Calculating 'regen' with an alternator

[Ecky]

Originally Posted by redpoint5

The alternator energy is only free when you are in DFCO, with the engine being turned by momentum and no fuel being delivered to the engine. The actual brakes have nothing to do with it.

An ideal system would monitor for open loop and then enable the alternator automatically, or any time battery voltage goes too low.

Yet surely there are times when you can't coast to a complete stop, even for someone heavily using DFCO, due to traffic reasons. My car will coast for a very long time before fully stopping (hell even small gusts of wind start it rolling on level ground) but the last minute or two of coasting before a complete stop I'd be going quite slow. That's not realistic unless you're the only person on the road. Plus, I'd have to time my DFCO very well to never use the brakes.

Regen like this makes needing to use the brakes more forgiving.

@Daox, a fun calculation to do might be to convert those amp hours into gallons of gasoline, and compare it a few ways to idle fuel consumption, or how much speed you can get back from your car using that same amount of energy.

Originally Posted by oil pan 4

Saving the battery is more important than saving a little fuel.
Since the cost of a battery is that of at least several fuel fillups.

Unfortunately, that's the conclusion many over on Insight Central came to about hybrid batteries. The battery makes the car a lot more drivable, and leaning on the $2,000 battery with a ~10 year lifespan very heavily to save a bit of gas and prolong the life of a $500 engine which easily lasts 300,000 miles doesn't actually make much economic sense. Better to use it as a driving aid than a fuel economy one, if the latter subtracts from its effective life. $2,000 buys about 50,000 miles worth of gas.

[Daox]

Someone on MirageForum asked a great question and I thought I'd share it here.

Originally Posted by FloridaG4

During your work week will you be using more battery supply vs regeneration by braking where you would have to recharge the battery every few days or a on a weekly basis?

That is a great question! Not to mention another great way to look at this mod. We will have to run the numbers to check it out for sure.

Math time! Again we are going to estimate the car uses an average of 20 amps while in use since I haven't tested that quite yet. My commute is about 25 minutes long.

20 amps * 25 minutes = 500 amp minutes

500 amp minutes / 60 = 8.3 amp hours

The car uses 8.3 amp hours, but we get 2.8 amp hours regenerated. This washes out to (8.3 - 2.8 = ) 5.5 amp hours used. The trip home would also use about 5.5 amp hours for a daily total of 11 amp hours.

Now, the battery holds about 80 amp hours, but we never want to use more than half of that. That gives us 40 amp hours to use. 40 / 11 = 3.6 days worth of commuting.

So, I can theoretically go 3 days before having to charge. Not too shabby. However, if I use more power than normal, that cuts it down. Eg. using headlights vs just running lights, wipers, more HVAC power, rear defroster, or the PTC heater would probably also suck a lot of power as well. Those all reduce that range.

In the end, I find it much easier to plug in every night. That gives me a full charge so I don't even have to worry about it at all unless I go on a long trip. If that happens, I just turn the alternator back on and get a little worse fuel economy. I also have a block heater that I run in the mornings, especially in winter. This necessitates plugging in every night, so I kind of do this already. Might as well top off the battery too.

[lico]

Hi, have you ever think to make an alternator swap with one of the continental, mild hybrid belt drived?
I find this looking for else
https://www.continental-automotive.c...rter-generator

[teoman]

Looks good. Do you have any pricing info.

[lico]

Not really, i can't find any new. Used it's very variable, from 400 to 800 euro.
this it's the part number 4N0903028D.
mounted on A8 and Q7 from 2017, 3000 tdi hybrid.
I find a pictures with the label, will put in the post.
I find some other element made from Valeo, fitted on PSA group ( Peugeot Citroen and DS) and volkswagen group, its not 48v capable but it's used as starter motor and output it's 210 amp.