71–80 of 231 posts
Does regenerative braking work with a motor like this?
Yes: IIRC some large generators work exactly like this, as the energized rotor gives a lot more flexibility in managing frequency and power output.
Earlier quoted context omitted.
A lack of wear components. A permanent magnet motor uses permanent magnets on the rotor, but an electrically excited synchronous motor has an electromagnet on the rotor. This requires a rotating electrical contact which has normally been made with slip rings and carbon brushes. These wear over time and need replacement. Most large electric generators are externally excited synchronous generators using carbon slip rin…
To a layman that seems like a really small efficiency tax if you can't get your hands on the magnets for some reason.
Earlier quoted context omitted.
A lack of wear components. A permanent magnet motor uses permanent magnets on the rotor, but an electrically excited synchronous motor has an electromagnet on the rotor. This requires a rotating electrical contact which has normally been made with slip rings and carbon brushes. These wear over time and need replacement. Most large electric generators are externally excited synchronous generators using carbon slip rin…
To a layman that seems like a really small efficiency tax if you can't get your hands on the magnets for some reason.
Earlier quoted context omitted.
To a layman that seems like a really small efficiency tax if you can't get your hands on the magnets for some reason.
It's a small difference, but if you had a choice between "more efficient AND less maintenance" and "less efficient and more maintenance" then it's easy to see why the permanent-magnet solution is preferred.
They've been used to great success since we had the needed power electronics to drive the electric trains of Europe.
It's interesting that this is a brushed design. In the RC car community, brushless motors are generally regarded as superior, but those of course have the rare earth magnet problem. Technically the brushes can wear out, although there are claims they are good for 150,000-250,000 miles it seems.
Brushless DC motors don't arc -- because they switch stator polarity with electronics that sense the position of the rotor without rubbing parts. (They can also fine-tune the stator current spikes to make the motor very efficient over a wide speed range, which brushed DC motors cannot do.) The lack of arcing is more important than the fact that they don't have rotating contact points.
Brushed AC motors have rotating contact points (slip rings) but they don't arc (ideally), so the contact points don't degrade as fast as brushed DC motors do. But they do carry a lot of current because their purpose is to energize the rotor. Brushed AC motors are not ideal, but making an AC motor "brushless" is not nearly as big a win as making a DC motor brushless.
Wait. You're saying DC motors require current that's constantly switching polarity? So they're sort of really AC internally?
Yep. All motors require constantly changing current. The distinction between AC and DC motors is whether you feed the motor externally with current that is already alternating sinusoidally, or whether the motor itself turns external DC into some kind of AC.
Earlier quoted context omitted.
A lack of wear components. A permanent magnet motor uses permanent magnets on the rotor, but an electrically excited synchronous motor has an electromagnet on the rotor. This requires a rotating electrical contact which has normally been made with slip rings and carbon brushes. These wear over time and need replacement. Most large electric generators are externally excited synchronous generators using carbon slip rin…
To a layman that seems like a really small efficiency tax if you can't get your hands on the magnets for some reason.
It's like how laptop power bricks used to be big and get hot, and now they aren't and don't.
Earlier quoted context omitted.
The cheapest EV model Renault sells is around €20K, the cheapest BMW EV is around €65K. It's safe to say the companies are not in the market bracket, no?
The bit the gets me more than the sale price is servicing. BMWs have a terrible record for needing expensive repairs. I know you shouldn’t rely on anecdote, but it seems I do.
If you get into an accident or let the bmw get into disrepair via neglect, yeah it’s not cheap to clean up. Body work is expensive on any car though, and I don’t have sympathy for people who own higher-end cars and don’t take care of them, they deserve to pay the price for it.