DIY Electric Car Forums banner

1 - 20 of 32 Posts

·
Registered
Joined
·
7 Posts
Discussion Starter #1 (Edited)
We’re thinking of converting a Land Rover Defender but am concerned that the regen braking may not be sufficient to replicate the compression braking from the original ICE. If this is to be a serious off road vehicle then this is a fundamental requirement. I’ll retain the original drivetrain.
Are there any other ways to achieve this? What have everyone else done.
Cheers
Ed
 

·
Registered
Joined
·
7,837 Posts
We’re thinking of converting a Land Rover Defender but am concerned that the regen braking may not be sufficient to replicate the compression braking from the original ICE. If this is to be a serious off road vehicle then this is a fundamental requirement. I’ll retain the original drivetrain.
Are there any other ways to achieve this? What have everyone else done.
Cheers
Ed
Hi Ed,

Regenerative braking will be able to out perform engine compression braking. I see no problem with that.

Regards,

major
 

·
Registered
Joined
·
1,025 Posts
... especially if you keep a transmission.

Regen on my xB is set for a maximum of battery 100 amps (this is at 320v) which means about the equivalent of 40hp of braking, though I only see that much when the batteries are warm and at a low SOC, otherwise max voltage limits the braking to about 50A or 20hp.

This is pretty modest by regen standards (especially compared to a lot of the current generation OEM EV's) but still enough that much of the time on freeway off ramps and coming up to traffic lights I can do the single-pedal driving and get down to 10-15mph before I touch the friction brakes. Descending a hill, I can hold 25-30mph on a grade up to 10-12% before I need to start tapping the regular brakes.

This is all with a direct drive with 4.8:1 ratio. If you retain a gearbox you can get much stronger braking if the batteries you choose can absorb the charging current. (any OEM grade EV battery pack would be way better than the ~2C LiFePO4 pack I have)
 

·
Registered
Joined
·
7 Posts
Discussion Starter #4
That’s great news. We’re only interested in this project if it enhances the vehicle through conversion.
Ed
 

·
Registered
Joined
·
1,364 Posts
I only see that much when the batteries are warm and at a low SOC, otherwise max voltage limits the braking to about 50A or 20hp.
This is an important point... regenerative braking needs somewhere to put the energy it's recovered and if your battery is full (or at low temperature) you'll have nowhere to put the energy and therefore no braking :eek:

I see this on my Tesla Roadster when I do a 'range' charge (i.e. charge battery until it's 'full')... for the first 50 miles or so I only have limited regenerative braking and on several occasions I've almost run into another vehicle because I'm so used to driving one pedal with a low SOC ('standard' charge mode stops at 80% SOC).

Basically, if you need regenerative braking from the get go you'll need to charge to a lower SOC and possibly use a larger battery.
 

·
Registered
Joined
·
2,049 Posts
The biggest advantage of regen in your case (4x4) is you wont lock the wheels.
Regen by nature cant lock the wheel like a friction brake unless you get one wheel in the air then it might turn backwards through the diff and you will lose all rgen braking on that axle, theres the disadvantage !!!.
If you get a wheel in the air with friction brakes, the wheel still on the ground will continue braking so you will find you will be using both regen and friction in the rocks.
 

·
Registered
Joined
·
217 Posts
Im building a LandRover EV at present , I have installed a 5k pot on the dash so that I can adjust the level of regen braking required, In low range it will be certainly able to lock the wheels on a slippery slope , so can back off regen to regain traction level required . in high range or higher low range gears will be a useful hill decent control.
 

·
Registered
Joined
·
7 Posts
Discussion Starter #8
This is an important point... regenerative braking needs somewhere to put the energy it's recovered and if your battery is full (or at low temperature) you'll have nowhere to put the energy and therefore no braking :eek:

I see this on my Tesla Roadster when I do a 'range' charge (i.e. charge battery until it's 'full')... for the first 50 miles or so I only have limited regenerative braking and on several occasions I've almost run into another vehicle because I'm so used to driving one pedal with a low SOC ('standard' charge mode stops at 80% SOC).

Basically, if you need regenerative braking from the get go you'll need to charge to a lower SOC and possibly use a larger battery.
So without reducing SOC is there any ‘parallel’ system that could be incorporated and left in a low SOC to be brought ‘online’ when temporarily needed when the battery bank is fully charged? Just trying to have my cake AND eat it.
 

·
Registered
Joined
·
7 Posts
Discussion Starter #9 (Edited)
Im building a LandRover EV at present , I have installed a 5k pot on the dash so that I can adjust the level of regen braking required, In low range it will be certainly able to lock the wheels on a slippery slope , so can back off regen to regain traction level required . in high range or higher low range gears will be a useful hill decent control.
Hi GB. I’m glad that I’m not the only one seeing the advantages of an EV 4x4. I know that Land Rover have already looked at this back in 2013 but things have moved on since then. Have you got a build thread or Facebook page going for the project?
Ed
 

·
Registered
Joined
·
1,364 Posts
So without reducing SOC is there any ‘parallel’ system that could be incorporated and left in a low SOC to be brought ‘online’ when temporarily needed when the battery bank is fully charged?
You need to provide the motor with some work to do during regen if you wish to slow down the vehicle. If you're not charging the battery then providing a resistive load could work but I suspect it needs to be very large to absorb the energy generated by a heavy vehicle going down hill (iirc the Roadster generates 40kW and Model S 60kW during peak regen).

Do you have any idea what motor you'll be using and how much it can produce when used as a generator?
 

·
Registered
Joined
·
4,894 Posts
So without reducing SOC is there any ‘parallel’ system that could be incorporated and left in a low SOC to be brought ‘online’ when temporarily needed when the battery bank is fully charged? Just trying to have my cake AND eat it.
Yes: a really big resistor - always at zero SOC, never charges up. Seriously; they're a routine feature of diesel-electric locomotives, which have no batteries. Of course you would only use this to dump energy when you can't store it.
 

·
Registered
Joined
·
7 Posts
Discussion Starter #13
Yes: a really big resistor - always at zero SOC, never charges up. Seriously; they're a routine feature of diesel-electric locomotives, which have no batteries. Of course you would only use this to dump energy when you can't store it.
Thanks Brian. I was thinking of some way to temporarily recover the additional energy to be used for other systems. Could a large capacitor be used instead, maybe discharging through a heater element when needed?
Ed
 

·
Registered
Joined
·
7,837 Posts
As far as overcharging the battery from regenerative braking, all it takes is some advance planning and common sense, not additional hardware. After all, the OP question was with respect to engine compression braking not a freight train on a 8 mile down grade. Yes, braking resistors work, very well. But are in fact redundant because the vehicle is outfitted with friction brakes which also convert kinetic energy to heat.

A capacitor to store recovered kinetic energy (or potential energy due to elevation change) is also redundant. Modern batteries are fully capable.

major
 

·
Registered
Joined
·
7 Posts
Discussion Starter #15
As far as overcharging the battery from regenerative braking, all it takes is some advance planning and common sense, not additional hardware. After all, the OP question was with respect to engine compression braking not a freight train on a 8 mile down grade. Yes, braking resistors work, very well. But are in fact redundant because the vehicle is outfitted with friction brakes which also convert kinetic energy to heat.

A capacitor to store recovered kinetic energy (or potential energy due to elevation change) is also redundant. Modern batteries are fully capable.

major
Thanks Major. Just overthinking things a little as it relates to off roaders.
I’ll stick to the KISS principle.
 

·
Registered
Joined
·
1,364 Posts
Modern batteries are fully capable.
Correct but the OP asked for alternatives which is why we suggested some :rolleyes:

is there any ‘parallel’ system that could be incorporated and left in a low SOC to be brought ‘online’ when temporarily needed when the battery bank is fully charged?
 

·
Registered
Joined
·
4,894 Posts
... the OP question was with respect to engine compression braking not a freight train on a 8 mile down grade. Yes, braking resistors work, very well. But are in fact redundant because the vehicle is outfitted with friction brakes which also convert kinetic energy to heat.
Yes, the scale is very different, but the scenario is very similar: continuing regeneration without changing speed, in a vehicle which does not have energy storage available.

Trains (and trucks, and every vehicle using an electrical, electromagnetic, or hydrodynamic retarder) have friction brakes, too. People familiar with the intended sort of off-road use typically understand the issues with using friction brakes to control speed of descent.
 

·
Registered
Joined
·
4,894 Posts
I was thinking of some way to temporarily recover the additional energy to be used for other systems. Could a large capacitor be used instead, maybe discharging through a heater element when needed?
Capacitors work, and are often considered (but rarely actually implemented) for energy storage in electric and hybrid vehicles for situations where high power (but not large energy storage capacity) is desired. Since this isn't a high-power situation (compared to what the battery can already handle), and there are substantial control complications to using capacitors, this doesn't seem like a good fit.

Just overthinking things a little as it relates to off roaders.
I’ll stick to the KISS principle.
I don't think that considering all of the conditions and possibilities, then making an informed selection between them (including the simplest solution) is "overthinking" anything. :) It certainly beats not thinking about possible issues.
 

·
Registered
Joined
·
4,894 Posts
Regen by nature cant lock the wheel like a friction brake unless you get one wheel in the air then it might turn backwards through the diff and you will lose all rgen braking on that axle, theres the disadvantage !!!.
If you get a wheel in the air with friction brakes, the wheel still on the ground will continue braking so you will find you will be using both regen and friction in the rocks.
All true, and true of any form of engine braking - braking torque distribution between the wheels is determined by the drivetrain (so the conditions at one wheel affect the others if there are open differentials), rather than by the hydraulic pressure to the brake calipers (or slave cylinders).
 

·
Registered
Joined
·
319 Posts
I don't understand where your original brakes have gone - that could be your parallel system if the batteries are fully charged and you cannot used regen (?)
 
1 - 20 of 32 Posts
Top