# Regen Braking - How Effective?



## Own Little World (Sep 5, 2016)

Dear Forum Members,

Before performing my conversion, I have been going through the motions of making sure that the running gear of the project car is all up to snuff.

Now then, many of the people who perform restorations of my particular project car recommend upgrading the brakes from their original 60s/70s form to something more modern and capable. (The car is a 70s sports car with all-round disks).

A lot of money seems to be spent on top notch 4 pot callipers and fully vented disks etc.

My question is: if I would be using the disk brakes in conjunction with regenerative braking, is there any need to go to all that expense?

Would it be sufficient just to use some nice slotted/dimpled disks and some slightly larger Green Stuff pads (for example)? How much assistance will the regenerative braking offer?

Many thanks for your comments.

Alec


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## Duncan (Dec 8, 2008)

Hi Alex
I remember my pal had one of those - it's brakes were OK for normal use but got very hot on a track day! 

Re-gen will only work on the driven end - rear?
Which means the front will be friction
As most of the braking is done by the front end you should still think about upgrading your front brakes

I would look at getting some vented discs - it is the cooling that is important
But there is no advantage in fancy four pot calipers over sliding two pot calipers

Your problem nowadays is going to be getting brakes that are small enough to fit inside your wheels

I have had a number of Subaru's - and my "Device" uses Subaru Discs
http://www.diyelectriccar.com/forum...-dubious-device-44370p9.html?highlight=duncan

I first built it with bits from my 93 Legacy - 14 inch wheels
Then I got some less worn bits from a 97 Legacy - the wheels wouldn't fit had to go to 15 inch
Then I got a 2000 model with 16 inch wheels and bigger discs
I now have a 2004 model with discs that won't fit inside the 16 inch wheels!!!!

I suspect you will have 13 inch wheels - so even the smallest Subaru brakes would be too large


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## Own Little World (Sep 5, 2016)

Thanks for the insights Duncan - that all makes sense.

I think there are quite a few options available for smaller wheels so I will have a poke around.


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## Duncan (Dec 8, 2008)

Hi Alex
Do you intend using it on the track?

If you are just using it on the road
It is a Lotus! it's brakes will be good enough for most people

Back in the day we used to use high temperature pads when being a hooligan

The trouble was that the real "racing" ones didn't work very well when cold 
But you could get intermediates
IMHO modern disc brakes are massively oversized - just for looks - like modern tyres


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## Own Little World (Sep 5, 2016)

Hi again Duncan. Thanks once again for getting back to me.

Yes it is rear wheel drive. I like to think I would get it "track-capable" but in all honesty I don't know if I would ever get round to track days. My life is just too busy these days.

So really, I need to aim for "motorway-safe" instead. I don't think racing spec pads are what I will need to aim for.

I hadn't really thought about the regen braking being back end only. In any case, I suppose it would be best to have the same disk type all round, rather than better gear at the front only?


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## Sunking (Aug 10, 2009)

I am far far away from an expert on Regen Braking. Having said that I am an Electrical Engineer and have built a couple of Racing Golf Carts, and the current golf cart does have Regen.

There is one golf cart manufacture, EZ-GO, makes two models called RXV and Two-Five. The RXV is the Golf Cart version, and the Two-Five is the street legal RXV version. The RXV does not use any mechanical brakes, just Regen and it works very well. Anyway my point is I have the Two-Five as my racer because it already had the proper Differential Ratio gearing I needed. It has both Regen and 4-wheel wet disk brakes. However rarely do the mechanical brakes ever engage. Only if I stand on the brakes. Only thing I do not like is, the Regen only is applied to the rear wheels. The problem is at full Regen Braking is so aggressive the back tires can lock up and skip on wet pavement, sand, dirt, or if there is sand/gravel on the pavement. Worse of all if you are in a hard turn, you are going to reverse ends and be driving with your rear view mirror. 

What I do know about any Regen Braking is where the heck do you dump the power. Unless you have a substantially over sized battery, that is not near full charge, cannot absorb that much energy that fast. What EZGO did to get around the problem is do what Train Locomotives do, dump it into a Power Resistor Bank and burn the power off as heat. 

The best work around that has been done is to use Ultra/Super Capacitors to absorb the Regen Brake Power, then release it during the next acceleration cycle.


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## Own Little World (Sep 5, 2016)

Yes, I think toning down the regen braking and relying on mechanical may be the most balanced and safest way to do it in a 2wd car. I like the idea of super caps. Sort of like an EV turbocharger.


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## Duncan (Dec 8, 2008)

Hi Alex
Supercaps are a waste of time - much heavier and more expensive than batteries

As far as "the same discs all round" - NO they have different jobs to do - and should be sized accordingly

Re-gen will be on the rear wheels only
Have you driven the Elan much?
Three of my pals had Elan+2's - each of them spun them at least once
I think it was under power coming out of corners - not under braking going into the corner

The Elan is a light grippy sports car - when it lets go it lets go FAST
You go from - great fun - to - why am I going backwards? - in a heartbeat

So be very careful with the re-gen - and with "improving" the brakes


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## rmay635703 (Oct 23, 2008)

The regen issues discussed above pertain mainly to lead acid.

My lithium powered car dumps up to 50kw during regen.

Just food for thought


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## Hugues (Jul 13, 2014)

On my motorbike, engine breaking is just beautiful. Tuned properly, I barely have to touch the breaks. And it's progressive, slightly roll back the throttle, it brakes just a little, roll back more, brakes more, until neutral where I have maximum engine break. Never locks the wheel. A pleasure to drive.

Hpevs AC-23 with Curtis 1238-7601 280 kgs bike without driver.

But I don't think it's the same benefit for racing conditions or a car.


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## Duncan (Dec 8, 2008)

Hi Hugues

On the track if you just use the rear brakes the whole grid will pile past you on the first corner!


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## Caps18 (Jun 8, 2008)

Does it really matter if you just charged your batteries to 100% and are now driving down the road and have to use regen? Wouldn't the battery be depleted more than what power the regen will put back into them?


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## AntronX (Feb 23, 2009)

I get 8.75% of my Leaf's average DC energy use recovered by regen.


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## Own Little World (Sep 5, 2016)

Thanks for all the responses folks.

I have not yet ever driven an Elan, even under normal circumstances, I have to admit - my project is a barnfind.


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## prensel (Feb 21, 2010)

Enough has been said already but i'd like to add one thing though:

Just clean/overhaul the original brakes and get that Lotus on the road a.s.a.p. You can always think about mods and improvements later on but i guess your biggest challenge at this point is: how-to-get-it-on-the-road-as-an-EV 

Just my 2cts


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