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EVTV questions whether regenerative braking is worth the bother

We've discussed regenerative braking quite a bit here on AutoblogGreen – the process of capturing energy during deceleration and storing it for future use – and pretty much every electric vehicle with an AC motor utilizes it. And why not? On paper, putting energy back into your batteries should extend your driving range. But what if it didn't? Would it be worth the expense or hassle?

The questions arose after the EVTV team of Jack Rickard and Brian Noto set out to establish exactly how effective the regen was on their most recently constructed electric '57 Porsche 356A Speedster replica. This build features a 3-phase AC-50 motor from Hi Performance Electric Vehicle Systems, 180AH Sky Energy LiFePo4 batteries and a Curtis 1238-7501 controller with adjustable regenerative braking capabilities. They took their sweet piece of retro-automotive art on three separate drives over the same 75-kilometer (45.6-mile) stretch of road using different regeneration settings on each trip and monitored the energy flowing out of and back into the battery pack. The first used strong throttle and braking regen, the second trip only had the strong regen when braking while the final drive used no regen whatsoever. The results? Come with us past the break to see some interesting numbers.

[Source: EVTV]

1. Full braking regen with full throttle regen

Actual distance driven: 75.2 km
Actual net AH consumed: 77.7 AH
AH per km: 1.033245

2. Braking regen only

Actual distance driven: 76.6 km
Actual net AH consumed: 78.2 AH
AH/km: 1.02088

3. No regen braking at all
Actual distance driven: 76.6km
Actual net AH consumed: 78 AH
AH/km: 1.018277

There was no difference between the various settings. Or at least not very much. In fact, it seems the less regen used, the better the outcome.

Somewhat surprised by the results – they had expected at least some amount of efficiency gains – EVTV decided to try the same drive in their somewhat heavier electrified 2009 Mini Clubman. This time only two outings were made but the results were similar. With light regen on the throttle and heavy regen on the brake, the Mini used 47.1 amp hours from the battery pack and with the regen turned off, it used 43.8 AH. That's 3.3 AH, or seven percent, less than the first drive. No regen wins again.

So, how did they get this seemingly counter-intuitive result? It's not extremely clear (to this writer, at least) but it could have something to do with how driving style is affected by the different set ups. Without regen, more coasting is done and that could be more efficient than collecting energy on the downhill to reuse when climbing the next.

What are the implications? A handful of tests doesn't necessarily change the order of the universe but it ought to instigate others to examine for themselves the real world benefits (or lack thereof) of regen. It may mean that some EV builders or converters might want to consider using less expensive DC motors.

To more thoroughly examine the issue and look at the testing, check out the two EVTV blog entries and corresponding videos (1 & 2) that cover it. If you think you have insight into their results or what it could mean for the industry, let us know in the comments below.

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