Starting a multi-mile decent with a full battery (v11)

[BlckRck2014]

I am new to EUC's and my v11 is my first.  I am loving it so far.

With my Tesla (car), if my car battery is at 100% charge the engine breaking will not engage and I have to use normal (wheel) breaks.  I believe it is a safety function so that the batteries are not over charged.

What happens on a EUC if my battery is 100% and I begin a ride is a decent ahead of me?  Will it cut-off?  Will it warn me and stop me from riding?  If so, should I start this kind of ride with a reduced battery level?

Edited February 9, 2021 by BlckRck2014

[Ádám Szitás]

It will tell you to stop because of overcharge and tilt you back. If you ignore this you may cut-out yes. Starting these rides with reduced battery is indeed a good idea.

Going slow, not braking hard, carving also helps with this.

Edited February 9, 2021 by Ádám Szitás

[Tawpie]

In a pinch, you can ride back up the hill to use some of the charge. You'll never recover all the charge coming back down, so you'll get a bit further before it hits overcharge warnings again. Makes for a longer tour, but that's not automatically a terrible thing! You could even go really fast uphill with your arms out and your coat open Titanic style to use more energy. Or carry some rocks on the way up.

Edited February 9, 2021 by Tawpie

[meepmeepmayer]

46 minutes ago, Tawpie said:

Or carry some rocks on the way up.

Believe it or not, this is not the first time this idea has come up And it would work.

[null]

Kind of difficult to read with all the adds (couldn't find a clean source) but this mining truck does just that. The regenerative braking from going downhill fully loaded is enough to cover most of the energy uphill empty. Really cool, also fun that it could have been done with a spring or other energy storage.

[RagingGrandpa]

1 hour ago, Ádám Szitás said:

Going slow

Theory is fun sometimes:

If we're describing a ride where you need to descend 500 vertical feet and then come to a stop, the amount of energy absorbed due to the grade is the same whether you do it quickly or do it slowly.

And the more quickly you ride, the more wind resistance. Wind resistance is a 'braking' force, which helps reduce the load on the motor and batteries when descending.

So, for the same vertical distance, I expect cruising downhill at 25mph creates less regeneration than cruising downhill at 10.

And a side-note: there is also a power limit to remember- the speed at which you descend will change the rate at which energy is recovered. At some speed and grade, the power absorbed will exceed the power limits of your controller, and you'll overlean in the braking direction. But I think this is only a concern on grades steeper than public roads.
 

I agree with the concept of the posts above- it's best if the battery pack has been discharged by at least the amount of energy recovered during the descent. But 4.2V is not a 'hard limit' and over-charging is not an instant catastrophe. We just want to minimize it. The advice of 'ride uphill for a few minutes' or 'U-turn after a few minutes and ride uphill again' seems especially practical, if your EUC starts beeping with an over-voltage warning.

[BlckRck2014]

If I were doing about 6.9 miles (driving distance) of decent (vertical feet is going from about 1700 down to 200), what battery percent should I start at?  Would 80% suffice?

[RagingGrandpa]

27 minutes ago, BlckRck2014 said:

vertical feet is going from about 1700 down to 200

what battery percent should I start at?

Assuming you plus the EUC total 100kg, that descent will release 123 wh of energy.

Riding 7 miles on level ground at 25mph should require about 280wh of energy.

280 > 123

My napkin math says you'll use more power than you absorb, meaning if you begin the ride at 100%, you'll be less than 100% by the end (not overcharged).

 

If you don't trust me, a safe way to test it would be to start at 75% SOC, and then check your SOC again after descending at 25mph. If it went down, I'm right. If it went up, I'm wrong. Safe either way

[mrelwood]

As @RagingGrandpa calculated, the descent shouldn’t be an issue at a steady speed. But if you brake hard, the regenerative braking creates a power spike and the wheel will probably at least warn you.

 I’ve been able to engage an overvoltage warning on the 16S about 400 meters after start, on level ground.

On 2/9/2021 at 11:07 PM, RagingGrandpa said:

So, for the same vertical distance, I expect cruising downhill at 25mph creates less regeneration than cruising downhill at 10.

There are speed and braking power thresholds that must be overcome before the regen takes place. At least in some wheels the speed threshold is 10km/h. I don’t know if they all use the same threshold.

[Zacterry]

On 2/10/2021 at 9:31 AM, RagingGrandpa said:

Assuming you plus the EUC total 100kg, that descent will release 123 wh of energy.

Riding 7 miles on level ground at 25mph should require about 280wh of energy.

280 > 123

My napkin math says you'll use more power than you absorb, meaning if you begin the ride at 100%, you'll be less than 100% by the end (not overcharged).

 

If you don't trust me, a safe way to test it would be to start at 75% SOC, and then check your SOC again after descending at 25mph. If it went down, I'm right. If it went up, I'm wrong. Safe either way

We are talking about a 7 mile descent with a vertical drop of 1500 feet. Surely no or very little energy is required to do this(allowing for the odd flat or uphill section). Why do you need 280wh of energy when you are in fact generating 123 wh. How are you generating and expending energy simultaneously?

[mrelwood]

4 hours ago, Zacterry said:

Why do you need 280wh of energy when you are in fact generating 123 wh. How are you generating and expending energy simultaneously?

I believe then calculated the horizontal and vertical vectors separately.

[RagingGrandpa]

I triggered someone badly enough to cause a new user registration and a first post. A good sign  

On 12/28/2022 at 11:18 PM, Zacterry said:

Why do you need (-)280wh of energy when you are in fact generating (+)123 wh.

Those components will be summed together. 

Potential energy is being released because of a mass moving in the same direction as gravity.
In my estimate, 123 wh of potential energy is released and converted to motion. 

And also, energy is being lost to friction (drag), whenever the rider is moving (in any direction). 
In an imaginary weightless world without gravity, in my estimate, about 280 wh of energy will be lost to friction in the process of moving 7 miles at 25mph airspeed.

So, the output from the battery must be the net of those two external factors. 280 - 123 = 157 wh discharged.

And then consider: Traveling the same route more slowly would reduce drag, but would not change the potential energy release, and could shift the net battery energy from discharge to 'recharge' for very slow speeds.
 

Edited January 9, 2023 by RagingGrandpa

[Josiah]

On 2/9/2021 at 12:01 PM, Tawpie said:

In a pinch, you can ride back up the hill to use some of the charge. You'll never recover all the charge coming back down, so you'll get a bit further before it hits overcharge warnings again. Makes for a longer tour, but that's not automatically a terrible thing! You could even go really fast uphill with your arms out and your coat open Titanic style to use more energy. Or carry some rocks on the way up.

Is there someway they can dissipate the energy through the motor without charging the batteries, if the wheels fully charged? Also I’ve heard that when the wheel reaches 100% it’s not truly 100% this can be measured with a voltage meter. Some people leave it on the charger longer measure again with the voltage meter until it is truly at 100%.

Edited January 9, 2023 by Josiah

[RagingGrandpa]

2 hours ago, Josiah said:

dissipate the energy through the motor without charging the batteries

Yes, the controller has the ability to short-circuit the motor, causing a huge amount of braking force... but the energy will be dumped totally to heat, with inevitable damage to the controller and/or motor.

[Nostris]

For what it’s worth, my drive way is 1 kilometre long and descends by 100 meters..330ft. If I try to take the garbage out on a full..100% battery, I get about half way and get the tilt back and the Overload…Please Get Off! Message. It’s best to start the decent at 95/98% battery in my opinion. 

Edited January 30, 2023 by Nostris
Auto spell…again!

[alcatraz]

On 2/10/2021 at 6:31 AM, RagingGrandpa said:

My napkin math

It's the best kind!