Using diode bridge to drive a DC motor at 2 speeds

[heypaisa]

A cheap hand blender I got from Walmart broke down after two years of use,
so I crack it open. The circuit is very simple. Just a diode bridge rectifier,
a switch, and a DC motor (circuit schematic in attached image).

The interesting part is, it has two speeds: "high" and "low". The high speed is
just a standard diode bridge. My question is, why does it work at low speed?
I looks to me like driving the motor half of the time and short circuit half of the time.

The diodes are "N5399 MIC" and the motor is "HRS 5512SP".

**broken link removed**

 

[Nigel Goodwin]

On half speed it's fed via a half wave rectifier (a single diode), on full speed it's fed from a full wave rectifier (a bridge).

It's as simple as that - the half wave diode is the bottom left one.

 

[heypaisa]

Hi Nigel. Thanks for a quick reply. You are right. Half of the time, the bottom left diode works as a half-wave rectifier.
What about the other half of the time? Don't we have a short-circuit on the bottom right diode?

 

[Nigel Goodwin]

Hi Nigel. Thanks for a quick reply. You are right. Half of the time, the bottom left diode works as a half-wave rectifier.
What about the other half of the time? Don't we have a short-circuit on the bottom right diode?

Yes it does - I suspect it can't be wired like that?.

 

[heypaisa]

Thanks again Nigel. You are right. I didn't look careful enough initially. Taking a second look, I found
another diode hiding under a heat-shrink tube on the "low speed" wire. Now everything makes sense.

 

[Grossel]

Yes it does - I suspect it can't be wired like that?.

Not only do I suspect, there will be a short cut path on the half wave rectifier.