JeanVapeur wrote: ↑Sat Jul 10, 2021 6:17 pm1. In a hotel at the top of a Mountain in the Alps I load accidentally the Battery up to 100%,
then I drive 30km down the pass to the valley.
- Do I have motor braking?
- Where do the current go?
- Will this damage the motor windings or the Inverter or the battery?
- Can I use the energy of the battery for backwards torque for (motor-)braking?
- How do the OEM's handle this?
- You probably do not have motor braking no, because the motor is functionally not being "asked" to slow down by clamping the battery onto it, it's already at full charge, so it's not loading the motor at all trying to charge it. Same as when charging a battery, when the battery voltage matches the charging voltage, there's no power flowing anymore.
- There won't be any current, because the voltages will be equal. Think about it like putting a pasta strainer into a bathtub. At first water rushes in because the level of water in the collander is lower than the tub. But soon after, the levels are equal. Your question is then "What happens to all the water flowing in?", well, there isn't any water flowing it anymore, the water level is equalized.
- The only way to get more current to flow, is to have the regenerative brake set itself to a higher-than-max battery voltage. If so, then there will be a voltage difference again, and current will flow into the batteries again. This is overcharging the batteries, which ruins them and maybe makes them overheat and catch fire. You won't damage the motor, presuming you're not overspinning it. You will probably damage the inverter because it was probably only rated for the max voltage it expected to see, which was the battery voltage (not necessarily true, but, that's all it was rated for).
- Yes you can do that, but that's irrespective of the battery at 100% situation. One type of braking would be if the motor is spinning and you use it like a generator connected to batteries, charging them. Another type of braking is to use the spinning motor and connect it to a big resistor bank, bleeding the energy off as heat in the resistors. That's less efficient than regenerative braking (because you're just heating the resistors, not charging the batteries), but it still works as braking. A third type of braking would be to tell the motor to try to spin in the reverse direction. This is called "plug braking" and it's how electric forklifts brake. Here you're not just wasting the energy of the motor spinning, you're actually adding energy to the motor trying to get it to rotate backwards. This heats the motor up a lot. From the motor's perspective it's like climbing a hill.
...
In short, if you can use regenerative braking, you might as well. If you can't, resistive braking would be an option if your vehicle was built that way (else you could just turn on a bunch of accessories, AC, heater, etc, and at least this energy being drained from the battery would otherwise be recovered by the regen). And otherwise, plug braking could be done, but it's rather violent and difficult to control.
In OEM vehicles, far as I know they only have regen braking, and friction brakes as a backup. You'd need friction brakes anyways as a backup. As this situation is quite rare, no OEM I know of bothers to use resistive or plug braking (if plug braking is even a thing on AC motors).
2. A Motor with a max voltage of 400V.
- Can this motor produce in regen mode only max 400V or more?
That depends on your definitions of "max" and "can".
Motor voltage is not the same as battery voltage, but, let's say they are.
In this case, what a motor's "max" voltage means is that the insulation is only rated for that voltage, above which it may start to puncture and short. Most motors can handle a healthy amount of voltage above their rating. AC motors especially. My 48V forklift motor is likely no different than a 220v motor in terms of insulation on the windings, and would probably be fine.
In any case, there's no actual max, there's just a "what happens when you go over this amount".
The controller will figure this out, (which also has a max voltage rating) and generally anything is reversible.
3. And if this 400V-motor is drive able with a lower voltage,
for example: you drive a 400V motor with a 300V Battery and a 300V Inverter.
- What happens at full speed at the autobahn when you switch downhill to regen?
- Are there more than the 300V possible?
- Will this damage something?
Driving a motor with less than its max voltage just means it spins slower. In fact, when you are accelerating, your inverter is probably not sending full voltage to the motor anyway. It's gradually ramping it up (along with frequency) to make it spin faster. It's quite common to test 400v motors with 50v or whatnot on a bench, because you don't need them rifling along as max speed.
- You won't reach "full speed", a motor limited to 300v will not go as fast as that same motor given 400v. This may or may not be in a range that's useful to you. When you hit regen, no difference, the lower voltage limiting your speed will also mean you probably can't get as high of a voltage back out of it.
- Depends.
- It will damage something if you give something higher voltage than it can handle, or more current than it can handle.
4. A constructor always think about 'what if' in worst case...
- What happens at full speed if the main fuse blow or one of the contactor collapsed?
Ok the drive failed and the car rolls out but can the regen energy damage something?
- If there's no connection to the battery or motor, then the motor cannot be loaded down by the battery. So it will have no load on it. The regen will do nothing.
(wishful thinking)