There are two field windings in a Universal motor, one on either side of the stator.

Thanks, Max, I had realised that there was a winding for each magnetic pole of the field, but as they are in series, I considered them a single winding.

From what I've seen seperate field windings are more often used in power tools, but it will work just the same with a series winding field, that's actually the way most brake coils are wound.

I am initially trying one that is a marraige of AN958 and the AN-3006.

Oh, AN958 is very similar to what I've been using to build phase control circuits, except with atmel chips. It works well and the part count is very low. Even when adding current and speed sensors 8 pin is juuust enough. In my opinion isolation is prefered but not required when the end user is not gonna be in direct contact with any conductive part of the circuit like a metallic potentiometer or something. And pot that thing with resin (or maybe water based caulk?) for added safety and durability.

 

From what I've seen seperate field windings are more often used in power tools, but it will work just the same with a series winding field, that's actually the way most brake coils are wound.


Oh, AN958 is very similar to what I've been using to build phase control circuits, except with atmel chips. It works well and the part count is very low. Even when adding current and speed sensors 8 pin is juuust enough. In my opinion isolation is prefered but not required when the end user is not gonna be in direct contact with any conductive part of the circuit like a metallic potentiometer or something. And pot that thing with resin (or maybe water based caulk?) for added safety and durability.

Fields are wound opposite direction for dual poles, see Flemings left hand rule.
The mains direct version is no different from the standard off the shelf dimmer.
Nylon pot shaft is recommended.
Max.

 

Fields are wound opposite direction for dual poles, see Flemings left hand rule.

I know that rule by heart, man, I have to redesign armature and field windings very often.

The mains direct version is no different from the standard off the shelf dimmer.

In what sense do you mean?

 

In what sense do you mean?

In regard to being direct mains powered.
Max.

 

In my opinion isolation is preferred but not required when the end user is not gonna be in direct contact with any conductive part of the circuit like a metallic potentiometer or something. And pot that thing with resin (or maybe water based caulk?) for added safety and durability.

In this case it could be totally enclosed as a pot is not required for a soft start.
Max.

 

Evidently there is a custom IC for the soft start purpose, MLX90805, not sure of the availability, however.
Max.

 

Evidently there is a custom IC for the soft start purpose, MLX90805, not sure of the availability, however.
Max.

This is a nice chip, and for soft-start, needs only five other components - including the triac. However, a bit of Internet research didn't turn up many sellers - only one, in fact. On Ebay, KWL Electronics (China) claim to have 800 in stock, and there's a Hong Kong outlet with 4200 - but no price is given, and I have a feeling from the company names that they would want to be selling more than one at a time. Lots of people are offering the datasheet, but not the chip.

I previously mentioned the U2010B, which is available on Ebay. Its internals look more complex than the MLX90805, and the data sheet shows 21 components surrounding the chip in the only application circuit given. It's possible that it can be configured with fewer components for soft-start only, but the data sheet doesn't spell it out.

 

I previously mentioned the U2010B, which is available on Ebay. but the data sheet doesn't spell it out.

I think I would rather spend the effort on a simple 12F pic solution.
Max.