# Alternator with boost converter for regenerative braking



## major (Apr 4, 2008)

Regenerative braking is great, when you get it for free, or close to it, as in an AC drive. But when regen comes at an extra cost, in money and mass, you'll undoubtedly be better off putting that same money and mass into better or more battery, unless there is some unique mission requirement for the EV. 

And boost converters of the type you'd need cost a lot and/or are massive.


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## Moltenmetal (Mar 20, 2014)

The part that got me was the "rather, for extending their range a bit". Yes, if you use this for regenerative braking, it will allow you to put a bit of energy back into the batteries. It will also represent a frictional loss due to the belt, bearings etc., plus the losses in the alternator and the boost circuit, as well as added weight. 

The weight being added is less than 10% of the car's total weight so that would push you in the direction of a little more than break even assuming decent efficiency from the alternator and electrics, given that regen braking tends to give a 10%-ish range boost on an AC car (i.e. without the extra drag or parasitic weight). But the frictional losses are there all the time, whether you're braking or not. It's likely not worth the bother.

Of course you're not suggesting that it'd be of any benefit if you used it while driving rather than just while braking- that's obviously a way to decrease your range, not increase it.


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## Matej (Dec 4, 2015)

So the consensus is that it is not worth it on a DC setup, correct?

I only became interested after I read about the old experimental BMW and Mercedes Electro cars that used DC motors with regenerative braking. Though of course even they eventually switched to experimenting with AC setups in the 80s.

The Zebra batteries are still neat though.


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## evmetro (Apr 9, 2012)

Even if you got a fancy car audio alternator, the most you will get out of it is about 2500 watts. The 2500 watts is only at a certain rpm, and you will get less and less as the rpms drop. I typically see about 50,000 watts of regen in my little geo metro. It does not seem like it would be worth it for such a trivial amount of regen, but if you did do it, there is a plausible path for a small gain. In order to get that small gain, you would have to ensure that it is only used at the exact right times such as the need to slow down or stop, and that there is no regen at any other time.


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## ken will (Dec 19, 2009)

It sounds like it is not good idea for the average person in an average environment.

However:

If you hate replacing brake pads, it might be an option.

If you have a lot of Stop signs at the bottom of hills, it might be an option.

If you would like to experiment and learn about Regen, it might be an option.


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