wife's '21 Palisade is smooth as can be. I don't know how much it contributes to efficiency, but it's averaging ~22mpg in mom-taxi carpool short hops around town. Not bad for a n/a 3.8L V6 in a 4400 lb AWD 7 seater.

[Toretto]

Start/stop tech is a sure way to shorten turbo life. I always disable the function on turbo engines. There is a minimal amount of oil starvation.
As well as preventing the oil from warming up properly. The function is enabled way too soon temperature -wise. Which also negatively impacts emissions....

[savefuel]

As a longtime hypermiler I stop my ICE whenever it makes sense to increase mpg (prior to and during stops and EOC).
Unfortunately Start/Stop systems work only if certain conditions determined by the manufacturer are fulfilled (eg. Temp, battery status, engine temperature etc.). I'd like a system where the driver cuts the engine but the restart is automatic (eg. when hitting the accelerator). As no manufacturer offers this I prefer hybrids or do it manually on my ICE.
Never had any issue on my turbo (diesel). It's important to 'manage' your electrical consumers in order to keep the 'juice' in your (only) battery when you perform wise manual stop/start.. I use the battery with the highest Ah for my vehicle.

[MetroMPG]

Originally Posted by savefuel

I'd like a system where the driver cuts the engine but the restart is automatic (eg. when hitting the accelerator). As no manufacturer offers this I prefer hybrids or do it manually on my ICE.

It's been a long time since I owned my 2000 Honda Insight hybrid or my 2004 Prius, but I added a manual kill switch to both.

With the Insight, the automatic stop/start system remained functional... but I almost ALWAYS stopped the engine well before the computer would have, and at higher road speeds.



Man, I miss that car! Amazingly efficient.

The Prius kill switch turned out to be more useful than I was expecting:



It was essentially just an "EV mode" switch (which was present from the factory in the Prius in other countries outside of Canada/US).

The factory programming for the Prius stop/start was far better than Insight's at stopping the engine when not needed. So I thought at first the manual over-ride EV switch wouldn't be much of an efficiency advantage, but it turned out I used it a lot. Mostly because the Prius wouldn't shut the engine off unless the car had completed at least one full stop (among other conditions) after start-up.



Man, I miss that car.