View Single Post
Old 02-28-2015, 02:17 PM   #15 (permalink)
EVmetro
EcoModding Apprentice
 
Join Date: Feb 2015
Location: Sacramento
Posts: 202
Thanks: 3
Thanked 225 Times in 91 Posts
So here is where things get even better in the world of efficiency. I have done research, reading, road testing, and lots of learning about the use of regenerative braking. What I have learned, is that the principle of regen really does work, but the only way that it can actually improve efficiency is if it is utilized correctly. Unfortunately, manufactured new EVs, as well as all of the conversions that I have seen, do not utilize it correctly.

The most common use of regen out there is off throttle regen, where you get some regen when you let off the accelerator. It does in fact harvest energy that would have been wasted as heat coming off of the brakes, but there is a big catch to the deal. When you use regen, you also destroy the kinetic energy of your car traveling at a steady speed. It takes more energy to speed up than it takes to maintain a speed, so the most efficient way to travel is at a steady speed. Off throttle regen causes an unsteady speed, whether it be very tiny fluctuations in speed as you would see in an experienced eco driver, or big fluctuations of speed that you would see if the driver is bull****ting with a passenger or talking on his cell phone.

If you see a red light ahead and want to back off to time things so that it is green when you get there, it is often the best to "freewheel" in neutral or with the clutch pushed in, so that you never have to use the accelerator or brake, so that the car keeps as much kinetic energy as possible. There are also times when a little braking or acceleration are needed to maintain the steadiest speed, and this is where my circuits come into play. I wanted the freewheeling capabilities of a DC motor, but I also wanted the benefits of regen that come with going AC. Off throttle regen typically is set for about 10% of total capability, so if you have off throttle regen, you are missing out on the other 90% of what is available.

What I have done, is add an "on demand" variable regen button to my conversion that allows me to utilize all of the available regen capability, but only when I want it. I set my controller up to give me no off throttle, so it feels like I am driving a DC system instead of AC.

Here is my on demand variable regen button project:

I picked up an automatic shifter over at pick n pull out of an old Buick. I was looking for something that would look as close as possible to a manual shifter, but I was after the button as well. The Buick shifter was severed in half, and same with the Metro 5 speed manual shifter. They were grafted together, and this potentiometer added.



When the button is not pushed, there is no resistance.



As I push the button down, I get variable (and very smooth) resistance all the way up to 5k. In this pick, I have the button all the way depressed for maximum regen.



When I went to put the center console in, my big cage around the potentiometer (so the shift boot does not interfere) was right where the shifter passes through the center console, so the center console was interfering with my shift pattern. I had to modify it a little to get the shifter hole below the potentiometer.

Here Is a factory unmodified center console just like the one I modified. This is in my beater gasoline powered Metro, just a reference photo.



I cut a slice out of my console (seen in the foreground) and lowered the surface. (That's a few hours of reshaping) Here it is after I modified it.



Now the opening is just below the potentiometer on my shifter. I have the boot pulled back so you can see the clearance while it is shifted into reverse.



Here it is all installed with my custom shift boot installed too. It should resemble a regular 5 speed shifter.

  Reply With Quote
The Following 3 Users Say Thank You to EVmetro For This Useful Post:
bespurcell (01-12-2016), mikeyjd (03-19-2015), NeilBlanchard (03-27-2015)