Comment by TD-Linux | Hacker News Reader

Comment by TD-Linux | Hacker News Reader

The two strangest parts of this are probably the door locking mechanism and the DC motor supply. The door locking was pretty well explained, but I was really surprised at the DC motor. From previous pictures I had assumed it was a 170VDC motor (using just a rectifier + filters for noise) but according to this it's actually a 330V active power correction boost converter. I guess that gets you 100-240V range support, but it seems horribly expensive for driving a motor. Even 170VDC permanent magnet motors are pretty uncommon - they fill an awkward middle ground where the motor is too big to reasonably use a low voltage DC one (due to power supply costs), but too small to use a universal AC motor directly off line power. The only tools AvE has reviewed of this design are the Kitchenaid mixer and Drill Doctor, for reference.

Also, I don't believe "330V 15A" for a second. Maybe 2A...

> 330v 15a

Just do the math. You get about 13a tops on a 115v plug before any household circuit will trip. That is over twice that. Same with those '5hp' power tools.

1.5a 330v would make more sense (or in this application, less nonsense).

6 and a half horsepower.

The 330V is for sure a misprint. It doesn't look like they have the insulation for a high voltage motor, so my guess would be 30/33V @15A. Reading the linked spec sheet confirms it's in the range. That would put it much closer to a cordless drill motor. (450W, not 5kW, which is obviously impossible on 120VAC/15A)

I actually think the insulation is adequate for a line voltage motor. You can also see that the brush holders were heavily modified (and kinda ugly) in the Juicero motor compared to the spec sheet [1], likely due to the higher voltage.

Though the most telling is that the only isolated supply is the 5V Meanwell, the whole bottom half is at line potential as evidenced by the lack of transformers and the optoisolators right below the Meanwell supply (for controlling the H-bridge below).

One thing that still seems to be missing is active PFC - it was implied by the article, but I don't see enough components for it. Maybe it's just a rectifier into 170V/330V, and the in the case of 330V they drive the motor at half the duty cycle.

One other question was "why not a series-wound motor?" It was pointed out to me that one potential reason is that a series-wound motor introduces 60/120hz hum and vibrations, and maybe they found the noise objectionable.

[1] http://en.jiaai.cn/products_detail/productId=65.html

I think a series-wound motor would be cheaper than a custom high voltage DC motor. I'm not sure about the power output tradeoffs, though.

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