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Inboard battery and braking: Fresh <> Full


#1

Hi all, I’m trying to cut through Inboard’s marketing-speak to figure out the physics involved. They didn’t really confirm that they will undercharge, but if they’re not force-feeding a full battery and have no secondary rheostatic or friction-based braking, there’s no other way for the BMS to instamagically make the regen current disappear, right?

Inboard: However, when the battery is full, the current has nowhere to go and braking is disabled to avoid damaging the battery. With the M1, you’ll still be able to engage the brakes with a battery that’s fresh off the charger."

Gongfu Xiongmao: My physics teacher is a hardcore e-skate builder. He said that if you can brake with a M1 “fresh off the charger” the board is converting the current to heat somewhere or putting back into the battery (electricity). Does this mean that the M1 will always be charged under capacity to leave room for braking regeneration current? Isn’t this sacrificing distance for those few clients who happen to live atop large hills? Top speed would be lower, since a lower charge would also mean less top voltage/power too?

Inboard: Hey Gongfu. For us addressing this was more of a safety issue than anything else… not as much for the few clients who live on top of a large hill, but those who don’t but may occasionally start on top of a large hill and expect the brakes to work on a fresh battery. Without this feature they’re in for a dangerous surprise. I can only say we’re using the BMS to manage this extra power, and so far this is not sacrificing advertised distance or advertised top speed.


#3

Looks to me they’re undercharging the battery to prevent customers living on top of a hill losing their braking function due to a full battery. But the braking current will be so small and of such short duration, I don’t think they need to undercharge so much that it will affect range.


#4

how much current is actually generated during braking above and beyond the current used to actually do the braking? And is that even enough to worry about? it seems like the steeper the hill the more current it would take to keep you slowed down.


#5

I believe they are trying to focus on those who don’t brake down hill. Not sure it matters though. That energy has to go somewhere.


#6

Ah, of course. I was too busy thinking about the braking instead of the not-braking. I suppose they don’t want to just cut the current at the ESC and let the motors dissipate the heat via those cool fan-shaped wheel hub covers.


#7

No current is used in regen (induction) braking; just the opposite. (“DC injection braking” on the other hand, is the use of a separate power source to create a static magnetic field which slows the motor.)

Cutting the current before the ESC would be bad. Or impossible. The more kinetic energy being converted into current, the stronger the braking. If 0 current is pulled from the motor, there is no braking. Like psychotiller said, the current has to go somewhere. Also, the first place where you really don’t want excess heat is the motor…the battery can at least be replaced more easily.

Rheostatic/dynamic braking would give you what you are looking for longhairedboy. If the current or load is too high for the battery to take, the BMS will shunt it to a resistor, converting electricity to heat (and global warming!) and dissipating it. Mellow Drive is the only e-skate setup that I know of with this secondary braking ability.

Question to the forum: For rheostatic braking…why a resistor? Would it be possible to dissipate electricity with a big huge spark from a huge capacitor, like a Taser? Also, wouldn’t that be bad-ass? The Max Max e-skate.


#8

When you’re going downhill and braking your motor management electronics are allowing the motors to generate a current which is then fed back to the battery. This current flowing through the motors creates an electromechanical force which tries to slow the motor down.

When you’re going downhill without braking (neutral), your motor managment electronics are not allowing this current to flow, thus preventing the electromechanical force from slowing the motor down.

So basically if you start down a hill with a full battery and the electronics don’t allow the current to go anywhere, you don’t have brakes.


#9

I have had a board stop on a hill I was coasting down. The batteries were dead so I was pushing my way home. In fact it got to the point that just trying to push on flats was impossible. The motors generate power even when coasting. And if the power has no where to go, things happen.


#10

That’s weird.
I can easily push my board with an empty battery (or even turned off).
May have something to do with individual controllers ESC/VESC whatever.


#11

Yeah I never figured it out. It was a castle controller. One of many. It was the only build I had that did it. I accepted it as just that board’s personality. Tore it down , rebuilt, same esc, different result. I know that it’s possible now though, and it is always in the back of my mind.


#12

Latest video from CES has a shot of Inboard’s battery label: hello 12s1p!!!


#13

I have been thinking, what if we introduced a chiller plate for excess regenerative current? I have not done any calculations yet but it would be a good use of the excess regen.


#14

Awesome. Talk about conservation/conversion of energy: Electric (wall socket) to chemical (battery) to electric (current to motor) to kinetic (riding!) to electric (braking) to thermal (chilling) to chemical (cold beer) to biological (buuuurrrrp).

Those poor electrons do so much work for us.


#15

This is a 12v 5 amp module: Peltier Thermo-Electric Cooler Module - 12V 5A

It measures 40mm x 40mm so it would be perfect match for the VESC. Would only add 3.5mm to the height.


#16

I don’t get your intentions here @chaka, you want to actively cool the VESC ?


#17

if it could be done only while braking or coasting it might make sense in extreme use cases like racing.


#18

I seem to have misinterpreted what the chiller plate was for. Sorry. Hic.


#19

I suppose you could use the excess energy for anything you like. Cooling the system just seems to be the most practical use. The esc would most likely be very hot if you have already been using the brakes heavily. You would need to develop a circuit of course but it can be done.

@Calhoun You can use these chiller plates for all kinds of projects. The specs state a max temperature differential of 66°C.


#20

the problem with the peltier “chiller plate” is that in order to get cold it needs to get hot on the other side, so you will need to heat sink the hot side thus almost negating the relatively slim hight of the plate.


#21

You could pop it through the enclosure. I think that kind of thing looks nice when done right.